I'm 5'8", 165lbs.
The medium fit well, but I wanted more length, so returned them for large.
Much better. But, it still may be just a touch too short in the front (I like longer jerseys when mountain biking). I thought it would be 24-3/8” long, but I'm getting about 23.5.
I know cycling tops tend to be shorter in the front.
Not a huge deal really, but not sure if I will keep them.
My wife says they look great, so...
5 stars for a very nicely made top, and excellent customer service. I asked some questions and they answered quickly.

Had to return both shirts as the body was too short and the sleeves too long (size large). They wore and felt awkward.

I just received this jersey today and it appears to be of great quality. Can’t wait to take it out tomorrow.

I’m 6’ 185lbs and the L sport fit was perfect size for me.

I bought this shirt because I don't enjoy roadie jerseys for mountain biking, and I wanted something a little less fitted. This was a good purchase. I am 175-180lbs, 5'9", and not super skinny due to liking IPAs. The large in this shirt is a good fit. It's not hanging off of me, but it's also not snug. A medium would have been too small. I think XL would have fit in the torso but may have been too long. I've worn the shirt in hot/humid NC summer weather. Works great, and it looks good too.