Bicycle Mechanics - how do you measure stem length?

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Bolo Grubb
10-29-07, 07:16 PM
Is it from the center of the fork clamp to the center of the bar clamp? Does the rise angle affect the length?

I am trying to update an older bike and bought a threaded fork adapter so I could use an old stem that I that I have. Turns out that old stem has a 1" fork clamp and the stem adapter has a 1 1/8" clamp area.

So I either need to get a new adapter or a new stem. But I am not sure what the length of the old stem is so not sure what to order for a new stem.

Ingleside
10-29-07, 07:21 PM
center of the steer tube to the center of the handlebar
jwa
10-29-07, 08:14 PM
center of the steer tube to the center of the handlebar

Yup.
http://www.cyclingnews.com/tech/fix/?id=roadposition

Bolo Grubb
10-29-07, 08:17 PM
thanks guys
sivat
10-29-07, 10:18 PM
And for the second part of your question, the angle will affect the effective length of the stem (i.e. how far the bars are from you) but it will not affect the measurement.
Bolo Grubb
10-30-07, 07:59 AM
perfect. Thanks Sivat.
Scooper
10-30-07, 08:58 AM
Not to be picky, but the dimension from the stem longitudinal centerline to the center of the handlebar is called the stem extension, not length. The angle will affect the reach and the rise.

http://i32.photobucket.com/albums/d7/k4drd/Bicycles/MeasuringaStem.jpg
Bolo Grubb
10-30-07, 10:50 AM
That graph is very helpful to my understanding. Thank you very much.

Now I need to read up on how to do the actual mechanic work ;)
jwa
10-30-07, 09:17 PM
http://i32.photobucket.com/albums/d7/k4drd/Bicycles/MeasuringaStem.jpg

Hey Scooper -

Is the QBP catalog from which this is clipped available online?

Thanks!
Scooper
10-30-07, 09:56 PM
Hey Scooper -

Is the QBP catalog from which this is clipped available online?

Thanks!
Sorry, I dunno. I scanned it from a hardcopy.
JiveTurkey
10-30-07, 11:43 PM
Use some basic geometry to measure the effective length.

You can use: http://www.carbidedepot.com/formulas-trigright.asp

Angle A = (90 - HT angle) + stem rise [for example, for a standard 73-degree head tube, a 10-degree rise stem would be a 27, flipped over at a negative 10 degree rise it would be a 7]
Side C = stem extension

Calculate...Side b will be the effective length coming straight out from the steerer tube parallel to the ground.

I use this site to figure which stem I need to change the effective length and height of the handlebars with a new stem. If you run the geometries of two stems, you can see the difference in both reach (side b) and height (side a).