Bicycle Mechanics - Help determining stem size needed...

Hi all, I want to buy a different stem for my Cervelo P3, but I need help making sure I get the right one.

The bike has a bullhorn bars with Syntace clip-on aero bars. The stem is 120mm and I want to replace it with a 100mm. How do I definitively determine what size my bullhorn bar is? I've looked everywhere, but I don't see a size printed anywhere on the bar. Any help will be greatly appreciated!

I'd get someone with calipers to make sure.

Bikepedia says the 2004 p3 came with a 1" Cane Creek Headset and a Cervelo Base Bar, most of which seem to be 26.0 mm clamp diameter.

It says the 2007 p3 carbon came with a 1-1/8" headset and a Vision handlebar, most of which are wing-type...so I'm guessing that's not your bar.

Hey thanks for the reply.

I should have mentioned that I live waaaay out in the middle of nowhere. The nearest bike shop is in Hawaii with about 2200 miles of Pacific ocean between. It takes weeks to get anything shipped here. Luckily the previous owner lives on this island so maybe I can find out exactly what I need from him. Heck, he may have a shorter stem in his stash of parts.

Oh yeah, it's a 2003 P3.

First, determine whether you have a threaded or threadless setup: http://sheldonbrown.com/handsup.html

I'll assume threadless...

There are two diameters to check: 1) Steerer tube clamp and 2) handlebar clamp.

1) Most any threadless stem you find will be 1-1/8". If your headset calls for 1", just use a shim.

2) Likely 26mm or 31.8mm; it's a large enough difference that you can usually tell them apart once you've seen one of each. If you can't tell and don't have access to calipers, try this: wrap a string around the current handlebars, measure the length of the string with a ruler, and divide the length by 3.14. (If you're using a non-metric ruler, remember that 1" = 25.4mm). The answer should be pretty close to either 26 or 31.8mm.

Thanks Jive... I was able to find out from the guy I bought it from. I see what you mean though, the bar on my P3 is noticeably smaller than the one on my road bike.

I should have mentioned that I live waaaay out in the middle of nowhere. The nearest bike shop is in Hawaii with about 2200 miles of Pacific ocean between.

You win. In 3 years on this board that is the first good explanation of why someone can't just go to the bike store to get the answer.

Stock up tubes when you do get there!

jim

:-) I sorely miss my LBS way out here in the middle of nowhere. I do call them from time to time and they are still a great help. A good LBS is worth a million.