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Somewhat hardcore math question RE: stem angle/reach(25 posts)

Somewhat hardcore math question RE: stem angle/reachfloatch
Apr 22, 2002 8:43 AM
I've recently acquired a roadbike, and the bars are too low for me. My seat is about four inches higher than the bars!I'd like to get new stem to raise my bars, but have some questions first.
First of all, I have a 7 degree rise 80mm stem on my bike now (it's angled slightly up). I'd like to raise my bars about two inches, by using a new stem. The reach on my stem is good, but I'm wondering what length and rise stem I will need to raise my bars about two inches, but keep the current reach.
I see salsa offers their SUL stems in 105 and 115 degree rises, which I assume is another way of saying 15 or 25 degrees above 90, or no rise at all. Am I right? If so, which stem angle and length would I need to raise my bars about two inches, but keep the same reach? I realize this is a pretty difficult question to answer, so if you need any additional info, I'd be happy to supply you guys (and girls!). Thanks so much for your time!
re: Somewhat hardcore math question RE: stem angle/reachBecky
Apr 22, 2002 8:56 AM
what's the current rise from the point where the stem clamps to the steerer and the point where it clamps to the handlebar? i'm thinking that this is a trig question....
I'm not sure trigonometry is involved, but...floatch
Apr 22, 2002 9:13 AM
My headtube's angle is 72.5 degrees. My stem has a 7 degree rise, that is to say 7 degrees up from no rise at all. The stem is 80mm long. The stem is pointing up, not down, so the bars are currently at their highest point.
Quill or ahead style? (nm)Nessism
Apr 22, 2002 9:18 AM
Sorry- it's threadless, and spaced as high as the fork allows-nmfloatch
Apr 22, 2002 9:41 AM
the answerjim hubbard
Apr 22, 2002 7:53 PM
you want a 118° rise stem, this allows you the 8cm length
re: Somewhat hardcore math question RE: stem angle/reachGalibier
Apr 22, 2002 9:49 AM
You should check with a local bike shop. You are mostly guessing on your reach and bar height -- but that's OK because formulas can't tell you what is comfortable. In your case, raising the handlebar height effectively decreases the reach, so you would want a longer stem to compensate. (I still say an 80mm stem is really short, especially since you feel your frame is too small.) If you go to an LBS, they might let you try different stems to see what ends up working best for you. On my current bike, I went through four different stems before I found the setup that works best for me. My LBS let me swap out the stems until I settled on what I wanted. Just use stems with removable face plates so changing them out is easy.
Not many LBS's have 15+ degree rise stems laying around...floatch
Apr 22, 2002 9:58 AM
I'd love to be able to do this, but not too many shops stock goofy high-rise road stems. That's why I figured I'd take the math route. It'd be good if someone around here had one of those adjustable angle/length stems I could use to measure. I'm thinking a 25 degree 90mm might fit my needs, however.
Another questionNessism
Apr 22, 2002 10:12 AM
Could you please give me some more information regarding your current stem? Is the 7 degrees up as noted relative to the horizon or is is 7 degrees up relative to 90?

Some manufactuers call a 90 degree stem a 0 degree.
Ah, it could be called a 97 degree.floatch
Apr 22, 2002 10:26 AM
Assuming a 90 degree and 0 degree stem both leave the steerer tube perpendicularly, my stem has a 7 degree rise, pointing up. 7 degrees is NOT relative to the horizon, but to the steerer tube.
some shopsSteveO
Apr 22, 2002 12:15 PM
actually have an 'adjustable' stem you can borrow for a month-or-so, so youre no swapping stems every saturday morning.. came in real handy for my first setup.
I'll take a quick shot at it.Quack
Apr 22, 2002 10:01 AM
Knowing that your 7 degree stem is a rise and that your stem is 80mm long, to raise 2 inches and leave your bars in the same position relative to the seatpost, you would need about a 37 degree rise stem and a 100mm stem length. If the current reach is good but too low, you probably want to get a little less of a rise and a longer stem as your reach will get shorter as the bars come up. Maybe a 30-35 degree 110mm or something close. Good luck.
You are right assuming stem= 7 degrees above parrallel to groundBDBike
Apr 22, 2002 10:24 AM
Here is how:
sin 7 * stem length = 9.7mm rise
cos 7 * Stem length = 79.4 mm effective length
to raise 2" = 50.8 mm
so 50.8mm + 9.7mm is the height you want
so the Inverse tnagent of some angle = (50.8+9.7)/79.4
witch = 37 degrees.
(50.8mm+9.7mm)/sin 37 = 100mm

your stem should be 37 degree rise over parrallel to ground and 100mm Length.
Yowza! That's some pretty heavy mathematics! -Question...floatch
Apr 22, 2002 10:33 AM
I understand what you've done so far, I think. If my bike is built with a 72.5 degree head tube angle, what stem angle should I order? Length?
Wait! My stem's 7deg rise is versus the steerer, not the ground!floatch
Apr 22, 2002 10:34 AM
My guessNessism
Apr 22, 2002 10:48 AM
First off we are saying that 90 degrees = 0 degrees depending on how the stem is measured. This means the stem comes out at a right angle to the steerer tube.

Given that your current stem is 97 (or +7) degrees and 80 mm reach, you will need approximately 110 mm reach and 120 (or +30) degrees depending on how the stem is measured.

