I'm trying to figure out what is the difference between a 9 speed crank and a 10 speed crank on mountain bikes?

Can a 9 speed crank be used if I wanted to convert to a 10 speed cassette/chain/derailleur?

What kind of problems could I encounter if I do this?

Thanks!

Since you didn't say the name of the parts manufacturer it may be a 10 speed chain ring is thinner than a 9 speed chain ring. Roger

Not significant .. There are just 1, 2 or 3 in front .. the other numbers refer to the Back Wheel, a count of How many Cogs.

You can use a 9sp crank with a 10 sp chain and shifting.
I use a 7sp crank with a 9sp chain and shifting. I also use a 10sp crank with an 11sp chain and shifting.

There is a theory, from what Ive read, that the chain can skate over the ring during shifting if the crank isnt the same speed as the rest of the drivetrain. Havent had that happen though.

Lennard Zinn has addressed your question and specifically stated its fine to do, and he kinda knows his stuff.

Gotcha. Was thinking of eventually converting my Crosstrail over to a 10 speed from the original parts on it to give me some different gearing while on various trails.

Thanks for everyone's responses!

But it won't make a difference, since the inner chain width (roller width) of 6 to 11 speed chains is exactly the same - it's the outer width (thinner plates) that varies.

1) Bicycle chains compatibility - Cycle Gremlin