rear wheel flex under sprint/climbing. wheel rebuilt and have tried all the obvious
 

The rear wheel is a DT Swiss RR465 32 spokes laced to a powertap pro+ (I think, its a few years old, wireless).


The hub has been rebuilt with new bearings, and the wheel has been trued and re-tentioned by a great mechanic.

Bike is a 2002 Bianchi Giro frame with shimano 105 5600 group (10-speed) I will be trying the wheel on my 2006 caad 8 to see if frame flex could be an issue.

So here I am, with a high spoke count wheel that I've heard good things about. fully serviced and inspected by a great mechanic/wheelbuilder. and even with the brakes all the way open (lever almost touches the bars when I brake as hard as possible) I still get rub while sprinting. I am a pretty heavy rider (195 lbs.) but I notice rub even when I'm not putting out crazy power. rubbing starts at around 1000w.

Thoughts? Anything else to try?

I have a ****ty trainer skewer on there, any way a proper skewer could help?

Thanks

Without seeing the bike and how you ride I can't answer. It could be hub play at the bearing, axle flex, frame flex, spoke flex, or simply that your brake is too close to one side and you could solve the problem by moving it over slightly.

IMO with seeing it, you can safely rule out the skewer because that might cause the wheel to move, but it won't cause it to flex.

Thanks for your input. There is no hub play. I just had the hub rebuilt by a trusted mechanic with new bearings. It doesn't feel like there is really any play in the hub at all.

I have checked the brake, and it is really even from side to side. I have also been riding with it all the way open (lever can almost touch the bars when I brake all the way)

I think ​I have ruled out all of the obvious causes, but I'm not 100% sure, which is why I'm here.

There's always the possibility of wheel or frame flex. I don't know what spokes were used, but wheel flex isn't realted to tension, it's related to the sum of the cross sections of the spokes. So a wheel built with DB spokes will be more flexy than one built with heavier spokes.

If the flex always causes rubbing to the same side, you might try moving the brakes off center slightly.

BTW- I don't know how much or how often it rubs, but slight rub isn't a serious issue. Because there's little pressure holding the shoe to the rim, there's correspondingly little friction produced, so a bit of rub when sprinting won't matter.

Doesn't make sense.
With the wheel installed and secured grab the wheel by the tyre and push it back and forth and see whats moving.
Are the brakes sticking closed?

Yeah, unfortunately I bought the wheel used (before having it rebuilt, trued, etc) and I don't know what the spokes are. They are round (not aero) and they look pretty thick, but I don't know really.

It seems like it rubs every time I hit ~1000w, so it will only be one or two times per race (or maybe none at all if I'm not in contention for any sprints/prims) I'm not really too worried about the .005 seconds I'm going to lose in a sprint, but having my bike functioning at 100% helps keep my mind clear and free of distractions. I guess this issue is really common, so I'm not going to lose any sleep over it, just trying to learn.

Thanks

yes, a good way to eliminate variables. of which there are too many. bike, wheel, rider, etc.

i'd remove the wheel in question and put on another one i was satisfied with and see if it is as satisfying on the bike in question. if so, it'e the wheel. if not, it's something else. until i'd done that, i'd just be, well.... spinning my wheels?

BTW, as a reference point: with the bike leaning against the wall and my weakest hand grasping the seatstay and rim i can squeeze the rim at least a centimeter in both directions. for a total distance of at least two centimeters. i know this doesn't happen when riding, even under extreme circumstances, because if it did my tire would be constantly rubbing the brake pad, and it doesn't, never. tested on six bikes.

With the wheel installed and secured I can push the wheel all the way to the brake pad on either side with moderate (pushing on it pretty hard but not beating on it) effort (with the rear brake all the way open.) It doesn't look like play in the hub, and the brake is not sticking closed. I don't have another wheel with me at the moment to compare to.

I have tried with another wheel, and the wheel in question seems to be a bit "flexier" side to side, but not extremely so... Kind of hard to describe in writing... I guess the wheel in question is about ~25% "flexier" as a rough estimate when pushing on the wheel with my hands. The wheel that I'm happy with is a williams WS 30, and both wheels are 32 spoke.

OK, assuming all is OK, and it's just flex, there are two sources. Lean flex because the bike is tilted when sprinting putting side loads into the system, and chain load flex because the chain is pulling one side of the rear forward with great force (minimum 2x the pedal load).

You can test for both. Check lean flex by leaning the bike, and putting root pressure directly on the BB or chainstay. Do this from both sides and observe. Chain flex is tested by putting the bike along a wall in a corner with the front wheel against the other wall. Mount the bike and set the pedal at 3 o'clock and try to ride through the wall (hopefully you won't be able to). You'll need a friend to observe for flex at the brake.

As I said, some flex is normal, and more at high loads or when the bike is off plumb is expected. The testing is more for your reassurance than anything, but may show an actual problem, such as a cracked chainstay.

More of a question than an answer, but should spoke tension be checked as a possible factor? Compare tension in the flexy wheel to tension in the other wheel (Williams) that the OP has?

(I believe I could output 1000 w for about 1/1000th of a second, so no answers based on personal experience here.)

I had my mechanic/wheelbuilder check and adjust the spoke tension of both wheels. I forget what he said the number was, but he was happy with both.

No, see #4

Spoke tension does not affect wheel stiffness assuming a minimally taut spoke at least.

Spoke count and as FB stated, spoke cross sectional area are the main determinants along with bracing angles of the spokes. The higher the angle from the vertical, the stiffer the wheel. And it is a squared function, so fewer spokes on the high angle(NDS) side make a big difference. Are there very few spokes in this wheel. Are there only 1/2 the number of spokes on the NDS as on the DS? If either is true, that could easily be the answer.

Also a very stiff rim will rub the brake more readily than a flexible rim. That is because the flexible rim bends across its mid-line and the upper half of the wheel doesn't move very much. A stiff rim doesn't bend so lateral force at the road or mid line gets transmitted all the way to the top. With a very stiff rim, you need very stiff spoking to prevent the wheel from tilting around its center diameter axis.