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I heard somewhere (I don't remember where) once that a seat post clamp should be oriented with the gap at the front of the seat tube, opposite of the gap in the top of the seat tube. The logic behind this was that it supposedly exerts more equal pressure around the entire seatpost.

However, I've noticed that bikes off the rack are almost always sold the other way around, with the two gaps on top of each other.

Does it really matter? Is one way better than the other?

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Don't know that it matters much. Some bikes come with an integral clamp and it necessarily "faces backwards", since there's only one "gap". "Loose" clamps are usually oriented the same way, but probably as much for looks as anything. –  Daniel R Hicks Sep 26 '13 at 3:25
    
My current mountain frame has a pair of cut outs, what to do there, sideways? I prefer to have the clamp facing forwards as it keeps the threads a little cleaner. –  alex Sep 26 '13 at 5:32
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My mechanical intuition says you want the gaps lined up, but my common sense says unless you've got a $10K bike and you're competing professionally at world-class levels, it probably doesn't make one damn bit of difference. –  Carey Gregory Sep 26 '13 at 5:38
    
On my seat clamp, this moves the seat about 2 inches forward, so I prefer it, however, is there a geometric reason why the seat shouldn't be this far forward? –  JFA Jan 26 at 19:54
    
@JFA I think you're confusing the seat post clamp with the seat clamp. The seat post clamp, the clamp to which this question refers, is at the top of the seat tube and keeps the seat post from sliding down into the seat tube. –  jimirings Jan 27 at 0:49

4 Answers 4

up vote 4 down vote accepted

Typically, for an aluminum post you align the gaps. For a carbon post you turn the clamp 180 degrees from the gap in the seattube to minimize the chance of crimping the seatpost. Some manufacturers have their own recommendations, but they're typically in line with what the aforementioned guidelines.

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This makes sense. Just for the sake of completeness: what about steel or titanium? –  jimirings Sep 30 '13 at 21:46

My two cents:

If you align the gap in the tube with the gap in the clamp, the grip will be much stronger. You'll need less force in the lever to hold the seatpost in place.

If you keep them counter-aligned, you'll exert considerably less pressure, and there is a chance that the pressure will be "more evenly" distributed, although I don't "feel" it to be necessarily like this, since it is only the frame itself that actually deforms to grip the seatpost, and I think it tends do deform the same way on both cases (a lot of common-sense here, that would need experimental data to be totally sure).

My advice would be: use first option UNLESS you have reasons not to do so. Such reasons could be: sensitive seatpost (carbon fiber, delicate metals), or a tendency from the clamp to leave marks/grooves in the seatpost.

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According to a forumer working in bike building industry (SUNN, France), mounting the seat post clamp with its gap on top of the seat tube gap is important to ensure an equal and secure gripping.

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+1 In my experience, some clamps don't grip properly unless the gaps are lined up. The same is true of shims inside the seat tube. –  James Bradbury Sep 26 '13 at 7:45

Aligning the gaps will allow the clamp to compress the tube a little better, therefore reducing the amount of tension needed from the clamp to hold the seat post in. And less tension means a longer life for your seat post clamp.

Now, there's the issue of which way your clamp lever faces if you use a quick release clamp. Most have it facing backwards so it doesn't interfere with clothing and doesn't catch on anything while riding. But, with something this small and utilitarian, I think you can put it any way that keeps your seat post from falling and it's probably OK.

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