Heated discussion on big brake conversions.

[gareth]

while we're slightly off topic, argos, where did you find a pic of an arse like that!!!!!

[Demlotcrew]

If the pad area is excessive, then the second part is compromised.

Why?

Gareth, Rob has a 3.2l Evo engine in his car so its quite a bit quicker than yours.

From the link you posted up it says

"An interesting result of this equation is that in the case of sliding friction of hard surfaces, the friction is independent of the area of the surfaces. In other words, it is just as difficult to move a 1 square-cm object as a 1 square-meter object, if they both are pressed to the surface with the same amount of force."

This is true, but you are assuming that the pressure produced by my caliper is the same as that of WMS which we could calculate if i had the size of the pistons. But i suspect my caliper to be producing much more pressure and thus being able to produce more friction with the larger surface area between the pad and the disk.

There is no doubt that Four pot calipers are better than single piston ones, but for my application the single piston caliper proved to be the best one. If i could get round the clearance issues of four piston ones i would have fitted them, the conversion i have done to my car was far from being cheap and i can assure you Andrew that its far from being nasty (unlike your cam belt changing abilities, i pitty the person who buys your 2.7 engine, we all know why that Red 325i touring went on ebay )

"single piston calipers are like trying to crush a coke can with one big hand - multi piston calipers and like crushing it with two slightly smaller ones".

Did your man at AP tell you why this was?

[Demlotcrew]

But please DO tell us why the 325i went on ebay - we're dying to know!!

You did a cam belt on it, the car ran shit (because it was timed wrong) but like the experienced and very good engine builder that you are you thought it must be the tappets making that ticking noise (when it was the valves hitting the pistons) so you tightened them up even more which didnt help! But like the honest guy that you are "Worn camshaft" was used to sell the car. Now who would buy an engine built by a total spastic in a council lock up with a rocker cover painted with left over Sport Evo touch up pens (because this is how tight this guy really is) Nice and shiny rocker cover bolts wont fool anyone Everett, hows the gearbox on the Seven?

[maxfield]

here we go again

[bigkev]

i thought this(very long)thread was about a guy who has a wheelbarrow full of money and is shovelling it into a scabby E30 BMW at high speed(i must admit its been a while since i've read it)

[gareth]

Gareth, Rob has a 3.2l Evo engine in his car so its quite a bit quicker than yours

granted in this instance it is more powerful but it's hardly E30 M3 spec is it? (2 more cylinders for a start), but i suspect it's still lighter than mine. the point i was making was that my car is easily as hard on its brakes as a M3.

From the link you posted up it says

"An interesting result of this equation is that in the case of sliding friction of hard surfaces, the friction is independent of the area of the surfaces. In other words, it is just as difficult to move a 1 square-cm object as a 1 square-meter object, if they both are pressed to the surface with the same amount of force."

This is true, but you are assuming that the pressure produced by my caliper is the same as that of WMS which we could calculate if i had the size of the pistons. But i suspect my caliper to be producing much more pressure and thus being able to produce more friction with the larger surface area between the pad and the disk.

do you have piston areas and C of P coordinates for your calipers or are you purely speculating? seems like a bit of a wild claim. oh, did you also reduce the effective power of the whole braking system by changing the M/C?

on a totally serious note, do you actually have any engineering knowledge? i just need to get a grasp of how in depth i need to explain things, eg: basic engineering terminology or primary school examples...

a point to remember with 4 pots (or any configuration that avoids poxy sliders) is that sliders will always have far larger frictional losses than a multi-pot caliper and this will cost power. this is most often seen with sliders creating uneven pad wear.

[bigkev]

WOW i think i got off lightly with scabby doors and some holes in the lower apron so far so good no other rust problems
so i have ripped off the head
windows out
all trims off(respray carbon wrap)
doors off(respray)
bonnet off(respray make mould )
wings off(respray make mould)
boot off(mould)
interior bits and bobs (carbon wrap)
rebuild head/fit head

yeah should be finished by about 2009

[Demlotcrew]

do you have piston areas and C of P coordinates for your calipers or are you purely speculating? seems like a bit of a wild claim. oh, did you also reduce the effective power of the whole braking system by changing the M/C?

No what i did do was to create an even balance of braking between the fronts and rears. And less pedal travel. I drive so many cars where the brake biting point is too high or too low to be able to have the right amount of bite on the pedal when its at the same height as the accelerator (this is important to me). How one can reduce the effective braking power of the whole system by changing up MC size is beyond me, but im not a F1 brake engineer buying off the shelf kits.

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.

