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Old 01-09-04, 06:29 AM   #1
fatman
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How to shim disc rotors?

Hi!

I have a set of wheels with mountain bike tires and I'm currently preparing a second set of wheels with road tires. The idea is to swap wheels as necessary. That's going to be done frequently. My bike has the Hayes HFX-9 disc brakes and the wheelsets are not the same. One is the Mavic SpeedCity and the other is the Bontrager SuperStock. I was told that I will possibly have to re-calibrate the brake pads each time I swap wheels or that I have to shim the rotors so they match exact position. The idea is to swap wheels quick and easy so I think that is better to shim the rotors.

I have no idea on how to shim the rotors and what is required. Can you please explain to me not only how to do that but where can I find all the parts needed?. I did a search on a couple of online bike stores and I can not find anything under rotor shims.

Also one wheelset is going to use a MTB cassette (11-34) and the other is going to use a road cassette (12-27) I was told that I can possibly have mismatchs with the rear deralier (Deore XT) and the length of the chain. What adjustments are necessary to avoid those problems?
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Old 01-09-04, 08:15 AM   #2
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Never shim the rotors. They need to have solid contact and load distribution on the hub surface. Shims only go on the calipers.

The design of the AVID mechs makes this situation a non issue. I can readjust my AVIDS to match a new wheel in less time than it takes to install a water bottle cage. That is one other reason I threw out the Hayes, Magura, etc...
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Old 01-09-04, 09:40 PM   #3
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Quote:
Originally Posted by SamDaBikinMan
Never shim the rotors. They need to have solid contact and load distribution on the hub surface. Shims only go on the calipers.

The design of the AVID mechs makes this situation a non issue. I can readjust my AVIDS to match a new wheel in less time than it takes to install a water bottle cage. That is one other reason I threw out the Hayes, Magura, etc...
Sam thanks for sharing your concern I will take it in serious consideration still, since I don't want to do that to ride off-roads, how you shim rotors? My disc brakes are hydraulic and I have no plan to change them in the near future.
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Old 01-09-04, 09:49 PM   #4
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If I had no choice but to shim them then this is what I would do.

Take an exact measurement of the gap that must be closed to make the rotor fit in alignment with the caliper using a machinists caliper or micrometer to the nearest .005 inch or .01mm.

Have a machine shop mill the exact bolt hole pattern into a true ground peice of stainless steel stock which can be purchased in your specific thickness. They will make you a spacer/shim that will exactly match the bolt hole pattern and bolt hole size if you take them a rotor that has been removed from the wheel.

I would never use washer style shims for this application like those used to shim the calipers.

this is the only way i would do this if it were mine. Others may not agree but just make sure you know what you are getting into. I'd contact the brake manufacturer and get their perspective on it.
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Old 01-09-04, 09:53 PM   #5
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Have you considered mavic new budget minded Crossland wheelset? I just bought a set for 229.00 for both front and rear. Disc ready and strong.
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Old 01-10-04, 04:03 PM   #6
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ADBOT thanks for the links I will check them.

Quote:
Originally Posted by SamDaBikinMan
Have you considered mavic new budget minded Crossland wheelset? I just bought a set for 229.00 for both front and rear. Disc ready and strong.
Sam my bike is a 29er. I already have a Bontrager wheelset for offroads use and the Mavin Speedcity wheelset for road use.
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Old 01-16-04, 01:36 PM   #7
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Just to update.

Recalibrating the brakes is not as bad as I was thinking, so I decided not to shim the rotors. Things seems to be fine now.
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