Bicycle riding- how much leg room?

Watching a feel-good story on Bo Jackson. Former double professional athlete. Decided to ride his bike across Alabama to help raise funds for the Tuskaloosa tornado victims. A very cool gesture.

Here’s the question. Bo- and all of the cyclists around him- did not fully extend his leg when pedaling. When I watch high-end cycling, those cyclists do not extend either. In working on seat/ fork height, I am finding that when I approach a fully extended leg as I pedal, my knees hurt less. I ride a basic mountain bike on city streets.

Don’t mean to say that my knees should lock as I pedal. Rather, I’m asking if it is better in terms of endurance AND in terms of leg/knee health if I endeavor to let my leg straighten out as much as possible.

The rule of thumb is you want your leg to almost get straight, but not quite, at the bottom of the stroke. It should be impossible to lock your knee at the bottom of the stroke.

I have no idea what Bo Jackson’s riding looks like, but I wouldn’t be surprised, with his injuries, if his doctor has recommended a different riding style.

I’ve biked for, wow, nearly four decades now… funny I don’t feel that old. And to answer your question, as bup said, ideally the knee should not come to full extension.

The way to set your proper ride height (as I have always done) is to stand on the ground, next to the bike, and the saddle should be right at the hip joint, ensuring a not-fully-extended-knee when riding.

Now, I ride on paved paths as a general rule, but when I need extra power I can always rise from the saddle and put my full weight on each pedal, but I’d hate to ride all day like that- it’d be murder on my (already poor) knees!

My 2 denari…

Measuring from the ground depends on a lot of other factors, particularly in MTB (frames often built for ground clearance and groin clearance).

The best way I know is to sit on the seat next to a wall or something that you can use to hold yourself up.

Put your HEEL on the pedal - adjust the seat height so that, at the very bottom of the downstroke, your leg is straight.

That should put your pedal at the proper setting for riding, with your leg not quite fully extended at the nadir of your stroke.

Raising your seat height to give the proper leg extension will save your knees - I’ve known a few folk who mucked their knees by sitting too low. It also increases your efficiency and performance.

Oooh this is really good stuff. Thank you all !! When it stops raining, I’ll get the bike out against the garage wall and check things out.


I have been fit on my road bike and have done laymen’s fittings for a few people and the general rule of thumb is between a 15 and 30 degree bend in the knee with your foot at the bottom of the pedal stroke (6 'o clock) and your feet flat (i.e. no toe pointing or pushing the heal down).

If you’re able, just go to a bike shop and ask them to make sure your bike is set up correctly. Might cost you a few dollars though (I think a simple one here is around $25).

Yes your knee should be bent at the bottom of the stroke. You should be able to pedal fast without dropping your hips. People with too high a saddle will start to bounce on their seat at a much lower cadence than someone with a properly set up bike. Measuring the angle of knee bend is the most accurate way and it seems that 25º with the crank at 6 o’clock is the optimum angle for power and efficiency.

As for ways to set the saddle if you don’t have someone with an angle measuring device, I wouldn’t use jimbabweosu’s method as there are too many variables that aren’t accounted for. Setting the seat height so your leg is straight at the bottom of the stroke with your heel on the pedal and no dropping of the hip is a good way to get a rough height. When you put your foot in the proper position with the ball on the pedal you’ll have a bend in your knee. You may have to make slight adjustments after you ride for a week or two. I do a lot of riding and have had a couple of fittings done for new bikes but I’ve generally found the best results after making my own adjustments based on experience.

All I can add is I’d find someone to hold your bicycle steady for you while you sit on it and back pedal until the crank on one side is at full down. They’ll have to straddle the front wheel and hold your handlebars. Full extension of the leg with the HEEL on the pedal is the best coarse adjustment. You may want to mark that on your seat post with a permanent marker before you do any fine adjusting after a week or two of riding.