NQSBBK Porsche Boxster 986 front calipers

[pandaman]

This caliper upgrade is a popular choice, I was wondering if someone who has them installed could measure them for me? so I can check that they will fit under my wheels.

Or, even better, if someone has them installed and also happens to have BBS CH R's (18x8.5 ET47), do they fit without spacers?

Just want to check if they fit before I bite the bullet and get some off ebay that need restoring.

Thanks

[breeze]

OP this may be off topic a little, but please indulge me…

There is a mistake that people often make with caliper upgrades.

It is related to piston sizing. In simple terms, if the caliper you are upgrading to has a larger piston area than the one you are replacing, it will shift brake bias *rearward*. This is exactly the opposite of what you want for a performance car. It will also change pedal feel (generally making it longer).

I’ve made this mistake before and I know others who have too. We tend to get focused on whether a caliper will fit behind a wheel and whether adapters are available but do not do the piston sizing maths. Fitting a larger master cylinder will not fix the problem because the ratio of piston size front to rear will still be different.

I haven’t looked at the specific case of Boxster calipers, but I would do the maths if you have not already. I wouldn’t assume it will work for you because others say it will be fine.

[pandaman]

OP this may be off topic a little, but please indulge me…

There is a mistake that people often make with caliper upgrades.

It is related to piston sizing. In simple terms, if the caliper you are upgrading to has a larger piston area than the one you are replacing, it will shift brake bias *rearward*. This is exactly the opposite of what you want for a performance car. It will also change pedal feel (generally making it longer).

I’ve made this mistake before and I know others who have too. We tend to get focused on whether a caliper will fit behind a wheel and whether adapters are available but do not do the piston sizing maths. Fitting a larger master cylinder will not fix the problem because the ratio of piston size front to rear will still be different.

I haven’t looked at the specific case of Boxster calipers, but I would do the maths if you have not already. I wouldn’t assume it will work for you because others say it will be fine.

Thanks I had no idea this was a thing, so I did some research and maths!

First, as a 4 pot caliper, to calculate the effective area you only calculate for one side not both as per a sliding caliper.

Secondly i found someone elses work of the stock calipers and a few more examples.

Stock GTI/Ed. 30: ATE FN3 54 mm = 2290 mm²
R32/6R/S3 8P/TTS/Cupra mk2: ATE FNRG 57 mm = 2552 mm²
Brembo 18Z (30/34/38 mm): 707 + 908 + 1134 = 2749 mm²
GTI PP/Ed. 40/7R/S3 8V/Cupra mk3: TRW 60 mm = 2826 mm²

And finally I worked out the area of the Boxsters

Boxster 986 (36/40 mm): 1018 + 1256 = 2274 mm²

So with a difference of 16 mm², is it safe to say they will feel and act pretty much the same as the stock Gti calipers I have now? but being a larger disc and i assume larger pad have more of a bite?

Thanks again your were right, I was more concerned whether they fit rather than if they will work.

[terrier]

my 986s have passed 4 MOTs so 

[breeze]

OP this may be off topic a little, but please indulge me…

There is a mistake that people often make with caliper upgrades.

It is related to piston sizing. In simple terms, if the caliper you are upgrading to has a larger piston area than the one you are replacing, it will shift brake bias *rearward*. This is exactly the opposite of what you want for a performance car. It will also change pedal feel (generally making it longer).

I’ve made this mistake before and I know others who have too. We tend to get focused on whether a caliper will fit behind a wheel and whether adapters are available but do not do the piston sizing maths. Fitting a larger master cylinder will not fix the problem because the ratio of piston size front to rear will still be different.

I haven’t looked at the specific case of Boxster calipers, but I would do the maths if you have not already. I wouldn’t assume it will work for you because others say it will be fine.

Thanks I had no idea this was a thing, so I did some research and maths!

First, as a 4 pot caliper, to calculate the effective area you only calculate for one side not both as per a sliding caliper.

Secondly i found someone elses work of the stock calipers and a few more examples.

Stock GTI/Ed. 30: ATE FN3 54 mm = 2290 mm²
R32/6R/S3 8P/TTS/Cupra mk2: ATE FNRG 57 mm = 2552 mm²
Brembo 18Z (30/34/38 mm): 707 + 908 + 1134 = 2749 mm²
GTI PP/Ed. 40/7R/S3 8V/Cupra mk3: TRW 60 mm = 2826 mm²

And finally I worked out the area of the Boxsters

Boxster 986 (36/40 mm): 1018 + 1256 = 2274 mm²

So with a difference of 16 mm², is it safe to say they will feel and act pretty much the same as the stock Gti calipers I have now? but being a larger disc and i assume larger pad have more of a bite?

