Originally Posted by datlas

It's been awhile since I did physics on a regular basis.

But on today's ride, I noticed that my fellow riders were really out-descending me. By a few MPH.

It appears that, if you assume negligble rolling resistance and that coefficient of drag are the same for each rider (which is a leap, bigger riders are likely to have more frontal area and thus more drag), that terminal velocity while going downhill is directly proportional to the square root of the mass of rider + bike.

Therefore, assuming that my fellow riders + bike weight are 20% more than me (which I think is accurate since my weight + bike is around 170 and theirs is around 205, which is 20% more than mine), their velocity going down a hill is roughly 10% faster than mine (square root of 1.2 is 1.095).

Any physics people out there to comment? I would like to think my assumptions and calculations are roughly correct. The calculations do seem consistent with what I observed, they were going around 10% faster than me.

If I screwed up anything obvious, please let me know and correct me. Please don't split hairs over rolling resistance (tire pressure etc.) or different frontal areas, I am assuming these are all the same for each of us.

P.S. from what I can tell, this analysis is correct regardless of the downhill slope. Yes??