4 Puck vs 6 Puck

[Rabbi010]

Now, I've been searching an all over the internet people have been saying 4 puck engages harsher than the 6 puck. That made no sense to me because the 4 puck has less material to stick onto than the 6 puck.

Then, I saw this video. PRI 2006 - StreetFire.net does a technical intervi - Car Videos on StreetFire (http://www.streetfire.net/video/PRI-2006-StreetFirenet-a_91227.htm) . In it, the professional explains that the only reason the 4 puck and 6 puck grab harsher than the clutch disc is that it has harsher material on it. Which means if they both had the same material, the disc would grab just as much or better.

He said the reason you use pucks is because it's lightweight and its cooler. With these ideas, this leads me to conclude that the only difference between the 4 puck and 6 puck clutch is that the 4 has lighter weight and better cooling, which is necessary for track use.

So people saying that the 4 puck grabs harder than the 6 puck are just repeating what they heard when actuality, if they were both the same material, the 6 puck would grab harder because it has a higher surface area.

Ideas?

[SlideOrDie831]

the more pucks means lighter engagement. the less means harder engagement due to less pucks.

6 puck is good on the street.

[HYPNOTIK]

You are half right. If a 4 puck had the same material as 6 or full disc it would have nowhere near the holding capacity, because it has half the surface area. Surface area and spring pressure are the only two things that can make a clutch hold more power. A 4 puck HAS to have harsher material or it wouldn't work. Having owned a 3 puck, my current 6 puck, and full discs I can say for certain that a 3 puck engages the most harsh. That shit is on or off. For a full track car it's not a problem but I wouldn't want to drive that shit everyday. Even my 6 puck gets annoying sometimes and I still stall it out after having it a year.

[Rabbi010]

Thanks HYPNOTIK.

So, basically the 4 puck is harsher because it has a better quality frictional material AND, usually, in the combo it comes with a really strong pressure plate.

But if it was the same quality and same pressure plate as a 6 puck, the 6 puck would grab harder, right? Because it has more surface area.

So like the video says, the only true benefits are its cooling abilities and lighter weight?

If there was a rep system, I would rep you.

Someone should write an article on this, i can't find any quality articles on this. Only forum posts

[Def]

You are half right. If a 4 puck had the same material as 6 or full disc it would have nowhere near the holding capacity, because it has half the surface area. Surface area and spring pressure are the only two things that can make a clutch hold more power. A 4 puck HAS to have harsher material or it wouldn't work. Having owned a 3 puck, my current 6 puck, and full discs I can say for certain that a 3 puck engages the most harsh. That shit is on or off. For a full track car it's not a problem but I wouldn't want to drive that shit everyday. Even my 6 puck gets annoying sometimes and I still stall it out after having it a year.

Totally wrong.

The only thing influencing how much torque a clutch can hold are CLAMPING FORCE OF THE PRESSURE PLATE and the COEFFICIENT OF STATIC FRICTION between the surfaces. Surface area is not a variable on the physics equation of friction, F = mu*N, or friction force = coef. of friction * clamping force in the case of a clutch.


The reason a 4 puck engages "harsher" than a 6 puck all things equal is that for a given travel of the pressure plate the 4 puck will tend to ramp up to fully engaged more suddenly. The higher face pressure gives the ceramic-metallic material more "bite" into the smooth steel PP/flywheel surfaces, so the coefficient of kinetic friction changes. Material is usually the same between a company's 4 puck and 6 puck.

In general, this is a huge generalization, and the difference of driving the clutches on the street isn't that huge. Having a sprung hub makes a bigger difference.

[Rabbi010]

Totally wrong.

The only thing influencing how much torque a clutch can hold are CLAMPING FORCE OF THE PRESSURE PLATE and the COEFFICIENT OF STATIC FRICTION between the surfaces. Surface area is not a variable on the physics equation of friction, F = mu*N, or friction force = coef. of friction * clamping force in the case of a clutch.


The reason a 4 puck engages "harsher" than a 6 puck all things equal is that for a given travel of the pressure plate the 4 puck will tend to ramp up to fully engaged more suddenly. The higher face pressure gives the ceramic-metallic material more "bite" into the smooth steel PP/flywheel surfaces, so the coefficient of kinetic friction changes. Material is usually the same between a company's 4 puck and 6 puck.

In general, this is a huge generalization, and the difference of driving the clutches on the street isn't that huge. Having a sprung hub makes a bigger difference.

Why? I don't understand. The 6Puck has more to grab on to which makes me think that it would grab on better and quicker than the 4Puck (with all other factors being similar.)

You're saying that because there are less pucks, there is more pressure going to each one? Even with a 6, the pressure would be the same because the pressure plates applies it evenly.

[HYPNOTIK]

Totally wrong.

The only thing influencing how much torque a clutch can hold are CLAMPING FORCE OF THE PRESSURE PLATE and the COEFFICIENT OF STATIC FRICTION between the surfaces. Surface area is not a variable on the physics equation of friction, F = mu*N, or friction force = coef. of friction * clamping force in the case of a clutch.



Is that not the entire point of a multiplate clutch? More surface area so not as much spring pressure is needed to obtain the same holding capacity, or at the same spring pressure it has a higher holding capacity.

For example an OS Giken TS2B and TS3B. Both have 1000n.m clamping pressure, both have a 204mm disc but the twin plate handles 2/3 the power of the triple. 600hp vs 900hp. And both use the same friction material, the plates are interchangeable between the two.

[thefro526]

Totally wrong.

The only thing influencing how much torque a clutch can hold are CLAMPING FORCE OF THE PRESSURE PLATE and the COEFFICIENT OF STATIC FRICTION between the surfaces. Surface area is not a variable on the physics equation of friction, F = mu*N, or friction force = coef. of friction * clamping force in the case of a clutch.




Def is dead on with this one.

Basically when you have two uniform or essentially uniform surfaces, like a clutch and flywheel, clamping force is independent of surface area. It's a hard concept to grasp, since it goes against most people's understanding of force of friction (Most people are most familiar with force of friction when talking about traction - which has two non-uniform surfaces).

[HYPNOTIK]

Did you read my example? I'm not arguing that I'm right, I just want to understand.

And how is a clutch and a flywheel two uniform surfaces? Ceramic or Organic material vs Metal. I would think a clutch would work much the same as a brakes. More clamping force(pistons) and more surface(more pad surface) equal higher capacity. I know it's not exactly the same but it is similiar in theory.

The way I'm understanding what your saying is this; if I took my brake pads and sanded the edges so that it came to a point half the size of the original pad, the braking capacity would be just as much as the original with only half the surface area.

