When to replace front brake rotors?

[Candide13]

After 42K miles and some 40 hours of track driving my OE front rotors are near the recommended replacement thickness of 28.4 mm. Apart from that there has been no drop off in performance, no obvious cracks between the holes etc.

So I was wondering when do people who track their car replace the rotors? Do you go by the thickness, or wait for cracks, or wait for brake performance to be affected?

I don't mind the expense, you have to pay to play, but I don't want to replace them unless it makes technical sense. So would be great to hear what others are doing with their own cars and rotors.

Pointers welcome, thanks.

[doogee]

The minimum thickness is on the rotor for a reason!

[chamba002]

I would go by minimum thickness... I have been told before to replace it once you get vibration when you brake but honestly you don't want it to get that bad especially on a track day. You'll end up cutting you your session short.

[admranger]

It depends. Minimum thickness is a required replace, in my opinion.

Cracks that catch a finger nail mean the rotor is done.

Cracks between two holes means the rotor is done.

Cracks that go to the edge of the rotor means the rotor is done.

When in doubt, perform a float test. Toss the item into the nearest body of water. If it floats, you can use it.

[Candide13]

Originally Posted by admranger

It depends. Minimum thickness is a required replace, in my opinion.

Cracks that catch a finger nail mean the rotor is done.

Cracks between two holes means the rotor is done.

Cracks that go to the edge of the rotor means the rotor is done.

When in doubt, perform a float test. Toss the item into the nearest body of water. If it floats, you can use it.

I like it... When you replaced yours did you go with OEM or a different rotor set up?

[macdude357]

Originally Posted by admranger

It depends. Minimum thickness is a required replace, in my opinion.

Cracks that catch a finger nail mean the rotor is done.

Cracks between two holes means the rotor is done.

Cracks that go to the edge of the rotor means the rotor is done.

When in doubt, perform a float test. Toss the item into the nearest body of water. If it floats, you can use it.

^ This (not sure about the float test though. Sounds an awful like the "if she weighs as much as a duck, she's a witch", test

[admranger]

Originally Posted by Candide13

I like it... When you replaced yours did you go with OEM or a different rotor set up?

What is your intended purpose for the car? Street and track? If so, then look at the stoptech slotted or, if you budget allows, get the PFC direct drive rotors.

Stock are fine for street/track, but they wear your pads pretty quickly.

[admranger]

Originally Posted by macdude357

^ This (not sure about the float test though. Sounds an awful like the "if she weighs as much as a duck, she's a witch", test

Float test is legit. It hasn't failed me yet.

[macdude357]

Originally Posted by Candide13

I like it... When you replaced yours did you go with OEM or a different rotor set up?

I went with the Stoptech AERO rotors. They are $800 shipped from Tire Rack. If I had to do it over, I'd seriously consider the PFC DD rotors. They are about $300 more per set, but the new PFC DD V3 rotors have a new system for attaching the hat to the friction ring that is really simple. The friction rings on the DD rotors are a bit cheaper than the StopTechs as well. Combine that with the ease of replacing the rings and the price difference doesn't look that bad.

I've noticed that the PFC DD rotors have a warning to only use PFC pads (or at lease to make sure your non-PFC pads will fit because the hat is a bit smaller than stock). Not sure if this is a real concern or just a way to get you to buy their pads.

[admranger]

Originally Posted by macdude357

I went with the Stoptech AERO rotors. They are $800 shipped from Tire Rack. If I had to do it over, I'd seriously consider the PFC DD rotors. They are about $300 more per set, but the new PFC DD V3 rotors have a new system for attaching the hat to the friction ring that is really simple. The friction rings on the DD rotors are a bit cheaper than the StopTechs as well. Combine that with the ease of replacing the rings and the price difference doesn't look that bad.

I've noticed that the PFC DD rotors have a warning to only use PFC pads (or at lease to make sure your non-PFC pads will fit because the hat is a bit smaller than stock). Not sure if this is a real concern or just a way to get you to buy their pads.

On the E46M3, the rear rotor hat is sized a bit differently than stock and requires a slightly smaller pad than stock as the stock pads hit the bolts (version 1 of PFC DD Rotors). Ask me how I know...

That being said, the DD rotors are super sweet. You won't regret having them...unless you turn around and buy a BBK the next week.

[NoCarrier]

What do you guys use to measure the rotor thickness? I have a set of digital calipers but I don't get an accurate reading because the pads wear a flange into the edge of the rotor that's thicker than the pad wear area.

[admranger]

Originally Posted by NoCarrier

What do you guys use to measure the rotor thickness? I have a set of digital calipers but I don't get an accurate reading because the pads wear a flange into the edge of the rotor that's thicker than the pad wear area.

You can get something purpose made like this: Brake Rotor Thickness caliper

Or you can use a regular vernier caliper like this:

Vernier caliper will be less accurate due to it measuring the peaks of the ridges instead of the valleys.