Fib

When you are riding your bike and the pedal goes down as far as it can, should your leg still be slightly bent at the knee, or should it be straight?

From stuff I've heard, and just what I think, is that it should still be slightly bent, like almost straight but still bent. Because if it's straight then you could possibly hyperextend (pretty sure that's not the word I'm looking for, but I'm not sure) your knee.

I'm asking because a friend of mine from school was on his bike earlier while we were talking. I noticed his seat was so high his feet could barely even touch the ground, so I pointed it out and said he should probably lower it a little bit, because his legs were probably fully extending while riding his bike. He said they were but that there's nothing wrong with it. Later he sent me a video trying to prove me wrong, only to prove me right (according to the guy in the video) but he still disagrees.

I honestly don't care too much about my friend's seat or if he'll injure himself because 1. I warned him and he didn't want to listen. And 2. If he's been riding it like that, is comfortable, and hasn't hurt himself then he must be fine.

So, should your seat be low enough so that your legs are always bent at the knee while riding, or does it not really matter? Or... Does it depend on the person and how their body is built?

dabac

Reaching the ground or not is entirely uninteresting for saddle height for efficient seated pedalling.
The thing that makes leg straight or slightly bent tricky is that it doesn't take ankle angle into account.
And that can make a considerable difference.
A "safer" recommendation is "leg straight with heel-on-pedal".
This usually leaves you with a slight bend when the pedal axle is below tha ball of the foot and the ankle in its natural angle.
Don't forget the double-check of hips not rocking while pedalling, which would mean the saddle is too high.

79pmooney

The test I use is to sit on the bike leaning against a wall so I am almost upright, wearing only socks. I place my heels on the pedal spindles. There is a very definite seat height where I can either lock my knee or bend it keeping contact with the pedal and not rocking my hips.

I like a lowish seat. Some do this test wearing their cycling shoes. I don't claim this is perfect for all, but it is right for me and it allows me to set up any bike with any seat to the right seat height quickly.

For me, a straight knee is a seat way too high. But again, I like a seat lower than many. I started much higher, brought it down at the suggestion of the club vets when I started racing. As I rode years of long miles, I evolved to the test above.

Ben