Heated discussion on big brake conversions.

[Andy335Touring]

Moderator comment:

I've split this thread away from Rob's thread as it was way off topic. Please continue this discussion here.

Cheers,

Ian (ian332isport)


Looks like the pad/caliper isn't big enough for the disc ?

[ed325i]

Looks like the pad/caliper isn't big enough for the disc ?

That is what I said about these ones and its the reason I went for the 312mm ones like on www.300mm.de and not the wms ones.




ED

[ed325i]

Dont know what MC I am going to use, but thinking about it a e34/e32 one should be ok.

ED

[ed325i]

Demlot used 23/23mm on his dont know what it is off.

ED

[keri-WMS]

Looks like the pad/caliper isn't big enough for the disc ?

That is what I said about these ones and its the reason I went for the 312mm ones like on www.300mm.de and not the wms ones.

lol, ok lets try again!

The basic POWER of a braking system is torque. One way to get this is bigger pistons or "sticky pads" (coefficient of friction for the technically minded ), but that's not the issue here so we'll forget about that for now.

The other way to get torque is through leverage. The further out from the hub the pad is the more torque is applied, this is why bigger discs create more powerful brakes.

HOWEVER...............

The effective point that the pad applies it's force (ie, the "end of the lever") is dead in the middle of the pad. So a pad that is 40mm high (WMS and MOST MOTORSPORT pads) by say 100mm wide will give you MORE POWER than a pad that's 80mm high (like most OEM pads) by say 100mm wide when both types are aligned to the outside diameter of the same disc.

To put it yet another way:

A 80mm high OEM pad on a 300mm disc has a effective radius of 110mm - so it behaves like a 220mm disc
(300mm/2=150mm. 80mm/2=40mm. 150mm-40mm=110mm)

A 40mm high WMS pad on a 300mm disc has a effective radius of 130mm - so behaves like a 260mm disc
(300mm/2=150mm. 40mm/2=20mm. 150mm-20mm=130mm)

Hands up who doesn't understand.....?

[stevetigger]

Hand flies into the air, faster than the North Koreans can fire them damn missiles at the good Ole US of A

[keri-WMS]

Hand flies into the air, faster than the North Koreans can fire them damn missiles at the good Ole US of A

lol! Would the equation help? I'll have to host/post a jpg as there are lots of daft symbols in there...

The bottom line is there's more power this way, it's intentional.

[stevetigger]

I sort of get it!

If a plate was spinning and you tried to stop it with your finger, then tried to stop it with your hand.....The hand would be better, regardless the size of plate!

[keri-WMS]

I sort of get it!

If a plate was spinning and you tried to stop it with your finger, then tried to stop it with your hand.....The hand would be better, regardless the size of plate!

Nope, nearly!

More like: You're spinning a HEAVY plate (think it terms of a lot of energy there, call it a 2-inch thick iron plate!), a few fingers against the edge will have an easier job than shoving your palm into the middle and trying not to get a twisted wrist...

Does that help?

[MFree]

LOL

Go keri!

;)

(cross fingers they fit, dont rub on the ball joints, fit under dem splitties... etc etc)

We will know today (gulp)

[tim_s]

While I understand what you're saying, surely considering the amount of effort required is only part of the story?
Sure the centre of the pad is where the piston applies its force, but when the pad is pushed against the disk, the whole surface area of the pad is acting upon the disk. So it may require more pedal effort (which is where MCs and so forth come in), but the larger pad will ultimately have greater stopping power, no? surely the 20mm difference in leverage is much less important than the massive difference in pad area?
In other words i'm suggesting a big-ass 80mm x 100mm pad covering the whole disk will give greater stopping power than bicycle brake blocks on the outside of the disk to exaggerate the point.

[Demlotcrew]

Those look good but it's still single piston stuff which is slightly gash even though BMW use them on everything these days.
Single piston calipers are like trying to squash a coke can with one hand but make them big enough and I guess they'll do the job. What master cylinder are you using out of interest?

The WMS ones look superb though and multi piston calipers are better - if a lot more money.

The expert speaks again!

Ed my MC is off a E30 M3. But i dont think thats big enough im now on the lookout for a 25mm one.

Andrew

[ed325i]

I understand what you are saying but when you look thru you nice wheels and see this big gap it will look crap. For me they would have to perform well and look good I would hate to be at shows and people pointing saying them cailpers are to small

ED

[TommyC]

I know from my college days that the coefficient of friction is independant of surface area.......But that's about as much as i can remember...(i'm sure this has an effect on whats going on here).

(Keri, i can smell the dispare!!!!!)

BUT, trying to design a brake kit to improve dramatically over OEM stuff - whilst taking into accout all the fit/clearance, factor of safety, 'manufacturers-little-quirky-ways-of-doing-things-to-make-production-cheaper' issuses - designing a new caliper for each kit with the 'correct' pad surface area for each disc used, would see the kits costing THOUSANDS!!!!! And a confusing number of caliper designs.

