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I borrowed my son's bike (a simple mountain bike) and I have problems with the saddle: I pushed it as far as possible to the back (so that it tilts down as much as possible otherwise I have the feeling of riding on the back wheel) but it does not want to stay put.

After a few kilometers on a good road, it starts to wiggle and I have to stop to tighten the screw. Right now I tightened it almost as much as I could but I am afraid to break it by going too far.

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Question 1: is there a better way to fix that saddle?

Question 2: I am considering buying a new one - is there something that I can improve (from the perspective of the stability of the fixing)

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    Can you pull out the saddle with the seat post? You could find easier to work to tighten it up if you can turn it upside down. You could also bring it to a shop and ask if they have a toothed washer the right size.
    – FluidCode
    May 19 at 11:46
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    You risk breaking the saddle rails or seatpost this way. Most saddles have markings on the rails which tell you not to clamp in the area where you are clamping. I very much doubt it’s necessary for your seating position to have the saddle this far backwards. If the bike feels too short, get a longer stem (or bigger frame).
    – Michael
    May 19 at 16:18

3 Answers 3

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It may be that the bike is the wrong size for you causing you to need to shift the seat back further than it was designed to go. There are several answers for how to find the right sized bike.

When you slide the seat all the way back on the clamp there is very little seat post clamp surface area holding the seat rail so there isn't as much support as there should be which is contributing to the bolt working loose.

In the spirit of trying the easiest thing first, something to try is removing the seat post clamp bolt and putting a little (very little) grease on the threads of the bolt. Given your picture I doubt this will help but it's worth a try.

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There are seat posts designed to have more movement that can be purchased.
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Seat post diameters are not standard and it may be a challenge finding one that fits your bike. Measure carefully before you buy.

The best solution is to have the right sized bike but I get it, sometimes you have to make due with what you have

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You have a single bolt style of saddle-rail clamp. They are renouned for not staying tight.

Additionally, you've got everything a long way back, which increases the leverage.

I suggest you look for a replacement seat post of the same diameter, but with some setback. Make sure the clamp has two bolts, sometimes called "micro-adjust"

Ultimately it may be that this frame is just too small for you, and you're really needing something larger.

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In addition to the above answers, with the saddle so far back, when pedaling you are putting rotational forces on the mount. With such a small amount of rail in contact, this will be allowing micro twisting movements around the bolt, which is loosening it.

A medium strength (blue) thread locker would help prevent this, but is not really the correct way to solve the problem. As already indicated, moving the seat forward into a correct position should fix the problem.

Do not carry on riding the bike like this. Each time it comes loose the both the bolt and threads are subject to forces that will eventually cause a fatigue failure.

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