I'm 5'9" to 5'10 with around a 32" inseam and ride a 19.5 inch fuel .. a 2006 before the 18.5 was avalable.. I got some standover concerns, but I have an inch or 2 .. i installed a shorter stem which I like..

I's say 18.5 would be a good size ... but a 17.5 or 19.5 may also be workable.. leaning toward the 17.5 more than the 19.5 ...

I ride a 56cm road bike.. also had to shorten the stem on that one too. maybe just not used to it as I just got it.. I have a box of stems now though haha


edit .. the standover on the 19.5 is 30.6 inches which sounds too big, but I'd suspect your inseam is bigger unless you've shoved a book in your crotch to measure .. plus the shoes jack you up an inch.. and I think trek measures 12 inches from the seat tube so it'll slope down where you actuall stand over it. I'd buy it if it was cheap. throw a 75mm stem on and hit the trail. it may be hard to throw around, but you'll gain some stability as your more centered on the bike

when I was shopping for a hard tail the bike store guy eyeballed me and said 19.5. I didn't go with a trek then, but got a bike about that size a 17.5 center to center.