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Confused over finding right size bike online
#1
I'm confused about sizing a bike to fit me. My current bike is a Trek 7300 hybrid with 700x35 tires and I want to upgrade to an entry level road bike. I'm considering bikesdirect.com, an online store. My seat tube has a decal that says 44cm, 17 1/2 inches on it. I could fit a little larger one but not too much. When I told a guy at a Trek LBS about my 7300 decals and my desire to upgrade he said I would need a 54cm road bike. That's when I got confused. I was wondering if a road bike is sized differently from my hybrid. At bikesdirect they have a chart for bike sizes and a 44cm is an xsmall for someone who stands 4' 11" to 5' 3". I'm 5' 9". My legs are maybe a little shorter than average but they aren't that short. the 54cm on the bikesdirect chart is for guys 5' 10" to 6'.

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#2
Your Trek has a sloping top tube whereas a standard road bike obviously has a horizontal one.
Normal road bikes are measured from the centre of the bottom bracket to the top of the top tube where it meets the seat tube.

See Sheldon browns explanation:
http://www.sheldonbrown.com/frame-sizing.html

A nominal starting point is 10 inches less than your inside leg measurement. Stand barefoot and measure tightly to your crotch - 10". Obviously with a sloping top tube this has to be taken into consideration so your LBS would not be far out at 54cm.

More important though is the reach to the handlebars and you really have to take this into consideration when sizing a bike. I would advise you to check out your existing bike and/or try others for reach. Reach can be slightly accommodated for by altering the handlebar stem length and also by the type of bars you have. (drop bars can help as you can hold the "tops" or "hoods" or down on the drops.

If you go for a sloping top tube then you will need a longish seat stem but this does help if you have short legs compared with a long body.

You can lower the saddle but get a "long" top tube to suit your body / arms.

Here are 2 more sizing articles - use which one suits.
http://www.peterwhitecycles.com/fitting.htm
http://www.rivbike.com/article/bike_fit/...

Hope this helps and hasn't confused you to much.
[font=Trebuchet MS]Ride hard or ride home alone![/font]
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#3
I found this site a while back as well. You will need a friend to make all these measurements, but it will give you a good idea of what size you need. http://www.competitivecyclist.com/...FIT_CALCULATOR_INTRO

Another thing I would consider doing is talking to bikesdirect.com or any other online store to get a measurement of at least the standing height (floor to the top of top tube). As you may have read in the sheldon brown site, the sizing for different brands can be different. And, geometry of the angle of seat post can also decide how high the top bar. In other words, the closer the seat post is to 90 degrees, the higher the top bar is going to be.

And, finally road bikes are generally taller than mountain and hybrid style bikes. Mountain bikes allowed for more room between the tender parts and top tube because they are often taken off road and there needs to be more leeway.

Hope this helps and good luck finding the right bike.
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