Join Date: Mar 2012
Bikes: '09 Trek 2.1 * '75 Sekine * 2010 Raleigh Talus 8.0 * '90 Giant Mtb * Raleigh M20 * Fuji Nevada mtb
Short answer is frame size is always important, just not as super-critical for us casual riders. Get the better bike, that is more comfortable when you test ride it. Rough estimate is maybe 1 to 2 inches between your jewels and the top tube. Then also make sure that your torso is at a comfortable angle and you are not leaning on the bars. My guess would be 21 inch.
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Disclaimer: 99% of what I know about cycling I learned on BF. That would make, ummm, 1% experience. And a lot of posts.