Rotor replacement advice

The ONLY way to check to see how worn the rotor is to measure the thickness in the middle. The min thickness is stamped on the rotor.
Your real concern should be the pads and their condition and thickness. Many times if the pads are getting worn you do not need to turn or replace the rotors at all. Just replace the pads.

 

Honestly, they look ok. It never hurts to replace them but, they do look fine. Looking at them is really not a true test though. There is minimum thickness and that has to be determined by using a micrometer.

 

They look good. And from the picture wear lip on them looks so small that it very unlikely that they are too thin.

 

New rotors are 23 mm thick and should be replaced if at 19 mm or less. Making a judgement from your pictures "not very scientific" I would say you have at least 22 mm left and are in good condition. Seeing the inboard surface of the rotor is difficult but is worth checking as often the working surface is reduced to about 50% the rest being rusty.

John

 

Not conclusively. To satisfy yourself, check the thickness of the two sides with a caliper. Also, if you take the rotor right off you can really see the inside condition: installed the dustshield covers virtually all of it. A couple of M8x1.25 bolts can be screwed in on the hub, to bust it loose.

 

Rotor looks very good. So unless it’s bad on the inside I see no reason to replace it.

Proper way to measure disk thickness would be to measure it from the wear areas with caliper measuring tool. As the rust ridges on the edge won’t effect it’s measurement.

 

Anybody know have the spec's on second gen rotor min thickness, runout? See I posted gen 3 above, not really relevant.

Anyway, those rotors look good. Are you noticing anything, pulsing for example? If not, no real need to replace. Check thickness against spec with a micrometer or similar. How are the pad thickness?

 

22mm standard 20mm minimum.

0.05mm maximum runout. But really only time the run out should be measured is when installing new discs. And even then it’s probably not needed.

 

One thing I've read: if you remove but intend to re-install existing rotors, mark a stud and the rotor, and put them back on in the same orientation, hopefully to avoid increasing runout. The theory being that if you re-install in different orientation, it can change things.

 

If you change pads without machining rotors, the new pads will immediately wear exactly like the old pads were, if you change rotors without changing pads the new rotors will wear quickly to look like the old rotors.

So, if you have the metal, resurface (machine shop) the rotors and put on new pads, if you don’t have enough metal, new rotors and pads, aftermarket will probably be better than oem.

 

If you just replace the pads they will take the contour of the rotor surface. But they won’t be like old pads. As of course the new pads have lot more material than old ones.

Unfortunately really no point in machining the old rotors as it’s basically the same price as new aftermarket rotors.