All Things Mk5 > Mk5 General Area

NQSBBK Porsche Boxster 986 front calipers

(1/4) > >>

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:

--- Quote from: breeze on February 01, 2022, 12:08:05 pm ---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.

--- End quote ---

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  :happy2:

breeze:

--- Quote from: pandaman on February 01, 2022, 07:03:42 pm ---
--- Quote from: breeze on February 01, 2022, 12:08:05 pm ---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.

--- End quote ---

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.

--- End quote ---

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!

Navigation

[0] Message Index

[#] Next page