VetteDrmr

I know we've discussed this before, but usually within the realm of DEs. I autocross my car primarily, with one or two DEs a year. My front rotors have been spiderwebbed for some time now, but when I check them with my fingernail nothing would catch.

Until now. Now I've got some small cracks, none close to the edge, that my fingernail is just beginning to catch. The issue is not replacing the rotors from a cost standpoint, but more from just when is the right time to swap them out?

TIA, and have a good one,
Mike

95jersey

Change them when the crack all the way through...it will eventually happen. No reason to waste money. If they don't crack by the end of the season, they you may want to change them.

VetteDrmr

By "all the way through" I assume you mean to the edge of the rotor?

Thanks, and have a good one,
Mike

redvetracr

I think he means not all the way across the face but across the edge, which is when I change mine.
...redvetracr

Racer-38

you can buy them from rockauto for about $20/rotor.....change the damn things already!!!!!!!!!!!!!!!!!!!!!!
If they crack and come apart on you, who knows what could happen. But if something does...I'll bet its more then $40!!!!!!!!!!!!!!!!!!!

VetteDrmr

Bob,

Read my initial post again: I mention that cost is not the issue; the question is to understand how much is acceptable and how much isn't.

I don't change engine oil after 500 miles; I don't change out brake fluid after every autocross event; these things just aren't necessary.

Obviously some amount of spiderwebbing is acceptable, since that starts occuring after your first couple of events. My basic barometer is that if I can't feel the crack with my fingernail, then it's OK. Now that I've found some I can feel, my question is "is that a good measure?"

Redvetracr, I have no cracking of any kind into the edges of the rotor.

Thanks for your comments, and have a good one,
Mike

Racer-38

But Mike....you see cost is the issue!!!

I don't think there is a "minimal acceptable limit to cracking" and if there is it would be next to impossible to try to describe on a written forum. I have seen rotors that have had hairline cracks go 2-3 track events and never have a problem. I have had rotors with no cracks come apart during a session.

SO....to answer your question >>>when I start to see cracking (even minimally) I replace the rotors...because they are so cheap. and because my time is worth more then $40 to take the tires on and off and continue to monitor the rotors to see if I can get every last bit out of them.
I've had a rotor come apart at Lowes going into turn one. It exploded and came out the back of the car....scared the hell out of me and I barely stopped the car in the runoff. That taught me to just change them.

UstaB-GS549

There are so many variables that it's hard to predict when they will crack thru.

I just tossed out a stack of maybe a dozen or so cracked rotors recently. One was shiny silver and blue with one huge fracture from the hat to the outside diameter. It was two days old. Another one was crusty, rusty and had hundreds of little spiderweb cracks and one large crack. That rotor was on the car most of the season. There was one pair that were taken off before cracking thru, but I think the spider cracks were getting pretty large. They were all on outside surface of the rotor. Some were very difficult to see in certain ligting conditions.

I'm pretty sure they all cracked during the cooling process while sitting in the pits if that's any comfort. I have missed spotting cracks before going out on track and it shows up as vibration under braking. Sometimes the vibration can go away as they heat up if you choose to continue on track. Don't be misled by "just a little vibration" or "it went away. I think that's when it's really dangerous and you need to get off track as soon as practical and change the rotor out.

VetteDrmr

For track events, I understand. But, for autocross, I don't know if the same criteria would apply. But, am I to understand that when you start seeing minor spiderwebbing you immediately replace the rotors? Seems like you'd be replacing them after every session.

And, it's not just cost; it's also parts availability, planning, the work itself, seasoning the rotors, etc.

Not flaming, not even arguing, just conversing.

Have a good one,
Mike

VetteDrmr

Never experienced that, but will do!

Thanks, and have a good one,
Mike

95jersey

I mean cracked from the hub through the outer edge. I have cracked several on the track while driving fast and it just caused a bumpy pedal feel. Their not carbon rotors that will disintegrate or something. If I thought for a moment it was a safety issues, I wouldn't hesitate to replace them with just spiders, but after 6 years at the track and dozens and dozens of rotors, it was never an issue. Just replaced them when the crack went all the way through

wtknght1

Look guys, Bob is right! (God, did I just say that?!?!! ) It takes a total of maybe 15 minutes and less than $30 to replace a rotor. But having said that, and to avoid wasting those 15 minutes and $30, you don't need to replace a rotor until it cracks ALL THE WAY TO THE EDGE. To make it even clearer, if you look at the edge of the rotor (like from the front of the car, or the top of the wheel well) and you don't see where the crack came all the way to the edge, then it's OK to run. Once you hear that distinctive "TING" while it's cooling off in the pits, then you know it's time to change it. If in doubt though, it's $30 and 15 minutes...just do it.

Bill Dearborn

Mike,
If you can feel the crack change them. I wouldn't wait until it cracked all the way through to change it. Reason being, When is that going to happen? If you change the rotor at home in the comfort of your garage it is a lot easier than changing it at the site of an autocross or track event or getting stranded along the highway someplace. Since I live in NY I have to take rotors with spider webs off the car before I take it in for state inspection. The guys will not pass the car if it has any visible spider web cracks in the rotors. Currently I am driving with some pretty bad looking spider web cracks in the rotors but I cannot feel them. However, my first track day is May 5th and new rotors are going on this weekend.

Bill

VetteDrmr

To all,

Thanks a bunch to everyone who's responded. As you can probably tell from me starting this topic, I'm already on the fence to swap out the rotors. I mainly just want to know what the folks that do this stuff *really* seriously use to make their judgements.

Thanks for the education, and have a good one,
Mike