frame flex and brake rub
 

I wonder if most or some of the riders can climb very heavy out of saddle and at high torque get the rear brakes to rub? I have notice in my the past year as my quads are getting stronger I am much better at really putting pressure on the pedals and can at times cause the rear brake to rub. Now I really keep the brake pads close to the rim I like to have very little action to get the brakes to work, they are less than mm away from the rim about 1/32 of an inch. I have 2 CF bikes and this particular one is a little more flexy the other I cannot get to do this. It is not the wheels I check this and build my own wheels. I just wondered how common this is under high torque.

It is not something I am worried about but years of long distance running make for quads that are not really strong. Now that I added the bike the quads are much stronger so I can push now like I never could. It has also helped my running.

Why do you say it's not the wheels ?

if you divulge your weight and/or wattage output, we can probably tell you if its your frame that's noodly, or your legs that are beastly. or perhaps both. "stronger" is relative. watts are absolute.

otherwise, your wheels are probably flexing a bit too, even if you build them up yourself. even the strongest of wheels are going to flex some amount, and when you run your brakes with such ludicrously tight tolerances, that's going to be a consequence (between any frame flex, and wheel flex).

you have a few options:
1) loosen the brakes by a mm or two, and deal with brakes that are looser than your delicate sensibilities would prefer. (see rule number 5)
2) deal with the brake rub (also see rule number 5)
3) ride your other bike
4) start engineering better carbon fiber frames yourself, in your spare time.

It's common, but with only 1/32 of an inch in between the two, it should be expected. Open your brakes a little, and then try it out.

yeah thats pretty common. you could move your pads further away from the rim.

I think even I could flex the wheels/frame enough to get brake rub with only 1mm clearance. That seems way, way too close. Also, I'd be curious why you say the wheels aren't flexing. go out to your bike and push the wheel over with your thumb. Can't you get it to move? Don't you think rocking the bike back and forth while climbing is causing some wheel flex?

1/32 of an inch? Really.

Seems way too close. I like a lot of daylight between the pads and rim.

I am well aware of the options I am reasonable mechanic and I simply opened the brakes up a little and it went away. I weigh 173 pounds at 6'2 and have no idea the watts I don't have a power meter. Yes the wheels do in fact flex I just wonder if anyone else have had brake rub in these situations. For me it was never an issue till I have gotten much stronger on the bike. As a runner I have plenty of wind and endurance but the quads were pretty weak. I hated to even stand at all to pedal it was to tiring but I could easily pedal all day. Well now I sort of like to get up and climb out of the saddle on short grades going up, it gives the rear a rest and I go faster over all. I guess it just took me by surprise and it even leaves me questioning just how true a wheel needs to be. I get anal and with a well made rim can get the them laterally true to less than a 1/3rd of a mm. They have fellows in the mechanic forum getting wheels to have almost no runout.

Eh I could flex my old aluminum fuji that had a 20-spoke rear for about 3mm of lateral deflection. of course that was only above something like 400W.

my S1 and R3 wont flex even 1mm at that power though. this is with 32-spoke open pros.

a few weak factors can add up: noodly bottom bracket, low-tension spokes, not enough spokes

Why would you even use the rear brake? It will only lock up and get you into trouble. Loosen it till it won't lock up when you pull the lever to the bar at 20 mph.

I'm not strong enough to make that happen, but I see the pros reach back and open their brakes at the start of a decent climb. It may just be the way it needs to be.