Crank Length/Seat Position

Lee Joo Mong in Singapore is one of our regular readers and question askers; he is thinking of fitting longer cranks and wants some advice on adjusting his saddle position with the new cranks.

Question:
Any harm if I replaced with longer cranks for more torque, and adjust the seat forward so that my knees are above the pedal spindle (directly above the spindle/about 90 degrees seat angle)?

Hi Lee,
It always good to receive your questions.

When you fit longer cranks you do need to move your saddle further forward so that your knee is above the axle of the pedal so that you have the correct downward force when pedalling. Remember that also you need to lower the saddle or you will be stretching too much, as you lower the saddle this also moves it fractionally forward, so you need lower it first so you are comfortable with a slight flex in your knee with the pedal at its lowest.

Once you have the height set correctly then check the fore and aft of the saddle so that the point just behind the knee cap is above the centre of the pedal axle.

The best way is either with a string with a weight on the end or a straight edge like a door post or a similar part of a building that is at right angles to the ground.

With this method you can position yourself with your knee and pedal against the door frame and have someone check that the cranks are horizontal.

Always make sure that the door is at a right angle with a spirit level first, a spirit level is a must to have in your tool box to also make sure that your saddle is level.

To have a similar position as before you may have to check your handle bar height and stretch as you have moved you saddle, there is a few different things you need to do when changing your crank length.

Remember also that your feet will now be making a bigger circle and it will feel different from before.

You may find that you have difficulty spinning a small gear, but pushing a bigger gear should feel easier as you will have more leverage.

If your thighs are short then your cranks need to be short as you would not have the leverage to push them round, longer thighs can push longer cranks.