Draw me a picture with crayon's, I want to understand this. What is the formula?

[daryl337]

Def,

You are actually not completing the equation. You are simply using 2 variables under the assumption of equal sized objects.


The complete formula should be F ● Rg ● N ●µ where F = clamp load (force), Rg is radius of gyration (clutch disk size), N is friction surfaces (not to be confused with number of pucks! 1 clutch disk has 2 surfaces, Multiplates will be 2X number of clutch disks) , and µ is the friction coefficient.


Notice that radius of gyration =/= surface area. A wider 3 puck clutch can have less surface area than a smaller complete disk.


To help you out hypnotik in regards to why Multiplates (or number of surfaces in general) helps increasing torque capacity without the "surface area" being a factor... in lamens terms it is because after each disk, the amount of un-managed force has been mitigated by a certain amount.

The first disk is going to manage as much load as possible until it has reached its slip point, and then the unmanaged load will become the responsibility of each subsequential disk. In this way, you are essentially trickling the load among multiple friction surfaces until it has all been managed.




A factor that you do need to consider with surface area however, is heat resistance.


A clutch with fewer pucks may be lighter, but once it starts to slip it will be easier to ruin. That is the only reason puck clutches are harsher to engage... because they ramp the clamping load up on the clutches so there is less of a slip upon engagement. Slip creates heat, and heat will destroy the clutch.

Utilizing a full disc face will allow the heat to dissipate, but you won't get an increased torque/load bearing figure. You will just get much more of a streetable/controllable engagement (You can slip it more without worry that it will fry)

[Rabbi010]

The reason a 4 puck engages "harsher" than a 6 puck all things equal is that for a given travel of the pressure plate the 4 puck will tend to ramp up to fully engaged more suddenly. The higher face pressure gives the ceramic-metallic material more "bite" into the smooth steel PP/flywheel surfaces, so the coefficient of kinetic friction changes.

I'm still trying to understand this post. Why does the 4 puck ramp up to fully engaged more suddenly? From my understanding, if all factors are the same (spring force and frictional coefficient,) the 6 puck clutch would have more areas to clamp onto; making it ramp up harsher.


Tell me if I'm wrong with this idea. The frictional coefficient and the spring force defines the quality of the friction; how strong it is. The area of the frictional material is what defines the quantity of the friction; how many points of interest are applying that friction.

[daryl337]

The thing is, a 4 puck will require a faster engagement to prevent slip, so "all factors"
can not be the same. The spring force may have an end result of xxx lbs, but the rate that it is applied will be higher out of necessity, otherwise you will end up a burnt clutch, not from being out torqued, but because the slipping action of applying the clutch and disengaging will burn it.


In theory, you could have a piece of string that extends to the outer diameter of your flywheel, so your surface area will be very, very low. However, because you have a long radius to apply the torque to, (assuming that your friction coefficient is the same as another material) the string should be able to handle the same torque load as an entire disc. The issue however, is that applying the clutch from a disengaged position is an action that requires slippage. There is almost never a "not engaged" to instantaneous
engagement. That minor slippage creates heat. If the string cant take the heat, it glazes over, thereby reducing the friction coefficient.



So, this means by a simple deduction... a clutch with less surface area (assuming materials all the same) will still have the same torque hold capacity, but will have less of a tolerance to slip.

The less tolerance to slip that you have, the harder (more rapid) that you must engage the clutch to minimize that slippage. This is why a 6 puck clutch has less of a drivability feel than a full disk. 3 pucks are even less drivable than a 6 puck. Etc. Not directly because the design of the clutch disk itself, but because altering the design of the disk *requires* that you update the design of the pressure plate to accomodate the slip allowed. So why go to a puck system at all? To reduce weight. Using a puck system, especially in racing, will allow you to use a longer radius clutch while reducing the rotating mass. Since the arclength increases with diameter, you are increasing the speed of the outer portion of the clutch significantly. Lightening the clutch reduces the forces involved.

Using a puck clutch that is the same diameter as a disc clutch offers little benefit other than weight saving.

[Rabbi010]

The thing is, a 4 puck will require a faster engagement to prevent slip, so "all factors"
can not be the same. The spring force may have an end result of xxx lbs, but the rate that it is applied will be higher out of necessity, otherwise you will end up a burnt clutch, not from being out torqued, but because the slipping action of applying the clutch and disengaging will burn it.


In theory, you could have a piece of string that extends to the outer diameter of your flywheel, so your surface area will be very, very low. However, because you have a long radius to apply the torque to, (assuming that your friction coefficient is the same as another material) the string should be able to handle the same torque load as an entire disc. The issue however, is that applying the clutch from a disengaged position is an action that requires slippage. There is almost never a "not engaged" to instantaneous
engagement. That minor slippage creates heat. If the string cant take the heat, it glazes over, thereby reducing the friction coefficient.



So, this means by a simple deduction... a clutch with less surface area (assuming materials all the same) will still have the same torque hold capacity, but will have less of a tolerance to slip.

The less tolerance to slip that you have, the harder (more rapid) that you must engage the clutch to minimize that slippage. This is why a 6 puck clutch has less of a drivability feel than a full disk. 3 pucks are even less drivable than a 6 puck. Etc. Not directly because the design of the clutch disk itself, but because altering the design of the disk *requires* that you update the design of the pressure plate to accomodate the slip allowed. So why go to a puck system at all? To reduce weight. Using a puck system, especially in racing, will allow you to use a longer radius clutch while reducing the rotating mass. Since the arclength increases with diameter, you are increasing the speed of the outer portion of the clutch significantly. Lightening the clutch reduces the forces involved.

Using a puck clutch that is the same diameter as a disc clutch offers little benefit other than weight saving.

Dude you explained it so well. So a with material being alike, the only reason a 4 puck holds on, or engages, better is because the pressure force is[has to be] stronger. If the pressure force wasn't strong then the 4 puck clutch could burn out quicker.

Do you know why it would burn out quicker? Is it because it is being introduced to more friction being separate pucks, instead of a whole disk, which would cause it to wear out quicker?

Where did you study all this stuff? I can't find any good information like the way you explain it. You're an engineer? Thanks once again.

[Def]

Is that not the entire point of a multiplate clutch? More surface area so not as much spring pressure is needed to obtain the same holding capacity, or at the same spring pressure it has a higher holding capacity.

For example an OS Giken TS2B and TS3B. Both have 1000n.m clamping pressure, both have a 204mm disc but the twin plate handles 2/3 the power of the triple. 600hp vs 900hp. And both use the same friction material, the plates are interchangeable between the two.

