AP J hook life

[3209X]

Hi everyone. I have a AP Racing kit and this is what my AP rotors look like. I know they beginning to be near the end of their life. My question is if I can still run them on the track for another weekend? There are no cracks on the rings at either the inner edge or outer edge. I removed the rotors to inspect. The brakes still feel really amazing. Its the j hooks that are starting to wear off but they arent completely flat or worn off. The track I am going to is not heavy on brakes.

[yahh]

There should be a minimum thickness measurement on the outer ring of the rotor or contact AP and ask them what the spec is. Measure it and you will have your answer. Realistically, if you don't have any cracks touching the edges they are probably fine especially if it's not a high-speed track.

[tdott]

Is there a minimum thickness stamped on the rotors? If everything else looks good and you aren't below the min thickness, then send it.

[Ximian]

You're unlikely to find the minimum thickness information for AP rotors. The J hooks can also function as wear indicators as once they're gone, that rotor is completely done.

When inspecting the rotor, it's best to remove it so you can check both sides. Any crack going to an edge and especially around an edge means the rotor should be replaced. Cracks where your fingernail will catch on it is also risky for a track day.

Cracks going to edges but not around should still be drive-able if you need to get home in an emergency, but I wouldn't risk it for a track day.

[3209X]

Originally Posted by Ximian

You're unlikely to find the minimum thickness information for AP rotors. The J hooks can also function as wear indicators as once they're gone, that rotor is completely done.

When inspecting the rotor, it's best to remove it so you can check both sides. Any crack going to an edge and especially around an edge means the rotor should be replaced. Cracks where your fingernail will catch on it is also risky for a track day.

Cracks going to edges but not around should still be drive-able if you need to get home in an emergency, but I wouldn't risk it for a track day.

Thanks for the perspective. The min thickness is 34mm and it is above that but I do recognize the j hooks are starting to go.

[Redd]

They're fine to use until the slots are nearly gone.

[sc_tr0jan_m3]

No cracks don’t look back!

[3209X]

Update: Got 4 more track days out of the disc lol

I will be getting replacements in 2 weeks.

[jmeenach]

LOL you ran those pretty deep!

[3209X]

Originally Posted by jmeenach

LOL you ran those pretty deep!

YOLO lol

I took the discs apart and there were zero cracks on them. Technically they are above the min. thickness as well.

My replacement rotors are coming in two weeks.

Never buy AP Racing brakes from Stillen
They used AP rotor rings that even Essex and AP in Europe don't even stock

[tdott]

Originally Posted by 3209X

Never buy AP Racing brakes from Stillen
They used AP rotor rings that even Essex and AP in Europe don't even stock

ahh, those hats look different.

Did you have to buy a completely use set of hats/rings? or were you able to find the replacement rings?

[3209X]

Originally Posted by tdott

ahh, those hats look different.

Did you have to buy a completely use set of hats/rings? or were you able to find the replacement rings?

I had a company come up with a new hat and ring design. They did this all within 3 weeks, which is remarkable. Price was $1.3k. The replacement rings are $200ea. Not bad...

[tdott]

Originally Posted by 3209X

I had a company come up with a new hat and ring design. They did this all within 3 weeks, which is remarkable. Price was $1.3k. The replacement rings are $200ea. Not bad...

can you share some pictures of the new hat / rotor? Thanks,.

[Dekab]

Originally Posted by 3209X

I had a company come up with a new hat and ring design. They did this all within 3 weeks, which is remarkable. Price was $1.3k. The replacement rings are $200ea. Not bad...

Details?

[M3SQRD]

Essex is now the exclusive AP Racing importer of competition and road brake kits. The Essex/AP Racing road kit appears to use the same calipers and rotors (380 mm front and rear) as the Stillen kit but it uses the AP Racing patented floating rotor design so the hat designs are different.

Edit: the rotor and caliper offsets may be different from the Stillen kit so before purchasing new rotors with hats please verify with Essex that the offsets are identical. If not, you’d need new caliper adapter brackets to use the Essex hats and calipers.

Front kit
https://www.essexparts.com/essex-des...61380mm-bmwE90

Rear kit
https://www.essexparts.com/essex-des...mm-BMWe90-rear

[DRLane]

Originally Posted by M3SQRD

Essex is now the exclusive AP Racing importer of competition and road brake kits. The Essex/AP Racing road kit appears to use the same calipers and rotors (380 mm front and rear) as the Stillen kit but it uses the AP Racing patented floating rotor design so the hat designs are different.

Front kit
https://www.essexparts.com/essex-des...61380mm-bmwE90

Rear kit
https://www.essexparts.com/essex-des...mm-BMWe90-rear

Street get 380x36 front and 380x32 rear, while Radi-Cal gets the 372, 355? Huh.

[M3SQRD]

Originally Posted by DRLane

Street get 380x36 front and 380x32 rear, while Radi-Cal gets the 372, 355? Huh.

One is for bling (large rotors, painted calipers) and one is for performance (min required diameter, hard anodized or ENP calipers). I have the Essex/AP Racing competition brake kits (372/365) on my f82. 380 mm front and rear rotors are not needed on a tracked f8x with a GTS level ecu tune so 372/355 is fine for the e9x M. If you think 372 mm OD is too small, custom caliper adapters for AP 378 mm OD rotors and hats and Paragon 380 mm OD rotors and hats are available.

[M3SQRD]

Originally Posted by DRLane

Street get 380x36 front and 380x32 rear, while Radi-Cal gets the 372, 355? Huh.

Edit: redid the Essex/AP cals for the e9x M 355 mm rear rotor OD

I was curious to see which kits had the highest torque outputs. So I calculated the brake bias and torque output of the Essex/AP Racing competition (accidentally did f8x, not e9x M) and road sport brake kits.

Brake bias:
Comp f8x kit 0.61 front biased
Road kit 0.62 front biased
Comp e9x 0.68 front biased

Front torque (only one side of the caliper)
Comp f8x kit 7434 lbf-in
Road kit 7229 lbf-in
Comp kit e92 7434 lbf-in
-Comp kits have 2.8% more applied torque

Rear torque (only one side of the caliper)
Comp kit 4671 lbf-in
Road kit 4367 lbf-in
Comp e9x kit 4049 lbf-in
-Comp f8x kit has 7.0% more applied torque than the Road Kit but the Comp e9x M kit has 7% fewer applied torque than the Road kit

So the CP9668/CP9449 Comp f8x kit has higher torque outputs with the 372/365 OD rotors than the CP9561/CP9541 Road kit with 380/380 OD rotors. Brake bias is negligible at 1% difference between the two kits. Larger rotor diameter, especially with a large pad radial depth, doesn’t always produce the highest torque output.

So the CP9668/CP9449 Comp e9x M kit has higher front and lower rear torque outputs with the 372/355 OD rotors than the CP9561/CP9541 Road kit with 380/380 OD rotors. Brake bias is 6% more forward for the Comp e9x M kit than the Road kit. This is a noticeable difference and some may prefer it. I prefer a more rear biased setup but you can adjust front-rear brake bias by running a higher or lower friction level rear pad relative to the friction level of the front pad. At certain tracks I run the same rear compound or a rear pad with a higher friction level than the front. VIR is a track where a higher CoF rear pad can be used to brake later on the uphill section of the back straight. I also experience no rear ABS kicking in while braking for turn 1 on the long front straight and I’m able to brake later for turn 1.