The STR calipers have more pad volume than our previous parts for more pad area and more grab with less effort. To increase stiffness the calipers have a bridge bolt.
The rear AeroRotors are 328x28mm and have modest CFD optimized venting, about the same level as our previous front brakes did. Our old rotors were solid. Our new rotors will run much cooler. Even with the added thickness, the new rotors are not much heavier than our old solid ones were.
You can see the venting on the new hats between the rotor friction ring and the hat itself. This helps keep the hub and rotors cooler just like the front rotors.
The bracket bolts actually thread into the knuckle for maximum clearance.
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What is the purpose of the cross drilled rotor with integrated slots from the drilled hole? Does it prevent cracking from thermal expansion?
I looked all over Wilwood’s website but couldn’t find those particular rotors.
Its mostly to vent the pad outgassing. It actually makes the rotor more prone to cracking and isn’t done much anymore.
Those are thermal expansion slots, which certainly would have been to extend the time before cracking started. When iron rings heat up to competition temperatures, the expansion must be planned for. If not, then iron will crack sooner (beyond the normal “crazing”). There are better ways to deal with this, yet the sprint car/dirt track market typically operate on tight budgets,, so this would be one way to get there.
On the one hand it seems funny that Stoptech keeps coming up… but they really are at kind of a sweet spot. I know from pricing stuff up what a quantum leap up it is to go to the next tier of brakes, and I’m not sure, say, an Alcon TA6 (same pad shape too, I think) is more than incremental gains for the 4x (or so) price jump. I like that some of the newer calipers they’re doing are using more common racing pad shapes than the Brembo shapes the 40 calipers use.
I really like StopTech because they have the tremendous range of piston sizes which enables them to match OEM proportioning. People don’t realize how critical this is and how it affects a car’s electronics nowadays and if the car is an older car, how it affects pedal feel and balance. That’s not the case in this car because it is a race car with a pedal box but for cars with a single master cylinder, it’s amazingly good.
For their street kits, Stoptech also has rigorous validation testing. to assure the vehicle dynamics are safe. When developing frictions and caliper systems, they have OEM level brake dynos and do extensive validation that way as well. They also have a PHD tribologist and develop their own frictions in-house.
Sure Brembo and AP have some more advanced calipers but those are not the ones people typically use for street and grassroots applications. Those are no better than StopTech. StopTech’s engineering office is right down the street from us and they are very generous with help and technical support.
Brembo or AP’s engineering department would probably roll their eyes at the thought of working with a drift Team or not even have any knowledge that drifting has advanced to a high-level motorsport.
Yeah; I have to respect the niche that Stoptech has carved out for themselves. It was a little funny because until I looked it up I didn’t realize the STR60 was using as big of a pad as it is; I like that and a lot of their recent design decisions, and that’s leaving aside the validation they do.
I look at it sort of like… yeah, you end up using Stoptech in a lot of builds. But I know walking pits and looking at prototypes and GT cars and stuff in the 90s to recently (there’s more good options now but you know what I mean) basically everything would have Penske shocks… well, sometimes there is just a “best” solution given constraints.
The pad surface area doesn’t change braking performance, just pad life.
It looks like that kit was a little over engineered for this setup – you could have gone lighter and replaced twice per season? It just depends how much different rotational weight/inertia makes to chassis and tyre dynamics. And team budget of course!
We didn’t just throw some stuff on the car, I worked with StopTech’s engineering department to come up with a system that would solve our problems and improve our brake performance. Pad area doesn’t change the amount of brake torque produced but it can greatly affect the fade characteristics of the brake besides just affecting wear! The system is not overbuilt, it is sized correctly to take the thermal loading that the car produces. With our previous system, we had to run a very high mu aggressive pad with a narrow effective temperature range. Brake temperatures were sky high, the rotors would glow red hot and wear was extreme. Consistency was also an issue due to the pads narrow temperature operating range. Overall performance was adequate. Our new system is only 1.5 lbs per corner heavier in the front and 1 lb per corner in the rear. We are running a 335mm low mass front rotor, not the internally thicker and heavier high thermal capacity rotor. To reduce the capacity would run the thinner rotor, you would only be saving weight with the vane thickness not by reducing material in the friction surface, not worth it in my book.
Great answer Mike – I love your articles. Keep it up!
@Mike Kojima – how important is lightweight brakes (unsprung weight) and small discs (low inertia) for drifting suspension and chassis setup?
Well, you have to have enough brake to do the job, and too much is just weight in a bad place. Having enough brake is the most important thing.
Great answer Mike – I love your articles. Keep it up!