Bicycle Mechanics - Saddle Constantly Tilting - indicative of poor frame fit?

Hi all,

Despite levelling my saddle (sometimes even using a level) and tightening the bolt, the saddle tilts to a nose-up position within one or two rides. I asked the LBS and showed the wrench my MTB. He said that the seat rails and seatpost clamp were bent (I'm not sure about that, but then I don't recall what they looked like previously!) and that replacing both would fix the problem. However, I am not sure this is the problem, as the same problem occurs on my road bike (see below.)

Could it be that my frames are too small (I suspect both are a bit) and thus my riding position forces the saddle to that position despite how tight it is? Or is my riding position just wonky and this will happen no matter what? Or is my LBS correct, and I just coincidentally have a bent saddle/seat post clamp on both bikes? Or is it something else entirely? I'd appreciate any thoughts you may have!

I should mention that I don't find this really uncomfortable, although I suspect it's because I'm used to it since I've given up on levelling the saddle every few rides!

As an example:
http://dmcope.freeshell.org/moulden_updated.jpg

A seat clamp in good repair should be able to hold your seat in any position you wish. If you want it level, it should not be drifting at all unless you are smashing your whole weight down on it with a violent and unusual force. As to your rails being bent, sounds like bs to me. If your seat rails and or seat post were bent into that position, you would not be able to level it. Unless the mechanic was talking about some bend or series of bends that didn't allow the seat clamp to hold the seat completely along the length of the contact point. Check to be sure the rails are parallel and on the same plane. After that, just looks like a good-old-fashioned worn-out seat post clamp. That it's happening on both bikes is a bit strange, though probably coincidence.

Your problem sounds like your seat post to me too. A good post won't slip! I prefer the "two bolt" posts instead of the single bolt, but both can work fine.

How heavy are you? :) It looks like you bent the seatpost clamp and/or saddle rails.

One guess is that you have the saddle shoved all the way back in the clamp because the seat post has too little set-back and you need a different design. A too-small frame would exacerbate this by making you shove the seat way back to compensate for a short top tube.

How heavy are you? :)

I'm 145, so I doubt that's the problem ;) If it is.. someone could make a killing by designing a better seatpost ;)

I'll take a closer look at both seat posts tomorrow and see what I can come up with.

Cheers,

It sounds to me like you're saying that the saddle stays tight in the seatpost clamp. If that's the case, a different seatpost isn't going to solve the problem. Actually, since you're having this issue with two different bikes, I'm even less inclined to think that a different seatpost is going to help.

I'd be inclined to experiment with your position on the bike. I wonder if you are pushing yourself way back on the saddle creating enough leverage to bend the saddle rails. If that's the case you might want to experiment short term with a longer handlebar stem and longer term with a frame that has a longer top tube.

Listen to the mechanic who looked at your problem and try a new saddle and seatpost.

The frame has nothing to do with the problem.

You may just want a seatpost with more setback than what you have now. It really sounds like you're just suffering the effects of a post that won't hold the saddle level, but until we see pics of the saddle rails in question we're really mostly talking out of our bungholes.

Looks like an SR type seatpost. There are teeth on the top of the post that lines up (clicks) with teeth on the seat-clamp itself. What happens a lot is sometimes the clamp is tightenedd with the teeth not meshing all the way, like the tips of the teeth sitting on top of each other. Then on the ride, with weight and wiggle, the clamp then slips down fully into the teeth engagement. But this ends up causing the bolt to be too loose. The looseness lets the clamp rock back and forth and eventually strip the teeth off the seatpost. So now you've only got friction holding the saddle tilt-angle, which easily slips over time.

I'd recommend taking apart that seat-clamp completely and examining the teeth on the post and clamp. Install just the clamp on top of the post and rock it by hand back and forth to see how well the teeth lines up and holds the position. If it engages pretty well, then put the seat and top-clamp on. The trick is to hold down the lower-clamp with one hand so that the teeth is fully engaged. Then install the seat and upper-clamp with the other hand while not disturbing the lower-clamp. Use some blue loctite on the bolt-threads and really, really crank on that bolt. Should be about 20 lb*ft of torque.