Talk:Small-wheel bicycle

Aerodynamics

The background to my edit of the article regarding wheel aerodynamics is this:

The aerodynamic drag of items of similar shape but different size is roughly proportional to coefficient of drag Cd x Area x speed^2.

The aerodynamic drag of wheels and tyres is disproportionately more important than any other part of a bike, since the top of the tyre is advancing at twice the speed of the bike, and aerodynamic drag is proportional to airspeed^2.

Thus taking the most significant areas of different wheels to be the surface areas of the tyres and wheel rims, and if the tyres and wheel rims have the same cross section and tread pattern, then the areas to be used in the formula are proportional to wheel diameter (Correction agreed: not wheel diameter squared. GilesW (talk) 23:31, 2 October 2009 (UTC)).[reply]

'All else being equal' (to quote the article), on that basis we would expect the aerodynamic drag of a racing Moulton's 16" diameter wheels to be about 60% of a racing bike's 27" wheels, and BMX 20" wheels (as used on some all-purpose Moultons) to be about 76% of that of mountain bike's 26" wheels (at the same speed).

All things being equal (rider position, gearing, tyre sections, pressures etc.) experience tells us that aerodynamic drag at high speeds dominates all other sources of drag, including rolling resistance. This is one reason for road racing bikes with thin tyres being so much faster than bikes with fatter tyres.

In the 1960s, racing versions of Moulton bicycles with small wheels, high pressure tyres, and full suspension proved to be faster than conventional racing bicycles. They were banned from professional cycle races: the other cycle makers did not want to have to reinvent the bicycle. Arguably this protectionist ban set conventional bicycle design back 40 years. Furthermore a Moulton still holds a cycling world speed record that is open to conventional racing bicycles. GilesW (talk) 22:23, 2 October 2009 (UTC)[reply]

Excellent. I had no idea the air drag on my wheels was so much larger than the air drag on my bloated body. Anyway this can go in the bike racing article as the explanation why all entries use the smallest size wheels allowed by the rules. Jim.henderson (talk) 05:13, 28 December 2010 (UTC)[reply]

Gyroscopic stability

I've moved this unsourced claim to here for discussion:

Smaller wheels have weaker gyroscopic stability, requiring more steering strength to remain vertical, especially at slow speeds.

I suspect no reliabale source will ever be found to confirm this because the gyroscopic effect of rotating wheels has already been shown elsewhere to be nice but unnecessary for easy handling. In particular, at slow speeds it is negligible. -AndrewDressel (talk) 13:42, 8 November 2010 (UTC)[reply]

Yes, there is little hope. After a few tens of thousands of miles with 27" wheels and a few thousand with 16" I feel that the steering of small wheels is is more "twitchy" at slow speeds than can be accounted for by gyroscopic considerations. Maybe this is due to lesser moment of inertia about the handlebar axis or some other difference. As for strength, I have to call that an error. It just requires a bit of extra alertness and caution. Indeed I switched to small wheels when an accident left me temporarily too weak to be comfortable on a bike designed for the young and strong. Anyway I also found it easy to become accustomed despite my advanced years and slow learning curve in most matters, and alas I don't qualify as a "reliable source". Jim.henderson (talk) 12:20, 10 November 2010 (UTC)[reply]