Heated discussion on big brake conversions.

[Jhonno]

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

+1

[M3Compact]

Not forgetting of course that a given amount of fluid will travel faster through a small bore tube than a fatter one...........

Thinking back to my (long gone) Mini days, a later non servoed 1275GT with front discs had a slightly smaller bore master cylinder (with a larger reservoir) than a drum braked car. I wonder why??

Small bore gives a better feel.

[buster]

Hello guys.

Ive fitted a 25mm master cylinder to mine,but i still have standard brakes.
(pedal is stiffer and requires more effort to work).
I am still trying to decide which brake upgrades to go for though.Dont know what im going to use up front,cant decide if the 312mm disks that demlot is using with single piston caliper or maybe use the same disk but make my own braket for a 4 pot caliper maybe better.Maybe WMS could do a kit like this using the 312mm disk ?? also where can i get the 280 mm rear disks from ?

cheers
andy

[M3Compact]

Indeed - and reduced braking effort.

But - and it's a big but - does that mean that a small bore MC is like having a longer brake pedal (more leverage), i.e meaning that an equal effort at the pedal equals more clamping force at the calipers when using a smaller bore MC?

Not sure on this..........

I'm not a brake expert at all Andy, but afaik the relationship between total caliper piston area and MC size dictates MC input pressure to pad pressure, the higher the ratio, the less effort req'd. It all gets a bit dark, deep and complicated when calculating multi piston caliper volumes.

It isn't correct to assume that the pistons in a two pot caliper require the same volume of fluid to operate as an equally sized sliding caliper. (Even assuming that the sliding caliper piston moves twice as far as each of the twin pot pistons.) Seal flex is significant and clouds the issue.

Brakes are far too complicated.

[ste]

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?

Anyone in this situation needs to ask themselves why they are fitting the bigger brakes.

I'm guessing they are for circuit use, or for posing. If you're fitting them for the latter you really aren't going to be bothered about brake balance issues...

If your fitting the brakes for curcuit use you may find increasing the effort the fronts can exert comparatively over the rears to be a bonus.

Conventionally road cars come out of the factory with a brake balance suited to road use (surprisingly).

A usual step in building a race car is to move the brake balance forward significantly. This is more useful on a circuit (different for rallying where more rear bias can be a bonus) where your rear brakes become almost redundant. Simply put, and not attempting to teach anyone to suck eggs, but we all know the weight of the car moves forward under braking. Under repeated severe braking on circuit the rear brakes are continuously unloaded of weight and tend to do very little. With a factory brake bias rear wheel lock can be prevalant.

When I built my race car the regs specified I had to use standard calipers. Hence I was restricted to a standard sized disc and all I could really play with was pad choice and brake bias. Pad choice aside I fitted a bias valve and after testing found the bias full forward (i.e. the rear brakes effectively turned off) was the best by a long way.

Speaking to a multi-championship winning driver of 20-odd years (Slick 50, Blue Coral, Track and Race Cars Saloons etc) he told me a trick he used to do when he raced in a series that didn't allow the brake bias to be altered, either with independant mc, bias valve, kinking of pipes or drilling/blocking restrictors. He would actually run his rear brakes with the pistons welded solid in the calipers so he had no rear brakes whatsoever.

Basically what I'm getting at in a rambling fashion is that you can't assume changing the brake balance is necessarily a bad thing.

[ste]

I drove to Plymouth in it and it was a great laugh. Cut slicks on the road have to be recommended. Stopping every 100 miles to 'fill up' because the petrol tank has more holes than an Arran tank-top should be avoided though.

He sold it for £400!? That was about a month after buying my track wheels off me for £500. He threw them in as part of the deal....

[Demlotcrew]

Basically what I'm getting at in a rambling fashion is that you can't assume changing the brake balance is necessarily a bad thing.

No but when the rears are braking more than the fronts because the fronts have larger pistons is not ideal either.

Andrew

[ste]

No of course not. But again, if you're fitting the brakes for circuit use, spending a few quid extra on plumbing an adjustable bias valve in would be money well spent.

