4 Puck vs 6 Puck - Page 2 - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

Def · 05-31-2011, 01:46 PM

Quote:

Originally Posted by 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?

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 · 05-31-2011, 03:37 PM

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

herbieS13 · 05-31-2011, 04:11 PM

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

'97 S14 SE Turbo · 05-31-2011, 05:51 PM

Quote:

Originally Posted by 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.

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 · 05-31-2011, 06:55 PM

Quote:

Originally Posted by '97 S14 SE Turbo

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 · 05-31-2011, 07:33 PM

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

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

daryl337 · 06-01-2011, 09:08 AM

I'm not an engineer, Def is.

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

'97 S14 SE Turbo · 06-01-2011, 06:35 PM

Quote:

Originally Posted by Def

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 · 06-02-2011, 01:39 PM

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 · 06-02-2011, 02:37 PM

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 · 06-02-2011, 03:32 PM

It is the pressure applied. Higher pressure on less area

Def · 06-02-2011, 06:40 PM

Quote:

Originally Posted by 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.

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 · 06-03-2011, 06:28 PM

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:

Quote:

"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
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 for the KA application, with the 225mm od, 200mm id clutch, using a full face organic material. And this is the link 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 · 06-03-2011, 06:45 PM

Quote:

Originally Posted by '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:

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 for the KA application, with the 225mm od, 200mm id clutch, using a full face organic material. And this is the link 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 · 06-03-2011, 06:47 PM

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 · 06-03-2011, 11:55 PM

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.

Code:

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.

Code:

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

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?

Here's an example where it's not true.

'97 S14 SE Turbo · 06-04-2011, 12:36 AM

Quote:

Originally Posted by 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.

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 · 06-04-2011, 01:39 PM

Quote:

Originally Posted by '97 S14 SE Turbo

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 · 06-06-2011, 10:49 AM

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 · 05-02-2012, 09:22 AM

Quote:

Originally Posted by Def

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 · 05-04-2012, 01:23 AM

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

06-01-2011, 09:08 AM	#37
daryl337 Zilvia Junkie Join Date: Aug 2005 Location: Pac NW Age: 35 Posts: 589 Trader Rating: (1) Feedback Score: 1 reviews	I'm not an engineer, Def is. I'm more of a mathy-sciency, supernoob. __________________ This is my clever and witty signature.

06-02-2011, 01:39 PM	#39
daryl337 Zilvia Junkie Join Date: Aug 2005 Location: Pac NW Age: 35 Posts: 589 Trader Rating: (1) Feedback Score: 1 reviews	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. __________________ This is my clever and witty signature. Last edited by daryl337; 06-02-2011 at 01:43 PM.. Reason: -to continue with my reasoning.

06-02-2011, 03:32 PM	#41
daryl337 Zilvia Junkie Join Date: Aug 2005 Location: Pac NW Age: 35 Posts: 589 Trader Rating: (1) Feedback Score: 1 reviews	It is the pressure applied. Higher pressure on less area __________________ This is my clever and witty signature.

06-03-2011, 06:47 PM	#45
Def Post Whore! Join Date: Apr 2004 Location: Houston, TX Posts: 2,701 Trader Rating: (16) Feedback Score: 16 reviews	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. __________________ S13 Hatch - Goes around tracks quickly DEFSPORT

06-03-2011, 11:55 PM	#46
'97 S14 SE Turbo Zilvia Member Join Date: Aug 2010 Location: Tempe, Az Posts: 165 Trader Rating: (1) Feedback Score: 1 reviews	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. Code: 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. Code: 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 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? Here's an example where it's not true.

05-31-2011, 03:37 PM	#32
Rabbi010 Zilvia Member Join Date: Feb 2007 Location: Long Island, New York Age: 31 Posts: 186 Trader Rating: (0) Feedback Score: 0 reviews	If you look up '4 Puck vs 6 Puck' anywhere on google, nobody gets this technical. I love it

05-31-2011, 04:11 PM	#33
herbieS13 Zilvia Junkie Join Date: Nov 2008 Location: FT Campbell, KY. Posts: 329 Trader Rating: (2) Feedback Score: 2 reviews	i used to think i was a half intelligent guy until this thread came along

05-31-2011, 07:33 PM	#36
Rabbi010 Zilvia Member Join Date: Feb 2007 Location: Long Island, New York Age: 31 Posts: 186 Trader Rating: (0) Feedback Score: 0 reviews	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 What do you guys think (since you're the engineers)?

06-02-2011, 02:37 PM	#40
BeerBringer Join Date: Apr 2004 Location: Sweden Posts: 27 Trader Rating: (0) Feedback Score: 0 reviews	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.

06-06-2011, 10:49 AM	#49
daryl337 Zilvia Junkie Join Date: Aug 2005 Location: Pac NW Age: 35 Posts: 589 Trader Rating: (1) Feedback Score: 1 reviews	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. __________________ This is my clever and witty signature.

05-04-2012, 01:23 AM	#51
Tantwoforty Nissanaholic! Join Date: May 2009 Location: Riverside ca Age: 31 Posts: 1,890 Trader Rating: (20) Feedback Score: 20 reviews	i have a 4 puck exeedy and it feels totally smooth and street able.

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