Carbon wheel imbalance

tomrob36

Thought I would share and see if others have had this issue. I own a 2016 TCR Advanced SL2 M/L with 30mm SLR1 wheels. I noticed while coasting at high speed an imbalance on the bike coming froming the rear of the bike. At first I thought the rear wheel was out of true. When at home I hung the bike for cleaning etc. I checked the wheel and it was out a little bit and being a larger guy I brought it to the shop for an adjustment. They felt is was in tolerance but worked on it for about 20 minutes to get it better which it was. Kudos to the shop wrench! I mounted the wheel on the bike without the tire or tube and cranked up the rear wheel to high speed and the imbalance was much better. Mounted the tube and tire and it was worse than before. Mounted the wheel magnet opposite of the valve stem. Was better but ended up adding two more wheel magnet s to smooth it out. First time using carbon wheels and never seemed to notice this as much with aluminum wheels. I have a set of Hed Ardennes and doesn't seem as much of an imbalance. Rolf Vigor RS very little imbalance. Any other folks notice this with carbon. I chalk it up to light rims ergo less rotating mass so any imbalance is more noticeable. After doing some research some manufacturers balance their wheels such as HED, Campy etc. On our next ride the bike was much better at high speed coasting. I have to add that the imbalance was less noticeable under load of pedaling. I would not want to have this experience on the front wheel on a high speed decent. I shared this on a forum and one other person with the SLR0 wheels experienced this. I plan to shoot some video showing what I found. The guys at my shop thought I was a bit crazy at first.

jgsi

Maybe for a guy carrying extra, you just need a stiffer wheelset.. more spokes ?
I have yet to see bike wheels with lead weights attached like they are car wheels... but then again I am ready to be learned.

ugo.santalucia

Sounds like the valve. You have a longer valve than you had on alloy rims, hence the imbalance feels greater. I have never spun at speed a rear wheel that wasn't mildly imbalanced... bicycle wheels are simply not balanced and that is normally not an issue

sungod

with no weight on the bike, the typically lower mass of cf wheels means the imbalance introduced by the valve stem+extender is larger wrt to the mass of the wheel

it may jump around if spun up on a stand, but with weight on the bike, unless you have a massive imbalance it's really a non-issue

from old notes when i was looking at this effect, for a road bike, a 10g imbalance at the rim with an overall system mass of 83kg will give c. 6% peak reduction/increase in contact force at 100kph at 13Hz

this is per wheel, if both were in phase and the same imbalance, you just add the two for worst case 12% peak, out of phase is more complicated (but less)

at 40kph it's more like 1% at c. 5Hz

for different masses, the % increases/decreases linearly in proportion

the effect of this is on downforce, the tyres act as (stiff) suspension, the actual physical deflection will be a fraction of a mm

i just came back from cycling holiday, descending happily on unbalanced cf wheels at 80-90kph and taking swoopy corners at 70 - that i'm sure others with more skill/guts can do even faster - it's not an issue

trailflow

Was the wheel checked for radial trueness ?

Check the thickness of the inner tube at the value connection. They can be quite thick and bulge there. That would be my guess or maybe a bulging tyre or a combination of both or the tyre began to unseat from the rim. What pressure were you running ?

I would inspect the rim edges inside for consistency and there is no excess resin anywhere, and they are not beginning to warp/delaminate.

I also wouldn't count out a bad road surface playing tricks with you.