M235i Brakes on a 135?

[Suhb]

Will the 4 pot + 340mm rotor clear a 17 inch rim like the 135i caliper/rotor?

[WhatsADSM]

Originally Posted by Suhb

Will the 4 pot + 340mm rotor clear a 17 inch rim like the 135i caliper/rotor?

It depends on the design of the wheel. Some 17s will fit some won't. Aftermarket wheels like apex that generally have a lot of clearance to the spokes and barrel will fit best. I think I read also that f2x 17" wheels fit.

One note on fitment. The stock pads that come with these calipers from BMW have these weird metal ears on them that are pressed into the pads (see picture posted earlier). It appears that they are there for ease of installation. These ears on the pads actual protrude out of the top of the caliper and reduce the clearance to the barrel of the wheel. You will have to remove those or get new aftermarket pads if you need a little extra clearance to the barrel.

[juld0zer]

Correct, any 17" F20 wheel will fit over the calipers with no spacer.
The stock E82 wheels wont clear the spokes and some designs will foul the damper weights.

The weights dampen noise - like applying dynamat to door panels to add weight thus reduce the resonance. The weights on the ends of the pads made the pads heavier, thus vibrate at a different frequency. Their secondary purpose happens to be aiding handling

[WhatsADSM]

Originally Posted by juld0zer

Correct, any 17" F20 wheel will fit over the calipers with no spacer.
The stock E82 wheels wont clear the spokes and some designs will foul the damper weights.

The weights dampen noise - like applying dynamat to door panels to add weight thus reduce the resonance. The weights on the ends of the pads made the pads heavier, thus vibrate at a different frequency. Their secondary purpose happens to be aiding handling

That makes sense to me. Yea additional mass will change the frequency or potentially eliminate it.

Do you know if stock 18" 261 wheels will clear with a minor spacer? I thought I remember you saying that before.

[juld0zer]

261Ms will fit with a small spacer. I reckon 5mm will get you out of trouble but dont take my word for it. Test fit with some washers first to determine how thin you can go. I went with 10mm because i also changed to rear rims all round (245 all round) and it fouled the strut. But 10mm brings you into fender rubbing territory.

[deesea]

Lots of talk here about using the calipers fitting the 340mm rotors keep almost the same brake bias. Would the 370mm affect brake bias significantly?

Rather, is it the piston bore size that determines the difference in brake bias or a combination of factors?

[Gangplank]

its a combination of factors. Brake master cylinder, bore size, rotor size, etc. I'd love to test stock vs 340 vs 370

[juld0zer]

I wished it was that easy to fit the 370mm version. The car could do with more front brake which could be provided by the larger diameter discs (greater brake torque effect).
Once i wear out these stock pads i'll look at something with more initial bite. Stock F car Brembo pads really lack initial bite compared to E car Brembo pads.

By fitting 19" rims, tyre profile becomes too thin for comfort but the Z4 and E9x mobs with the 370mm kits love them.

[WhatsADSM]

Originally Posted by deesea

Lots of talk here about using the calipers fitting the 340mm rotors keep almost the same brake bias. Would the 370mm affect brake bias significantly?

Rather, is it the piston bore size that determines the difference in brake bias or a combination of factors?

There is no reason that the 370mm rotor can't be fit. Mounting points are the same. The issues are:
1) Clearance to wheels. Although I'll bet the 18" 1/2 series apex wheels clear. I fit 380mm discs for my M3 under a set of 18" arc-8s
2) Front-to-rear brake bias. Bias is (primarily) a function of piston bore area, lever arm (disc radius) and brake pad friction coefficient (μ). So changing to a 370 from a 340 disc would increase the bias ratio by about 8% which is noticeable for sure. You could correct this by increasing the rear brakes (piston area and/or disc size), and you could also attempt to correct it by selecting a more aggressive pad in the back (although that has other limitations).

The big rear f series brakes are 345mm 2-piston setups and when I did a rough back of the napkin calculation it worked out almost perfectly in terms of bias (albiet with a bit less overall compared to the master). However the issue is the F-series stuff doesn't just bolt up in the rear like it does the front. Based on what I have read I *think* with a little massaging it would work for the 135i better due to the deeper hub, but I would have to actually have things in hand and try it out to be sure.

[Gangplank]

There's a set of the blue 235i calipers on fleabay for $725 but one looks a bit scratched up.

[WhatsADSM]

Originally Posted by Gangplank

There's a set of the blue 235i calipers on fleabay for $725 but one looks a bit scratched up.

