Rotor cracks; Watch or replace?

[swiftdrivr]

The cracks are about 0.1 to 0.12 inch, not through and through. Is this something to keep an eye on, or time for new rotors?

[billtebbutt]

The cracks are about 0.1 to 0.12 inch, not through and through. Is this something to keep an eye on, or time for new rotors?

Uh, I would chuck that rotor as far as I could. Ever see what happens when they come apart? But I am a worrywart......

FWIW, and it may just be my eyes/your pic, but I would like to see a nicer chamfer on the holes.

cheers,
bt

[Garey Guzman]

Personally, I would not run swiss cheese rotors on my car. Visible or not-visible cracking can lead to unhappiness.

[Lotus7]

Too early to discard the rotors if those are the only two cracks, but for sure monitor the cracks each session. Often they will just migrate to the nearest adjacent hole. At that point just watch for how many cracks in total.... then it becomes a judgement call regarding disc integrity.

[stonebridge20]

How many miles or hours on those?

[Thomas Wirtz]

FWIW,
I was being chased for a pass by another FC car into corner five at Road America. Suddenly he was gone from my mirror. The next lap conner 5 is under yellow, there is the car against the wall drivers left heavily damaged. I talked to the diver latter in the pits to see what happened. He said his new drilled rotor exploded and the car hooked left. It was the end of his weekend and racing season. Just say'n.

[DaveW]

IMO, if cracks appear, no matter how small, it's time to discard the rotor. I've seen them go from barely noticeable, as in the OP's photo, to cracked all the way across in one session. I do make an exception for fine surface "checking" that only is 0.001 or 0.002" deep. That is not usually a reason for replacement. That usually appears over much of the surface. Real cracking will almost always start at some stress concentration like a mounting point radius or a drilled hole.

I had one (a solid rotor, BTW), back 40+ years ago at Road Atlanta on my Z10, go from working OK to cracking all the way across and locking up the brakes while the car sat between two sessions. I have mentioned before that I think I'm very lucky...

And I will not use drilled rotors for 2 reasons - the fact that (1) they crack more easily and (2) they have less heat capacity than solid rotors. The heat capacity is important for consistent brake performance (maintaining more consistent rotor temperature) over a long lap. Another reason I don't like drilled rotors is that they eat pads too fast, but that's not as big an issue as the previous two.

[swiftdrivr]

Looks like it's a risk not worth taking. At least I have time to fix it before spring. Winter maintanence pays off, even when it's late winter. Thanks for the input, guys.

[DanW]

Every sharp edge of every hole is a potential stress raiser.

[DaveW]

Every sharp edge of every hole is a potential stress raiser.

They don't even need to have a sharp edge to be a stress riser, but a sharp edge makes them much worse.

[Jnovak]

And I will not use drilled rotors for 2 reasons - the fact that (1) they crack more easily and (2) they have less heat capacity than solid rotors. The heat capacity is important for consistent brake performance (maintaining more consistent rotor temperature) over a long lap. Another reason I don't like drilled rotors is that they eat pads too fast, but that's not as big an issue as the previous two.

Pay attention! Mr racer speaks truth!

[Jerry Kehoe]

Dave's right in that lots of rotors will get checking on the surface but a real crack can progress fairly quickly. As far as drilling, ever notice Heavy Duty rotors are always thicker ( translation more mass) than the supposed light duty? Drilling a bunch of holes certainly removes material, food for thought! Besides rotors don't have to be an arm and a leg to buy. Coleman makes virtually any size and configuration and my guess is that a lot of them for sale by various shops were made by Coleman.

[Jim Edmonds]

A BMW friend had a front rotor explode at ~110mph on the banking on the Las Vegas American Lemans Series track in maybe 2004. The rotor shards poked numerous large holes in the car's belly pan as they exited the rear of the car. Luckily not the fuel cell. That might have been unpleasant.

We looked at the shards after they were picked up off the track. I have thought about rotor shards going close to my helmet, Ha.

Be conservative and replace. Rotors are cheap when you consider the cost of failure.

Odds are you could get away with using them some more but in my opinion it's just not worth adding even the small amount of risk.

Have fun today.

Jim

2017 MV Agusta F3 track bike
2001 VD FF
1995 VD FC

[EYERACE]

Your question has a simple answer that is phrased in the form of a question. > Is your life worth more or less than the cost of a replacement rotor ?

To rephrase: if you bought such part and it came that way, would you use it or send it back ?

[Robins Ken]

The cracks are about 0.1 to 0.12 inch, not through and through. Is this something to keep an eye on, or time for new rotors?

Light tap with something metallic should ring. Cracked they will thud.

Maybe i am old. Thought everyone did this.

[DaveW]

Light tap with something metallic should ring. Cracked they will thud.

Maybe i am old. Thought everyone did this.

They will still "ring" if the cracks are very small as the OP noted. The cracks have to be large enough so that the vibration causes the sides of the crack(s) to rub against each other and damp out the ringing. Also, they may not ring if they are mounted to hats, and not one-piece. The mounting area will rub and damp out the ringing, similar to having large cracks.

[Ralph Z.]

When faced with questions regarding safety, I always ask myself "what would a pro team like Penske do?". The answer is always obvious. Replace.

[Mondial]

If your curious. Have them Magnafluxed. Then you will see why to throw them out.

[kea]

Get rid of that stupid design, go solid.
They aren't going to fix themselves.

[DaveW]

Get rid of that stupid design, go solid.
They aren't going to fix themselves.

That summarizes this entire thread...

[stonebridge20]

Didn't that Hazelton kid have a set of those rotors on his RF92 for something like 11 years?

[reidhazelton]

Didn't that Hazelton kid have a set of those rotors on his RF92 for something like 11 years?

Something like that. Granted the car has sat for the later of that, but it was still a good five years of "full-time" running. And that is a lot of racing at Blackhawk that is the hardest track I've been to for brakes and tires as there is no time for them to cool off. And yet, no cracks. By the looks of them, they will 'groove' out before they crack. There are some grooves between the holes on the fronts, but nary a crack. The rears look brand new.

The freezy stuff works.

[stonebridge20]

The freezy stuff works.

Yea Baby !

[Rick Iverson]

I’d drop them like third period French.