An extra plate adds the same frictional force as the first plate. It's not a surface area thing, but a "there's an extra plate that is interfaced with a stationary plate and the pressure plate."

Def,

You are actually not completing the equation. You are simply using 2 variables under the assumption of equal sized objects.


The complete formula should be F ● Rg ● N ●µ where F = clamp load (force), Rg is radius of gyration (clutch disk size), N is friction surfaces (not to be confused with number of pucks! 1 clutch disk has 2 surfaces, Multiplates will be 2X number of clutch disks) , and µ is the friction coefficient.


Notice that radius of gyration =/= surface area. A wider 3 puck clutch can have less surface area than a smaller complete disk.


To help you out hypnotik in regards to why Multiplates (or number of surfaces in general) helps increasing torque capacity without the "surface area" being a factor... in lamens terms it is because after each disk, the amount of un-managed force has been mitigated by a certain amount.

The first disk is going to manage as much load as possible until it has reached its slip point, and then the unmanaged load will become the responsibility of each subsequential disk. In this way, you are essentially trickling the load among multiple friction surfaces until it has all been managed.




A factor that you do need to consider with surface area however, is heat resistance.


A clutch with fewer pucks may be lighter, but once it starts to slip it will be easier to ruin. That is the only reason puck clutches are harsher to engage... because they ramp the clamping load up on the clutches so there is less of a slip upon engagement. Slip creates heat, and heat will destroy the clutch.

Utilizing a full disc face will allow the heat to dissipate, but you won't get an increased torque/load bearing figure. You will just get much more of a streetable/controllable engagement (You can slip it more without worry that it will fry)

My equation was correct for a basic physics lesson in friction of two nondeformable bodies. I was trying to keep it simple.

Dude you explained it so well. So a with material being alike, the only reason a 4 puck holds on, or engages, better is because the pressure force is[has to be] stronger. If the pressure force wasn't strong then the 4 puck clutch could burn out quicker.

Do you know why it would burn out quicker? Is it because it is being introduced to more friction being separate pucks, instead of a whole disk, which would cause it to wear out quicker?

Where did you study all this stuff? I can't find any good information like the way you explain it. You're an engineer? Thanks once again.

The coefficient of friction changes based on the pressure pressing the two materials together on things like a ceramic metallic material. It's exactly like how some brake pads will have really crappy initial bite, but then the torque really ramps up with just a slight bit more pedal pressure.

The 4 puck just get to higher material pressure sooner than a 6 puck so it seems from the driver's seat to be a little more "on/off" even though the torque holding capacity is very similar or the exact same as a 6 puck.

[Rabbi010]

The coefficient of friction changes based on the pressure pressing the two materials together on things like a ceramic metallic material. It's exactly like how some brake pads will have really crappy initial bite, but then the torque really ramps up with just a slight bit more pedal pressure.

The 4 puck just get to higher material pressure sooner than a 6 puck so it seems from the driver's seat to be a little more "on/off" even though the torque holding capacity is very similar or the exact same as a 6 puck.


Thanks. What I'm trying to understand is why the 4 puck gets to the higher material pressure sooner. Because I always thought the 6 would get there quicker. Do you have any insight on this?

[daryl337]

My equation was correct for a basic physics lesson in friction of two nondeformable bodies. I was trying to keep it simple.



Yeah I wasn't saying you are wrong, I just thought by using that formula as it relates to a rotational object would help people understand the idea of the radius being important, but not surface area.

[Def]

Thanks. What I'm trying to understand is why the 4 puck gets to the higher material pressure sooner. Because I always thought the 6 would get there quicker. Do you have any insight on this?

Less area, same force = higher pressure

It's that simple.

[jr_ss]

The 4 puck just get to higher material pressure sooner than a 6 puck so it seems from the driver's seat to be a little more "on/off" even though the torque holding capacity is very similar or the exact same as a 6 puck.

Couldn't this be described as the load being applied to the 4puck vs the 6 puck?

Think of it like this; Most manufactures use the same PP clamping load for both the 4 and 6 puck clutches. Lets say that X amount of pressure being applied to both the 4 and 6 puck disk by the PP. The 6 puck is going to take that pressure easier making it "feel" less harsh because it has 2 extra pucks to absorb that clamping force versus the 4 puck.

I see that Def, just wrote exactly what I explained.

[fliprayzin240sx]

Wow...this shit went beyond technical. THis shit went down to the engineering stand point.
But bottom line, if you plan on daily driving the car and you are debating on whether or not to get ACT 4 puck vs 6 puck, GET THE 6 PUCK. You'll hate traffic and hill with a passion.

['97 S14 SE Turbo]

Oh noes, not the surface area and clutch torque capacity... Some people might know about that thread on FA....

For those that really understand the mechanics of material and yield strength, Surface Area matters...

Otherwise we all be driving on skinny narrow tires.

Surface area comes into play, because in the real world, everything is deformable/destroyable. If something is a perfect material and does not yield to shear loading, then SA wouldn't matter.

What other people keep on pointing out as "heat capacity" is basically a layman's version of understanding the shear yield strength of the material. For a given shear force, when spread over a SA, and doesn't not reach anywhere near the yield strength of the material, you don't have to worry about the material failing.

Here's a quick description of shear stength Shear strength - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Shear_strength)

Notice how force in a perpendicular direction doesn't matter, and SA matters. And that's why multi-plate clutches make do with smaller individual SA, but backs it up in multiple disks (SA multiplier)

And that's why the WB SPL uses a 240mm OD clutch disk vs the OEM 225mm clutch disk. And also why the 350Z uses a 250mm OD clutch disk... And also why the Porsche Carrera GT has a 170mm OD clutch with 4x disks...

...bottom line, SA matters!!!

[Rabbi010]

Less area, same force = higher pressure

It's that simple.

Wow! I can't believe I forgot that! That's the same reason with how master cylinders pressure is more if the cylinders area is smaller. Thanks for reminding you.

Wow...this shit went beyond technical. THis shit went down to the engineering stand point.
But bottom line, if you plan on daily driving the car and you are debating on whether or not to get ACT 4 puck vs 6 puck, GET THE 6 PUCK. You'll hate traffic and hill with a passion.


Yeah, for me to understand something, I need to get to the core of it. I'm writing an article about the differences in between 4 and 6 puck and I had to get to the core. A lot of places online just don't explain it in detail like this thread just did; it's just people saying "this is what it is and now accept it." Now I understand it fully. Thanks guys!

[Def]

Oh noes, not the surface area and clutch torque capacity... Some people might know about that thread on FA....

For those that really understand the mechanics of material and yield strength, Surface Area matters...

