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Changing rotor size

Old 05-15-18, 07:47 AM
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PixelPaul
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Changing rotor size

I just bought my first bike with disc brakes, they are TRP Spyre-C mechanical discs. It came equipped with 160mm rotors. Would there be any compatibility issues if I want to try 140mm rotors? Is it just a matter of changing the rotors, or would other adjustments need to be made?
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Old 05-15-18, 07:53 AM
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caliper has to grip the disc, so it's mounting has to be lower to stay on the disc,
of course.

but the materials the discs are cut from remain same as larger of same
make & model..
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Old 05-15-18, 08:02 AM
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Really depends on how the calipers attach to the frame-- most post/IS mounts have a minimum rotor size, and pretty much all frames have a maximum rotor size. For instance my Ritchey can run a 160mm rear rotor, and no other. The caliper cannot be mounted 10mm lower to fit a 140mm rotor, and the frame will not clear a 180mm rotor.

There is absolutely no benefit to a smaller rotor other than saving a tiny bit of weight-- about 10-15g per rotor. You could achieve greater savings by switching to lightweight rotors like Ashima AiRotors, going to titanium fasteners, or both.
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Old 05-15-18, 08:24 AM
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Originally Posted by PixelPaul View Post
I just bought my first bike with disc brakes, they are TRP Spyre-C mechanical discs. It came equipped with 160mm rotors. Would there be any compatibility issues if I want to try 140mm rotors? Is it just a matter of changing the rotors, or would other adjustments need to be made?
If (see other posts for reasons why this is "if") you can change the rotor, you'll need the proper length adapter as well. For post mounts, you might not need an adapter for the smallest size rotor but the other rotors will need the properly sized adapter. The pads should grab as much of the rotor as possible without jamming up against the caliper.You don't want the rotor to hit the top of the caliper or the braking surface to be below the caliper. The adapter places the caliper where it needs to be.
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Old 05-15-18, 09:50 AM
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If there are adapters under the brake calipers then 140 mm rotors will probably work.

If the calipers mount directly to the frame/fork with no adapters then 140 mm rotors will not work.

TRP recommends 160 mm rotors on the front when using Spyre calipers.

The whole topic begs the question of why anyone would go through the trouble to replace 160 mm rotors with 140 mm rotors.


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Old 05-15-18, 10:32 AM
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Originally Posted by TimothyH View Post
TRP recommends 160 mm rotors on the front when using Spyre calipers.
They do? Is that as a lower limit? That would make sense. As an upper limit restriction, less so. Last year I bought a set of Spyres for our tandem and at the same time I bought adapters (TRP has adapters and rotors up to 203mm) so I could mount 180mm rotors front and rear. The LBS did not think this was a bad idea. Usually its the front end that has no upper limit on rotor size because there is nothing to get in the way. The front end is also where the greater capacity brake can do the most good. I recently bought another high performance tandem that I requested be equipped with Spyre calipers. It came with 160mm rotors f/r and I was planning to move the rear 180 from the older tandem to the front of the new one. Can you point me to the information from TRP that explains this restriction on rotor size?
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