Fwiw my front grey calipers were around $100 a piece to my door. Just saying.

[Gangplank]

Hmm...

[crowtrobot]

Originally Posted by WhatsADSM

Fwiw my front grey calipers were around $100 a piece to my door. Just saying.

Any advice on where to get them so cheap? car-part.com junkyard searches seem pretty pricey (though my guess is that these are blue/orange/red calipers that are mis-classified), and I've only seen new on ebay. Found a post or two in the F30 classifieds here, but none at that price.

Also just to be clear, no hope of these calipers fitting in 262 17" rims, even with spacers? Was hoping to move up in rotor size from stock in my 128i before the track season starts this year, but getting two new sets of wheels/tires to accommodate the brakes is going to blow that budget up quite a bit...

...still, there's that Apex group buy going on, so it's not out of the question I guess.

[WhatsADSM]

Originally Posted by crowtrobot

Any advice on where to get them so cheap? car-part.com junkyard searches seem pretty pricey (though my guess is that these are blue/orange/red calipers that are mis-classified), and I've only seen new on ebay. Found a post or two in the F30 classifieds here, but none at that price.

Also just to be clear, no hope of these calipers fitting in 262 17" rims, even with spacers? Was hoping to move up in rotor size from stock in my 128i before the track season starts this year, but getting two new sets of wheels/tires to accommodate the brakes is going to blow that budget up quite a bit...

...still, there's that Apex group buy going on, so it's not out of the question I guess.

That's where I got mine. Although it think I found the cheaper set so those are gone now

The key is to not look for a set that has the fancy coloring then the junk yards don't ask so much . Search for a 2014 335i, without the m performance package. Those are the grey calipers. I just looked and it looks like a lot of them have been snatched up but they still had two yards with them. (one was $85 a caliper the other was call).

[juld0zer]

Originally Posted by WhatsADSM

There is no reason that the 370mm rotor can't be fit. Mounting points are the same. The issues are:
1) Clearance to wheels. Although I'll bet the 18" 1/2 series apex wheels clear. I fit 380mm discs for my M3 under a set of 18" arc-8s
2) Front-to-rear brake bias. Bias is (primarily) a function of piston bore area, lever arm (disc radius) and brake pad friction coefficient (μ). So changing to a 370 from a 340 disc would increase the bias ratio by about 8% which is noticeable for sure. You could correct this by increasing the rear brakes (piston area and/or disc size), and you could also attempt to correct it by selecting a more aggressive pad in the back (although that has other limitations).

The big rear f series brakes are 345mm 2-piston setups and when I did a rough back of the napkin calculation it worked out almost perfectly in terms of bias (albiet with a bit less overall compared to the master). However the issue is the F-series stuff doesn't just bolt up in the rear like it does the front. Based on what I have read I *think* with a little massaging it would work for the 135i better due to the deeper hub, but I would have to actually have things in hand and try it out to be sure.

Can i ask what formulas/calculations you did? What are the specs for the masters or did you base it on piston area of the calipers matched with that master? Im just trying to see if i am on the right track with my calculations.

Based on piston area alone, the F series front Brembos would take slightly more fluid to exert the pistons an equal distance versus stock 6 pot Brembo fronts on a 135i. Using the stock 135i master would therefore be sufficient but other models will need to either add SPBR to their VO or do a physical modification such as changing the master cylinder.

All things considered, i reckon a 370mm front with the stock rear on a 135i would be pretty sweet and it would probably give it the sharp brake feel of the M cars.

[WhatsADSM]

Originally Posted by juld0zer

Can i ask what formulas/calculations you did? What are the specs for the masters or did you base it on piston area of the calipers matched with that master? Im just trying to see if i am on the right track with my calculations.

Based on piston area alone, the F series front Brembos would take slightly more fluid to exert the pistons an equal distance versus stock 6 pot Brembo fronts on a 135i. Using the stock 135i master would therefore be sufficient but other models will need to either add SPBR to their VO or do a physical modification such as changing the master cylinder.

All things considered, i reckon a 370mm front with the stock rear on a 135i would be pretty sweet and it would probably give it the sharp brake feel of the M cars.

Correct I did it assuming a stock 135i front caliper, since I have a 135i. For the overall bias calculation (not just hydrolic sizing) you also should take into account the slightly larger rotor in the 340mm (or much larger rotor in the case of 370mm).

