Need help with Sizing issue...

I'm far from a professional fitter, and the best advice is to be fit by a professional with the explanation of what you have in mind to do, however...

From my experience and understanding, it's generally accepted that if you were going to err on a bike size, it would be better for the frame to be a bit small than too large. A smaller frame can be more easily "fit" with saddle position, seatpost and changes in stem & bar extensions. A too-large frame will always be too large and you will always be too stretched out somewhere in your positioning; a zero offset or foreward oriented seatpost will help get you forward and in a steeper seat angle, but stems can only be shortened so much. Also generally speaking, a tri set-up allows for sizing down a frame size from a road bike set up, so your thinking is on the right track.

Will you be swapping the bars and seat  post through the LBS you will be purchasing the bike from? The best plan would be to have your LBS set up the smaller frame size with the modifications and actually test it out and be fit.

Thanks for the comments.. Hard to know which way to go.. the 2 shops telling me 54cm have a 54cm '08model they are trying to cut a deal to me (but not a 56cm).. and the other shop has a 56cm '08 model they are trying to get rid of... neither shop has a huge inventory so I think they are trying to sell what they have..  I really am not sure if it will matter either way as I can't believe that 2 cm is going to make a huge difference.. b/c honestly a 58cm feels comfy to me..  I may simply just get the 56cm which is the "right size" for me put the short aero's bars on it and not fool with the seat mod any time soon..

 *** Although one of the 54cm is a heck of deal...

DON'T just buy a bike because it's cheap. For the love of God. Make sure it fits. And yes, 2cm can mean the difference between a pain-free century and a bike you can't stand.

The majority of shops unfortunately do a horrible job with fitting--especially those with limited inventories. Strangely enough, they'll always seem to have a bike that "fits you" in stock...

Another thing to try is to go to www.competitivecyclist.com and try the fit calculator. Measure precisely, and get someone to help. It'll give some great info on getting fitted. They also have a fit calculator for TT/Tri bikes. Read through their stuff and use it wisely.

The fit we talk about is more detailed than this feels comfy.

My bike fit guy can tell me if any bike can fit me or not. The closer the bike geometry is to what a custom bike would be, is ideal. The more adjusting you do the less the bike rides like it was designed.

Not all 54's are the same from brand to brand.

Here is a good article about difference between road and tri bikes and the angle of the seat posts and reach. poke around on the website as they have lots of good articles and probably have one on bike fit.

A great deal on a bike that doesn't fit isn't such a good value. Research more...take your time and enjoy the process.

Ride them.  Read as much as possible.

And if all else fails, go with the smaller size.  I didn't and paid the price.

For what it's worth, I'm going to do the same as you are and am going with a 54 frame (I'm 5' 9", and have a long inseam...about 33).  However, I also rode a 58 with a fast forward seat and aero bars and had no issues at all, it was comfy.

Now I ride a 52cm tri bike, have been pro fitted, and seems like it's ok (been injured all summer, so can't really tell).

Good luck!

READ READ READ