# Bicycle Mechanics - Help Needed With Stem Math

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View Full Version : Help Needed With Stem Math

BillyBob
02-21-05, 11:21 AM
After much research into the night, I want to run my calculations past some people with math and mechanical skills which I lack.

I am attempting to raise my handlebars. I have been trying to calculate the effect of increasing the angle on the rise and reach of the handle bars.

Current stem is -6 degrees and a length of 110mm. I calculate a rise of -11.5 mm and a reach of 109.4 mm.

If I were to acquire a +17 degree stem at a length of 110mm. I calculate the rise would be 32.2 and the reach would be 105.2 mm.

Changing from the -6 degree stem to a 17 degree stem of the same length, I figure that my handle bars would be 43.7 mm higher and 4.2 mm closer.

Am I correct?

moxfyre
02-21-05, 11:24 AM
Yep, I ran the numbers through my calc. Looks like you've got your trig right.

531Aussie
02-21-05, 11:30 AM
I don't know the maths, but when I'm comparing bikes, I measure reach from the middle of the handle bars to either the tip of the seat or a spot on the seat post. It's obviously not like using a theodolite. but I get a good idea.

When comparing bar height form bike to bike, I get a rough straight line from the top of the bars to the middle of the fork steerer, then measure this point to the bottom of the steerer. This way you don't have to subtract head-tube length, head-set stack height, spacers and stem height.

moxfyre
02-21-05, 11:35 AM
I don't know the maths, but when I'm comparing bikes, I measure reach from the middle of the handle bars to either the tip of the seat or a spot on the seat post. It's obviously not like using a theodolite. but I get a good idea.

When comparing bar height form bike to bike, I get a rough straight line form the top of the bars to the middle of the fork steerer, then measure this point from the bottom of the steerer. This way you don't have to subtract head-tube length, head-set stack height, spacers and stem height.
I think he's considering swapping out his current stem, so he just wants to know how much of a difference it'll make by putting in a new stem.

BillyBob
02-21-05, 11:49 AM
Yep, I ran the numbers through my calc. Looks like you've got your trig right.

Thanks. I had to put myself through a Trig refresher course last night!

BillyBob
02-21-05, 11:52 AM
Thanks 531Aussie. This information will come in quite handy for my another project that I am looking at.