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Theoretically, is the 90 degree stem the stiffest design?(8 posts)

Theoretically, is the 90 degree stem the stiffest design?Fez
Mar 20, 2003 8:12 AM
Why is the standard stem angle 80 degrees? I can understand the quill angle of 73, since it makes it parallel to the ground, but wouldn't 90 degrees for threadless be ideal?

For a given handlebar position, the 90 degree stem allows for the least amount of stem length (less length = stiffer).

Also, since 90 degree would be perpendicular to the steer tube and has no bends, wouldn't it also be stiffer since it is straight? Or does it not matter because most creaks are at the contact points such as the faceplate and bars?
My Two Centssievers11
Mar 20, 2003 8:36 AM
This is a guess...

It would matter on which way the stiffness is being tested. If vertical up and down are being tested, then yes 90 would be...but if just up then a negative degree would be stiffer and visa versa.
80 degree is more versatileNessism
Mar 20, 2003 8:58 AM
80 degree is more versatile than 90 degree since it can be flip floped go give a little rise. This is why most stems have printing on both sides.

As far as stiffness is concern, I think the 90 would be stiffer but not enough to matter.

Ed
Versatile? Maybe on a bike with many ridersFez
Mar 20, 2003 9:10 AM
I agree with you that the 80/100 has a broader market since it can be sold to more different customers (those needing 80 and those needing 100).

But once a person buys it (assuming 80degrees), he is probably not flipping it on his own bike, barring a severe change in fitness or an injury. The difference is just too severe at 3cm +/- or so. You could better fine tune your position by leaving a few extra spacers on the tube.
angle has nothing to do with stiffness....C-40
Mar 20, 2003 9:27 AM
The stem angle is strictly for bar height positioning. An 80 or 84 degree stem helps to make up for the loss of stack height with the threadless headset.

A 90 degree stem is also not the shortest for a given reach, since reach is measured horizontally. A 73 degree stem is the shortest for a given reach.

A stem with any angle greater than 73 degrees will have a shorter reach than the advertised length, since the length is measured parallel to the extension, not horizontally. The reach is the advertised length times the cosine of the angle from the horizontal. For example, a 110mm 84 degree stem will have a horizontal reach of 110 x cos(84-73) = 108mm.
Confusion with the terminologyFez
Mar 20, 2003 9:47 AM
I think we are thinking about different things.

I said that for a given handlebar position (assume 73 degree head tube angle and also assume we make custom stems for this application), the one that is 90 degrees will be slightly lower on the steer tube and will also have less metal length than the one that is 73 degrees, which will be higher on the steer tube. If you hypothetically installed both stems on the steer tube, they would form a right triangle and a^2 + b^2 = c^2 would confirm that the 73 degree stem would be longer in length.
I understand....C-40
Mar 20, 2003 12:46 PM
Yes, you're right, IF you can get the bars low enough with a 90 degree stem.

For example, a 105mm stem placed 32mm lower on the steering tube would provide the same reach and height as a 110mm, 73 degree stem. This is less than 5 percent shorter and insignificant when you consider that stems are offered in lengths ranging from 80 to 140mm, usually without a change in the diameter or wall thickness to increase stiffness.

Using a 90 degree stem with an average 110mm length raises the bars by almost 2cm, compared to an 80 degree stem. Some riders would would find this too high even with no steering tube spacers. I use an 84 degree with no spacers myself.
Probably, but probably not in the way you are thinking...timfire
Mar 20, 2003 11:33 AM
First on the practical side, when talking about stock stems and not custom stems; since stems are measured center-to-center, angle has nothing to do with length. Thus your idea about a 90 degree stem being "shorter," wouldn't really be true.

Second, before you can talk stiffness, you must figure out the angle that the stem will be bent in. Why? Because I believe that stiffness is only important in relationship to the angle of stress, not in relationship to the bike. I believe that a stem will be "stiffest" or strongest along its length, because in that direction it has the most material. It will then be weakest perpendicular to its length. (Try compressing a twig along its length. Not much happens. Then try and bend it, and see how easy it is.)

I don't know the exact angle that a stem is stressed. If the stress is straight up and down, then a more vertical stem will be stiffer then a horizontal one. But if the stress was up and back, like when you're pulling on the bars in a sprint, a stem with an angle might be stiffer then a 90 degree one (depending upon the angle).

But finally third (and this was probably what you were thinking). In realty, a stem that has rise to it with no spacers will probably be stiffer than a horizontal stem with spacers. That would be because the length of the rise-stem would be shorter than the length of the horizontal-stem + the length of spacers. In that case the stem with rise would have a shorter length of material to flex.

--Tim Kleinert