If you didn't want a bias valve in the cabin you could always plumb it in in the engine bay just after the mc, or you could hide it where the rear line comes down from over the tank, although adjusting / setting it up might be a pain and you lose the ability to alter it for dry / wet conditions.

If you didn't want to do that you could just put a restrictor in the rear lines, either an inertia type robbed off something like a 1.6 (rear drums) 205 GTI, or a load (level) type like a Mk2 Golf GTI in the scrappie or even squash the pipe for proper council flavour.

[Demlotcrew]

No of course not. But again, if you're fitting the brakes for circuit use, spending a few quid extra on plumbing an adjustable bias valve in would be money well spent.

If you didn't want a bias valve in the cabin you could always plumb it in in the engine bay just after the mc, or you could hide it where the rear line comes down from over the tank, although adjusting / setting it up might be a pain and you lose the ability to alter it for dry / wet conditions.

If you didn't want to do that you could just put a restrictor in the rear lines, either an inertia type robbed off something like a 1.6 (rear drums) 205 GTI, or a load (level) type like a Mk2 Golf GTI in the scrappie or even squash the pipe for proper council flavour.

Very true, i know that tilton do a really nice valve which can accept a in-cabin extension which will enable you to have the valve in the engine bay and control the ratio inside the car. (which is what i will end up doing and having the extension 'free floating' so that i can set it up close to me and then put it in the glove box when its not in use.

Andrew

[Jhonno]

As for the use of bigger brakes - you can never have brakes that are too good. Another little known mod is to fit calipers from an E32 7 Series or an E34 to an E30 M3. These are a direct swap on the E28 which has the same calipers the M3 used. Just how effective this is I don't know, but it's cheap enough (Calipers are @ 60-70 quid each from Euro Car Parts)

it requires a small tab machining off apparently then use of merc 500e discs to work on an m3 according to what ive been told.. i shall be going this route for now

[ian332isport]

I've been reading this thread for a few days now, and thought it was time I added my view on things. I would also like to add that this is based on my experiences with my car. It may not be very scientific or 100% accurate as far as Physics goes, but there you go...

Firstly, I would like to agree with Ste's statement that changing brake bias is not necessarily a bad thing. I've got some pretty big brakes (322x32) on the front of my car with standard rears (apart from Pagid fast road pads). I've been driving like this for over 4 years, and have never really noticed that the bias is wrong. The car stops very quickly from silly speeds and has never once felt like there was a problem. The only time I noticed a possible bias problem was at the Nurburgring where the back end was a bit twitchy going into some corners. I feel this is more down to my driving style than a huge bias problem (I was starting to turn in while still hard on the brakes). I guess some experimenting with a bias valve may improve things, but only under extreme conditions - learning to drive better is probably a better solution. That said, I am going to fit some 280mm rear discs to see if there's any improvement to be had. If nothing else, it will look a little less weedy behind my 17" rims

When fitting the large Brembo 4 pots, I initially kept the standard split bore (22.2mm/17.4mm) E30 master cylinder. This worked okay, but the pedal travel was noticeably longer than standard (more piston area requires more fluid). After a while I got used to it and never really gave it a second thought. When I did my engine conversion I changed to the 25mm/25mm master cylinder from the E32 7 series. This has bought the pedal travel situation pretty much back to standard. It's a bit hard to compare because of the time between driving with each cylinder, I also have the hydraulic brake servo setup (fitted at the same time as the 25mm cylinder), but what I have now seems to work exceptionally well.

Prior to fitting my current brakes, I had experimented with different sized front discs, but still using the standard calipers. Initially I used 280mm discs and later 300mm two piece discs (both from Hi-Spec). There was a noticeable improvement in brake performance with each jump in diameter. This is still using standard sized E30 pads, so the improvement is purely down to the diameter. I guess this follows with Keri's description above. My only problem with both of these kit's was that the disc's would warp very quickly (3 months of road driving). I never got to the bottom of this, and can really only put it down to poor quality disc's, but maybe it has something to do with the localised heating effect of the small pads that Simon mentioned previously. Since fitting my current setup, I have never looked back. I have basically deleted the word 'Fade' from my vocabulary. Even after a couple of flying laps of the Ring they showed no sign of even thinking about fading (the rears were also okay apart from a very squeaky handbrake in the queue to get off the track)

I guess I'll stop waffling now, but big brakes are good. Bigger brakes are even better. Fit the biggest and best you can afford and you will be much happier people

Ian.