Otherwise we all be driving on skinny narrow tires.

Surface area comes into play, because in the real world, everything is deformable/destroyable. If something is a perfect material and does not yield to shear loading, then SA wouldn't matter.

What other people keep on pointing out as "heat capacity" is basically a layman's version of understanding the shear yield strength of the material. For a given shear force, when spread over a SA, and doesn't not reach anywhere near the yield strength of the material, you don't have to worry about the material failing.

Here's a quick description of shear stength Shear strength - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Shear_strength)

Notice how force in a perpendicular direction doesn't matter, and SA matters. And that's why multi-plate clutches make do with smaller individual SA, but backs it up in multiple disks (SA multiplier)

And that's why the WB SPL uses a 240mm OD clutch disk vs the OEM 225mm clutch disk. And also why the 350Z uses a 250mm OD clutch disk... And also why the Porsche Carrera GT has a 170mm OD clutch with 4x disks...

...bottom line, SA matters!!!

So wrong.... so very wrong...

It's not surface area, it's radius of gyration that matters as was already mentioned. If you reduce the radius of gyration, to hold the torque you have to employ additional disks to get the holding capacity up.


The coefficient of friction with anywhere near a realistic pressure plate clamping force is not going to come close to yielding a material. Not sure why you blabbered on endlessly about shear strength...



Please... tell me you're not an engineer and you just taught yourself about this from Wikipedia.

['97 S14 SE Turbo]

Radius of gyration is just a moment arm. Bigger the diameter/radius, the less shear load faced by the material. The smaller the diameter, the higher the shear load. Same theory as brake disk diameter

I can have a 2x radius of gyration clutch with a single disk, function the same as a 1x radius of gyration clutch with 2 disk. The math works out the same. It's just 2 x (a x b) or (2 x a) x b. You can a 2x strength material, or just 2x the load carrying capacity.

As for " coefficient of friction not going to come close to yielding a material", you need to go check up on that. What happens at the molecular level when something wear? It's the micro peaks of the material yielding into failure, thus breaking off (also known as wear.)

And based on what you claim, stuff like clutch disk failure never happens in the real world. Dunno about you, but where I got my engineering degree, we were taught to understand the theory, and how to derive equations, not just blindly use them. Only type of program that doesn't teach those are associate degree programs.

Heck, just go do a FBD for a clutch using deformable solid? Do that, and then get back with me on this discussion.

[Rabbi010]

Oh noes, not the surface area and clutch torque capacity... Some people might know about that thread on FA....

For those that really understand the mechanics of material and yield strength, Surface Area matters...

Otherwise we all be driving on skinny narrow tires.

Surface area comes into play, because in the real world, everything is deformable/destroyable. If something is a perfect material and does not yield to shear loading, then SA wouldn't matter.

What other people keep on pointing out as "heat capacity" is basically a layman's version of understanding the shear yield strength of the material. For a given shear force, when spread over a SA, and doesn't not reach anywhere near the yield strength of the material, you don't have to worry about the material failing.

Here's a quick description of shear stength Shear strength - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Shear_strength)

Notice how force in a perpendicular direction doesn't matter, and SA matters. And that's why multi-plate clutches make do with smaller individual SA, but backs it up in multiple disks (SA multiplier)

And that's why the WB SPL uses a 240mm OD clutch disk vs the OEM 225mm clutch disk. And also why the 350Z uses a 250mm OD clutch disk... And also why the Porsche Carrera GT has a 170mm OD clutch with 4x disks...

...bottom line, SA matters!!!

So what you're saying is that the SA helps the clutch tolerate more heat/damage which in-turn virtually increases its shear strength. But the downside to increasing the SA is the increase in weight which is one of the benefits of going to a puck clutch, weight savings. Correct?

['97 S14 SE Turbo]

full face material and puck clutch runs different material so it's apples to orange comparison. The pucked material have a higher shear strength, but needs higher clamping pressure to "grip", and that, like Def had pointed out is done by having smaller pucks to get higher clamping pressure out of the same pressure plate.

What's a better comparison is to keep the material the same, and either double of half the surface area. Check the power rating charts for multi-plate clutch systems to see how the power rating is multiplied by the number of disks in the system.

As for the often thrown about "radius of gyration", it's being misunderstood by many people. Grab any engineering handbook for it's definition, what it describes is the equivalent distance for a given surface area. This is used because a clutch disk has an OD and ID. The radius of gyration is not just the (OD + ID)/2 but a radius where the outer SA is equal to the inner SA. It's close to the average, but it's not the same. I've put up numbers for the WB SPL (which is just 280ZX Turbo size clutch), and stock KA clutch, but also a theoretical setup where the OD matches the WB SPL, but the clutch face is actually only 1" wide like the OEM setup.

As you can see, you can increase radius of gyration going from WB SPL to the theoretical, gaining clutch torque capacity on paper, with the same exact pressure plate, but you lose out on "heat capacity" (term as used by folks in the clutch industry). Well, that heat capacity loss is explained here by the huge lost in SA. Without a change in clutch friction material, what worked for the WB SPL has to work with a loss of 35% in SA. And if we were to arbitrary use 10,000 newton of force, the Theoretical clutch has to deal with 55% more shear stress than the WB SPL.

For example:

Theoretical WB SPL OEM Carrera GT x4
OD 240 240 225 170 mm
ID 215 200 200 150 mm
OD+ID/2 227.5 220 212.5 160 mm

SA OD 45,239 45,239 39,761 22,698 mm^2
SA ID 36,305 31,416 31,416 17,671 mm^2
SA OD+ID/2 40,649 38,013 35,466 20,106 mm^2

SA,OD-ID 8,934 13,823 8,345 5,027 20,106 mm^2

Radius of Gyration 227.84 220.91 212.87 160.31 mm

Shear Stress 1.12 0.72 n/mm^2
Stress delta % 55%
SA % loss -35%

So, as it can be seen, talking about clutch torque capacity without thinking about SA just shows the lack of fundamental understanding of what goes on.

Also included are some numbers for the Carrera GT. With only 1 disk, there's not much to work with, but with 4 disks, there's more than plenty SA to take on the shear load.

[HYPNOTIK]

So, after all the BS surface area has a direct correlation to holding capacity?

[daryl337]

I like this discussion.

There is alot to be said about the material of the clutch that you choose.

The point I think def was making was more along the lines of: the friction produced between 2 materials is decided strictly by what we were establishing earlier.


Of course, the post I was making confirmed that, I did infer that the surface area of the material will be a factor as to whether it will stand up to the heat of slip. This would also be a factor in your shear stress analysis.


