End of life front brake rotor -- how thin is too thin?

masameet

masameet

Rawr!
My '05 DRZ400SM's front rotor is almost at the minimum thickness (maybe .9mm at 3.5mm). Am thinking of replacing the OEM rotor with an EBC rotor. What kind of braking problems will I run into if I keep riding & braking until the new rotor gets installed? Just had both brakes bled (rear rotor and pads still in near brand new condition) -- they were overdue and on a recent ride experienced a little front brake fade. Now with fresh fluid, the front brake at least seems to stop where I want to instead of just beyond.

Plus about 1500 miles ago I installed new OEM brake pads. After installing the new rotor, will I need to do anything to prep them beyond the usual braking/bedding in?

Thanks!
 
jraice

jraice

Well-known member
I would just give them a light sanding to remove any glaze which can happen on any brake system, especially one that is running hot like yours.
 
S

SikMoto

Well-known member
Confused by your comment .9 at 3.5 mm - most rotors have a MIN THICK right on them - the F4i Im working on right now says 3.5mm MIN THICKNESS on it. So you are saying yours says 3.5 and it measures .9? :wtf
 
masameet

masameet

Rawr!
Yes, the DRZ OEM front rotor minimum is 3.5mm. My mechanic measured the rotor's current thickness and it came out, I think, to .9 thicker than the minimum. (But then again, the number could be .09, if not .009.)
 
Flying Pig

Flying Pig

Still learning to ride
SikDMAX said:
Confused by your comment .9 at 3.5 mm - most rotors have a MIN THICK right on them - the F4i Im working on right now says 3.5mm MIN THICKNESS on it. So you are saying yours says 3.5 and it measures .9? :wtf
Click to expand...

I was confused at first, but figured it'd be 0.9 over minimum thickness, so a total of 4.4mm. :thumbup
 
mototireguy

mototireguy

Moto Tire Veteran
If you're confident with the thickness check being above the 3.5mm minimum then you can wait.

If on the other hand the brake rotor is well grooved or dished or you're dissatisfied with the braking performance then a fresh new brake rotor with new pads would be nice.
 
Mortifer

Mortifer

.
As they said- Roll what you have til the new one arrives, then lightly sand pads. No worries.

Does the old rotor have any "play", meaning can you wiggle it forward and backward like a free floating rotor?
I've never felt a DRZ rotor that wiggled at all, usually they are solid.
Mine is quite loose, I'm mildly concerned but too lazy to change it.
 
J

Junkie

gone for now
The rotor probably started out at 5mm and is now at 4.4mm, so it's got a lot of life left. It takes a long time to wear .9mm off a rotor.

I wouldn't replace it yet.
 
Motech

Motech

_-_-_-_-_-_
Agreed that .9mm is still a lot of meat. I would consider replacement a waste of money unless current performance is compromised by warpage or grooves.
 
masameet

masameet

Rawr!
Well, I'm a dork. Not only did I mess up on the preposition in the OP, I probably omitted a "0".

My mechanic compared the rotor's thickness over the minimum 3.5mm to that of a sheet of paper. I hate numbers (tend to be dyslexic when it comes to recalling them), so wasn't quite sure what he was talking about. Anyway I finally looked up paper thickness on the internet and it's about .004", which is .09mm. So in short, the rotor is about one paper thickness over the minimum.

Because braking is effected via friction, which produces heat, I was wondering how long more can I ride with the rotor and what, besides brake fading, I might encounter if I continue to ride before the new rotor gets installed. With fresh brake fluid, the front brake is working as it used to before last Sunday's ride. On that ride I didn't experience any wobbling on braking, only fading. (Which, I think, was similar to my experience with drum brakes.)

Hope this explanation is clearer.
 
Motech

Motech

_-_-_-_-_-_
"Fading" was probably crap fluid, bet it'll be better now.

Though .09mm is obviously much closer to minimum than .9mm, it still is above minimum. Since it feels good to you, why don't you just wait and budget for a disc when your pads wear down or you start feeling lever pulse? Get your monies worth from that stocker.
 
J

JimE

Rider
Do they make a big rotor kit like my KLR? If so it's the perfect excuse for an upgrade. Mine will come someday soon. Might not even need it at the time. My birthday might come first. Or xmas. Or it might be a Tuesday. Whatever.
 
DannoXYZ

DannoXYZ

Well-known member
Motech's got the right idea. Replace the rotors when the pads are done for as well. It'll give you new pads and rotors. Better than putting new pads on old rotors or new rotors with old pads.
 
J

Junkie

gone for now
JimE said:
Do they make a big rotor kit like my KLR? If so it's the perfect excuse for an upgrade. Mine will come someday soon. Might not even need it at the time. My birthday might come first. Or xmas. Or it might be a Tuesday. Whatever.
Click to expand...
it's a tard so it already has a big rotor.
 
MotoMatthew

MotoMatthew

Well-known member
I'd run the pads and rotors until they reached the minimum thickness, but that's just me. And racers are cheap. And sometimes dumb.
 
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