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 . 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.

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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

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.

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Rabbi010

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

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.

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thefro526

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).

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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?

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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)

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Rabbi010

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.

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Rabbi010

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

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."

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

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.

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Rabbi010

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

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.

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Def

Less area, same force = higher pressure

It's that simple.

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jr_ss

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.

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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.

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'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

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

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.


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

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.

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'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

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:

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?

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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.

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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

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.

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Def

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.

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