I suggest you get a protractor and metric ruler then make a full size drawing. Very simple to do.

Ed
Okay...In that case, any good online retailers for custom stems?floatch
Apr 22, 2002 11:01 AM
I've checked around, and found no online sources of custom length/reach stems. Any suggestions?
Custom welded stem, new frame, new fork???Quack
Apr 22, 2002 12:21 PM
I also checked around and saw nothing over 15 degrees. A 30+ degree stem could be custom made by a welder if you provided them with a super long neck to work with. However, it would probably look like a mid 80s mountain bike setup and be silly on a road racer. A new fork with super long steerer and 4" of spacers would look equally silly. So I guess a larger frame would be the best but most expensive solution.
Bars still 4" lower?elviento
Apr 22, 2002 1:11 PM
If the bars are still 4" lower than seat given the 97 degree rise stem and already as many spacers as allowed, I'd say either the frame is way way too small or you have very unconventional body proportions. Or even both.
A couple of ideasNessism
Apr 22, 2002 12:39 PM
Steelman and Brew make custom stems but they are not cheap. No doubt many other custom frame builders will TIG something together also.

Another option is to use a mountain bike stem and get some matching 25.4 mm bars. This will be the cheapest solution.

Check out the following links.

Dimension stem - $22
http://www.bikeusa.com/components/stems/stems2.htm
http://www.bikeusa.com/components/stems/images/SM4555.jpg

Bontrager 25.4 mm bars - $31
http://www.bikeusa.com/components/handlebars/handlebars3.htm
been theretarwheel
Apr 22, 2002 12:47 PM
Floatch, I was in the same situation a year ago. You've got some options, but it might be more expensive than you realize. The biggest rise that I have found for a threadless road stem is the Salsa SUL 105. The SUL/105 in a 10 cm stem will provide about the same amount of reach and 5.5 cm (2 inches) of rise compared to a 73 degree 8 cm stem. A SUL/90 in 9 cm will provide you slightly more reach and 2.5 cm (1 inch) of rise compared to a 73 degree 8 cm stem.

Stem geometry can be confusing because when people say 0 rise they might be referring to a 90 or 73 degree stem. Here's why. A 73 degree stem will give you a stem upper surface that is approximately parallel to the top tube on your bike, so some people call that zero. Others call a 90-degree stem a zero because it's at right angles to the steerer tube. Go to this website for a good chart explaining all the angles (and where I calculated the numbers above) -- www.habcycles.com/fitting.html

If the Salsa 105 doesn't provide you with enough rise, you've got several options:
-- Buy a new fork with an uncut steerer tube that is long enough to accommodate more spacers between your headset and stem, thus providing more height. You'd probably need a fork with a steel, aluminum or ti steerer rather than carbon because carbon forks are not supposed to have a lot of spacers used.
-- Buy a Look Ergostem, which is adjustable for both rise and reach. These cost about $180 new, but you can sometimes find them for sale on eBay or roadbikereview classifieds.
-- Get a "stem riser" made by Zoom and others, if you can find one to fit. For some reason, they only seem to make these for 1-1/8 stems, but not 1".

Good luck. In my case I ended up buying a new frame because I didn't want to spend $250 on a new fork for a frame that didn't really fit me right to begin with. I had the steerer tube left uncut, and set up the bike with a Salsa SUL 105 stem with about 4-5 cm of spacers. It's not the most aero bike, but it fits me. Not everyone can ride with a large amount of drop to the bars.
Best Advicegrzy
Apr 22, 2002 1:43 PM
Your advice to buy a frame that better fits your body is right on. Ttrying to "make" the wrong frame fit is ultimately an expensive and frustrating experience. You can get all funky with stems and spacers and never get away from the fundamental problem that the frame isn't sized correctly for you. Not everyone has the flexibility and pain threshold of a 20 year old promissing racer.
http://www.habcycles.com/fitting.html (nt)MGS
Apr 22, 2002 5:35 PM
NT
easy question....C-40
Apr 22, 2002 5:49 PM
Really basic math for us engineers, but your description is confusing. There is no decent standard regarding the term "rise". The MTB crowd takes it to mean the number of degrees from perpendicular to the steering tube. To me, it should be the angle with the ground. I take it that you're using the MTB definition, so you have a 97 degree stem.

Take a look at the chart on this site, it should help. http://www.habcycles.com/fitting.html

The problem with stock road stems, is that they come in only a few angles. 80 degree is the most common. An 80 degree stem can be flipped to 100 degrees, which won't help much. A few come in 73 degree angles that can be flipped to 107 degrees.

Also keep in mind that you will need a longer stem, as you increase the angle.

It sounds like you may have bought a frame that is too small (head tube too short). A properly sized road frame will not have a 4 inch distance from the saddle to the bars with spacers under the stem and a substantial angle to the stem. A 4 inch distance from the saddle to the top of the bars is quite common on roads bikes. Mine has that much distance, but with a standard 80 degree stem, and no spacers.
Protractor, Ruler, Paper and pencilBigRingKing
Apr 22, 2002 7:13 PM
is all you need.

Draw a line on some paper. Mark a point. Use this point for the protractor. Draw a line through various lengths and angles to determine the required stem length and rise.

Gary.