Any floating rotors available for Steel brakes GT3?
06-18-2004, 01:21 PM
#16
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Someone sent me an email asking what pad knockback is, so I thought I would post here so all can see.
When you load the suspension undercornering, there is deflection of all the parts. Rotors move and so do calipers. When they move enough, relative to each other, the brake pads get pushed away from the rotors. The next time you apply the brakes, much of the travel is used to return the pads to their place against the rotor. There is almost no braking force until the pads are returned.
If mild, then the pedal travel is a bit longer than normal. If severe, the pedal will drop to the floor with no braking force applied. I pump of the pedal will bring the brakes back to full operation. Since this is induced by certain cornering forces, it tends to repeat in the places you feel it on a track. For example, you may only experience this on the right hand corner following some fast Esses, but no where else. It is also caused/aggravated by loose wheel bearings.
Faster formula and sports racers tend to have this issue due to very light weight parts (opportunity for lots of flex) and high g loads as well as limited us of brakes in many sections. Aggrevating the situation is the fact that because these cars are so low to the ground, the master cylinder may be lower than the calipers - aiding the back flow of the brake fluid.
Solutions include; residual pressure valves in the brake lines (keep a small amount of pressure behind the pads to resist the knockback forces), anti knockback springs (placed behind the pistons) and floating rotors (the flex does not move the rotor relative to the caliper). Floating rotors are generally the best way to fix this, but also the most expensive and complex to install.
When you load the suspension undercornering, there is deflection of all the parts. Rotors move and so do calipers. When they move enough, relative to each other, the brake pads get pushed away from the rotors. The next time you apply the brakes, much of the travel is used to return the pads to their place against the rotor. There is almost no braking force until the pads are returned.
If mild, then the pedal travel is a bit longer than normal. If severe, the pedal will drop to the floor with no braking force applied. I pump of the pedal will bring the brakes back to full operation. Since this is induced by certain cornering forces, it tends to repeat in the places you feel it on a track. For example, you may only experience this on the right hand corner following some fast Esses, but no where else. It is also caused/aggravated by loose wheel bearings.
Faster formula and sports racers tend to have this issue due to very light weight parts (opportunity for lots of flex) and high g loads as well as limited us of brakes in many sections. Aggrevating the situation is the fact that because these cars are so low to the ground, the master cylinder may be lower than the calipers - aiding the back flow of the brake fluid.
Solutions include; residual pressure valves in the brake lines (keep a small amount of pressure behind the pads to resist the knockback forces), anti knockback springs (placed behind the pistons) and floating rotors (the flex does not move the rotor relative to the caliper). Floating rotors are generally the best way to fix this, but also the most expensive and complex to install.
06-18-2004, 04:08 PM
#17
RL Technical Advisor
Mark:
Nice explanation of pad knockback,....
Floating rotors were designed and intended for competition cars and can be noisy on the street at low speeds. There are 2 main reasons to use them:
1) Reduced pad knockback
2) Reduced heat warpage. Floating rotors operate at more even temperatures (inside to outside) and do not turn into "belleville washers" at high temps.
Weightwise, they are slighly lighter than a bolted up equivalent and both designs permit one to swap rotors without buying replacement hats.
Just remember, floating rotors make some knocking sounds at slow speeds from rotor backlash on the drive dogs until they get hot and expand.
Porsche used floating rotors on the '78-'79 930's and they stopped using those after that for cost reasons and some complaints. For pure brake performance and freedom from rotor warpage, you cannot beat 'em,...
Nice explanation of pad knockback,....
Floating rotors were designed and intended for competition cars and can be noisy on the street at low speeds. There are 2 main reasons to use them:
1) Reduced pad knockback
2) Reduced heat warpage. Floating rotors operate at more even temperatures (inside to outside) and do not turn into "belleville washers" at high temps.
Weightwise, they are slighly lighter than a bolted up equivalent and both designs permit one to swap rotors without buying replacement hats.
Just remember, floating rotors make some knocking sounds at slow speeds from rotor backlash on the drive dogs until they get hot and expand.
Porsche used floating rotors on the '78-'79 930's and they stopped using those after that for cost reasons and some complaints. For pure brake performance and freedom from rotor warpage, you cannot beat 'em,...
06-18-2004, 04:21 PM
#18
Lifetime Rennlist Member
Steve,
Thanks for the insight on warpage. That does not tend to be an issue on 800 lb sports racers. <g>
BTW - I hear that you (and partner) may be doing some things with Stohr?
Thanks for the insight on warpage. That does not tend to be an issue on 800 lb sports racers. <g>
BTW - I hear that you (and partner) may be doing some things with Stohr?
06-18-2004, 07:36 PM
#19
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Too much rotor float will also cause knockback as well
With the Champ Car we had terrible knockback problems at Road America (year 2000). Both on our test days there and the race weekend. We tried every tension knockback spring we could find and could never completely cure the knockback. Driver had to give a quick dab just before his braking zone going into turn one.
After some time, we came to the conclusion it was the combination of the super long front straight and the brake cooling air flow that was pushing the pads away from the rotors. We redirected the brake/bearing cooler air flow and that basically solved this problem. Strange, strange,strange!
With the Champ Car we had terrible knockback problems at Road America (year 2000). Both on our test days there and the race weekend. We tried every tension knockback spring we could find and could never completely cure the knockback. Driver had to give a quick dab just before his braking zone going into turn one.
After some time, we came to the conclusion it was the combination of the super long front straight and the brake cooling air flow that was pushing the pads away from the rotors. We redirected the brake/bearing cooler air flow and that basically solved this problem. Strange, strange,strange!
06-19-2004, 02:05 AM
#20
RL Technical Advisor
Hi Mark:
Indeed, we are Stohr dealers and are finishing up a car to run this year,...
Hi Chris:
You are right on! The design of floating rotors may appear simple but its certainly not,... One measures peak rotor & hub temps and attempts to calculate expansion rates that allows minimum float. Even the Nextel Cup guys have that same problem as they are dealing with stopping a 3400 lb, 750 HP monster with 13" rotors.
Indeed, we are Stohr dealers and are finishing up a car to run this year,...
Hi Chris:
You are right on! The design of floating rotors may appear simple but its certainly not,...
One measures peak rotor & hub temps and attempts to calculate expansion rates that allows minimum float. Even the Nextel Cup guys have that same problem as they are dealing with stopping a 3400 lb, 750 HP monster with 13" rotors.
06-21-2004, 12:22 PM
#21
Lifetime Rennlist Member
Chris - Interesting stuff. I guess we can generalize that:
1) In racing, nothing is as simple as it looks.
2) If it looks simple, keep looking.
3) If it is simple, it doesn't work.
LOL
One more thing for those considering floating rotors for the street. These tend to be noisy with a fair amount of clicking and rattling sounds. Maybe some designs eliminate this, but if brake squeal bothers you, then floating rotors may too.
1) In racing, nothing is as simple as it looks.
2) If it looks simple, keep looking.
3) If it is simple, it doesn't work.
LOL
One more thing for those considering floating rotors for the street. These tend to be noisy with a fair amount of clicking and rattling sounds. Maybe some designs eliminate this, but if brake squeal bothers you, then floating rotors may too.
