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Old 09-12-10, 05:51 AM
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mawtangent
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Yeah, I think tires make a big difference in speed/rolling resistance (especially the extremes of smooth verses knobby).

Something else to consider, sorry if I'm stating the obvious (and you may have taken this into account already) but the gearing (the assorted sizes of the cassette gears on back and the chain-ring gears on front) of each bike you observed might be much different, so say, if all of you where in the 3rd largest gear in the back and the largest chain-ring on the front, you still might (because of differing gear sizes) be dealing with very different amount of power transfer (I think I've read the term "gear-inches" used when making comparisons between different gearing combinations when this has been discussed in the past).

In my experience mountain bikes don't have as much "high" gearing, you might "run out of gear" if you try to go very fast down a paved hill on a mountain bike. Some road bikes (especially conventional two-ringed chain-ringed ones) might not have the "low" gears some desire for climbing steep hills.

The effect of different gearing is that, with each peddle stroke, the back wheel is rotating at a different rate. Three different people on three different bikes might be peddling at the the same rate (say 70 "strokes" a minute) but with differing gearing the back wheels are turning at different rates and accelerating the bikes at different speeds.
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