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new brake rotor too big?

Old 05-07-22, 03:56 PM
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tyrion
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new brake rotor too big?

I wanted more braking power so I got a 203mm rotor and adapter from ebay and it's not working - seems the rotor is too big or the adapter is too small. The rotor is rubbing on the caliper housing. The adapter packaging is labelled "180mm R", which I thought was the correct adapter for a 203mm front.

Has anyone encountered such a problem? (This isn't my first rotor upsizing - I went to a 160mm to a 180mm on this same bike without issues.)

This is the 203mm rotor/adapter that doesn't work:

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Old 05-07-22, 05:31 PM
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Is that adapter reversible? For my flat mount front caliper the adapter is installed one way for 140mm rotors and rotated180º for 160mm rotors. Any chance your adapter works similarly?
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Old 05-07-22, 06:02 PM
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Originally Posted by HillRider
Is that adapter reversible? For my flat mount front caliper the adapter is installed one way for 140mm rotors and rotated180º for 160mm rotors. Any chance your adapter works similarly?
The 180mm adapter (that worked) has the standoff strut at the bottom, so I just copied that orientation. And just eyeballing it, it seems to me reversing it would bring the calipers closer to the axle, which wouldn't work at all.
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Old 05-07-22, 06:09 PM
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2 bolts with washers on them came with the adapters, also with the adapters came 4 extra washers. Might the 4 extra washers be used between the calipers and the adapter, to push the caliper out a bit? Doesn't seem like good engineering to me, but maybe that's accepted practice?

edit: a little googling indicates it's not uncommon to put washers between the adapter and caliper: https://www.google.com/search?q=wash...hrome&ie=UTF-8

Last edited by tyrion; 05-07-22 at 06:33 PM.
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Old 05-07-22, 07:26 PM
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I'd swear that adapter is backwards. Isn't there an arrow on it somewhere to indicate 'up'? Also not sure why you wouldn't try it just to be sure instead of posting here.
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Old 05-07-22, 08:45 PM
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Originally Posted by cxwrench
I'd swear that adapter is backwards. Isn't there an arrow on it somewhere to indicate 'up'? Also not sure why you wouldn't try it just to be sure instead of posting here.
There's no arrow on the new adapter, there is on the old one, an arrow and an "up". Below is a pic of the old 180mm rotor and adapter. I just used that same orientation when I installed the new 203mm adapter.




edit: here's a pic of a Shimano 203mm adapter with an "up" arrow:


Last edited by tyrion; 05-07-22 at 08:54 PM.
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Old 05-07-22, 08:58 PM
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I think the adapter I got is for a 200mm rotor. I bet the seller of that adapter would tell me to put those washers in between adapter and caliper for a 203mm rotor.

Just going to order a Shimano 203mm adapter.

Last edited by tyrion; 05-07-22 at 09:06 PM.
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Old 05-09-22, 05:55 PM
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I've found that certain configurations just don't seem to work well. I have a Surly Pugsley that had 203mm rotors when I got it and I went back to the stock 160mm rotors. I tried several of the IS-to-post adapters as pictured in this thread and only one fits the rear brake really well. It seems that different adapters, even being the "same size" (like 160mm R), put the caliper at a slightly different position and/or angle. I had to buy a few to find a really good fit on the rear. The front seemed to dial in quickly, but the rear took me a few tries.
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