Actually, over here in the uk last year, some mates of mine got into a conversation with Craig Drescher over wheels. One interesting comment he said was that he found spoke wheels to give more steering than dish... guess what happened at the next meeting, loads of people running spokes (Proline attacks look good... but i always prefered the multi-spokes
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Now more than anything thats to do with the way the wheel flex's under load. With a dish the edge of the rim will be supported all the way round, whereas with a spoke there will be sections that flex, and hence more grip.
Now there would also be an aerodynamic effect, but given that you can't shrink air, it's hardly noticeable, even for a pro (i.e. not me
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Still it's a bit of a moot point for me atm, most of the series I'm currently running have pre-guled control tyres, and they are all dish wheels. At least it's the same for everyone.
HiH
Ed