Weight Weenies

Got a set of cheap carbon clincher wheels off ebay,60 mm deep on lovely silky smooth alloy hubs,Weighed 1715g for the pair.Spinning them by hand I felt a heavy spot,which turned out to be exactly where the hole for the valve is.But on the 1st couple of rides they felt great on the bike,at least a 1km improvement on my avg speed over a 50km familiar flatish route.Then I went up a local hillclimb,my best on my lighter weight alloys is 7.56 min,and I did a 8.05 mins,so I was very happy with that,as these new carbon rims are 235g heavier.However on the downhill,once above 55km per hour,the weight inbalance made the bike dangerous,so I had to keep the speed below 50kph.

So today,with bluetack and metal nuts I balanced out my carbon clinchers.It took 20g of added weight directly opposite the valve hole to balance the both wheels.Then I went to my local, friendly,car tyre garage and got 4 X 10g sticky tyre weights.Stuck 2 each of the lead weights either side off the rim opp the valve to balance out the wheels.I made sure the added weights did'nt hit the brake blocks/caliper arms.

Took the bike for a 55kph blast down the nearest hill and no vibration's,so problem cured!!Only bad bit is as a weightweenie,it sucks having to add 40g to my wheelset!!!!

Some more expensive wheels have similar feature.

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Yeah its pretty common for wheels to have an imbalanced hop in them. Look at Fulcrum wheels what use heavier spokes opposite the valve hole for example.

My Reynolds carbon clinchers have a heavy spot at the valve too. Actually all my wheels, carbon or not, have a heavy spot. But the deeper rims use a taller valve stem which makes for a more unbalanced rim.

I have not added weight (sacrilege!) to balance any of my wheels, and I've never noticed the unbalance even at over 50 mph. The only place I notice it is when the bike is on the workstand.

I wonder if using tubes with short valve stems and aluminium extensions would be lighter than the long brass valve stem?