We all know that your ideal saddle must be the right size and adjusted to the right height, reach and tilt for your body.
But that’s not all. To make sure it is safe and reliable, it also has to be attached to the seat post according to specific criteria. Tightening the clamp exerts a force on the rails of the saddle, which, because of friction, prevents it from slipping or moving. But it’s precisely because of this force that care needs to be taken to avoid cracks or damage which could prove even more dangerous.
- First you must check that there are no sharp edges or burrs on the jaws of the clamp which could “mark” the rails and make it more fragile at that point. If there are, use sandpaper to smooth them down.
- Next you must establish the correct tightening torque (indicated in Nm – Newton metro), which is the product of the applied force and the length of the lever, which in this case is the wrench. Of course, you don’t need to do complicated calculations to work out how much to tighten the clamp, you can just consult the manufacturer’s instructions, which should always list the maximum value. But to be on the safe side, it’s best to stay slightly below the recommended value.
Especially on saddles with very lightweight rails where over-tightening could crush the tubes risking breaking them.
Carbon fibre rails are also very sensitive to the so-called “notch effect”, and an increased force exerted at a specific point could result in it breaking.
- But in practice, how do you make sure you don’t exceed the specified torque? When tightening the screws on the seat post (or any part of the bike for that matter), it’s best to use a torque wrench. A torque wrench allows you to tighten to a set value, thanks to a click mechanism that warns you when you have reached the desired torque.
- One final detail which requires attention is the contact surface between the rails of the saddle and the seat post. It’s difficult to give standard values because it all depends on the geometry of the rails, but it’s safe to say that clamps shorter than 30 mm could cause problems because they wouldn’t guarantee a good connection between the rails of the saddle and the seat post.
Selle Italia regularly carries out dynamic and static testing in the laboratory with different types of seat posts and with the tightening torques recommended by manufacturers.
The parameters of international standard ISO 4210 on Safety Requirements for Bicycles includes so-called “fatigue” testing, with a force of 1,000 Newton applied at a specific point on the saddle for 200,000 fatigue cycles.
In order to give cyclist the maximum safety guarantee, Selle Italia exceeds these parameters and subjects its products to over a million cycles and strains.