DISCLAIMER: this is LTO (i.e. left turn only, not to be confused with lettuce, tomato, onion)
Some tracks where we race require little to no braking, while other tracks require heavy braking. Our car is currently equppied with heavy rotors to accomodate the tracks with heavy braking requirements. We are pondering if it's worth swapping out rotors when going to no / light braking tracks? We can swap in 5lb lighter rotors which would enable us to move 20lbs (4x5lbs) total to the center of the car.
Considering we'd be moving this unspring weight on the outer edges to sprung weight to center of car, in theory this sounds like a significant win / win. But in this business sometimes theory just costs a lot of money and doesn't make much of a difference in performance.
Appreciate any thoughts / advice on the topic.
In my opinion, this sounds like a win. Not only are you reducing unsprung weight, but also yaw inertia. Depending on the quality of the surfaces you run on, the gain in yaw inertia could be a bigger gain than the unsprung weight. It sounds like you've got a minimum weight that you have to ballast up to. Just make sure you put the ballast as low down and as close to directly underneath the CoG as you can.
As an example from another part of the racing world, a lot of my background is in endurance racing. It's normal to have two different brake specs for different race formats. We would normally call anything less than 3 hours "sprint racing" and anything longer "endurance". For sprint racing we would use significantly thinner discs for the same reasons.
There's also a reduction in the rotational inertia - the flywheel affect.
The disc rotors are basically just heatsinks, if you can dump the energy into them and still maintain acceptable temp's, it should be a win, win, win situation.
You may even be able to run the ligher rotors on the 'heavy braking' tracks, too, if you have the right pad material?
This bit of latteral thinking may not be that useful, because of wheel sizes and finding them at reasonable cost, but have you considered checking out the more exotic car wreckers/dismantlers for carbon-ceramic brakes for additional mass reduction and/or heat tolerance?
Thanks for the replies Tim / Gord.
> You may even be able to run the ligher rotors on the 'heavy braking' tracks, too, if you have the right pad material?
So I called Wilwood and they advised the same (i.e. we probably don't need to run these heavy rotors on the rears anywhere). They asked me to send them our current configuration and they'll recommend a comparable lightweight package.
Yes, another good point about rotating inertia, Gord.
It's a good idea to speak to your brake supplier Richard, they are spent their days helping people size these components for different applications, so are the experts!