Lip on rotors

[Unholy707]

Front rotors have developed a pretty deep lip. More on the inside of the rotor than the outside. Can they be turned down? What is the spec? I have calipers, I'll measure thickness with lip, how deep the lip is, and then subtract the lip. Is this the correct procedure to get the thickness? Does anyone have the spec so I can tell if they're able to be turned? Thanks

 

[rayzazoo]

Front rotors have developed a pretty deep lip. More on the inside of the rotor than the outside. Can they be turned down? What is the spec? I have calipers, I'll measure thickness with lip, how deep the lip is, and then subtract the lip. Is this the correct procedure to get the thickness? Does anyone have the spec so I can tell if they're able to be turned? Thanks

For the Dodge Hellcat (Challenger/Charger SRT Hellcat) front rotors,
34 mm nominal thickness
32 mm minimum service thickness

OEM Pad Thickness
Front Pads:
Brembo P37018 (15mm thick, 93mm height) Semi-Metallic, Performance
Brembo P37018N (16mm thick, 93mm height) Ceramic, Dust Reduction, Non-Asbestos Organic (NOA)

Rear Pads:
Brembo P11024 (15mm thick, 69mm height) Semi-Metallic, Performance
Brembo P11024N (15mm thick, 69mm height) Ceramic, Dust Reduction, Non-Asbestos Organic (NOA)

 

[MikeD1]

I vaguely recall reading somewhere that Dodge recommended against turning these rotors (2 mm is not much to play with) - but I could be wrong.
@BULL any thoughts?

 

[BULL]

I vaguely recall reading somewhere that Dodge recommended against turning these rotors (2 mm is not much to play with) - but I could be wrong.
@BULL any thoughts?

Turning is ok in my mind, IF you can find a shop both willing and able to successfully do it.

You need a knowledgeable tech, sharp tools, and hat hardware in good shape to prevent chatter.

(if the ring isn't securely attached to the hat, it's going to chatter, unfortunately rings that need to be turned tend to go hand in hand with degraded hat hardware.)

The good news is that hat hardware is now available and can be replaced, unlike in the past where it essentially wasn't available.

 

[BULL]

Also, understand that even if you're at say something like 32.5mm (.5mm over min), there may not be enough to turn without going under the 32mm min.

And a bit about rotor min thickness, which I didn't learn until not all that long ago...

The FIRST reason that this is a concern ISN'T rotor thermal mass capacity (although that IS a secondary issue), the first reason is the caliper pistons are designed for a maximum extension.

So you have to consider min rotor thickness, AND min pad thickness, resulting in a maximum piston extension from the piston bore.

Further with our rigid calipers, this is further compounded if there is an asymmetry in either and/or the rotor and pads, unlike a floating caliper that can tend to find center of the system.

 

[rayzazoo]

Also, understand that even if you're at say something like 32.5mm (.5mm over min), there may not be enough to turn without going under the 32mm min.

And a bit about rotor min thickness, which I didn't learn until not all that long ago...

The FIRST reason that this is a concern ISN'T rotor thermal mass capacity (although that IS a secondary issue), the first reason is the caliper pistons are designed for a maximum extension.

So you have to consider min rotor thickness, AND min pad thickness, resulting in a maximum piston extension from the piston bore.

Further with our rigid calipers, this is further compounded if there is an asymmetry in either and/or the rotor and pads, unlike a floating caliper that can tend to find center of the system.

To that point:

For 6-piston Brembo front calipers (as used on SRT/Hellcat/Redeye/Demon), the maximum safe piston extension is about 8–9 mm. Anything beyond 10 mm is considered unsafe.

Three piston pairs
Usable/normal travel: 4–6 mm
Maximum safe travel: ≈8–9 mm
Absolute danger zone: ≥10 mm

Absolute rotor minimum: 32 mm
Caliper-travel-based pad minimum (rotor at 32 mm):

• ~7 mm friction for P37018 (starts at 15mm)
• ~8 mm friction for P37018N (starts at 16mm)