The ability for the clutch to actually not come apart is largely influenced by the material's ability to withstand shear. If we are using a poor material, then of course increasing the area that we are applying the load to is going to increase that materials chances to withstand the shear.

The point being made however, is that it does not directly have an effect on the ability of the clutch to prevent slippage. It does have an effect on the clutch to reduce the effect of wear, and prevent the clutch from coming apart. There is why we won't install a giant shear pin and call it a clutch. If it slips, then it has no use as a clutch.



So what you are introducing then, is a different issue regarding clutch selection. The destructability of the clutch itself.

I would argue that increasing surface area of a clutch should be a lesser priority than purchasing a clutch made of better materials. Don't install a 4 ft. marshmallow.



Hypnotik: I think it needs to be clear that the type of forces he is discussing is different than slip.


Its still failure however, as ultimately the surface would come apart.

[supersayianjim]

i have a 6 puck i daily drive with now. i love it. excellent engagement and not too harsh(for me). if i was doing a drag only car i would get a 4(unsprung) disc.

[Def]

Radius of gyration is just a moment arm. Bigger the diameter/radius, the less shear load faced by the material. The smaller the diameter, the higher the shear load. Same theory as brake disk diameter

I can have a 2x radius of gyration clutch with a single disk, function the same as a 1x radius of gyration clutch with 2 disk. The math works out the same. It's just 2 x (a x b) or (2 x a) x b. You can a 2x strength material, or just 2x the load carrying capacity.

As for " coefficient of friction not going to come close to yielding a material", you need to go check up on that. What happens at the molecular level when something wear? It's the micro peaks of the material yielding into failure, thus breaking off (also known as wear.)

And based on what you claim, stuff like clutch disk failure never happens in the real world. Dunno about you, but where I got my engineering degree, we were taught to understand the theory, and how to derive equations, not just blindly use them. Only type of program that doesn't teach those are associate degree programs.

Heck, just go do a FBD for a clutch using deformable solid? Do that, and then get back with me on this discussion.

So at least now you admit that surface area does not directly impact clutch torque capacity.

Wear on a microscopic scale is not the same as a shear failure, and NO engineers would ever equate the two. Yes, there is shear loading, and a very very minute amount of wear for each clutch slip, but it is not a wholesale "shear stress induced failure" like what the term would imply.


I know quite a bit about the equations and real world application of clutches. You seem like the one that's twisting words and "reaching" to try to prove yourself wrong.


My original post to you still stands, and is 100% correct.

[Def]

So, after all the BS surface area has a direct correlation to holding capacity?

No... '97 S14 SE Turbo has put his foot in his mouth and is trying to hard to twist it around to where everybody else is just "misunderstanding" him.

[Def]

So what you're saying is that the SA helps the clutch tolerate more heat/damage which in-turn virtually increases its shear strength. But the downside to increasing the SA is the increase in weight which is one of the benefits of going to a puck clutch, weight savings. Correct?

I'd say surface area is a minor variable in heat capacity of a clutch. Primary variables would be (thermal) mass of the clutch disk and its friction and material strength response to elevated temperatures.

More surface area does allow the clutch to cool down faster via conductive heat transfer to the flywheel and pressure plate, but peak temps will be influenced by clutch disk mass and its specific heat. Material failure will be dictated by how much strength the material loses at elevated temperatures and obviously by mechanical construction.

[Rabbi010]

If you look up '4 Puck vs 6 Puck' anywhere on google, nobody gets this technical. I love it

[herbieS13]

i used to think i was a half intelligent guy until this thread came along

['97 S14 SE Turbo]

No... '97 S14 SE Turbo has put his foot in his mouth and is trying to hard to twist it around to where everybody else is just "misunderstanding" him.

What's with the e-thuggery? I had provided an example where a larger radius of gyration would have less torque capacity. Even by yor admission, now matreial shear strenght plays a factor, and we all now that is dependent on SA. You are definitely not atanding by your words.

[Def]

What's with the e-thuggery? I had provided an example where a larger radius of gyration would have less torque capacity. Even by yor admission, now matreial shear strenght plays a factor, and we all now that is dependent on SA. You are definitely not atanding by your words.

No, I said strength vs. temperature matters if you're pounding on a clutch to create a really high temperature situation and something like an organic material that's practically melting. During normal or even "hard" usage surface area and shear failure of a material is of zero concern.


So I'll say again, surface area isn't a primary design consideration in a clutch for a production based engine.

[Rabbi010]

I wrote a basic article for the average enthusiast to understand. Inspired by my confusion and the fact that I can't find a straight forward article like this anywhere.

Difference Between a 4-Puck Clutch and a 6-Puck Clutch | AutoNest | Birth Place of your Auto Race (http://www.autonest.org/autoeducation/difference-between-a-4-puck-clutch-and-a-6-puck-clutch)

What do you guys think (since you're the engineers)?

[daryl337]

I'm not an engineer, Def is. :)


I'm more of a mathy-sciency, supernoob.

['97 S14 SE Turbo]

No, I said strength vs. temperature matters if you're pounding on a clutch to create a really high temperature situation and something like an organic material that's practically melting. During normal or even "hard" usage surface area and shear failure of a material is of zero concern.

So I'll say again, surface area isn't a primary design consideration in a clutch for a production based engine.

And I'll say again you are ignoring a critical factor. If you don't put into consideration shear strength of the material, then you'd end up with either a marginal design or an overkill design. The strength of any design is only as strong as it's weakest link. In the case of clutches, it's the mechanical grip between the wear surfaces, the bonding/mounting of the wear material to the hub, and the wear material itself.

The heat you are talking is not as critical as you think because once a clutch has completely engaged, with no slip, it's strength is only as strong as the weakest links mentioned above. If heat is so critical, our vehicle's bell housing would be ventilated, with a fresh air intake port, and there would be heat fins on the clutch cover, etc for heat ejection. But we don't, nor do most manual transmission vehicles. If I was to design a clutch system designed to constantly slip, yes, heat rejection would be as critical. In most of those cases, they would use wet clutches, like the clutch packs for AWD cars, and LSDs on our cars.

I'm sure you know that in a typical design, the designer would specify a surface area that has from 20% to 50% margin, where the expected torque application would only generate from 50% to 80% the shear stress, that the given material, with X SA, can handle, for margin of safety. Now this being said, this particular clutch's maximum torque capacity would be limited to the max shear strength. What the designer can do, to minimize the shear stress on the clutch material, is what's typically being thrown about for clutch design. They can change the effective radius (radius of gyration), and increase SA.

