Bicycle Mechanics - Quick question on 17.5 and 20 frame

Hello all, I went to LBS today and took a look at the Trek 7.3. The salesman told me that if my height is 5'10 then I should get a 17.5 frame bike.

However, I read a few posts here and there online and it says that the 20' frame should fit anyone between 5'10 and 6'2. I'm looking for Trek FX line as I use it to commute to 7 miles school ride everyday.

So quick one is right for me at 5'10 and 175lbs? 17.5 or 20? Thank you very much in advance.

20. I'm 5"9" and the 20 fits me perfect. That said, you can ride the 17.5, but you'll be more upright. I prefer to be a bit more stretched out and the 20" worked perfect for me. My boss loved the bike and I sold it to him, and he's the same size as me and felt the same way. One of my co-workers has the 7.3 in 17.5 and we all agreed we felt more cramped.

Did you ride both? It's really about what feels better to you.

I haven't ridden the 20', but I felt comfortable with 17.5. May be I haven't tried the 20' to see if it's more comfortable. I'll try the 20' tomorrow at another LBS, thanks.

If you spend over 300$$$ on a bike, i think the price should include a fit, and a sales man who knows a thing or two about which bike size is right for you.

therefore, asking questions here about inchs, centimeters etc. is pointless.

I've been curious about this. I'm 5' 9 1/2", but I used to be a full 5' 10". Pants inseam is 29. My bike has what seems like a more "parallel to the ground" top tube than a lot of much newer bikes. My bike is a 19. By the old measure, it's probably about 3/4" too high. However, I also have about 6 inch of seat tube showing.

Seems now-a-days, it's 17.5 and 20. Having one LBS "fit you" really is going to depend on how good they happen to be... I can certainly foresee one saying 17.5, another 20. My guiess is I'd need to have a lot more seat post shwoing on a 17.5...

Ccrew, you really can stand straddling the top tube at 20"? Somehow I'm imagining a sloping top tube and not much seat post showing at all... right?

The one I went to was habitat bicycle in NYC. The salesman name was Chris. The store was so busy that I felt he didn't really try to sell me a bike. Plus he charge everything for installation, like fender ($35), rack ($10) which was all free at another LBS, Bay Ridge bike world, in brooklyn, so I finally backed off.

The point is, I didn't feel the salesman that knowledgeable, I thought "bike fit" should include at least some measurements like Reiverside_Guy said, not just eyes-guessing.