I would imagine that if both the brake assemblies that people have pointed out 'inadequate pad coverage' had been designed with expensive alloy bells and equally expensive rotors (discs) that would eliminate this, then the overall kit price would be much greater!!

Terefore the product is in no way inferior, but has been designed to eliminate the high cost of producing bells and rotors, insted opting to use larger discs from elsewhere (G60, E46 M3 etc, etc) to achieve the same thing.

So bacially, the 'un-used' friction area could be considered the much cheaper alternative to an expensive alloy bell, so your brake kit costs quite a few quid less than if you bought it elsewhere!!!!!! (and with a great deal less hassle...... any HiSpec customers out there may know what i'm hinting about)

[keri-WMS]

While I understand what you're saying, surely considering the amount of effort required is only part of the story?

There are other aspects, but they are independant of the pad size issue - with the possible exception that the pad can get hotter if it's maller. (however that makes more racey pads easier to use in less demanding applications as they heat up faster)

Sure the centre of the pad is where the piston applies its force, but when the pad is pushed against the disk, the whole surface area of the pad is acting upon the disk. So it may require more pedal effort (which is where MCs and so forth come in), but the larger pad will ultimately have greater stopping power, no? surely the 20mm difference in leverage is much less important than the massive difference in pad area?
In other words i'm suggesting a big-ass 80mm x 100mm pad covering the whole disk will give greater stopping power than bicycle brake blocks on the outside of the disk to exaggerate the point.

Ok, lets stick with your bicycle brake blocks verses a big 80x100mm pad, but to get everything a chance to work we'll say that both pads and the disc are all carbon fibre (otherwise the REALLY tiny pad will get unreasistically hot and fade - c/f keep on working to silly temperatures)

It this instance:

1 - the tiny pad will apply the same amount of drag (force at a tangent from it's centre) as the big pad as friction is independant of area.

2 - as the centre of the tiny pad is further from centre of rotation than the big pad, there will indeed be more rotational forc applied to the disc by the small-pad-setup!

One last point that people always mix up: extra PAD surface area gives no extra power (often less in fact as we've show, if it's taller), the only advantage being it's extra thermal mass and longer service intervals - people confuse this with extra PISTON area which does supply for force to the pad (at the expense of a softer pedal)!

[keri-WMS]

I understand what you are saying but when you look thru you nice wheels and see this big gap it will look crap. For me they would have to perform well and look good I would hate to be at shows and people pointing saying them cailpers are to small

ED

Ah-ha! So you choose your brakes based on looks rather than performance?

Seriously though, I can machine the spare parts of the discs off if people want, but it will of course cost extra money for no perfomance gain!

In my book that would be a "mod" that fits the same category as one of those stick-on metalic plastic fuel filler cap surrounds! (we don't normaly offer those either... )

[ed325i]

so your set up performs better than say this set up? because the pad is covering the whole of the disc. I am not having a go I am just trying to understand.




ED

[ed325i]

[quote="
Ah-ha! So you choose your brakes based on looks rather than performance?

[/quote]

No I said I want them to perform well and look good. EG I wouldnt buy a set of wheels if they looked crap but performed well I would want a nice looking wheel that performed well.

ED

[TommyC]

Just playing devils advocate here.....

If you look closely the inner edge of the friction material on that disc isn't covered by the pad either!!

More than is visible in the pic i would suspect too!!!



Keri, maybe you should do some chromed calipers...... for the bling factor!!

[tim_s]

cool, thanks for explaining, makes sense!
presumably the drawbacks of using a smaller pad that doesnt cover the whole disk braking area are in terms of heat, pad life etc then? I spose also you're likely to get a more powerful/bigger piston with a bigger caliper (persumably bigger caliper reqd for pad that covers the whole disk braking area).

[TommyC]

Yeah that's about right! Because the pads are a little smaller that means you can get away with running a more servere friction compound because they heat up quicker. So you can run EBC Reds instead of Greens to get more bite but you don't have shit brakes from cold because you have the increased leverage to counter-act it.

The down side though, as you said, is that you have to change the pads more often.

Engineering........ It's all about compromise

[Demlotcrew]

Keri i dont want to be rude or anything i know you are someone who understands whats going on with brakes, but you must admit that the kit you are proposing for the M3 is just not up to it, from the pic you posted up the pad seems to only just about cover the upper half of the friction surface, from experience such a small pad will not be able to exert enough leverage for a car which will be able to reach speeds of upto 155 and more. Im running 315*25 with a E36 M3 pad and those are just about good enough to brake the car at 100mph+ and the E36 M3 pad is huge! So is the disk. Im interested to see how this will perform as no doubt i will be fitting this kit to Robs car.

Andrew

[Brianmoooore]

I know from my college days that the coefficient of friction is independant of surface area)

True, and it applies to tyres as well!

