Cervelo P3 48 vs 51

Just like you I was sized by my local Cervelo dealer between 48 and 51. They only had a 51 in stock and as soon as I sat on it I knew it was just too big. I went with the 48 P3 with 650 wheels and totally love my bike. I TOTALLY LOVE my bike, 650 wheels and all! It's a perfect fit! No regrets.

Since you've sat on a 51 and it seemed big and you rode a 48 in an IM and loved it, then go with the 48. You can still find 650 stuff on line with no problem, it's just not readily available from your LBS. I bought an extra set of tires and some tubes so I don't have to wait for shipping should something blow.

Don't second guess your decision - you ordered the right bike.

Sounds like you fit on the 48 better so go with the 48. No one gave you a good reason to switch up. Stay on top of having spares and things for yourself and you'll be fine.

Get the bike that fits. You had a positive experience on it, so why would you want to deviate? As far as "Big Girl Wheels" go - I don't know what that means. I am a guy and am just under 5'8" - I ride a set up that has 650's on it, and I've known a few others my size range who have done the same. I love my bike - I could care less about not having the size wheel someone else has, as it's all about how the bike fits you. Sounds like you have a bike that really fits you well, so take it and enjoy it!

When I switch bikes one day, if the next bike fits me right and has 700's then I will go that route.

As mentioned before, the only drawback to 650's is finding tubes/tires on a whim. It doesn't mean you can't find them, but it does mean you need to be prepared with an extra tire and some tubes on hand. I bought 2 tires at IM Texas from an out of state shop that was at the expo, so even at an IM these were available

Send a pm to vbellino. He and I did the Cervelo share the ride. He's on a 48, I'm on a 51. He just did IM Cozumel.

49.5 what? Top tube length, if so measured from where to where? Or reach?

In terms of the wheel size... this is from personal experience... My wife wanted this tri bike and one of the big reasons was that she could use her Zipp 808's (700c, which she's been using on her road bike). We knew that the bike would be on the larger size of the spectrum, but our fitter was sure it would work. Well, it never really did... She was faster on her road bike than on her tri bike even if it was pancake flat. We just got her a new bike (with 650's) and that allows her to get in a much better position. Last ride, she was almost 2mph faster... The only drawbacks you will have with 650's over 700's is the lack of local shopping carrying 650 tubes (many time, you need to either order them ourself, or have the LBS order them for you, but when place the order, just get a couple extra and you're fine), most tire manufacturers do not make the high-end tires in 650's, so you either have to settle for something less, or look for the few that offers good tires in that size (and you will have the same issue as the tires, LBS' rarely carry them). The last drawback is the lack of race wheels... they do show up on the used market once in a while, but more often than not, they are then tubulars, not clinchers (which is not a major deal if you're willing to use tubulars, and there's nothing wrong with them).

The biggest benefit you will have with 650 wheels (for smaller bikes) is that it allows you to get into a much better fit.

Also, pay attention to the gearing. In general, you need 2 teeth larger front rings to compensate for the smaller wheels (just keep in mind that will not affect your power, that will be the same as the 2 tooth smaller for 700's), so if your'e riding a 50/34 (i.e. a compact) today, you will need a 52/36 (cassette being the same) to have the same gearing. Not a big deal at all, just something to be aware of.

I see used 650 race wheels on a regular basis for extremely good prices.