In most cases, radius of gyration is limited by packaging needs, but the cheapest way to achieve the results. Increasing SA has two options. Either widen the contact patch, or double/triple the number of disks to increase total SA to decrease the shear stress.

Remember, Shear stress is tau=F/SA... and torque = force x radius so, torque (max) = tau x SA x radius x n where n = number of plates... And to figure out the max torque capacity, you'd put in the shear strength of the weakest material, multiplied by SA, and radius. So, if you are limited in material choice, you can either decrease it's force, increase SA, or increase the number of plates (same as increasing SA). Alternatively, you can find a material with higher shear strength, and not change anything else. Also, without changing material, SA, or n, radius can be increase to improve the max torque capacity.

So, SA matters...

[daryl337]

The issue regarding heat *is* of a main design concern.

From a practical standpoint, in order to engage any clutch, you are going to have a moment of slip and heat.

Especially since we are talking about creating and upgrading clutches for performance use. Lets face it, most clutch disc failure comes down to slippage from heat. The hot spotting, and glazing of the clutch is directly related to excessive heat.

A "worn out" clutch slips because as the material thins, the pressure plate is unable to exert the same force on the disc face, resulting in a loss of friction. This loss of friction will cause the clutch to glaze over from excessive heat.

A "smoked" clutch is generally a clutch that has either exceeded its force limit as determined by its total friction, or was slipped excessively upon engagement (high rpm engagements with a slow foot can do that!) The hot spots created lower the effective friction coefficient of the material.





Shear stresses are present in the clutch disc. Namely, to transfer the frictional forces from the material to the central medium (the splines). Largely, however, the weak points are determined by the quality and method of the bonding of material to the disk itself, and by the material you choose. Especially in high performance clutch applications.

Talking about the shear strength of your material only introduces whether the material would be suitable for a load application in general.

Terrible example: you could take a piece of glass with high surface area, and try to turn it into a clutch. Unfortunately, assuming you have a low micron finish of the glass, it is not going to tract very well, and will result in a poor torque capacity. Likewise, your point regarding minimal surface area... if the material has such a small cross sectional area that it can't maintain a load well enough to transfer it to the base disc, then the material may fall apart. It then, is going to come down to the material that you use.

In terms of surface area then, we only need the minimum amount of material necessary to transfer the load to the medium without inducing a failure of the material. Further increasing surface area does not have any effect on the torque capacity that the clutch can produce.


However, as heat is one of the main destructors of clutches, the main consideration that should be done in regards to how much material is optimal is the materials ability to dissipate heat. Essentially, as Def pointed out, the mass and the materials strength response to heat are the primary factors that are going to be considered.

[BeerBringer]

Only the apparent contact area will change between the 4-p and 6-p clutch.
The true contact area remains the same!

I can't explain why but something makes the coefficient of friction change to the 'better' with less pucks.

[daryl337]

It is the pressure applied. Higher pressure on less area

[Def]

The issue regarding heat *is* of a main design concern.

From a practical standpoint, in order to engage any clutch, you are going to have a moment of slip and heat.

Especially since we are talking about creating and upgrading clutches for performance use. Lets face it, most clutch disc failure comes down to slippage from heat. The hot spotting, and glazing of the clutch is directly related to excessive heat.

A "worn out" clutch slips because as the material thins, the pressure plate is unable to exert the same force on the disc face, resulting in a loss of friction. This loss of friction will cause the clutch to glaze over from excessive heat.

A "smoked" clutch is generally a clutch that has either exceeded its force limit as determined by its total friction, or was slipped excessively upon engagement (high rpm engagements with a slow foot can do that!) The hot spots created lower the effective friction coefficient of the material.





Shear stresses are present in the clutch disc. Namely, to transfer the frictional forces from the material to the central medium (the splines). Largely, however, the weak points are determined by the quality and method of the bonding of material to the disk itself, and by the material you choose. Especially in high performance clutch applications.

Talking about the shear strength of your material only introduces whether the material would be suitable for a load application in general.

Terrible example: you could take a piece of glass with high surface area, and try to turn it into a clutch. Unfortunately, assuming you have a low micron finish of the glass, it is not going to tract very well, and will result in a poor torque capacity. Likewise, your point regarding minimal surface area... if the material has such a small cross sectional area that it can't maintain a load well enough to transfer it to the base disc, then the material may fall apart. It then, is going to come down to the material that you use.

In terms of surface area then, we only need the minimum amount of material necessary to transfer the load to the medium without inducing a failure of the material. Further increasing surface area does not have any effect on the torque capacity that the clutch can produce.


However, as heat is one of the main destructors of clutches, the main consideration that should be done in regards to how much material is optimal is the materials ability to dissipate heat. Essentially, as Def pointed out, the mass and the materials strength response to heat are the primary factors that are going to be considered.

Pretty much this.

Heat is a pretty big factor in any clutch taking off from a stop. It's not a huge amount of sustained heat input, but large spikes that are the problem. Hence why there aren't "cooling fins" on anything. The thermal mass and conduction of heat out from the disk primarily dictate its thermal properties.

Clutch material failure occurs where its bonded to the clutch disk, not from large scale shear failure. The bonding area is typically a small small small percentage of the total area of the friction material, typically rivets, with some type of adhesive/molecular bond as a backup.


Wholesale shear failure of a clutch disk just doesn't happen in reality or on paper. The material loaded by the bonding mechanism will fail way before that is even a remote possibility.

So again, surface area of a clutch is primarily a heat transfer driver and it is not a huge factor in clutch design, it's more a secondary design consideration. Shear failure does not just happen across the whole clutch material.

['97 S14 SE Turbo]

Bah, if your bonding mechanism is too small, it fill fail prematurely (too much shear stress, not enough SA). If the number of rivets is insufficient or undersized (not enough SA), it will fail.

and here's a quote from a reference handbook since there is are folks who refuse to see the elephant in the room:

"By far, the most widely used is the organic material which consists mainly of asbestos yarn, woven with copper or brass wire. The maximum operating pressure is 30 lb/in 2 for these materials, and the friction coefficient ranges from 0.2 to 0.45. A good design estimate for friction coefficient is 0.25. The torque requirement of the clutch will determine the size and the number of plates. These materials have changed very little over the past 25 years, and still perform satisfactorily at low cost in many applications."

Rothbart, Harold A.; Brown, Thomas H.. Mechanical Design Handbook (2nd Edition).
New York, NY, USA: McGraw-Hill Professional Publishing, 2006. p 795.
ebrary: Server Message (http://site.ebrary.com/lib/asulib/Doc?id=10180090&ppg=795)
Copyright © 2006. McGraw-Hill Professional Publishing. All rights reserved.

