Do you know rotors? Step inside.
Thread Starter
Race Director
Joined: Oct 2002
Posts: 10,864
Likes: 196
From: Southern CA
Do you know rotors? Step inside.
J55 stock rotor min thick is 26.4 mm (front - not sure rear)
New I think they are about 28 to 30 mm
Racers turn down new rotors to get less unsprung weight.
I have a shop that will turn mine down below min.
I would run new pads so as not to over extend the pistons.
What is the min I could go down to?
tia
New I think they are about 28 to 30 mm
Racers turn down new rotors to get less unsprung weight.
I have a shop that will turn mine down below min.
I would run new pads so as not to over extend the pistons.
What is the min I could go down to?
tia
Melting Slicks
Joined: Mar 2003
Posts: 2,472
Likes: 0
From: Toronto ONTARIO
If that little of a weight is so important than why not slap on 2 piece rotors? I saved almost 20 lbs changing all 4. I seriously doubt cutting down all 4 rotors thickness will save you less than 1/2 lb.
Race Director
Joined: Jun 2004
Posts: 13,960
Likes: 707
From: WI
Some places give you the discard thickness of the rotor. This link should, if not use napaonline.com for a stock rotor.
http://napaonline.com/masterpages/NO...r+Only+-+Front
Or Discard Thickness:1.039" stock 13"
http://napaonline.com/masterpages/NO...r+Only+-+Front
Or Discard Thickness:1.039" stock 13"
Drifting
Joined: Feb 2004
Posts: 1,277
Likes: 1
From: Santa Maria CA
Originally Posted by DieL
If that little of a weight is so important than why not slap on 2 piece rotors? I saved almost 20 lbs changing all 4. I seriously doubt cutting down all 4 rotors thickness will save you less than 1/2 lb.
NOT WORTH THE MONEY AND THE EFFORT FOR A MERE 1/2LB.
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Drifting
Joined: Feb 2004
Posts: 1,277
Likes: 1
From: Santa Maria CA
Originally Posted by CentralCoaster
Actually a 1/2 lb off the rotors is worth 1/4 lb in rotating mass.
So you save 3/4 lb per wheel.
So you save 3/4 lb per wheel.
SWEEEEET!
Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 15
From: backwoods upstate ny
Originally Posted by froggy47
I would run new pads so as not to over extend the pistons.
Le Mans Master
Joined: Jul 1999
Posts: 8,683
Likes: 6
From: Phoenix AZ
Some people that run under minimum thickness rotors will use shims in between the caliper pistons and the brake pads so they don't blow out a piston once the pads wear down. However, unless this is a track-only car, and you religiously monitor the brake system, I would NEVER recommend doing this. Not worth the huge list of potential problems and outcomes...but that's just my opinion. As stated above, if you want to save weight on your brakes, but some nice two-piece rotors! 
Le Mans Master
Joined: Jul 1999
Posts: 8,683
Likes: 6
From: Phoenix AZ
Originally Posted by redrose
old trick to make the trick work---alum spacers, swissed (as in cheese-holes) between the pad and piston...reduces heat transfer into the caliper also
Thread Starter
Race Director
Joined: Oct 2002
Posts: 10,864
Likes: 196
From: Southern CA
Originally Posted by DieL
If that little of a weight is so important than why not slap on 2 piece rotors? I saved almost 20 lbs changing all 4. I seriously doubt cutting down all 4 rotors thickness will save you less than 1/2 lb.
SCCA Solo stock rules prohibit.
Instructor
Joined: Sep 2004
Posts: 153
Likes: 0
Originally Posted by froggy47
J55 stock rotor min thick is 26.4 mm (front - not sure rear)
New I think they are about 28 to 30 mm
Racers turn down new rotors to get less unsprung weight.
I have a shop that will turn mine down below min.
I would run new pads so as not to over extend the pistons.
What is the min I could go down to?
tia
New I think they are about 28 to 30 mm
Racers turn down new rotors to get less unsprung weight.
I have a shop that will turn mine down below min.
I would run new pads so as not to over extend the pistons.
What is the min I could go down to?
tia
What you care about is the thickness of each face, not the overall thickness. On tracks I run the rotors until one face (usually the outside ) is 20% thinner or about 1.7mm thicnkess loss. The face thickness is then about 6.7mm.
As the rotor gets thinner their ability to dissapate heat goes down and cracking goes up. By this point my rotors usually have cracks which are about 50% to 60% of the width of the face of the rotor. Once I cracked an old rotor from the hub to the edge at Buttonwillow but that was my fault. On the first half lap, I nailed the brakes at about 120mph at the end of the backstraight and it went pop. The 250 mile drive home was fine though except for a strong brake shudder below 50mph.
For autocross you would probably be fine machining each face down to 6.7mm and replacing them at 6.4mm. The worst thing that will happen is that you will crack one and have to replace it.
