Replacing front brake rotors

[Candide13]

I have a question for those who track on OEM brake rotors and do their own maintenance: practically speaking, when do you replace the rotors?

I know the theory, i.e. replace either when the rotors reach minimum thickness (28.4mm down from original 30mm for the E9x), or when there are long cracks connecting the holes. But what if there are no cracks but you are getting close to the minimum thickness? Do you proactively replace the rotors? Conversely, do you not mind going down below the recommendation to 28mm, say?

For reference, I tend to replace brake pads once they are noticeable thinner than the backing plate; I don't like to run them down further because of the increased heat load when they are over 60% gone. I am not sure the same applies to the massive rotors, where the theoretical minimum corresponds to only 5% of the material gone.

Anyhow, happy to hear experiences or practical tips, thanks.

[ayao]

I tend to proactively replace given the speed at which things can happen on track. The last thing you need is a brake-related technical issue at speed.

[Estoril Blue]

Rotors are replaced so that you have at least minimum thickness at the END of an event. Thats assuming that there are no issues with cracks.

Pads need thermal capacity that comes from thickness.

Don't play the minimums when it comes to brakes.

[admranger]

Most rotors don't wear very fast. I don't have data on stock E9xM3 rotors, but on good rotors I'd be surprised to see more than 0.001 - 0.002" wear with race pads over a track weekend. This is track dependent with significantly more wear at Laguna than at Chuckwalla.

That being said, a failing rotor will give you a "that won't buff out" situation so err on the side of being conservative.

[Z K]

I replace the rotors when there's a noticeable ledge on the edge.

Depending on what pads you run, a set of rotors should last many years worth of track days.

[dparm]

Originally Posted by Candide13

I have a question for those who track on OEM brake rotors and do their own maintenance: practically speaking, when do you replace the rotors?

I know the theory, i.e. replace either when the rotors reach minimum thickness (28.4mm down from original 30mm for the E9x), or when there are long cracks connecting the holes. But what if there are no cracks but you are getting close to the minimum thickness? Do you proactively replace the rotors? Conversely, do you not mind going down below the recommendation to 28mm, say?

For reference, I tend to replace brake pads once they are noticeable thinner than the backing plate; I don't like to run them down further because of the increased heat load when they are over 60% gone. I am not sure the same applies to the massive rotors, where the theoretical minimum corresponds to only 5% of the material gone.

Anyhow, happy to hear experiences or practical tips, thanks.

Thermal capacity decreases as they wear, as you said. If they are nearing the minimum, I would just replace them. Brakes (and safety equipment) is not something you should pinch pennies on.

I agree with everything that has been posted in this thread.

OP, what pads do you use?

[Candide13]

I am using Stoptech Street performance pads, which worked very well for me at intermediate track driving level. The rotor thickness seems to have gone mostly over the last 10 track days or so, it feels like rotor wear is a sharply increasing function of nudging up of my average speed on the track and hence of the necessary braking. All in all, I don't complain after 42K miles and 22 track days..

Thanks all for the input; I already got the new rotors, so ready to install. I'll measure the thickness again and might squeeze in the first one-day event of the year before I make the change as then I can change pads and rotors together....

[chamba002]

I replace mine when I can feel a lip and below minimum thickness. I have tracked with rotors having a lip but not below minimum thickness, and no issues. I replaced my OEM rotors for ECS two piece rotors, in the front, becuase it was roughly the same price as OEM but better cooling.

[admranger]

Could always give the rotors the float test. Works every time on questionable items.

[SYT_Shadow]

Originally Posted by admranger

Could always give the rotors the float test. Works every time on questionable items.

That's my strategy as well

Since starting to track I have never worn a rotor down to min thickness. They always crack first

[decimation1]

Originally Posted by chamba002

I replace mine when I can feel a lip and below minimum thickness. I have tracked with rotors having a lip but not below minimum thickness, and no issues. I replaced my OEM rotors for ECS two piece rotors, in the front, becuase it was roughly the same price as OEM but better cooling.

Just curious, how much are the replacement rings with the ECS discount on just the rings?

[decimation1]

Originally Posted by chamba002

I replace mine when I can feel a lip and below minimum thickness. I have tracked with rotors having a lip but not below minimum thickness, and no issues. I replaced my OEM rotors for ECS two piece rotors, in the front, becuase it was roughly the same price as OEM but better cooling.

Just curious, how much are the replacement rings with the ECS discount on just the rings?

[chamba002]

Originally Posted by decimation1

Just curious, how much are the replacement rings with the ECS discount on just the rings?

I honestly don't know, I still have a lot of life on them still. I would think the rings would be cheaper then what I had paid for the whole set.

I can say they take track abuse well. Currently has 4 track weekends on em, with DTC-70 pads, and the rings still look good.

[decimation1]

Originally Posted by chamba002

I honestly don't know, I still have a lot of life on them still. I would think the rings would be cheaper then what I had paid for the whole set.

I can say they take track abuse well. Currently has 4 track weekends on em, with DTC-70 pads, and the rings still look good.

I contacted ECS and interestingly enough they do not sell the rings separately. They re-sell you a new complete set of rotors at a discounted price of $625 vs. $699.

[Candide13]

Originally Posted by chamba002

I replace mine when I can feel a lip and below minimum thickness. I have tracked with rotors having a lip but not below minimum thickness, and no issues. I replaced my OEM rotors for ECS two piece rotors, in the front, becuase it was roughly the same price as OEM but better cooling.

Interesting, how do the two-piece rotors function to give better cooling?

[Richbot]

Originally Posted by Candide13

Interesting, how do the two-piece rotors function to give better cooling?

Stock rotors are two-piece also, it's just a different arrangement than most aftermarket setups and the attachment of the hat to the ring blocks some of the vanes. The ECS rotors have a higher vane count and a different attachment mechanism which they claim allows for better air flow. The ECS rotors are also a bit lighter than stock

[bigjae1976]

If heat cracks aren't an issue...you can run them on the track to min thickness. You need to be aware that your pads will likely run hotter and not last as long.

You DO need the check the backside of the rotor for heat cracking. This means pulling off the rotor. You'll be surprised...I've typically had similar or worse heat cracks on the backside.

[roastbeef]

Originally Posted by Candide13

Interesting, how do the two-piece rotors function to give better cooling?

scroll half way down this page. this description is specific to a brake kit, but the explanation of how things work is universal.
https://www.essexparts.com/essex-des...p5060355mm-e92

[chamba002]

Originally Posted by decimation1

I contacted ECS and interestingly enough they do not sell the rings separately. They re-sell you a new complete set of rotors at a discounted price of $625 vs. $699.

Damn thats kinda lame :/ but I'll probably still go with them. They are pretty good at the track for me. Haven't had overheating issues with them.