Originally Posted by
sean000
Of course geometry varies from one frame to the next, so you can't just look at the seat tube length. Since my last bike purchased was a Rivendell, I went with their recommendation: 58.5-60cm. I actually went a little on the low side since the Atlantis comes in 58cm or 61cm, but nothing in between. I bought the 58 and have plenty of clearance standing over the top tube, and I have a lot of seatpost and stem showing... so I could easily ride one of their larger frames.
Sean
I should also add that, as someone else pointed out, trends change. Since you've been riding as long as I have you probably remember how racing bike angles got steeper and chainstays got shorter as the 80s progressed. The recommended frame size was also getting smaller. My most extreme racing bike was a Sannino with 75 degree angles and chainstays so short I had to be careful about tire selection. After a season on that I wanted something a little more comfortable and the Pinarello was relatively slack with 74 degree angles and an extra centimeter on the stays. Still an aggressive bike by early 80s European road racing standards though.
Racing bike trends tend to trickle down to recreational models as well, so people generally started buying more aggressive bicycles with lower handlebars and no clearance for tires and fenders.
My first racing bike was a 1984/85 Trek 640 with a Reynolds 531 frame, slack angles, clearance for larger tires and fenders, and braze-ons for a rear rack. It was called a "Sport-Touring" bike by Trek, and some companies called them "Club Racing" bikes. I still recall it as one of the best bikes I've owned. It was stiff and responsive (okay...so maybe the bottom bracket flexed more than the Pinarello), but also very comfortable and versatile. This is the bike I fondly remember that drove me towards Rivendell (since their Rambouillet can be described as a sport-touring/club-racing frame). That and my fondness for lugged steel.
When I read Grant Petersen's advice on riding position and choosing a frame size, it really seemed to validate what I had been feeling for years. Fitting a racing bike is not the same as fitting a recreational bike, touring bike, commuter, mountain bike, etc. Opinions and trends still vary, so not everyone agrees with Grant; but his advice has helped me get more comfortable on a bicycle and enjoy riding as much as I ever have.
As far as the original question of how to size a commuter... generally I agree with the sentiment that ideally it should fit well without being too large or too small. However, fit does tend to be a range. Personally I would go with a size that is big enough to get the bars up to a comfortable level while still allowing a small amount of standover clearance and a comfortable reach. The trend for a racing bike, or even an aggressive mountain bike, is to have the bars set significantly lower than the saddle... making a smaller size frame more desirable. I don't think most people want low handlebars on a commuter, so when it comes down to two sizes that will work I would definitely go with the larger frame on the commuter.
Sean