That said, unless you are consistantly fighting for that last .001 second, you will find no difference.
Cheers,
Lawrence
Thread Starter
Race Director
Joined: Oct 2002
Posts: 10,864
Likes: 196
From: Southern CA
Originally Posted by scorp508
Um, are you hoping to throw your rotors away real soon or something?
I am trying to win races, rotors are a disposible wear item. Actually I have 2 sets sitting in boxes in my garage. But what I want to know is how much below min can I go. If I win 1 race & trash the rotors I'm good with that.
Thread Starter
Race Director
Joined: Oct 2002
Posts: 10,864
Likes: 196
From: Southern CA
Originally Posted by Sidney004
What is your application? drag racing; track driving?
Sorry should have mentioned that, it's solo autox. It's in the sig. You can push the the limits on a lot of stuff in low speed autox & still be safe. I would NOT do this to track or drag cars.
Good point.
Last edited by froggy47; Aug 3, 2006 at 01:46 PM.
Thread Starter
Race Director
Joined: Oct 2002
Posts: 10,864
Likes: 196
From: Southern CA
Originally Posted by CentralCoaster
If your track has turns on it, then giving up braking heat capacity is the last place you want to look for weight savings.
Thanks, not track/drag car.
I should have mentioned low speed autox.
Thread Starter
Race Director
Joined: Oct 2002
Posts: 10,864
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From: Southern CA
Originally Posted by Zix
Some people that run under minimum thickness rotors will use shims in between the caliper pistons and the brake pads so they don't blow out a piston once the pads wear down. However, unless this is a track-only car, and you religiously monitor the brake system, I would NEVER recommend doing this. Not worth the huge list of potential problems and outcomes...but that's just my opinion. As stated above, if you want to save weight on your brakes, but some nice two-piece rotors!
Thanks zix
Thread Starter
Race Director
Joined: Oct 2002
Posts: 10,864
Likes: 196
From: Southern CA
Thanks for taking the time to post Lawrence, this is SPECIFICALLY what I was looking for. This forum ROCKS.
Let me ask you one more thing. The used rotors I took off are worn quite evenly, they just have a "lip" at the outermost circumference, no cracks. I actually just replaced them because I had gone thru 2 sets of comp. pads. So they no doubt are already lighter by some amount just because of the normal race wear.
Question, could I just keep using these rotors or is that "lip" going to interfere with something? I was going to get them turned just to get rid of the lip.
Let me ask you one more thing. The used rotors I took off are worn quite evenly, they just have a "lip" at the outermost circumference, no cracks. I actually just replaced them because I had gone thru 2 sets of comp. pads. So they no doubt are already lighter by some amount just because of the normal race wear.
Question, could I just keep using these rotors or is that "lip" going to interfere with something? I was going to get them turned just to get rid of the lip.
Originally Posted by TrackDayLT4
I have measured rotors and typically they are are 28.4mm overall thickness, and each face is 8.4mm thick when new. The minimum thickness stamped on them is 26.4mm.
What you care about is the thickness of each face, not the overall thickness. On tracks I run the rotors until one face (usually the outside ) is 20% thinner or about 1.7mm thicnkess loss. The face thickness is then about 6.7mm.
As the rotor gets thinner their ability to dissapate heat goes down and cracking goes up. By this point my rotors usually have cracks which are about 50% to 60% of the width of the face of the rotor. Once I cracked an old rotor from the hub to the edge at Buttonwillow but that was my fault. On the first half lap, I nailed the brakes at about 120mph at the end of the backstraight and it went pop. The 250 mile drive home was fine though except for a strong brake shudder below 50mph.
For autocross you would probably be fine machining each face down to 6.7mm and replacing them at 6.4mm. The worst thing that will happen is that you will crack one and have to replace it.
That said, unless you are consistantly fighting for that last .001 second, you will find no difference.
Cheers,
Lawrence
What you care about is the thickness of each face, not the overall thickness. On tracks I run the rotors until one face (usually the outside ) is 20% thinner or about 1.7mm thicnkess loss. The face thickness is then about 6.7mm.
As the rotor gets thinner their ability to dissapate heat goes down and cracking goes up. By this point my rotors usually have cracks which are about 50% to 60% of the width of the face of the rotor. Once I cracked an old rotor from the hub to the edge at Buttonwillow but that was my fault. On the first half lap, I nailed the brakes at about 120mph at the end of the backstraight and it went pop. The 250 mile drive home was fine though except for a strong brake shudder below 50mph.
For autocross you would probably be fine machining each face down to 6.7mm and replacing them at 6.4mm. The worst thing that will happen is that you will crack one and have to replace it.
That said, unless you are consistantly fighting for that last .001 second, you will find no difference.
Cheers,
Lawrence