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I purchased a hardly used road bike someone else had built up for a deal a few weeks ago, and am a bit disappointed with the fit - it's fine for rides less than a couple hours, but too aggressive for anything longer, for my tastes. In particular, the problem is that my saddle is about an inch and a half above my handlebars, even after inverting the 6 degree, 75mm stem that is installed currently.

So I purchased a 40 degree, 120mm stem to try and get the handlebars as high up as possible. However, I'm now a bit worried that having the handlebars so far from the steerer tube, which is carbon, will offer too much leverage and may cause the steerer to catastrophically fail when, for example, I ride out of the saddle.

Does this seem safe? Are there any guidelines for how long and steep a stem can be for safe use with a carbon steerer?

For what it's worth, I'm about 145 lbs and the fork is an Enve Road Fork 2.0.

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  • I have never heard of limitations on the steam size, and since you're not heavy you're probably good. One thing you can try is contacting the manufacturer.
    – super
    Commented Jun 16, 2015 at 2:14
  • I agree with @Super. Although 120mm is on the longer end of commonly available stems, the fact that it will make you much less hunched over the bars means that you'll probably have less force on the steerer than you would in the original configuration. Also, the "normal force" would probably be about the same because of the large angle.
    – Kibbee
    Commented Jun 16, 2015 at 13:58
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    I contacted Enve and they said it'd be safe. Thanks for the advice!
    – Tyler J
    Commented Jun 17, 2015 at 5:17

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Within "normal" standards of long and high angle, yes it is safe.

While there are some stems which use clamping styles which are not carbon safe, or other restrictions, these are usually clearly stated.

No restrictions are based on length or angle of the stem, that I am aware of. I have been a certified professional bicycle mechanic for 20 years, so I would think I'd have seen it by now, if it were an issue. :)

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Not a problem. However, do note carbon steerer needs support from the inside to clamp a stem on the outside. So adjusting stem height could lead to problems unless the new height has sufficient support on the inside.

But the leverage wouldn't be changed much assuming the stem length is normal. A 120mm stem is a 120mm stem, no matter what the angle is. A 120mm stem gives somewhat more leverage than a 75mm stem, but note that part of the leverage comes from the reach of the handlebars, so the proportional increase is not 120/75 but rather (120+reach)/(75+reach).

I would be worried only if you have something like a 300mm stem, which you obviously can't buy anywhere.

Usually when you raise handlebars, you want to move them closer to the saddle too, so I would have started my tests from maybe a 90mm 40deg stem or a 100mm 40deg stem. 120mm 40deg stem sounds like too long, unless the 75mm stem not only put the handlebars to a too low position, but also too close to the saddle.

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    I would assume that the most problematic lever is actually the distance between your hand and the steerer tube. This is barely influenced by stem length or angle and mostly dictated by handlebar width. When you sprint out of the saddle one hand is pushing down with full force, one is pulling up full force, all with a direction change about once every second. When you brake or hit a pothole the forces on the bearing interfaces are probably also greater than what the stem interface ever sees.
    – Michael
    Commented Sep 28 at 19:42

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