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So I was finishing my build today putting all pieces together on my Diverge 52 carbon frame when something come to my attention: the flat mount SRAM Red hydraulic brake calipers can barely clear the wheel spokes (about 1-2mm maximum) using 140mm Centerline X rotors on my CLX 32 wheelset (centerlock). Decided not to risk a disaster I put those 160mm old Ashima 6-bolt rotors mounted on a Shimano RTAD-05 adapter, so the brakes now clear the spokes (about 4-5mm) and the rear one clears the chainstay by about 2-3mm.

Caliper to spoke distance

Here's my question: since I have no other disc brake bike to compare, is it normal to have such tiny clearances on a gravel bike? My original project would be using a 140mm rotor, will it rub the spokes when pedaling out of the saddle or climbing?

Rotor to chainstay distance

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    I’m no expert on disc brakes, but 1–2mm between derailleur@largest cog and spokes is quite common. – Michael Jan 3 at 15:11
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    Yeah, I have no expertise to actually answer either way, but whilst wheels may flex enough to move 1-2mm at the rim, something is very wrong if they are flexing that much near the hub. – Andy P Jan 3 at 16:00
  • The caliper is so close to the hub that you have to basically fold your wheel over like a taco to move the spokes outward enough to touch the caliper. If your wheel is flexed/bent that far out of centreline you have much more serious problems to attend to first. – Rider_X Jan 3 at 23:30
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tldr: my road disc bike has tight clearances too and nothing rubs, so "it works for me".

Tolerances are always hit and miss, especially when multiple parts are involved like with fork/caliper/hub/spokes/rim/rotor combinations. That's a lot of parts to multiply tolerances by. There are no standards for caliper to spoke clearance besides what original manufacturer deems appropriate. Some calipers might protrude further inside than others (TRP Spyre is notorious), some do not.

Here's some personal experience: my road disc bike has less than 2mm clearance between caliper and spokes, both in the rear (Hope RX-4 caliper, post mount, 140mm rotor, bladed spokes) and front (RX-4 flat mount, non-stock fork, 160mm rotor); rotor to fork is about the same; this did not cause any issues as of yet. To compare, clearances on my MTB are a tad bigger at ~3-5mm.

Here's my question: since I have no other disc brake bike to compare, is it normal to have such tiny clearances on a gravel bike? My original project would be using a 140mm rotor, will it rub the spokes when pedaling out of the saddle or climbing?

Nobody can say for sure, it depends on various factors like your weight, pedaling style, power output, frame stiffness, if rotors are true or not, how stiff the wheels are, etc. You might want to confirm that no interference happens to be sure, but I think clearances you describe are on the lower end of acceptable and as long as nothing rubs in stand the bike should be fine.

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    Just an update here, the bike rode perfectly using the 160mm rotors. As there was no evidence of spokes/caliper contact, I felt confident swapping rotors for the 140mm I originally planned to use. Tolerances are frightening tight, but still no problem, even under load climbing or sprinting out of the saddle. Thanks everyone. – inibex Feb 1 at 2:11

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