HoserRacing
HoserRacing New Reader
4/4/09 10:07 p.m.

Ok, just got an e-mail from 949 racing where they have a kit to put an 11" rotor on an NA Miata (using the '89-91 Corrado rotor), but it still uses the same calipers as the '94-97 Miata. http://www.949racing.com/index.asp?PageAction=VIEWPROD&ProdID=207 I know that by moving the caliper further away from the center point of the rotor, it's providing greater stopping torque, and the increased mass allows for dissipation of heat, but how much of an improvement can you really expect? I'm hoping to be taking the former Mongrel Motorsports Miata out to Talladega Grand Prix this summer for some track time, and hopefully Roebling Road in the fall, I'm wanting to make sure I've got plenty of brakes for the end of the long straights. Is this a big improvement over stock, or am I better off going the Wilwood way http://www.good-win-racing.com/Mazda-Performance-Part/60-1093.html ? I like the price of the 949 set-up, but I don't want to find out I chintzed at the end of the straight at Roebling Thoughts, suggestions, input?

confuZion3
confuZion3 Dork
4/5/09 1:55 a.m.

If you can lock up your tires with your present brakes, you don't need more torque. That sounds like more trouble/time/money than it's worth. I'm assuming you have a '94 to '97 Miata, so you already have the upgraded Miata brakes. Just put on some good pads and you'll be fine.

Also, make sure you FLUSH your brake fluid if you haven't done so in the past two years. Bleed them if it's been less time.

HoserRacing
HoserRacing New Reader
4/5/09 6:56 a.m.

It's got the '90 brakes on there. I'm more concerned with fade over 20 minutes at a time on track at the much higher speeds with the V8 vs. what I was doing with my old supercharged car. Loved the brakes on the '96 M I had, but I was also dealing with 100-125 less hp at the wheels than what I have now.

AngryCorvair
AngryCorvair Dork
4/5/09 9:29 a.m.

KE = 0.5 * m * V^2

Kinetic Energy = one half times mass times velocity squared.

the kinetic energy goes up in direct proportion to the mass.

ie if new mass is 10% higher than old mass, new KE is 10% higher than old KE.

the kinetic energy goes up with the square of the speed.

ie if new speed at end of straight is 10% higher than old, the KE is 21% higher.

your car has stock brakes all around, but do you know how your corner weights compare to stock?

what tires are you running? remember, the brake system was designed with tires that had a peak grip of about 0.9. a hoosier A6 / R6 peaks at around 1.15, which is an increase of around 27% over stock. So at peak deceleration, there's 27% more weight transfer than there used to be, and this moves the balance toward rear-skid at max decel.

confuZion3 addressed the torque issue, but like Hoser said, the bigger worry is thermal fade due to pushing more energy (as heat) through the stock rotors.

so your proposed solution from 949 is a larger-diameter front rotor (more front torque for given pedal force, ie moving the car toward front-skid-limited, and more thermal mass) plus the '94 - '97 calipers which I assume have larger pistons than the '90 - '93, which is going to move the car even more front-skid.

if you want to improve the thermal capacity without changing the balance, you may be able to get away with some ducting to the front brake rotors. this should be your first effort, as it's cheapest and easiest to do.

if you still fade the fronts, and you really need more thermal mass, then you'll have to go to the bigger rotors and the revised caliper brackets.

if this change makes the car noticeably front-skid, you could go to a less aggressive front pad (as long as it can handle the heat), or a more aggressive rear pad, to shift the balance toward the rear.

without real numbers (corner weights, tire peak grip, dimensions of stock and replacement parts), improving balance is a trial-and-error process. with these numbers, we can make an educated choice that will probably be less expensive and less frustrating than trial-and-error.

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