Went to a local tri shop yesterday and went through the paces with upper and lower extremity measurements taken and then time on the trainer. The ‘formula’ assuming a 78 degree seat tube angle said that I should shoot for a 53 cm top tube for optimum fit. Given that fact, I am fairly certain I will buy a P3, so I can get to a 53 cm top tube length with either the 52 cm 700c wheel frame or the 54 cm 650c wheel frame. Any advantage to either frame outside of the usual argument for or against 650c wheels? I will use the bike for predominantly sprints and oly races on rolling terrain so theoretically a 650 wheel may be advantageous. However, I am not too crazy about having another size of tubes and tires I need to buy. Input?
The biggest issue is how low you want to be able to get in the front. Hopefully, an approximation of this came from the fit session also. If you prefer 700c wheels and can get low enough, go for it. If you have, or might have an aggresive position, you could easily find that you can’t get low enough without a lot of problems on the 700c. Then you can go for the 650c which will bring you several centimeters lower.
you could easily find that you can’t get low enough without a lot of problems on the 700c.
You can always get a negative-rise stem.
Very true, but I consider getting these odd stems to qualify as a lot of problems. It is a fair option though.
AHHHHHHHHAHHHHHHHHHHHHHHHHHHH! Stop. You don’t REALLY have a choice between 700 and 650c wheels, no more than you have a choice between size 8 shoes or size 13 shoes. One will fit, the other will not. Look at the wheel size section on Cervelo’s website. Study the geometry charts. One will fit better than the other, probably significantly better. Dan Empfield has written on wheel size and bike fit on Slowtwitch before, and has mentioned he will again. Read what he says. We see people in here all the time with the wrong wheel size. People who should be on 650c bougth a 700c bike for all the wrong reasons, people on a 650c bike should have been on a 700c… I don’t mean to be critical of your fitter, but if they didn’t tell you which size wheel you should be on they stopped the fit process when they were only 2/3rds done. 650c and 700c are generally not interchangeable in a given fit situation. They will produce different handling and fit characteristics. A realy good fitter understands that and uses that as one more tool in their fit arsenal to get your bike dialed perfectly.
Thanks Tom. No mention was made of which size would be better for me, but I did detect some subtle pressure towards the 700c. Just so happens that is the bike that they have in the store!!! I felt like this was a first step in the fit process but not the end all. Sounds like I need to get another fitting elsewhere. How important do you think it is to be fit on a computrainer or other objective power measuring device??
“Just so happens that is the bike that they have in the store!!!”
Imagine that. This is why I resist bike manufacturer’s pressure to stock 50 of their “hottest model”. Lean and mean on inventory gives you the ultimate luxury: Honesty. In praise of Cervelo, they have never, ever pushed bikes on us. To the contrary, I’m on the phone with them a few times a week begging for them! And they always come through too.