Bouncing front wheel

the_jackalcp

I have just purchased my first set of tubular wheels ( Farsports). I have noticed that when I spin the front wheel with the bike off the ground there is a rhythmic bounce, like the bike jumping slightly in my hand. I have noticed something similar on my previous rear wheel, which was a DA C24, so am curious as to what the cause is and if anything can be done to resolve it

Does anyone have an explanation as to why this is happening? Is it poor gluing of the tyre, the valve extender causing uneven weight balance, poor build quality or just the rim being badly made?

Thanks guys

ugo.santalucia

Unbalance? AS you say, it might be the long valve or maybe the wheel is off vertically?

If you want I can have a look at it, as you are local

sungod

as ugo says, sounds like simple imbalance

but it's unsprung weight, you only notice it in the situation you describe because the force from the imbalance is significant wrt to the mass of the bike, when riding it will make no difference