Stopping a saddle sliding along a seatpost clamp
Although these days most saddle rails will fit the grooves carved into a seatpost clamp, due to the sheer amount of seatpost clamp and saddle combinations possible, it’s still occasionally possible to run into problems.
Typically this means that even when tightened, a saddle’s railings (the metal tubes underneath a saddle) are not large enough in diameter for the saddle clamp to grip properly.
When this happens, in the most extreme of cases a saddle will freely slide up and down a seatpost clamp with ease. More likely however is that a saddle’s railings are only ever so slightly undersized and this in turn causes the saddle to ever so slightly move up and down a clamp.
This subtle movement can cause a rider no end of frustration as these subtle movements can gradually throw out a bicycle fit and cause a rider large amounts of frustration as the problem is not immediately diagnosable.
After working out a saddle is moving, it’s usually much more common to writing off a possible undersized saddle rail problem as the seatpost clamp itself moving on the seatpost.
Diagnosing a bicycle saddle sliding on its rails
To determine if a bicycle saddle is infact moving along its rails when fitted into a seatpost clamp, a simple check is all that is required.
All you need to do is mark the railings and observe them over a short period.
There are a few ways to do this but the easiest involves either some white-out (white correction fluid) or tape.
With the bicycle saddle fitted into the seatpost clamp, carefully mark both the outer positions of the saddle’s railings with whiteout as shown below:
If you don’t want to mark your saddle railings, an alternative is tape. Duct tape, electrical tape, masking tape – any will do so long as you can see it clearly.
Using a ruler, place the tape roughly 1cm (or any easily measurable distance, again on the outer sides of the railings.
When using tape, it’s important not to place the tape too close the seatpost clamp itself. If the saddle is indeed slipping along its rails, placing the tape too close to the clamp might stop the saddle slipping and falsely cause you to rule out railing slippage as the problem.
To gauge whether the saddle is sliding along its rails, go on a few rides and then remeasure the position of the tape relative to the seatpost clamp, or if using white-out have a look at where the whiteout markings are.
If the distance of the white-out markings or tape has increased or decreased, you’ve accurately established that the seatpost saddle sliding along its rails is the culprit.
Fixing a seatpost that slides along its rails
The easiest solution to a bicycle saddle sliding along its rails in a seatpost clamp is to either replace the saddle or the seatpost to get a better fit.
Unfortunately this is also the most expensive option and unless you can sell the part you’re replacing, also leaves you with a useless spare (unless you have multiple bikes).
Before you go down this route, with a bit of cheap DIY it should be possible to stop your saddle slipping.
By cutting some old tyre tubing to size,
you can wrap the saddle’s rails with the tubing and then secure it with some tape.
Note that in the photo above I’ve wrapped both rails with the same bit of tape and then secured it with tape. For a more snug fit, you’d probably be better off individually wrapping both rails with separate bits of tubing and then securing them with tape.
When wrapping the railings it’s important to note that you don’t need much tubing at all to create a snug fit in the clamp and that the tubing should be wrapped tightly, free of any looseness.
One drawback of the tubing is that it can be more difficult to adjust the saddle along its railings against the clamp (you’ll need to loosen the clamp more than normal when doing fine adjustments) – to get around this simply put some whiteout on either side of the tubing to use as reference points.
After a few rides the rubber tubing will naturally compress in the clamp so you’ll probably want to slightly tighten the clamp too.
For railings that are more drastically undersized another approach is to take an aluminum can and cut off the top and bottom of the can.
Then, again cut the can vertically so that you have a sheet of aluminum can just large enough to wrap around the railings to increase their size. Note that this is a bit more fiddly as, even if secured with tape, the aluminum wrapping is more likely to move and throw out your adjustment.
Be very careful when tightening up the seatpost clamp to make sure the aluminum wrap doesn’t move along the rails. If you can, get another person to hold the saddle in place while you tighten the clamp and watch the railings.
Both of the above methods should work for most bicycle saddle and seatpost combinations out there, if they don’t – unfortunately there just might be no way around the size difference between the railings and seatpost clamp.
In this case if your happy with the saddle and comfortable in it, it’s advisable to change the seatpost and clamp rather than the saddle itself.
Leave a Reply...