[keri-WMS]

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.)

I assumed we were talking about a single master cyl system as fitted to almost all production cars... Of course with a bias box / twin m-cyl setup you can change everything as you please!

When Demlotcrew said "this is because the E30 stock MC is 22.2 front 17.5 rear" I assumed he was referring to piston sizes and the MC was a typo.

My point is that if you fit bigger pistons to the front brakes that make your pedal too soft, then have to increase the master-cyl size (on a single m-cyl car), you're REDUCING the power available from the rear brakes for a given foot pressure! This is fine if you want to shift the bias heavily to the front, but that's the opposite of what Demlotcrew said he was trying to do hence my confusion.

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.

Ah, I missed that it's an E36! 280mm on a 4-pot or 300mm on a sliding caliper is about all you'll ever fit inside more 15's, possibly more if there are motorsport wheels that will give you more room?

[keri-WMS]

Not forgetting of course that a given amount of fluid will travel faster through a small bore tube than a fatter one...........

Thinking back to my (long gone) Mini days, a later non servoed 1275GT with front discs had a slightly smaller bore master cylinder (with a larger reservoir) than a drum braked car. I wonder why??

First thing is that drum brakes ARE the most powerful system! The brake shoe works right ut near the O.D., and also most are "self energising" - a sytem where the two brake shoes pivot outward from one end into the drum. As the drum is turning it then "pulls" on the shoe and adds extra free outward force! Much like a servo but without the softer / nasty pedal.

However, drum brakes are heavy, get full of crud, and don't cool very well (although you can drill and / or add fins!).

[keri-WMS]

Indeed - and reduced braking effort.

But - and it's a big but - does that mean that a small bore MC is like having a longer brake pedal (more leverage), i.e meaning that an equal effort at the pedal equals more clamping force at the calipers when using a smaller bore MC?

Spot on!

[keri-WMS]

Hello guys.

Ive fitted a 25mm master cylinder to mine,but i still have standard brakes.
(pedal is stiffer and requires more effort to work).

As to be expected, not a "problem" as such, just gives your legs a slightly harder time!

I am still trying to decide which brake upgrades to go for though.Dont know what im going to use up front,cant decide if the 312mm disks that demlot is using with single piston caliper or maybe use the same disk but make my own braket for a 4 pot caliper maybe better.Maybe WMS could do a kit like this using the 312mm disk ?? also where can i get the 280 mm rear disks from ?

cheers
andy

There are going to be more kits developed as time goes on, the next 4-stud E30 one will be a 298.5mm rotor on an alloy bell, this should JUST fit inside the 16" 'pina reps on a certain white 3.5 E30 M Touring!

As for the WMS 280mm disc, it's based on the VW G60 one. You can do them DIY, or WMS can supply them....

We are looking at doing a 280mm rotor/alloy bell version as a retro-fit upgrade at a later date as well!

Not sure about the 280mm rear one though...

[ste]

Do you have a list anywhere of the kits you supply?

I get more and more tempted by a set of Porsche Big Red Brembos, I can confirm that Ian332i's brakes are possibly even more impressive than his engine... Ideally i'd love something that fits under a 15" BBS though.

[keri-WMS]

Do you have a list anywhere of the kits you supply?

Ideally i'd love something that fits under a 15" BBS though.

We don't as we're revising the range at the moment....

For the E30 there is:

4-stud 280mm kit (a couple left in stock but with the other logo)
4-stud 298.5mm kit (under development)
5-stud M3 320mm kit (under development)

The 280mm one is about spot on for making the most of the 15" BBS, see photo for just how tight it is:

[Demlotcrew]

My point is that if you fit bigger pistons to the front brakes that make your pedal too soft, then have to increase the master-cyl size (on a single m-cyl car), you're REDUCING the power available from the rear brakes for a given foot pressure! This is fine if you want to shift the bias heavily to the front, but that's the opposite of what Demlotcrew said he was trying to do hence my confusion.