FWIW I just had my first track day with my 135i. I am known to be VERY hard on brakes, and with my 340mm F30 front brakes, stock 135i rear with PFC08 pads all around. It was flawless. It does also have a custom brake duct kit in the front which I'm sure helps a bunch as well. But in general I would say the 340mm F30 kit is actually a VERY capable track upgrade. I do reserve a bit of judgement until I get around to taking the track pads out and get a chance to inspect the pistons and boots to see how they held up.

[juld0zer]

Do you find the pedal response to be a bit vague initially? I guess you have aggressive pads so that might mask most of the vagueness. I need to drive this setup a bit more to gauge the difference. I had an M3 master in there for a few months. Brakes felt non linear the harder you push the pedal - it felt like it peaked and plateaued. Modulation is definitely lacking

[WhatsADSM]

Originally Posted by juld0zer

Do you find the pedal response to be a bit vague initially? I guess you have aggressive pads so that might mask most of the vagueness. I need to drive this setup a bit more to gauge the difference. I had an M3 master in there for a few months. Brakes felt non linear the harder you push the pedal - it felt like it peaked and plateaued. Modulation is definitely lacking

I put them on right before a track day so I just have the pfcs in so far. I'll let you know more once I put the street stuff in.

What pads are you running?

[juld0zer]

Had stock BMW pads with stock 135i BMW pads in the rear aswell.

[bNks334]

Why do people feel they need to upgrade the stock 6pot calipers?

I have 255's up front (200tw tires on 9in wheels) with PFC-08 pads and I have way more brake then I do tire... I generate about .9g to 1g of braking force right now and it's the tires that are the limiting factor for me. Once a PFC-08 pad is up to temperature it delivers almost double the brake coefficient a stock pad can and PFC-08 is a more endurance oriented pad than a comparable higher coefficient pad. Once these pads are hot, I can lock my tires up at will.

I have never had any issues with dust boots or pistons melting. I have always had my rotor shield bent all the way out to scoop air. I recently added brake ducts up front and I actually think I am over-cooling the pads now.

http://wiki.seloc.org/a/Brake_pads

Sounds to me like people are feeling a bit of a placebo effect with the F-series setup. The larger rotor means less brake pedal effort to achieve the same brake torque. This may feel better, but consider you'll now have less feel for modulating the pedal. I doubt the F-series brakes are decreasing stopping distance by any meaningful amount. In fact, stopping distance in the real world goes up the more you bias brake torque frontward. BMW has actually programmed DSC to shift brake line pressure rearward when you are riding on the threshold of ABS. The result is an undeniable decrease in stopping distance.

I'd argue that putting f-series brake up front is detrimental unless you increase the rears to match. You'll also need the master cylinder to match in order to maintain a bit more brake pedal effort (easier to modulate). Without the master cylinder upgrade you'll probably end up with a softer pedal and very grabby brakes (as people have noted above).

https://www.zeckhausen.com/catalog/i...Path=6446_6565

[juld0zer]

I had sticky pistons in my 6 potters. They would not extend evenly and one year ago, not long after i bought the car i started having all sorts of brake issues. The 4 pots i found on Ebay for a bargain - almost cheaper than two rebuild kits without pistons!

If 19" wheels were more practical on this car (ie, not having to use rubber bands as tyres) then i would look for the 370mm version

[bNks334]

Originally Posted by juld0zer

I had sticky pistons in my 6 potters. They would not extend evenly and one year ago, not long after i bought the car i started having all sorts of brake issues. The 4 pots i found on Ebay for a bargain - almost cheaper than two rebuild kits without pistons!

If 19" wheels were more practical on this car (ie, not having to use rubber bands as tyres) then i would look for the 370mm version

That's a good point, the rebuild kits using brass pistons are expensive lol Now consider though that your solution is instead to buy all new rotors and calipers, change the brake bias, increase rotational weight, and possibly spend more money to move to the larger bore of the M3 master cylinder.

The only issue with the 135i caliper is that the top part of the pistons are Phenolic plastic. This was done to prevent heat transfer, but the plastic itself has a tendency to degrade. I'd rather replace the pistons with new stock ones (for very cheap) every few years then to do all the above work. Titanium shims seem to help (which I also run). Or, move to steel/brass pistons in the 135i calipers.

No arguing that a complete M235i setup front and rear is the more capable brake setup. I just question the real world gains by doing the conversion on cars running street tires. Right now I need more tire, not brake, which I can't see being any different for every 1 series short of wide-body cars.