Stem Length?

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Donald in South Africa has a frame dimension question. He wants to know if it is better to adjust stem length as opposed to top tube or head tube lengths? This is a frame dimension and position problem and this is what we think



Question:

Is it better to adjust stem length versus top tube length and head tube length?

Hi Donald.

Yes, the stem length is the easiest way to make a bike fit your body, this is quite normal, the same as saddle height and stem height. The frame designer/builder will design and build the frame so that it will perform well when climbing, descending, sprinting etc. The performance of the frame all dependent on the frame angles, tube length and dimensions and have to be within certain parameters or the bike will just not ride well.

If you are having a frame built to your measurements you still need to make adjustments to your position with stem length/height and saddle position, to make everything perfect. This is the same as buying a stock frame off the peg that will be designed to function properly and fit a few different body sizes.

Many factory made frames are now made in small, medium and large and fit many different body sizes and shapes. Previously frames were sold with 1 centimetre or half inch size differences measured seat tubes with top tube lengths to match. This gave you a small frame with about the same seat tube as top tube (19 inch seat tube with 19 inch top tube), then as the seat tube gets longer the top tube will shorten to match (26 inch seat tube with a 24,5 inch top tube).
specialized
Sloping TT
Now with the new frame designers, instead of having nearly 20 different frame sizes, a shop only has to stock three main sizes and at the most five different frame sizes. Then with the stem length and the saddle adjustments, and sometimes crank length, you can fit anybody to a perfectly proportioned and performing frame.
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Stems come in many lengths from 8 centimetres to 14 centimetres in 5 millimetre increments and with different angles, if the stem is an Ahead stem then it can be turned over the other way which gives you two angles with every stem, level or with a rise.

Level TT
You must remember to set-up the bike so that your legs are positioned properly with your knee over the pedal when the cranks are horizontal and that the height of the saddle is correct with a slight flex in the knee when the pedal is at the bottom of its stroke. From then you can work out your stem length for your best comfort and power out-put. Getting measured properly for a bike is a very good idea and usually the cost is refundable when you buy the bike.
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2 Comments

  1. old iron rider

    very little stem adj. should be needed IF the frame is close to being correct. In the real world we pick up bikes that don’t quite fit. In that case the only option is the stem and seat position.

  2. Gabriel Enahoro

    I’m a big guy at 6’3″ and 100kgs. I ride a Ridley with a level TT and an effective TT length of 59cm.

    I started off with a 110 stem and it was too short. I then switched to a 120 and it was almost there. I flipped the 120 stem over and it’s perfect. I had to tweak the saddle position a little as well.

    Youmight have to make all these minot adjustments to get what feels right and treats your body correctly.

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