Child's bike for a small woman?

[smaryka]

This is more likely because the bike fits you than the size of its wheels.... I'm short too, but I've an odd body shape and my small 700c bike fits better. For me that one feels like it accelerates, climbs faster etc. (of course the way my 650 bike is built up these days its no wonder, its a bit of a pig compared to my race bike right now at 22.5 lbs)

It's a bit of both I think -- the 650c wheels are lighter, so that's an advantage, and the smaller diameter means less energy to get them going or to speed them up (see this page for the explanation). But then you lose out with the higher rolling resistance on the small wheels, so it takes more effort to keep them going and you lose more energy on bumps and rough road.

It's interesting because both my frames are the same size (48cm) by the same manufacturer (Cervelo). I wrote a blog post about this a while back comparing the two here. Biggest differences are that the 650c bike has a lower front end (smaller diameter wheel and its short headtube as a TT bike), and the seattube angle is steeper. No toe overlap as I have on the 700c bike. Both bikes descend and corner really well, but the lower front end on the 650c bike makes it a bit more aggressive for racing.

I think Cervelo's done a great job making a 700c bike in small sizes though, given the inherent geometry problems with that. After all there is a market for those wheels on a small frame, so it's nice that a manufacturer has thought through the problems and tried to find the best solution rather than compromise on handling. They also make a 650c carbon model (the RS), though the headtube on that is quite long so more a comfort than a racing bike.

[Eden]

It's a bit of both I think -- the 650c wheels are lighter, so that's an advantage, and the smaller diameter means less energy to get them going or to speed them up (see this page for the explanation). But then you lose out with the higher rolling resistance on the small wheels, so it takes more effort to keep them going and you lose more energy on bumps and rough road.

It's interesting because both my frames are the same size (48cm) by the same manufacturer (Cervelo). I wrote a blog post about this a while back comparing the two here. Biggest differences are that the 650c bike has a lower front end (smaller diameter wheel and its short headtube as a TT bike), and the seattube angle is steeper. No toe overlap as I have on the 700c bike. Both bikes descend and corner really well, but the lower front end on the 650c bike makes it a bit more aggressive for racing.

I think Cervelo's done a great job making a 700c bike in small sizes though, given the inherent geometry problems with that. After all there is a market for those wheels on a small frame, so it's nice that a manufacturer has thought through the problems and tried to find the best solution rather than compromise on handling. They also make a 650c carbon model (the RS), though the headtube on that is quite long so more a comfort than a racing bike.

The 650 accelerates thing is pretty much a myth. On paper it may look good, but in the real world its just doesn't show results. For a while it was very much in vogue for triathletes to all use 650's. They found in the end it was better to go with the best fit they could get and 650's are again rare on tri-bikes unless you actually need them. (good for me though... easy to find cheap 650 wheels for my TT bike these days)

The best thing is to go with a bike that fits *you* the best. If 650's are the way to go, and for many of us shorties they may well be then go with them. If 700's work better, like they do for me, don't discount them just because you happen to be short. Now I *do* have a TT bike with 650's, but that is a whole different animal. I wouldn't be able to get aero on a bigger bike and the position is quite different too.

[smaryka]

The best thing is to go with a bike that fits *you* the best. If 650's are the way to go, and for many of us shorties they may well be then go with them. If 700's work better, like they do for me, don't discount them just because you happen to be short. Now I *do* have a TT bike with 650's, but that is a whole different animal. I wouldn't be able to get aero on a bigger bike and the position is quite different too.

Yep agreed there but since the neutral service car won't always carry my 650c spare wheels I've had to compromise in some races and race the 700c bike.

I like 'em both, I feel they both work for me and fit me for various reasons... it's nice to have the option anyway. Thinking about whether I should try 650c for cross too but I wonder about the "rolling over rough ground" thing, whether I'll actually have to work harder with smaller wheels or not.

One of these days I'll get a custom-made TT bike with 24-inch wheels just so I can get myself even more aero in front (can you imagine the size of the chainrings I'd need though... ) Would be a cool experiment anyway.