heavy85

I’ve been reading positive things about the new Stoptech C43 calipers - only 4 lb purpose built race calipers with floating rotors - but have only found them adapted to NC Miatas not specific to the RX8. This is for NASA TT2 build. The stock brakes work well but aren’t as consistent as I would like and dropping tangible weight off the front would be ideal. V8R shows same kit for both but the stock NC brakes are smaller and looks like even has different master size so I would think the brake kits would be different between the two to get the best performance. Anyone seen these available developed specific for the RX8?

Cameron

TeamRX8

iTrader: (25)

it’s listed for both in the same identical configuration. What matters most is the size of the pistons and then the pad size, but I can’t find concrete info on the diameter(s) on this kit. Which their biggest issue is they’re probably one of the worst marketed companies around. At least in terms of end-user marketing. Which is pretty funny since they’re owned a by a marketing group. When I was finally able to locate the kit on their website the tech page fails.

So if you can find that out then I can give you an approximate reference against the front OE brake in terms of force.

There’s an ST-40 kit for sale on the forum, but they’re rarely seen around here. Again, just poorly marketed.

heavy85

And so you see why I asked. Their site is useless and makes it hard to know what they have. All I can find is that they are claimed to be same between NC and RX8. But I’m failing to understand why they would make them the same and therefore smaller than the stock brakes.

TeamRX8

iTrader: (25)

A lot of companies do the same thing because they’re directly interchangeable. However, in this case smaller is not necessarily less. If it has more piston and pad area it will provide more clamping force. The increased disk thickness adds heat capacity. I need to know the piston diameters to run the calcs for a full brake torque comparison with the rotor diameter factored in, but unless the pistons are small it will probably be an improvement over OE in both brake force and unsprung weight. My RacingBrake caliper has 38mm pistons, which is quite a bit more area/braking force than OE and I just modified it down to the non-Sport RX8 303mm rotor size to reduce weight. A smaller rotor is also less rotational inertia, though for this StopTech kit you’ll gain some back with the thicker disk.

My 303x24 2-pc rotor is 11.6 lbs compared to the Stoptech 309x32 rotor at a claimed 13 lbs. A good amount of that ST rotor width increase is larger vane openings to allow more cooling air to get through. It’s not all added brake surface metal thickness. Which my primary focus is lower speed autox rather than high speed track. That 13 lb weight is also for the ST straight vane rotor. This same kit also has a directional curved vane rotor option, but they weight about 3 lbs more each. So that might be worth considering for a RX8 track car that is approx 400 lbs heavier than an NC MX5 to offset your concern.

The RX8 ABS is programmed to automatically adjust front/rear bias. It can handle a pretty good amount of bias change in either direction. So don’t get so hung up on that.

heavy85

Thanks for the info. Called Stoptech and they said it’s part number 87.548.D900.R7. 309x32 rotor and 32/38 pistons. My main concern is to add capacity to get more consistent braking which is why the concern with smaller. You are right though there are many variables.

Edit - I didn’t create this but it’s my car.

TeamRX8

iTrader: (25)

I saw 32-38 listed in a part number sequence, but thought that was a bit odd and didn’t want to assume since it wasn’t fully clarified as such.

So running the numbers I come up with approx. 18.5% less front brake torque than the OE RX8 brakes. Even if it had 38mm/38mm pistons it still be down about 4.5%. By my calcs it’d need a 38mm/40mm piston combo to provide approx. OE brake torque. Which supposedly this caliper can go up to a 38mm/44mm max combo size. So you’d just have to ask and see if they can do that if you’re set on trying to go this route.

Brettus

iTrader: (2)

FWIW I run a wilwood caliper that has 2x 38mm pistons and on the stock 322mm discs I'd say they are slightly down on stock brake torque as per Teams calcs.

TeamRX8

iTrader: (25)

Well the RacingBrake 38/38 caliper with 323mm OE size rotor is just a bit better than OE, but the pad radial height plays into the clamping force. A shorter radial height pad has more clamping force and usually aftermarket caliper pads have less radial height than OE pads. It varies though. So without that reference value you can’t really make general statements. The total piston area is pretty close between the OE single 54mm caliper and a 38/38mm 4-pot caliper; just a couple of hundredths square inches difference. The reason it was down in the prior reply is because of the smaller 309mm rotor. So it needs one pair of pistons to be slightly larger to compensate.
.