Something like this is just not acceptable for me, i could not live with a car that faded the rears before the fronts! All that tells me is you have an uneven distribution of braking force and this will mean a very unstable car, but i guess you don't really care about that.

I said M3 not E30 M3!

I have some very basic engineering skills so if you want to explain anything then i can cope with primary school examples.

[M3Compact]

Interesting.

Any disc distortion anticipated due to the heat localisation?

How much unused/unreq'd rotating mass is there compared to a two piece set-up with custom alloy bell and appropriate rotor? (Obviously this isn't as cost effective, but could the increased initial cost offer better performance with a longer term good value return?)

Something like this is just not acceptable for me, i could not live with a car that faded the rears before the fronts! All that tells me is you have an uneven distribution of braking force and this will mean a very unstable car, but i guess you don't really care about that.

Agreed. A properly mated multi pot braking system will always out perform sliding calipers, but given the choice (from experience) I'd rather have a balanced single pot system than mis-matched front/rear brakes.

[M3Compact]

Hello Simon! Not seen you here for a while - how did you get on with the Compact in the end? last time I heard you were cursing it and threatening to sell!

One outing, one class win, one overall fastest stage time (beat all the 4WDs, Mitzys, 6R4 etc ), cooked the brakes.

Link.<--

[keri-WMS]

Interesting.

Any disc distortion anticipated due to the heat localisation?

Nope, should be fine - in fact the extra material acts as both added thermal mass (less fade) and a heat radiation surface. More below...

How much unused/unreq'd rotating mass is there compared to a two piece set-up with custom alloy bell and appropriate rotor? (Obviously this isn't as cost effective, but could the increased initial cost offer better performance with a longer term good value return?)

...you're right, this is the first kit and we intend to add an upgrade version of it that uses 320mm rotors on alloy bells. As you say, this will be lighter, but more expensive - horses for courses!

We'll be looking at trimming the first disc down a bit as well, but it might be pointless when the alloy bell option will be there.

Something like this is just not acceptable for me, i could not live with a car that faded the rears before the fronts! All that tells me is you have an uneven distribution of braking force and this will mean a very unstable car, but i guess you don't really care about that.

You're assuming brake bias (or "distribution of braking force") and fade resistance are the same thing - which of course they are not. Also as most modified cars have more rubber on the road than EOM as a rule, they can stop harder for a given road surface grip level, and therefore shift more weight to the front resulting in more front grip and a NEED for a higher front bias!

Before people say it.... yes, my "more rubber area = more grip" statement appears to conflict with what I was saying about pad area having no effect on drag/friction in a given system. However tyres work using STATIC friction which has different rules than friction between sliding surfaces. This is why you have suddenly less grip if you lock up! Also why a 245/35/18 has more grip than a 155/70/13, until the driver locks up......then both cars slide to a stop with the same level of deceleration. (assuming they weigh the same etc etc)

[massive]

Also why a 245/35/18 has more grip than a 155/70/13, until the driver locks up......then both cars slide to a stop with the same level of deceleration. (assuming they weigh the same etc etc)

I cant get my head around this theory. i understand the rest of what Keri is saying but this

[keri-WMS]

Also why a 245/35/18 has more grip than a 155/70/13, until the driver locks up......then both cars slide to a stop with the same level of deceleration. (assuming they weigh the same etc etc)

I cant get my head around this theory. i understand the rest of what Keri is saying but this

It's hard to get to grips with I know! (no pun intended)

I good comparison is if you can imagine (or remember I expect with most of us ) thrashing a nasty thin-tyred car around (Metro/Mini/Nova/Fiesta - whatever), and when it slides or locks up there's no big difference in the way the car moves. It just kind of goes "right, I'm a bit sideways, now I'm just a bit sketchy" etc with no real difference in the two types of grip/friction.

However with much bigger tyres you get more STATIC grip - so when you lose traction it does it in a BIG way relative to the grip you did have before the slide! An extreme example is the rather sudden and violent way an F1 car will spin off the track when it looked like it was fine on a given corner - they go so fast once they are sliding (sideways or backwards) they look like they are on coasters! This is because they have lost all STATIC friction and have dropped back to normal "sliding" friction.... (and they might as well HAVE thos 155/70/13's at that point!)

[M3Compact]

Also why a 245/35/18 has more grip than a 155/70/13, until the driver locks up......then both cars slide to a stop with the same level of deceleration. (assuming they weigh the same etc etc)

I cant get my head around this theory. i understand the rest of what Keri is saying but this

Stand on one leg on the scales, you'll weigh the same. The wider locked up tyre is distributing an equal force/weight over a larger area, therefore the actual force per sqmm is decreased, while the total force remains unchanged.