Thanks again your were right, I was more concerned whether they fit rather than if they will work.

Yes you only need to count one side. If the pistons are that close that is pretty good going.

Piston sizing contributes to pedal feel and brake balance. For feel (by that I mean how far you push the pedal before the pad bites) it is mainly the piston sizes. Balance is affected by all kinds of things like braking torque/pad compound/discs etc etc. Generally speaking, I wouldn’t worry about moving forward and have done things like update fronts (particularly with pads) in the past.

Some of the Toureg type calipers have much bigger pistons.

The only other consideration is how far the pistons are moving out of the caliper. If the discs you are using are much thinner (than those normally used with the caliper) you can have the pistons over extending and that can cause problems too. At least there are easy mitigations like anti rattle shims (acting like spacers) or not running your pads down too much.

Let us know how you get on!

[breeze]

I’ve just cut and pasted from elsewhere, so forgive me if the source is innacurate:

Brembo 6 pot 17Z - pistons 34/36/38 = 3060mm2
Brembo 6 pot 18Z - pistons 30/34/38 = 2750mm2

I think I would notice that.

I ran 840ci Brembos on an M3 Evolution years ago. Took me a while to figure out a. why the pedal was so long and b. why the rears wore out so quickly. 

[breeze]

my 986s have passed 4 MOTs so 

From the post above, it sounds like they are a good fit. Not that I’d trust an MOT to tell you if they weren’t!

[pudding]

FWIW, I found the difference in pedal feel between standard fronts and MK7R/S3/PP, was pretty substantial....and not in a good way. 

Before fitting the MK7 calipers, the front>rear balance always felt spot-on to me, but post fitment, the first cm of pedal travel was dead (a horrible delay at motorway speeds when feathering a little speed off) and the rears no longer contributed much, so the balance was ruined.

I've since gone back to stock and much prefer it.  I think the MK7 setup only works effectively when everything else from the car is transferred over.  Servo, pedal (different fulcrum point), ABS ECU, rear brakes etc etc.

[rich83]

I have TTRS calipers on mind IIRC 40/44mm pistons and the pedal is fantastic.

[terrier]

my 986s have passed 4 MOTs so 

From the post above, it sounds like they are a good fit. Not that I’d trust an MOT to tell you if they weren’t!

BBS CH 18 x 8 et50 with forge 11mm spacers

[FatWelshBoy]

7R brakes on my Ed30 and they are great. I didn't really notice a longer pedal until I fitted rear calipers with larger pistons. The extra pedal stroke is very slight and 100% worth it over running stock brakes. I came from a 7R to an Ed30 and the first thing that stood out was how crap stock brakes are. The slightly longer pedal is a bit like when you jump in a car you haven't driven before and have to get used to the clutch, before you know it you don't even have to think about the bite point.

[LC5F]

I understand that changing piston size effects the ratio between MC and caliper, but can't say I have noticed a long pedal with my Golf R calipers - or even the back end biting first.

[Lewo]

I've got the mk7r brakes on mine and have got used to them now. Did notice the slightly longer pedal travel to start with but part of that was down to a poor bleed. Re bled and bedded in properly now and even with the oe TRW pads they have more than enough power for me but yes, will get performance pads when I replace them, maybe lol.

[pudding]

Maybe some cars take to the 7R setup better than others in terms of pedal feel.  They are hugely more powerful than the stock brakes, not taking that away from them, especially with the oem Clubsport S discs and pads.  Could be ageing master cylinders, worn rear calipers, worn servo etc etc contributing to the pedal.  Either way, on my daily routes the dead pedal was bad enough to revert back to stock, and they are just as poweful at low to medium speeds.

Where the 7R works best is repeated high speed stopping, from say 100mph coming off a dual carriageway and standing on them.  The stockers definitely faded easily in that scenario.....especially if the off ramp is downhill as well as short 

Not knocking anyone's choices of brakes but sometimes some context paints a better picture.

What is weird though is my TDI has the same brakes as the GTI, but are considerably sharper.  Need to try and suss that one out at some point!

[LC5F]

What is weird though is my TDI has the same brakes as the GTI, but are considerably sharper.  Need to try and suss that one out at some point!

Different MC sizes to counter the boat anchor diesel?