Also known as SA... If your torque requirement puts too much stress, over the above mentioned 30lb/in^2, it will fail out right.

But if this not sufficient to make people realize that SA matters in clutch design, here's another easy to understand real world example.

Nissan 240SX KA clutches. Lets just look at what's available on the market, particularly one manufacturer to minimize material and bonding technique variation. This is the link (http://www2.advancedclutch.com/products/clutchkits.aspx?prod_id=7889#7889) for the KA application, with the 225mm od, 200mm id clutch, using a full face organic material. And this is the link (http://www2.advancedclutch.com/products/clutchkits.aspx?prod_id=8714#8714) for the Z31 Turbo clutch (aka WB SPL), with the 240mm od, 200mm id clutch.

Yes, there are differences in the pressure plate design, and clamping load, but the ultimate result we want to look at is the advertised torque capacity. Just look at the KA's XT NX1-XTSS, and it's advertised capacity of 340 ft/lbs, and the Z31's NX7-HDSS, and it's rated 360 ft/lbs. 20 ft/lbs rated capacity difference is not much, so we could somewhat compare it.

Using what's been said here, by others saying about SA being not critical, someone who's interested in purchasing a new clutch for his high-powered KA, would not know which product is better for his use. He would just see that NX1-XTSS has a 87% increase in clamping load, and see that the advertised torque capacity is pretty much the same.

But by knowing that having a larger SA on the Z31 application, that there will be less shear load/stress on the friction material, the lighter clamping load would mean a better drive-ability. (This is definitely true of the WB SPL. Those that have driven it knows how OEM it feels.)

This is also the same reason why JWT sells a 350Z clutch setup for SR. 350Z clutch is a 250mm OD clutch. Much better drive-ability, and life.

but hey, for those that are stuck on the equation and tries not to look at the whole system, they can have that hard to use NX1-XTSS clutch to use...

[Def]

Bah, if your bonding mechanism is too small, it fill fail prematurely (too much shear stress, not enough SA). If the number of rivets is insufficient or undersized (not enough SA), it will fail.

and here's a quote from a reference handbook since there is are folks who refuse to see the elephant in the room:



Also known as SA... If your torque requirement puts too much stress, over the above mentioned 30lb/in^2, it will fail out right.

But if this not sufficient to make people realize that SA matters in clutch design, here's another easy to understand real world example.

Nissan 240SX KA clutches. Lets just look at what's available on the market, particularly one manufacturer to minimize material and bonding technique variation. This is the link (http://www2.advancedclutch.com/products/clutchkits.aspx?prod_id=7889#7889) for the KA application, with the 225mm od, 200mm id clutch, using a full face organic material. And this is the link (http://www2.advancedclutch.com/products/clutchkits.aspx?prod_id=8714#8714) for the Z31 Turbo clutch (aka WB SPL), with the 240mm od, 200mm id clutch.

Yes, there are differences in the pressure plate design, and clamping load, but the ultimate result we want to look at is the advertised torque capacity. Just look at the KA's XT NX1-XTSS, and it's advertised capacity of 340 ft/lbs, and the Z31's NX7-HDSS, and it's rated 360 ft/lbs. 20 ft/lbs rated capacity difference is not much, so we could somewhat compare it.

Using what's been said here, by others saying about SA being not critical, someone who's interested in purchasing a new clutch for his high-powered KA, would not know which product is better for his use. He would just see that NX1-XTSS has a 87% increase in clamping load, and see that the advertised torque capacity is pretty much the same.

But by knowing that having a larger SA on the Z31 application, that there will be less shear load/stress on the friction material, the lighter clamping load would mean a better drive-ability. (This is definitely true of the WB SPL. Those that have driven it knows how OEM it feels.)

This is also the same reason why JWT sells a 350Z clutch setup for SR. 350Z clutch is a 250mm OD clutch. Much better drive-ability, and life.

but hey, for those that are stuck on the equation and tries not to look at the whole system, they can have that hard to use NX1-XTSS clutch to use...

You should brush up on your engineering. He's talking about clamping pressure, which is just something you do for the marcel spring and organic material to have a long life. He's not talking at all about shear loads.

His talk of the "size" or number of clutch plates is talking about the radius of gyration and torque capacity of the clutch. Again, has *NOTHING* to do with surface area.



So thanks for finding a quote that proves my point very succinctly - surface area is a secondary concern in clutch design (i.e. I don't want to overload my friction material with the clamping pressure if it's soft like an organic material).

[Def]

BTW - all your ranting about SA and clutching holding is worthless. That has everything to do with surface area and clamping pressure. A larger radius of gyration and less clamping pressure is needed for the same torque holding capacity. These variables are INDEPENDENT of SA - PERIOD!


If you keep arguing this, I really really hope you're not an engineer, as you obviously missed that whole important lesson on how friction actually behaves.

['97 S14 SE Turbo]

How can clamping pressure overload an object? It compresses it. Most material love compression stress. Are you actually telling me that your clutch material, with the metal mix material fails at 2 ATM of pressure? 30 psi!!!! In the 240mm and 225mm clutch example, that results in a clamping load of 642 and 388 lbs respectively.

However, shear loads is where materials fail relatively easier.

And by your argument, you should be running a 165mm width tire instead of a 255mm width tire. Care to be able to explain that? With your explanation, it's obvious you've missed out on mechanics of material. I can be sure you don't practice in a field where material strength is critical. Friction is a function of material interaction (deforming into each other, under pressure), and normal force. If the material is perfect, then the "grip" is solid, because nothing will fail, because the material has bonded/welded together. And molecularly, no material is perfectly flat, and will have high and low spots that grip. Why do rough grade sandpaper have more grip? it has more teeth to bite into another material. Then why does it fail after too much force is place on it? The sands on the sand paper got sheared off, or the material that it's in contact in, got gouged, and material removed.

Is that all you can do to explain it, other than making personal attacks? Trying to distract from the discussion? Keep on hiding behind "you can't be an engineer" comment. I'm bringing equations and using the most basic theory to explain everything away, even have an example of where a larger radius of gyration (equivalent radius), can have less torque capacity. If you truly are an engineer, try to explain that one away, but, you kept on skirting that discussion.

