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Discussion Starter · #1 · (Edited)
:confused: I've had a new Stan's aluminum coated rotor on my front Magura disc brake now for about 2 weeks. I just put a new Stan's rotor on my rear wheel. However, the rear rotor is scraping on the inside top edge of the caliper. You can see scrape marks developing on the outside edge of the rotor. However, when I hold my finger just above the outside edge of the rotor carefully bracing my finger against the top of the caliper, it appears that the outside edge is perfectly round and true. How can this be? I'm stumped. When I put my original Magura rotor back on, the scraping noise goes away. There is no scraping on the front with my Stan's rotor. AND, when placed side by side, the new rotor appears to be exactly the same diameter as the Magura rotor. But then why doesn't my Magura rotor scrape??
Also, Stan's braking power seems to be quite a bit less than my old Magura steel rotors.

Thoughts/opinions/advice anyone??
 

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Ask Stan

I would contact Stan about this. Sounds to me like he owes you another rotor. Maybe the rotor is expanding when it heats up? I would expect that Al rotors would expand more than steel.
 

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Is it warped?

I bet it has a slight cup shape to it. This would be virtually impossible to see with the rotor mounted. Remove it and place it on a very flat surface. If it is cupped, the outside edge won't touch all the way around on one side.
 

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Discussion Starter · #4 ·
barrows said:
I would contact Stan about this. Sounds to me like he owes you another rotor. Maybe the rotor is expanding when it heats up? I would expect that Al rotors would expand more than steel.
This is already a replacement rotor.
 

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Discussion Starter · #5 ·
barrows said:
I would contact Stan about this. Sounds to me like he owes you another rotor. Maybe the rotor is expanding when it heats up? I would expect that Al rotors would expand more than steel.
And it scrapes when it's cold......as soon as it is installed.
 

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Discussion Starter · #6 ·
B R H said:
I bet it has a slight cup shape to it. This would be virtually impossible to see with the rotor mounted. Remove it and place it on a very flat surface. If it is cupped, the outside edge won't touch all the way around on one side.
I place it on a very flat surface. It appears to be completely flat.
 

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Hey CMV,
I'll bet it has to do with your rear wheel "snugness" (if that is a word!! :p ). If your Quick releases aren't perfectly tight, or your rear dropouts for some reason don't grip the rear wheel really well, when you ride, your weight shifts can be enough to "flex" your rear wheel assembly a bit, sometimes to the point of making your rotor rub! Then when you get off to check it, no more weight flexing the rear assembly, and your rotor doesn't rub anymore! Assuring top rigidity in the disk assemblies is one of the reasons Magura doesn't recommend using Titanium quick releases... Too flexy!

If you have one handy, try replacing the QR with a steel one and see if that helps...

Anyways, that's my best try at explaining it!

Luego!

CODMAN MCM#101
 

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CMV, if I am reading this right it sounds like the rotor is too large of a diameter. If it is rubbing the top portion of the caliper rotor clearance hole when mounted, this would have to be the case.
I would suggest: loosen the caliper bolts (al or ti hopefully ;) ), hold up on the caliper while snugging them back up. If the interference is minor, the clearance holes in the frame may have enough slack to help you out. If not, send em' back.
 

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Discussion Starter · #10 ·
mtbbiker1 said:
CMV, if I am reading this right it sounds like the rotor is too large of a diameter. If it is rubbing the top portion of the caliper rotor clearance hole when mounted, this would have to be the case.
I would suggest: loosen the caliper bolts (al or ti hopefully ;) ), hold up on the caliper while snugging them back up. If the interference is minor, the clearance holes in the frame may have enough slack to help you out. If not, send em' back.
Stan said he would take them back if I'm not satisfied. Cudos to Stan for sure.

I will try to hold up on the caliper as you've suggested. But WHY don't my other rotors scrape?? The new Stan's rotor appears to be exactly the same diameter as the Magura rotor.
 

