Big Brakes.... Please can some one explain them

[paul mac]

Paul,

 

Do you know what the piston diameters are in your front calipers? I've got a monster list of caliper piston areas for various brake kits and OEM calipers but haven't found anything about these....

no sorry Dan, they are staggered, i will measure next time they are off

Now if you are using a std master cylinder etc, if this isn't up to shifting the extra fluid mass, you will have worse braking than the std system despite the increase in disc size as you are losing the advantage of the both! so be very careful in choosing a tried and tested set up that is known to work with the std master cylinder etc, unless of course you are intending to change everything, but its surprising just how many people don't even think about this.

 

i did actually believe i would have to change my master cylinder and rather than start trying to size up the correct one on piston areas and all that maths , i decided to just go with the master cylinder off a 55 amg, I know its not quite that simple but i thought it would be a good starting point. To my surprise the brake pedal travel was actually slightly firmer than my uk spec brakes which you would not expect having to shift more fluid, i can only surmise that the new generation calipers had a very small internal fluid volume compared to my ye olde uk spec calipers, i now its slightly off topic but has anyone else noticed any pedal feel differences (good or bad) on upgrading ?

[dandan]

If your ones are the same as the SLR 8 pots then they should be a staggered 32mm and 28mm combo up front in the 8pot beasts. This works out to be a shade smaller than the UK specs...just shy of 99% of the UK's piston area.

[Wez]

If your ones are the same as the SLR 8 pots then they should be a staggered 32mm and 28mm combo up front in the 8pot beasts. This works out to be a shade smaller than the UK specs...just shy of 99% of the UK's piston area.

 

Thats crazy isnt it.

 

Is this why the UK are such good brakes and stayed well near the top for a very long time?

[dandan]

Yes, the piston area is huge and it's very suprising when you start looking around. When you ditch the UK calipers for AP/KAD/Brembos the disc size generally has to get up to ~350mm or more to match the UK's braking torque for identical pad compounds.

 

I know the AMG also uses very deep pads and this reduces the effective radius and braking torque a little bit too....they're not the ridiculous, ABS inducing overkill people seem to think.

 

When I get to work tomorrow I will dig out the spreadsheet and post up some comparisons for our most common big brake kits...plus your Alcon numbers. I may need some pad depths or profiles for some of these brands though...like KAD and D2.

[dandan]

Wez,

 

With the Alcon 4 pot caliper you would need a 356mm disc (that gets you within 0.6%). A 343mm would mean you were 4.8% shy of the UK specs.

 

The Alcon 6pot on a 324mm disc would be 0.4% better than UK's. The Alcon's piston area is actually slightly less but the pad is shallower, increasing the effective radius for brake force squeeze onto the disc is a little larger.

[Wez]

Wez,

 

With the Alcon 4 pot caliper you would need a 356mm disc (that gets you within 0.6%). A 343mm would mean you were 4.8% shy of the UK specs.

 

The Alcon 6pot on a 324mm disc would be 0.4% better than UK's. The Alcon's piston area is actually slightly less but the pad is shallower, increasing the effective radius for brake force squeeze onto the disc is a little larger.

 

Great info as 6 pots on 324mm may fit under stock 17" wheels, interesting

[Tricky-Ricky]

Just a thought as a cheaper alternative, since the STD UK callipers are good anyway,

Either find a OEM lager disc from another vehicle that fits the Supra and make spacers for the calliper, or aftermarket bells and disc's to fit.

Done this with other cars, and its not that hard, and the results are pretty good.

[Wez]

Surely the caliper is designed to work with a specific size rotor.

[dandan]

Just a thought as a cheaper alternative, since the STD UK callipers are good anyway,

Either find a OEM lager disc from another vehicle that fits the Supra and make spacers for the calliper, or aftermarket bells and disc's to fit.

Done this with other cars, and its not that hard, and the results are pretty good.

 

Surely the caliper is designed to work with a specific size rotor.

 

Yes - you'll get to a point where the pad geometry looks a little off and also the disc will start running very close to the caliper at the extremities. That's not to say a small increase would be impossile though, I've never looked.

 

You could do a lot worse than a floating UK size disc, excellent pads and titanium caliper pistons for a minimum hassle "heat tolerant" approach for a track weapon.

[Wez]

I already have the floating UK setup and Performance Friction pads, just looking at caliper options when I am unable to get the pads I want

[bignum]

I already have the floating UK setup and Performance Friction pads, just looking at caliper options when I am unable to get the pads I want

Wez, have you tried the portefield r4 race pad, we`re all using them now and i reckon they arent far off pf.

[paul mac]

If your ones are the same as the SLR 8 pots then they should be a staggered 32mm and 28mm combo up front in the 8pot beasts. This works out to be a shade smaller than the UK specs...just shy of 99% of the UK's piston area.

 

really good info Dan and that really validates what i said about slightly firmer brake pedal feel, ok maybe 1% would be a bit hard to feel the difference , dont forget Dan that although the brake force applied through the hydraulic system will be the same, with a larger pad area the coefficient of friction rises so the the actual brake force applied to the disk will rise

[dandan]

really good info Dan and that really validates what i said about slightly firmer brake pedal feel, ok maybe 1% would be a bit hard to feel the difference , dont forget Dan that although the brake force applied through the hydraulic system will be the same, with a larger pad area the coefficient of friction rises so the the actual brake force applied to the disk will rise

 

Have a look here Paul... http://www.mkivsupra.net/vbb/showthread.php?t=225007 8th post

 

If you get chance it would be great if you could get some measurements of the pad depths to be 100% bang on...the numbers won't change but but it would be nice to be 100%.

[Tricky-Ricky]

Yes - you'll get to a point where the pad geometry looks a little off and also the disc will start running very close to the caliper at the extremities. That's not to say a small increase would be impossile though, I've never looked.

 

You could do a lot worse than a floating UK size disc, excellent pads and titanium caliper pistons for a minimum hassle "heat tolerant" approach for a track weapon.

 

You would be surprised just how much larger you can go without having those problems, a 40mm increase in disc size can be accommodated in most cases without a geometry problem,and makes a big difference, and the bigger the start size the more you can get away with;)

[Wez]

Wez, have you tried the portefield r4 race pad, we`re all using them now and i reckon they arent far off pf.

 

I have used the road pad and wasn't impressed, I think I would go for the CCX or try some Carbotech next.

[johnny g]

I have used the road pad and wasn't impressed, I think I would go for the CCX or try some Carbotech next.

 

I can highly recommend the Carbotech's, Wez. Very consistent pedal on that.

[Terminator]

Just a thought as a cheaper alternative, since the STD UK callipers are good anyway,

Either find a OEM lager disc from another vehicle that fits the Supra and make spacers for the calliper, or aftermarket bells and disc's to fit.

Done this with other cars, and its not that hard, and the results are pretty good.

 

 

We did exactly this on our RB25 powered 200SX's. I had ten pairs of brackets made up in stainless to reduce costs. Callipers from 300ZX and disc from BMW M3. The increase radius of the disc was never a problem in the calliper opening. The centre of the pad face was was moved out about 20mm, much improved braking as a result.

[dandan]

I can highly recommend the Carbotech's, Wez. Very consistent pedal on that.

 

Which compound are you running? I am trying to choose between the AX6 and XP8 right now. My only real concerns are increased noise plus faster disc and pad wear from the XP8's as they won't always be at optimum temp on the road (and apparently wear rates are higher when this is the case).

 

For the calipers I have the price difference from AX6 to XP8 is only about an extra £40 so price is not a concern.