When they aren't locked up, assuming an equal grip compound, the wider tyre is capable of transmitting more total force through its larger contact area while the force per sqmm remains unchanged.

Interesting.

Any disc distortion anticipated due to the heat localisation?

Nope, should be fine - in fact the extra material acts as both added thermal mass (less fade) and a heat radiation surface. More below...

The reason I ask is that I've previously used (regulation enforced) solid discs with pads that contacted predominantly on the od of the disc and had problems with discs warping. This was assumed to have been caused by the increased (due to localisation) heat associated with the smaller pad area being unevenly distributed across the rotor face.

Something like this is just not acceptable for me, i could not live with a car that faded the rears before the fronts! All that tells me is you have an uneven distribution of braking force and this will mean a very unstable car, but i guess you don't really care about that.

You're assuming brake bias (or "distribution of braking force") and fade resistance are the same thing - which of course they are not. Also as most modified cars have more rubber on the road than EOM as a rule, they can stop harder for a given road surface grip level, and therefore shift more weight to the front resulting in more front grip and a NEED for a higher front bias!

Ime a fluctuating bias can be caused by inappropriately matched disc/pad size and pad compound. (Discs temps moving across the optimum pad operation temperature unpredictably.)

[Demlotcrew]

You're assuming brake bias (or "distribution of braking force") and fade resistance are the same thing - which of course they are not. Also as most modified cars have more rubber on the road than EOM as a rule, they can stop harder for a given road surface grip level, and therefore shift more weight to the front resulting in more front grip and a NEED for a higher front bias!

Well i just cant see this being good, if the front end digs in the rear goes light and on a bend on a RWD car its not good! Smooth driving wins races not drifts.

All the E30 M3 ring regulars have upgraded to AP racing fronts then drilled out the rear brake restrictor so there is no reduction on the rear and they seem to find the car to handle much better, but if what you were saying to be true then they are all liars?

I have just upgraded my rears from 250*10 to 282*10 and i can also confirm the car fells much better and no where near as nose heavy as it was with the 315*25 front and 250*10 rear, the fronts would just lock up with medium pedal pressure and when the tires got really hot they would do it quite often, i just wasn't happy with this, the car was braking just on the front wheels (i could tell this by the fact the front wheels were really dusty and the rears has hardly any dust at all) So what i had to do was to get the rears matched to the fronts. So this means that when i press the pedal the fronts were producing 60% of the brake effort and the rears 40%. What i think is happening with Gareth's is that when he presses the pedal the rears are braking the car more than the fronts this is because his new front calipers take more fluid (bigger pistons *4) than the master cylinder can push in relation to the rears, this is because the E30 stock MC is 22.2 front 17.5 rear, it would be interesting to calculate whats actually going on, so if Keri could post the piston sizes of the WMS calipers we can see if my theory is correct.

Andrew

[keri-WMS]

Stand on one leg on the scales, you'll weigh the same. The wider locked up tyre is distributing an equal force/weight over a larger area, therefore the actual force per sqmm is decreased, while the total force remains unchanged.

Agreed - and also once the car is locked up there is less weight shift, not that it'll help at that point!

When they aren't locked up, assuming an equal grip compound, the wider tyre is capable of transmitting more total force through its larger contact area while the force per sqmm remains unchanged.

Yup!

Interesting.
Any disc distortion anticipated due to the heat localisation?

Nope, should be fine - in fact the extra material acts as both added thermal mass (less fade) and a heat radiation surface. More below...

The reason I ask is that I've previously used (regulation enforced) solid discs with pads that contacted predominantly on the od of the disc and had problems with discs warping. This was assumed to have been caused by the increased (due to localisation) heat associated with the smaller pad area being unevenly distributed across the rotor face.[/qoute]
Solid discs are rather more at risk of warping in rase use as they are not as physically stiff as vented ones, also they get hotter due to the reduced thermal mass and reduced cooling. By the way, most "warped discs" on road cars are in fact self-propogating raised hard spots caused by cheap/road pads abraiding the surounding iron, heating the lump, and forming a vicious circle! The disc does warp in use as the lumps get hot first, but they often cool "flat" again and are really annoying to sort out (the hardening can't even be removed by skimming the disc as it goes quite deep into the iron)

Something like this is just not acceptable for me, i could not live with a car that faded the rears before the fronts! All that tells me is you have an uneven distribution of braking force and this will mean a very unstable car, but i guess you don't really care about that.

