140 vs 160 Rotor Rub Question

Hi- I’m having problems with my front rotor rubbing when I’m out of the saddle and sprinting. I’ve gone through all of the steps that I can think of but can’t solve this one.
Frame- Trek Emonda SLR 2018
Discs- Shimano RT-CL800 (160 front and rear)

The rotors are straight/true and the calipers are centered. There is no rubbing unless I’m out of the saddle going hard. My only thought at this point is that the fork on the bike is flexing which is causing the rubbing. I don’t think that it is a performance issue but I would still like to get rid of the noise if possible.

I’m thinking of changing to 140 rotors. My thinking is that the smaller rotors wouldn’t be as likely to rub based on the smaller size. Does anyone have any experience/expertise with this?

I weight about 165 lbs and I live in the Chicago area so I’m not too worried about extended braking/heat build up.

Thanks for any input!

Is everything tightened to spec?

I think the assumptions you make are logical, so it’s probably worth a try.

Do you also have the latest caliper? It has more clearance than older ones.

I had that on my 2015 Trek Domane, with stock wheels and Enve 5.6 disc. Stand up, rotors rub against brakes. Two years ago I bought a Specialized Tarmac SL7, and the Roval Rapide CLX wheels seem a little stiffer and virtually no brake rub. Shimano disc brakes on the Domane, SRAM disc brakes on the SL7. Maybe something to do with the wheels? Seem to recall reading that the hub/spokes can influence the amount of flexing? Thats pure speculation, both bikes had bottom brackets that were stout and seem to be efficient at transferring power. I honestly don’t have a clue why, but it could be the wheels as the sprinting forces are directed at the bottom bracket and rear cassette which is attached to the hub. Just talking out loud, again thats pure speculation.

The culprit could be your hub, too. A little brake rub during standing sprints is something I could live with.

I’m curious if it always did this or if this is a new symptom.

I have a 2018 Emonda SLR 6 (Shim R8000) Disc with the same rub issues. I think the svelte build leads to fork deflection, maybe axle/hub too. Seemingly the rub happens once we introduce more lateral loading like standing efforts with the bike leaned each way.

Perhaps the smaller rotor will not get contact being closer to the center axis, but I wouldn’t be surprised if it still touches.

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Thanks for all of the replies. This forum is incredibly helpful!

Some follow up items:
-All torque has been checked.
-I’m using current generation Shimano Ultegra 8170 calipers.
-Wheelset is Enve 3.4 w/ enve hubs (last gen, not current). The wheels seem very well made and I’m guessing that the enve hubs would be fairly stiff.
-Did a little searching and it seemed like team trek used 140 rotors for that generation of Emonda. I’m wondering if the crazy light frame weight comes with a little flex. I will say that I don’t notice any flex at the bottom bracket though.
-Definitely not a huge issue but I was just curious if anyone had ever gotten ride of the rotor rub by switching to the 140’s.

I have the same on my Pinarello Gan from around 2018. 140’s were fine, 160’s rub. I just learned to live with it. If you think about it, if the lever was 5 m’s long and you moved it 1mm, 1cm from the fulcrum, at the end of the lever it would have moved about a foot. I think this is the cause. I assume it’s from older disc frames where they hadn’t quite figured out how to make forks stiff enough yet…

I have a 2023 Checkpoint SLR 9 and I also get some slight rotor rub when I’m out of the saddle sprinting or grinding. Not too concerned with it as I imagine there’s little to no watt loss. It seems to only rub initially for a few seconds then goes away.

This makes the most sense to me as well. I can live with the noise but at this point, out of curiosity I’m going to try 140 rotors to see if it completely takes care of the problem.
Thanks for the information!

It’s flex from both the fork and the wheels. Ya know that “compliance” term every brand throws around when they release a new bike… this is compliance haha

As long as they’re running rub free most of the time, I wouldn’t sweat it

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May be a silly question, have you gone and opened up the pistons all the way?

One time I was only ever getting rub out of the saddle, and once i opened my pistons all the way THEN went and retightened the caliper against the rotor to center it, problem was solved.

Sometimes a brake lever unintentionally gets touched with the wheel out and it’s just enough to close the calipers together enough to get that slight rub out of the saddle.

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That is a great idea for sure! I did check it earlier in the week and the pistons were fully open.