Everyone's taking a very scientific approach to this whole conundrum which is great.
By way of introduction, I'm the hypothetical 100kg rider kevinc discusses, except it's closer to 120. As for "ignoring air resistance", we can't even get the local council to sweep the gravel off the shoulder let alone removing all the air and creating a laboratory quality vacuum. So we'll have to treat this as a real world problem and keep air resistance in.
The thing that seems to be missing from the discussion is the correct perspective. Everyone is very strong on the point that acceleration due to gravity is identical for both riders. I don't argue that fact. But it's not gravity that should be considered here, it's the gravitational force which is 100% mass dependent.
It is then necessary to call upon Newton's second law.
In the absence of a value for [math]\sigma[/math] I will make a reasonable assumption; for a rider of any given height, their frontal area, and therefore drag coefficient, when properly tucked over the handlebars will be almost identical and also independent of mass, within a reasonable margin of error.
In the expression [math]\sqrt{\frac{mg sin\theta}{\sigma}}[/math] and with the above assumption in place, the terminal velocity is dependent on mass only.
Anyway, it all becomes irrelevant on August 10. After a club race there will be a downhill event. No drive chain on the bike, pure gravity. kevinc and myself are bringing together a group of riders and eliminating as many variables as possible. Friction will not be an issue as each rider will use the same bike. With the seat and handlebar height unchanged for each rider, shoulder and hip height/alignment and therefore drag should be fairly constant. Each rider will be given 3 timed passes (hopefully, time permitting) down a straight smooth 1km 5% descent.
I was going to drop a cheeky "if you choose to ignore quantum effects" into paragraph 3 until I remembered my audience and realised I'm probably closer to the centre of the IQ curve here than anywhere else I live.