You're assuming brake bias (or "distribution of braking force") and fade resistance are the same thing - which of course they are not. Also as most modified cars have more rubber on the road than EOM as a rule, they can stop harder for a given road surface grip level, and therefore shift more weight to the front resulting in more front grip and a NEED for a higher front bias!

Ime a fluctuating bias can be caused by inappropriately matched disc/pad size and pad compound. (Discs temps moving across the optimum pad operation temperature unpredictably.)

Also true. I'm going to go out on a limb here as there are some pads that heat up pretty uneavenly and can even make the bias shift left to right etc on the first few stops! I won't name the very popular pad I mean, let's just say I rate the EBC Red even for road use as a result due to it's far smoother response to varied temperatures (plus higher upper temp limit)!!!

[M3Compact]

Solid discs are rather more at risk of warping in rase use as they are not as physically stiff as vented ones, also they get hotter due to the reduced thermal mass and reduced cooling. By the way, most "warped discs" on road cars are in fact self-propogating raised hard spots caused by cheap/road pads abraiding the surounding iron, heating the lump, and forming a vicious circle! The disc does warp in use as the lumps get hot first, but they often cool "flat" again and are really annoying to sort out (the hardening can't even be removed by skimming the disc as it goes quite deep into the iron)

Sorry Keri, typo. I meant one piece vented discs as opposed to solid discs.

Agree about the hot spots/pad deposits. I read a Stop Tech article written by a race engineer that denied disc warping completely, I don't agree with that, I've personally seen plenty (correctly measured) warped discs. (Hot & cold.)

It was all worth it after all then.

Yep, but I need some smaller front brakes that work better than the large ones currently fitted.

[ed325i]

When you make a brake kit like the mws one how are they tested and do they have to be aproved by anyone? It seems bad if you go out and buy a brake kit fit it and it then upsets the balance of the car.

ED

[keri-WMS]

You're assuming brake bias (or "distribution of braking force") and fade resistance are the same thing - which of course they are not. Also as most modified cars have more rubber on the road than EOM as a rule, they can stop harder for a given road surface grip level, and therefore shift more weight to the front resulting in more front grip and a NEED for a higher front bias!

Well i just cant see this being good, if the front end digs in the rear goes light and on a bend on a RWD car its not good! Smooth driving wins races not drifts.

Down to the style of the driver, the type of motorsport and the setup of the car! You've never seen a Tarmac Rally Mk2 Escort in action then?

All the E30 M3 ring regulars have upgraded to AP racing fronts then drilled out the rear brake restrictor so there is no reduction on the rear and they seem to find the car to handle much better, but if what you were saying to be true then they are all liars?

Oooo yeah, I'm just an angry forum monkey that can be egged into calling people liars! Please...

What i think is happening with Gareth's is that when he presses the pedal the rears are braking the car more than the fronts this is because his new front calipers take more fluid (bigger pistons *4) than the master cylinder can push in relation to the rears, this is because the E30 stock MC is 22.2 front 17.5 rear, it would be interesting to calculate whats actually going on, so if Keri could post the piston sizes of the WMS calipers we can see if my theory is correct.

Your theory is back to front mate so I think you'd better consider the safety of anyone who might take your word for it before trying to put any numbers through it!

I think we've covered everything so far, I'll answer any more sensible questions people have.

[keri-WMS]

When you make a brake kit like the mws one how are they tested and do they have to be aproved by anyone? It seems bad if you go out and buy a brake kit fit it and it then upsets the balance of the car.

ED

It would be bad I agree. However it doesn't, so the point is moot.

[keri-WMS]

Yep, but I need some smaller front brakes that work better than the large ones currently fitted.

There are ways round this depending on the rules. You can get more power through bigger pistons and better pads or course, in terms of cooling you have these options:

- Ducts (the E30 already has pretty good ones, but you could pipe the cold air directly to improve things)
- Wheels - the alloy wheel acts as a big heat sink to an extent, not a lot to be gained here though unless you're doing 24h sportscar stuff!
- Upgrade discs - there are welded Titanium rotors available.
- Ceramic coatings, these help shift the heat into, then out of the disc.
- Floating rotors - this lets the rotor expend freely, with no buildup of stress as it "pulls" on the alloy bell or the centre of the iron disc.
- Carbon fibre pads/discs. These need to run HOT, but might be just what you need.

None of this is cheap though, and probably against the rules! The Ceramic coated Ti rotors were $800 each last time I looked them up...

[ed325i]

When you make a brake kit like the mws one how are they tested and do they have to be aproved by anyone? It seems bad if you go out and buy a brake kit fit it and it then upsets the balance of the car.