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Doesntplaywellwithmorons!
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The rotor isn't actually perfectly round, and if scrapes constantly its because it wasn't cut to the correct diameter either. Nothing like poor quality control from stan.
 

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Discussion Starter · #12 ·
DeeEight said:
The rotor isn't actually perfectly round, and if scrapes constantly its because it wasn't cut to the correct diameter either. Nothing like poor quality control from stan.
Please see my original post:

"However, when I hold my finger just above the outside edge of the rotor carefully bracing my finger against the top of the caliper, it appears that the outside edge is perfectly round and true."
 

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Discussion Starter · #13 ·
2 emails that just arrived from Stan:

1) "If you are not satisfied, just return the rotors for a refund. No problem at all. I still think your rear frame has the holes located to low." (I have a 2005 S-Works Epic)

2) "In the past the Marta rotors would hit on some frames so they may have made the rotor smaller just like I did. Then with my coating we made the rotor a little larger in diameter making it hit on your bike."
 

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Is this where it scrapes?

On my bike it looks like there is a small gap between the rotor OD and the inside of the caliper. It is very odd that the Stan's rotor would scrape if the Magura rotor doesn't - IF they truly are the exact same size. I suspect that the Stan's rotor is just barely larger and that is enough to cause the interference.

Can you try to move the caliper away from the rotor - taking advantage of the clearance between the screw and hole. Also try using your front Stan's rotor in the rear.

My experience is that it takes a few days of easy use to get the stan's rotor up to power. Brake pad material must be transferred from the brake pad to the pores in the rotor surface. After that the power is still not as good as with stainless, but close. Anyway I still run the stainless rotor up front.

cmv96 said:
:confused: I've had a new Stan's aluminum coated rotor on my front Magura disc brake now for about 2 weeks. I just put a new Stan's rotor on my rear wheel. However, the rear rotor is scraping on the inside top edge of the caliper. You can see scrape marks developing on the outside edge of the rotor. However, when I hold my finger just above the outside edge of the rotor carefully bracing my finger against the top of the caliper, it appears that the outside edge is perfectly round and true. How can this be? I'm stumped. When I put my original Magura rotor back on, the scraping noise goes away. There is no scraping on the front with my Stan's rotor. AND, when placed side by side, the new rotor appears to be exactly the same diameter as the Magura rotor. But then why doesn't my Magura rotor scrape??
Also, Stan's braking power seems to be quite a bit less than my old Magura steel rotors.

Thoughts/opinions/advice anyone??
 

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Discussion Starter · #16 ·
I just finished putting my original Magura rotors back on. However, when I did a brief test ride (w/ the magura rotors back on), I noticed that I had a shimmy, or shaking, in the front end under moderate braking. My magura rotors have about 200 miles on them. I checked the skewer and bolts to make sure everything was solid and it looks fine. The disc is perfectly centered between the pads. Any thoughts on why this shimmy appeared? Could it be the pads need to acclimate themselves back to the magura rotors? I only had about 20 miles on the Stan's front rotor.
 

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DeeEight said:
The rotor isn't actually perfectly round, and if scrapes constantly its because it wasn't cut to the correct diameter either. Nothing like poor quality control from stan.
Nothing like talking out your @ss. The rotors are laser cut, not likely the cut diameter is a problem.

By the way, I run the new rotors with Martas and don't have any problems. I think Stan's offer to take the rotors back is more than fair. It's possible there is a coating build up on the periphery.
 

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Discussion Starter · #18 ·
Mike B. said:
Nothing like talking out your @ss. The rotors are laser cut, not likely the cut diameter is a problem.

By the way, I run the new rotors with Martas and don't have any problems. I think Stan's offer to take the rotors back is more than fair. It's possible there is a coating build up on the periphery.
Stan and I both hypothesized that there might have been a coating build up on the periphery, however, I had the same problem on all three of the Stan's rotors I tried! But the brake works perfectly with the Magura discs bolted in.

I agree that Stan's offer to take the rotors back is quite fair.
 
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