Let's go back to the 30 psi limit for the material. Let's just plug that number into the example we have been using. Plugging them into the 240mm vs 225mm clutch, get relatively sane numbers that's on par with ACT's advertised torque capacity with a fair 100% margin of safety. It'd be insane to sell a product right at it's 100% max capacity.


radius of gyration 8.70 8.97 8.38 in

OD 240 240 225 mm
ID 200 215 200 mm
OD 9.45 9.45 8.86 in^2
ID 7.87 8.46 7.87 in^2
SA OD 70.12 70.12 61.63 in^2
SA ID 48.69 56.27 48.69 in^2

t=f/a 30 30 30 psi (max shear pressure)
total SA 42.85 27.70 25.87 in^2
max shearforce 1285.54 830.85 776.07 lbs (max shear pressure x SA)
radius of gy 0.72 0.75 0.70 ft
100% 931.71 621.08 542.00 ft-lbs
50% 465.86 310.54 271.00 ft-lbs



And let's use Def's definition and plugging them in.


radius of gyration 8.70 8.97 8.38 in

OD 240 240 225 mm
ID 200 215 200 mm
OD 9.45 9.45 8.86 in^2
ID 7.87 8.46 7.87 in^2
SA OD 70.12 70.12 61.63 in^2
SA ID 48.69 56.27 48.69 in^2

Total SA 21.43 13.85 12.93 in^2 (1x per Def's definition of crushing limit.)
max psi 30 30 30 psi (according to Def so it won't be crushed)
clamping force 642.77 415.43 388.04 lbs(max psi x SA)
mu 0.45 0.45 0.45 coefficient of friction (per handbook, from 0.2 to 0.45, using max)
Friction 289.25 186.94 174.62 Friction = force normal x mu
radius of gy. 0.72 0.75 0.70 ft
max torque 209.64 139.74 121.95 ft-lb


max torque 465.00 310.50 270.00 ft-lb (let's try to figure out what radius it takes to get the same level)
radius of gy. 1.61 1.66 1.55 ft (note, this is in radius!!!)


so, in conclusion, according to Def's definition, we will need clutches that is at least 3 ft in diameter to even meet the torque capacity of the OEM KA clutch. The numbers do not make sense.

In conclusion, after all the personal attacks about not being an engineer, etc, Def's definition show's that his knowledge in clutch design is lacking. What a load of

:bs:

PS: oh wait, see that example (middle column)? That's a clutch with a larger radius of gyration, with a smaller SA than the 240mm example. Look at the resulting torque capacity of both the real and Def's calculation. What's the result? The larger SA clutch still has more torque capacity...

again, radius of gyration being a key determinate of Torque? :cj: Here's an example where it's not true.

['97 S14 SE Turbo]

BTW - all your ranting about SA and clutching holding is worthless. That has everything to do with surface area and clamping pressure. A larger radius of gyration and less clamping pressure is needed for the same torque holding capacity. These variables are INDEPENDENT of SA - PERIOD!


If you keep arguing this, I really really hope you're not an engineer, as you obviously missed that whole important lesson on how friction actually behaves.

Anyone that demonstrates a lack of fundamental grasp of mechanics of material such as yourself should not claim to be an engineer.

Pressure IS dependent on SA! PERIOD!! It's force/SA....

Don't know what product you engineer/design, with what you have demonstrated, you won't survive in the industry I'm in. The last project I worked on, sends little care packages to native people hiding out in the desert, free of charge, courtesy of Uncle Sam.

[Def]

Anyone that demonstrates a lack of fundamental grasp of mechanics of material such as yourself should not claim to be an engineer.

Pressure IS dependent on SA! PERIOD!! It's force/SA....

Don't know what product you engineer/design, with what you have demonstrated, you won't survive in the industry I'm in. The last project I worked on, sends little care packages to native people hiding out in the desert, free of charge, courtesy of Uncle Sam.

...sigh... I like how everybody in here sees that you're a complete jackass and don't know what you're talking about... except you.

Only a jackass would think you can have a material that only has a shear strength of 30 psi and hold it onto a metal disk with rivets. I think jello has a higher shear strength than that... (that's a joke, but not a huge exageration).


BTW -if you think the maximum shear stress is a big problem in organic clutch disks, do the calculation of how much shear stress is around the few rivets holding the organic material to the metal disk.



I work in the Aerospace industry, on more complicated projects than you do I guarantee, and I'd tell you to go back to school if I heard a fellow engineer spouting off rubbish like you are right here...

[daryl337]

I'd like to point out for everyone to see, that the results are skewed in a very, very awkward manner. The reason the "torque capacity" is increased in his theoretical study is that he is applying a higher clamping force to his clutch. Period. Had he equalized the pressure plate, the friction would not have changed.

He gets away with applying the higher clamping load due to the surface area, as I suspect was partially his point. However, that is not due to shear stress, but as Def pointed out, max operating pressure of the material. Once again, this means that the surface area is only going be a factor of whether or not the material is suitable for needs we have. Surface area then, sets the limit for the construction of the material, and the max pressure we can apply to it.

So, the TL;DR version is, you could not take a 4 puck clutches pressure plate, and stuff it on a 6 puck clutch (which has more surface area), and expect an increase in torque capacity. It does not work. Period.

You could, however, take advantage of a clutch that has more material on it by applying a greater clamping force. This is assuming that the two clutches are made of the same material.


Material is still largely going to determine what we are capable of getting away with.



Also, to make a couple of notes about the tire contact patch comment.

Its fairly common knowledge among engineers that polymers follow a different characteristic with friction. Also, it is not the static friction of the tire that changes with a larger contact patch, it is the rolling resistance.

Think closely about the contruction of a tire. You have the sidewalls, which are a smoothed rubber, and then the shoulders, which introduce the tread, and the main tread.
As you sit from a stand still, you're weight is all located on the tread, which has the highest friction coefficient. (Tread increases friction coefficiency, due to the elasticity of the rubber coming apart as you go across pavement)
With the construction of a tire, the compound primarily affects how the tires will tract. If you go with a softer tire, you need to increase the contact patch to support the weight of the vehicle, otherwise the tire won't handle it. There is a secondary benefit to going with a wider tire. As road surfaces are uneven, and cornering changes the weight distribution, you are increasing the risk that your main tread is *not touching at all!*

With a skinny tire, chances are under a high weight shift while cornering, that the actual contact surface of your tire is no longer on the ideal treaded surface... instead it may now be riding on the shoulder of the tire. The shoulder, has a lower coefficient of friction. So by increasing the width of the tire, you are increasing the chances that you will be riding on a treaded contact area, vs. a shoulder.

[i3igpete]

So I'll say again, surface area isn't a primary design consideration in a clutch for a production based engine.

The coulomb friction model is not correct for clutches. In a clutch the stick-slip behavior is dominated by the micro-stiffness of the surface roughness (which are asperities or bristles depending on the model). More bristeles give better stiction. Read up on the LuGre friction model.

[Tantwoforty]

i have a 4 puck exeedy and it feels totally smooth and street able.