# Bicycle Mechanics - More rise = more length?

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View Full Version : More rise = more length?

SaiKaiTai
04-20-07, 11:40 PM
I find that, while the rest of the fit is fine, I have to "reach" for the grips more than I'd like and I don't feel like I have enough bend in my elbows.
I have a 60mm 10 degree stem on it now and think more rise is what I need.

I can't go shorter than 60mm and I have a choice between 17 and 25 degree stems.

So... Of the two, I think 25 degrees is a pretty radical change... a 12 degrees change? Wow. Sounds like a lot. Going from a 10 to a 17 sounds like the way to go to me.

Now, I know more rise means less effective length.
Should I compensate for that by going with -maybe- a 70mm? or an 80mm?
And if I should, doesn't that mean I'm reaching again?

Physics wasn't my best subject... help? I think I'm over analyzing this.

Tapeworm21
04-21-07, 12:11 AM
Just to kick this thread off.... how tall are you and what size frame are you riding? Bike style?

Rincewind8
04-21-07, 12:18 AM
For the effective/horizontal stem length:

a=b*sin(t-s)

where:
a: effective/horizontal stem length in unit lengths
b: actual stem length in unit lengths
s: stem angle in degree (where s > 0 if the stem is installed so it increases the rise)
t: head tube angle in degree

cs1
04-21-07, 03:16 AM
Not having seen you on the bike or knowing your size, I'm going to take an educated guess on the problem. If you can't bend your arms with a 6cm stem then you have an incredibly short torso or your TT length is way too long. It really sounds more like the frame size is wrong. Let us know the specifics. Good luck

Tim

rm -rf
04-21-07, 05:43 AM
The Habanero Cycles stem chart (http://www.habcycles.com/fitting.html) shows the changes with different angles and lengths. It looks like a 60mm 25 degree stem would raise it about 15mm and back about 5mm. A 17 degree stem would raise it around 8mm and back about 3mm. Since the stem is short, the different angles don't move the bars very much.

Can you tape something to the bars to simulate the change in height and reach, to see if it makes a difference?

I went from a 100mm 10 degree to a 90mm 7 degree and it made a big difference in reach to me. The change was only about 4mm down and 8mm back.

Retro Grouch
04-21-07, 06:05 AM
I wouldn't go overboard adding stem length. While it's certainly true that raising the handlebars will also bring them closer to the saddle, you also have to consider what's happening with your body angles.

As you raise the bars, you also straighten the angle of your torso at the hips. That moves your shoulders back so you'll probably want your handlebars a little farther back also.

HillRider
04-21-07, 06:52 AM
I calculated the differences assuming a 73° headtube angle. Your current 60 mm, 10° stem has a reach of 53.8 mm and a height of 27.2 mm.

A 60 mm, 17° stem would reduce the reach by 4 mm and increase the height by 6 mm. A 70 mm, 17° stem would increase the reach by 4 mm and the height by 11 mm.

A 60 mm, 25° stem would reduce your reach by 9 mm and increase the height by 13 mm. A 70 mm, 25° stem would actually reduce your reach by 2 mm and increase the height by almost 20 mm. An 80 mm, 25° stem would increase the reach by 5 mm and the height by 26 mm.

Portis
04-21-07, 07:25 AM
Seems pretty crazy for people to be giving advice when we don't even know the most basic detail, is this a comfort bike? A trike? Or what?

HillRider
04-21-07, 08:39 AM
Seems pretty crazy for people to be giving advice when we don't even know the most basic detail, is this a comfort bike? A trike? Or what?

We know he requested information on how much difference in reach and height a greater angle and/or longer stem would make. He got that. I didn't need his family history or anything else to answer that particular question.

Retro Grouch
04-21-07, 08:48 AM
Seems pretty crazy for people to be giving advice when we don't even know the most basic detail, is this a comfort bike? A trike? Or what?