Miata Turbo Forum - Boost cars, acquire cats.

- Suspension, Brakes, Drivetrain (https://www.miataturbo.net/suspension-brakes-drivetrain-49/)

- - Brakes Locking Up (https://www.miataturbo.net/suspension-brakes-drivetrain-49/brakes-locking-up-39373/)

Brakes Locking Up

This seems like a really silly question to ask, but I'm having some trouble determining a solution.

Several years ago when I went to track days on stock power the brakes were wonderful. At the time I had stock lines, stock fluid and EBC greens on average 195 yokohama tires.

Now, even at relatively low speeds at autox I can't push the brake all the way down or I guarantee myself a cloud of smoke from one or two tires. I've got fresh super blue fluid, stainless lines, Axxis Ultimate pads, and 225 RS2's. This is a subject that I don't have a great deal of experience with so any help will be appreciated.

Thanks

Michael

It's a combination of shitty grip from the RS2s when they're relatively cold (like at an autox versus track), the driver's fault, and maybe the choice of pads contributes too.

I've autox'ed my RS2s with Carbotech XP10/8 pads. They are wonderful track pads for stock power, but when they're cold they don't modulate worth a shit. They give subpar braking so you keep getting on the pedal harder and harder, until it goes from subpar braking to lockup. I don't have any experience with Axxis Ultimates, but I wouldn't think they need too terribly much heat. (?) But tires are also affected by temp. I can brake a shit ton harder on track with RS2s than I can at an autox, due to the higher temperatures on track. I have unintentionally locked them up a couple times at autox, but not once on track.

Things that will help for autox are brake pads with a lower MOT (but I think you're probably fine with Ultimates) and/or tires that grip better when cold. Bottom line though, don't step on the pedal so hard and they won't lock up. :bigtu:

If you "push the brake all the way down" and they don't lock up, then you've got a problem. You always want to have enough brake to lock up all four at will by standing on the pedal.

Is it the front tires locking up? If so, you may simply be exposing the extreme front bias of Miata braking systems. An adjustable proportioning valve would be the solution. And yes, you want to be able to lock all four wheels. The catch is all four wheels, not one or two.

I have ultimates too, front and rear. From past experience on other model cars I would characterize them as linear, easy to modulate and rotor friendly. However, on the miata my experience is the same as the opening poster. Front tires seem to be a bit easy to lock up unless I feather the brakes on. As the_man mentioned, I'm beginning to think it is brake bias too.

+1 on a prop valve and checking your pad compound what rotors are you running as well? Some nice drilled and slotted units could help you disipate heat faster and reduce lockup and fade. I know my FM units in the front fixed a ton of my braking problems. But overall the prop valve will do the most for you relegate 30% or so to the rear and the front end wont be as lock happy by far.

Were would you get one of these fidangling prop vavles.....!! lol

Just to update things, I ordered the Wilwood prop. valve from FM and it should be here before too long. Just have to decide if I want to get creative mounting it or just do it the standard way.
Magna, I'm still running factory disks. Will probably replace with NAPA disks when I change pads next time.
I'll keep you guys informed.

Michael