This is why i fitted larger disks on the rear after having the larger MC fitted.

Now do you agree that with a stock E30 MC and your callipers the rears will be providing more braking force?

And one final question does the 280mm kit that fits under the 15" BBS need spacers?

Andrew

[keri-WMS]

My point is that if you fit bigger pistons to the front brakes that make your pedal too soft, then have to increase the master-cyl size (on a single m-cyl car), you're REDUCING the power available from the rear brakes for a given foot pressure! This is fine if you want to shift the bias heavily to the front, but that's the opposite of what Demlotcrew said he was trying to do hence my confusion.

This is why i fitted larger disks on the rear after having the larger MC fitted.

Now do you agree that with a stock E30 MC and your callipers the rears will be providing more braking force?

Nope! Take a standard E30 325i for example, add either bigger front pistons (WMS adds 5.5% area over OEM) or bigger front discs (WMS adds 20mm dia over OEM) and you'll increase the front braking torque available from a given amount of foot/pedal pressure - the WMS kit adds (a bit of) both.

And one final question does the 280mm kit that fits under the 15" BBS need spacers?

No, it fits straight on (leaving "not much room" though!!). However as the flange on the G60 based 280mm disc is 2mm thinner than BMW's spec, you need to add a 2mm spacer to stop the bolts from going too far into the hub, correct the wheel offest (2mm is not a major issue though!) and to be sure that the centre of the wheel is not resting on the centre of the hub. (the BBS clears but the Alpina reps have a smaller bevel and NEED the 2mm spacers)

This applies to anyone who uses the G60 disc on their E30 by the way, so take note!

[ed325i]

Here is a pic of the cailper I am going to be using with 312mm discs which are being machined today. If you stop a e32 750 then they should stop the e30 ok.




ED

[keri-WMS]

Here is a pic of the cailper I am going to be using with 312mm discs which are being machined today. If you stop a e32 750 then they should stop the e30 ok.




ED

Meaty looking things!

Do you know how much they weigh?

[billgatese30]

what size wheels do they fit under ed?

[keri-WMS]

what size wheels do they fit under ed?

I'd expect them to fit 16's, but you might be very lucky and get them up 15's....? Just based on the average sliding caliper.

[billgatese30]

i wouldn't imagine they'd fit under 15" but recon it would be close to the 16" too

[ed325i]

They fit inside some 16" wheels, here they are in side 17" wheels.



ED

[ed325i]

Here is a pic of the cailper I am going to be using with 312mm discs which are being machined today. If you stop a e32 750 then they should stop the e30 ok.




ED

Meaty looking things!

Do you know how much they weigh?

The E32 750i calipers/Carriers + 1.8kg per side over stock cailper.

ED

[keri-WMS]

Here is a pic of the cailper I am going to be using with 312mm discs which are being machined today. If you stop a e32 750 then they should stop the e30 ok.




ED

Meaty looking things!

Do you know how much they weigh?

The E32 750i calipers/Carriers + 1.8kg per side over stock cailper.

ED

But how much does the stock caliper weigh? I was interested to see they compare as that's the other place motorsport stuff scores over OEM in most cases.

The smaller WMS caliper is 1.36kg, the bigger one is 1.77kg....

[ed325i]

I dont know what the stock ones weigh I just found that info in another post. But the whole set up is heavy, but it didnt cost me alot to put together. These are going on a cab with m30 3.5 engine not a light weight racer. If I was going to build a racer I would use light alloy calipers

[ed325i]

The discs are know back from being modded.





ED

[d6dph]

Looks good, just a small question and i'm not trying to put down your conversion, does that many holes in the bell not compromise the strength?

[ed325i]

Looks good, just a small question and i'm not trying to put down your conversion, does that many holes in the bell not compromise the strength?

It the same set up as www.300mm.de which have been tuv approved so they will be ok .

ED