Originally Posted by
mornview
My main bike is an 80's Concord New Yorker. I'm 5'8, with a 30.5" inseam. The bike's seat tube and top tube are both 21.5", with a 30.5" standover height. The bike fits me fine; the frame is basically an exact replica of the old diamond-frame English 3-Speeds (Raleigh, Phillips, etc.). It has ISO 590 wheels (same thing as 650A), so they're bigger than standard 26" MTB wheels, but smaller than 700c road bike wheels.
The thing is, I have developed a slight obsession with this brand. I got this bike for $25 and it has blown away anything else I've gotten my hands on. Through doing some research I've discovered that Concord made a few other models in the 80's, including a hardtail MTB and a few 700c Road bikes. I'd like to get my hands on both of these, but obviously I'll likely have to resort to something like Ebay, where I'll have no way of trying before buying.
Unfortunately, I don't have much experience with either of these two styles of frames. And what's more, I realize bike geometry has changed during the last few decades, so just because I can go to the LBS and find something that fits me, doesn't necessarily mean it'll hold true for an 80's bike. However, I'm just looking for a few GENERAL rules here.
It seems to me that since a MTB has smaller wheels than my New Yorker, I'd want a slightly larger frame to compensate for it, correct? I know that when I ride beach cruisers, which have standard 26" wheels and always seem to come in 18" frames, things always feel a little cramped compared to my Concord.
And would it be the opposite for the road bike? Because the road bike has larger wheels, if I didn't choose a smaller size frame, wouldn't the standover suddenly be too high? (as it is on the New Yorker I have 0 - .5 inches of clearance).
Thanks in advance, like I said, I'm very eager to build my stable of Concord's
!
I think one general rule is, standover doesn't matter while riding, and it doesn't matter at all unless you don't have enough clearance. It's not really viable any more as a central sizing criterion, but everyone needs some clearance, and many people are anxious if they don't have at least an inch.
If you are going to compare across styles, keep in mind the effect of riding position. On a 3-speed you are nearly upright, with a little forward lean of your back to reach the bars. The bars are generally placed closer to the saddle - old Brit 3-speeds had stems with nearly zero extension and handlebars with the grips not forward by much (the North Road style).
For better aerodynamics and better use of the leg and arm muscles, road bikes with drop bars are made for a back angle more like 45 degrees plus or minus, and hence your hands need to be able to reach farther forward for comfort and control - the fitting has more reach. Hence the longer stems and even longer effective top tube dimensions.
The seat tube height in a vintage bike with a horizontal top tube really tends to set the position of the top of the head tube, or, the minimum height of the handlebar. People who are taller have longer legs, can handle a higher top tube with adequate standover clearance, and don't need the bars so low to get a comfortable and efficient back leaning angle.
Saddle height is set by the adjustable seat post, so seat tube length doesn't really figure into it. Leg extension is a critical parameter, but it's set by saddle positioning.
Wheel size is not really a part of it. For a smaller-wheeled bike the designers don't let the BB be as far below the axle as with larger wheels. And besides, smaller rims often take wider tires, for an overall height that is about the same overall.
General rules? I guess those might be some general knowledge that could be helpful.