[Brianmoooore]

A brake is a device for turning kinetic energy (car moving along) into heat energy, and then to radiate that heat to the atmosphere. The purpose of the pad and the piece of the disc under it is to do the first bit, and the purpose of the rest of the disc is the second part. If the pad area is excessive, then the second part is compromised.

[keri-WMS]

so your set up performs better than say this set up? because the pad is covering the whole of the disc. I am not having a go I am just trying to understand.

It's not that simple - plus I can't predict how a competitor's products will perform in public.

However, they are shiny! Did you know red cars are faster?

cool, thanks for explaining, makes sense!
presumably the drawbacks of using a smaller pad that doesnt cover the whole disk braking area are in terms of heat, pad life etc then? I spose also you're likely to get a more powerful/bigger piston with a bigger caliper (persumably bigger caliper reqd for pad that covers the whole disk braking area).

Correct, although the extra heat is not that much of an issue with modern pads - ceramic EBC Reds for example.

Keri i dont want to be rude or anything i know you are someone who understands whats going on with brakes, but you must admit that the kit you are proposing for the M3 is just not up to it, from the pic you posted up the pad seems to only just about cover the upper half of the friction surface, from experience such a small pad will not be able to exert enough leverage for a car which will be able to reach speeds of upto 155 and more. Im running 315*25 with a E36 M3 pad and those are just about good enough to brake the car at 100mph+ and the E36 M3 pad is huge! So is the disk. Im interested to see how this will perform as no doubt i will be fitting this kit to Robs car.

Andrew)

Those "huge" pads will in fact give you less torque than smaller ones closer to the discs's O.D. as explained above - you can't argue with physics. In fact this kit is TOTAL overkill for anything sub 300BHP-ish.

Put it this way: This caliper family was designed for NASCAR! The NASCAR guys run 298.5/310mm discs as well, this first M3 kit has 320mm discs.

We'll find out when the kit if finished and fitted, but it's fair to say that I'm not exactly worried!

A brake is a device for turning kinetic energy (car moving along) into heat energy, and then to radiate that heat to the atmosphere. The purpose of the pad and the piece of the disc under it is to do the first bit, and the purpose of the rest of the disc is the second part. If the pad area is excessive, then the second part is compromised.

Also true!

[keri-WMS]

Nobody's answered my question yet - bigger or smaller bore master cylinders for bigger/multi piston calipers?

Ah, that is entirely dependant on the sizes of pistons used so there is no simple answer. As a rule we try to get a small increase in total piston area, but not so much that a bigger master cylender is needed.

Some WMS calipers don't have a range of piston sizes available, so in these cases a bias pedal box (not valve) or bigger master cyl might be needed!

[gareth]

Keri i dont want to be rude or anything i know you are someone who understands whats going on with brakes, but you must admit that the kit you are proposing for the M3 is just not up to it, from the pic you posted up the pad seems to only just about cover the upper half of the friction surface, from experience such a small pad will not be able to exert enough leverage for a car which will be able to reach speeds of upto 155 and more. Im running 315*25 with a E36 M3 pad and those are just about good enough to brake the car at 100mph+ and the E36 M3 pad is huge! So is the disk. Im interested to see how this will perform as no doubt i will be fitting this kit to Robs car.

Andrew

as one of the few owners of a WMS kit i can vouch for the fact there will be NO problems on a M3. my spec is as follows:
335i touring. (heavier than a M3) 220 bhp (about the same as one too) and as far as i can remember about 220lb/ft of torque (more than a M3). i have a 280mm WMS 4 pot setup with EBC reds and have no problems. i can intentionally cook them but this happens waaaaay after the rears are completely blue & smoking and the rear pads are toast. it took 15 mins of thrashing with the rears 'gone' to finally cook the fronts. (not recommended for anything except test pilot duties!)

so, a larger kit on a slower(? straight line only!!!)) and lighter car? the only problems will be your forehead leaving greasy marks on the screen!!!!!


regarding the engineering definitions mentioned above, these are true. i act as a consultant engineer for WMS outside of my 'proper' job (F1 force measurement system design engineer) where i am heavily involved in braking systems. i can't tell you any more or i would have to kill you all!!!!!!!! needless to say, this is all VERY fundemental stuff and you should all know better!

friction (resistive force from the pad):
http://schoolforchampions.com/science/f ... uation.htm

interestingly (though rather obviously), the pad on F1 brembo 6 pot caliper is only about 30mm deep, putting the centre of pressure 15mm in from the edge of the rotor... make of that what you will.....

[fuzzy]

what was this post originally about again,its went on that long i seem to have forgotten,and to think i was going mad at my conversion dragging on for 17 weeks!

[keri-WMS]

Keri, have you had much experience with Carbopads?

Can't say I've heard of them to be honest - I assume they are a Carbon/Metallic pad from the name?

I suppose we better start drifting back on topic soon!

[TommyC]

friction (resistive force from the pad):
http://schoolforchampions.com/science/f ... uation.htm

Can't argue with that!!! (however much people may try!!!!)