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Top Tube Fit(3 posts)

Top Tube Fitboat
Apr 29, 2003 6:35 PM
One question about top tube fitting: What kind of stem lenght used would you consider that the top tube of the bike fit? In the past, somebody used to tell me that if you are only using 110mm stem, then the bike top tube length fits you. However, I have seen the pros using stems as long as 130 or even 140mm. So what exactly is the right length? Is 100mm too short, and does that mean that the top tube length of the bike is too long?
bah. look at a cm. it ain't that much -- particularly in thatbill
Apr 30, 2003 9:00 AM
dimension. A cm difference in your saddle height can be huge, but I'll bet that riding conditions, muscle soreness, all sorts of variables account for a greater range of difference in the normal riding position than 1 cm either way of effective length of your reach (saddle setback + top tube + stem). A shorter stem is supposed to be less stable than a longer stem (compare the circumference of a smaller arc vs. a larger arc -- in the smaller arc, a smaller difference in degrees of rotation will cause an outsized effect in turning the steerer compared to the larger arc -- the lever effect). At a certain point the longer stem is supposed to require too much turning, so that the bike will handle sluggishly, the smaller, too little, so that the bike will be twitchy.
I've always heard that 110 was considered ideal, too, but a cm or two in either direction is just not going to be a very big deal. So, a 100 mm stem is well within acceptable. I think most people would say that 90 to 120 or even 130 is fine. I think that pros may use longer stems to get on even smaller frames and, let's face it, you don't do a whole lot of turning at speed in a road race with your handlebars.
depends on frame size...C-40
Apr 30, 2003 9:38 AM
Generally, the larger the frame the longer the "normal" stem length, but there are no hard rules for stem length.

I'ved used a 110mm stem on most of the 54cm frames that I've owned, but I recently started experimenting with my position by moving the saddle back 1cm. Had to shorten the stem to 100mm to retain the same reach.

I have noticed that my knee can come pretty close to the bars when climbing out of the saddle with the shorter stem. If I used a 90mm, I might touch occasionally.

As far as steering quickness is concerned it's easy to prove that the steering quickness is only increased by 15% when a stem is shortened from 120 to 60mm. The quickness will only be felt at very low speeds. At normal riding speeds, turning is done primarily by leaning into the turn, not turning the fork.

You will also find that it's rare for stock frames to vary much more than 1cm in top tube length for a given size. No matter what you buy, the required stem length is unlikely to change by more than 1cm.