Hello!

I am buying a bike for my Dad, and the only thing I know is that he's 5'7" with an 80 cm standover.
should i get a 50 cm? 52 cm?

He'll be visiting in Feb. and wants to go on a ride with me. I do have two bikes, one of them is 42cm but the other is 47cm with a 76cm standover.

Do you think my Dad can just make do with my spare bike? One thing I know is that he doesn't like aggressive riding positions, so on my 47cm the handlebar might be a bit low.

Any suggestions?

The 47 cm is going to be a bit too small for him. I'm 5'9", with a 32 in. inseam (about 81 cm). My bikes are either 54 cm or 55 cm. You're definitely in the right ballpark with the 50 or 52 cm. The 52 would be a good starting point to try out the fit... But I'm assuming your dad won't be around to test ride some bikes before purchasing?

What kind of riding will your dad be using this bike for? If he's not going to be on the bike a lot, a perfect fit might not be all that important.

Buy the bike WITH your dad when he gets there.