ED

It would be bad I agree. However it doesn't, so the point is moot.

So if you fit bigger brakes to the front which should be more powerfull than the standerd brakes it will not upset the balance between the front and rear brakes?Is there anything to say the wms brakes are any better than the standerd bmw set up? Its like you get people who sell chips and say you get 15 bhp more when they have nothing to back this up.

ED

[keri-WMS]

When you make a brake kit like the mws one how are they tested and do they have to be aproved by anyone? It seems bad if you go out and buy a brake kit fit it and it then upsets the balance of the car.

ED

It would be bad I agree. However it doesn't, so the point is moot.

So if you fit bigger brakes to the front which should be more powerfull than the standerd brakes it will not upset the balance between the front and rear brakes?Is there anything to say the wms brakes are any better than the standerd bmw set up? Its like you get people who sell chips and say you get 15 bhp more when they have nothing to back this up.

ED

Most WMS kits are designed so that you get a small increase in piston area and slightly bigger discs - the 4-stud 280mm E30 one for example. This gives you a bit more power: NOT enough to upset things but enough to deal with upgrades in grip and the resulting weight shift, added BHP/braking speed etc. The BIG advantage is you can abuse them MUCH more and they won't overheat and fade!

Then there are the options of huge discs and much bigger pistons for serious people who are re-engineering the whole setup from scratch, this is less of a plug and play situation as we can't predict what people will be doing so I can't make sweeping statements about these kits.

[M3Compact]

What i think is happening with Gareth's is that when he presses the pedal the rears are braking the car more than the fronts this is because his new front calipers take more fluid (bigger pistons *4) than the master cylinder can push in relation to the rears, this is because the E30 stock MC is 22.2 front 17.5 rear, it would be interesting to calculate whats actually going on, so if Keri could post the piston sizes of the WMS calipers we can see if my theory is correct.

Andrew

Your theory is back to front mate so I think you'd better consider the safety of anyone who might take your word for it before trying to put any numbers through it!

Could you explain that Keri? (Sorry if I've misunderstood, I'm more familiar with adjustable twin MC set ups, where front/rear MC sizes can be selected individually.)

I've always understood it to be the case that when you increase the overall front piston size/volume that you need to change the MC appropriately, believing as Demlot suggested that the increased volume of fluid req'd for the front calipers, necessitates further travel from the MC, which consequently increases the amount of fluid/pressure to the rears. (Which is then adjusted accordingly via the twin pedal/MC box, obviously this option isn't available to stock MC users.)

The issue may be clouded by the fact that the adjustable pedal boxes that I'm familiar with, are influenced in their biasing characteristics by the pressure req'd to operate the MCs individually. (The adjustment can only bias the MC input pressure without regard to 'resistance' from the MC input, which is obviously varied depending on MC bore.)

Yep, but I need some smaller front brakes that work better than the large ones currently fitted.

There are ways round this depending on the rules. You can get more power through bigger pistons and better pads or course, in terms of cooling you have these options:

- Ducts (the E30 already has pretty good ones, but you could pipe the cold air directly to improve things)
- Wheels - the alloy wheel acts as a big heat sink to an extent, not a lot to be gained here though unless you're doing 24h sportscar stuff!
- Upgrade discs - there are welded Titanium rotors available.
- Ceramic coatings, these help shift the heat into, then out of the disc.
- Floating rotors - this lets the rotor expend freely, with no buildup of stress as it "pulls" on the alloy bell or the centre of the iron disc.
- Carbon fibre pads/discs. These need to run HOT, but might be just what you need.

None of this is cheap though, and probably against the rules! The Ceramic coated Ti rotors were $800 each last time I looked them up...

My (E36) brakes are only regulated by the fact that I need to be able to use 15" wheels for gravel tyres, the current 315mm discs and E36 M3 calipers won't fit under less than 16" wheels and I don't want different brakes for 17" tar slicks and 15" gravel tyres. (Also regulated by the fact that $800 per disc is considerably over budget. )

I can source some AP motorsport rotors and alloy bells easily enough, but the only multi piston calipers that I can find 'off the shelf' for E36s involve using 320mm+ discs.

[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 ?

Nice one mate

[Demlotcrew]

I've always understood it to be the case that when you increase the overall front piston size/volume that you need to change the MC appropriately, believing as Demlot suggested that the increased volume of fluid req'd for the front calipers, necessitates further travel from the MC, which consequently increases the amount of fluid/pressure to the rears. (Which is then adjusted accordingly via the twin pedal/MC box, obviously this option isn't available to stock MC users)

Thank you!

Andrew