BILL BOSTON CYCLES

Top Tube Height
Home Up Feedback Contents Search Links

 

Up

Crotch Clearance

For most bicycles used for road riding (and track as well). The top tube height should be high enough to provide between 3/8 of an inch and 1 inch of clearance to your crotch in bare feet. Now you might say that 3/8 inch is not near enough and for some that may be true. For most of us however 3/8 inch is fine for several reasons

You will be wearing shoes.

You will seldom if ever have both feet on the ground at the same time while riding. If you do, you are not riding, but just holding up your bike while asking for directions or reading a map.

When you are standing over your bike with one foot on a pedal, your pelvis will be rotated and the clearance will be increased substantially.

How Top Tube Height affects overall frame design and fit

As top tubes on most road bikes are or should be horizontal, the top tube height effectively sets the handlebar position in the vertical plane.

With the old style quill type handlebar stems, the handlebars can be positioned between 3 and 4 inches above the top tube.

The new style handlebar stems provide about the same range with the top of the handlebars at about 3 inches above the top tube when they are mounted horizontal and about 4 inches when reversed. This of course will vary with the length of the stem with shorter stems providing less rise and longer stems giving more rise. It should be noted here that unlike the quill type stem that provides a range of heights between 3 and 4 inches, the new style provides either 3 or about 4 inches though some adjustability can be achieved by using spacers provided the steering tube has not been shortened.

As you can see, any change in top tube height will affect the difference in height between the handle bars and saddle as the saddle position is determined by leg length and crank length.

Higher top tube heights will provide a more upright riding position and allow a longer top tube length / stem combination.

Lower top tube heights will provide a lower shoulder position relative to the saddle and require a shorter top tube length / stem combination.

As long as the top tube height is high enough to provide crotch clearance in the 3/8 to one inch range, stem height and length can be varied to compensate.

Crotch clearance greater than one inch will have an adverse affect on riding position and top tube length.

      Things to watch out for!

If you see a road bicycle with a sloping top tube, ask yourself, " What was the manufacturer trying to do?" If it is a bike in a smaller size, and the obvious answer is to provide a lower stand over height, BEWARE. The minimum top tube height with 700c wheels is 30 inches above the ground while maintaining an adequate head tube length to support the fork and head bearings. It is possible to reduce the stand-over height by several inches by sloping the top tube, in most cases the top tube will still be too long, or the the head tube angle will have been reduced severely to provide adequate front wheel clearance when the top tube was shortened (see AccuTrax to find out more about this). To better understand building bikes to fit riders instead of a standard components, see Those Bikes with Small Front Wheels.

Crank Length

 

 

Back ] Home ] Up ] Next ] 

Copyright 2003 BILL BOSTON CYCLES
Last modified: July 09, 2014