Obviously much better to ride it first, and better still to have the shop relationship to go with. I’ve test ridden a couple used bikes so far, but it’s surprisingly sparse what’s out there in my size, or at least seems to be. I haven’t been too impressed in what I saw new in my price range at any of the local bike shops so far (not much!)
This is just the top result by googling “bike fit calculator”
#1, it’s really hard to measure accurately, even with a second person measuring. How long is your femur? Is it 22.25 inches or 22.5? That difference is easily made up in measuring error, and affects your fit greatly.
#2, it spits out numbers, okay…but can you use these numbers to fit yourself on a bike?
My personal experience: I was told I needed a 52.3 to 52.7cm top tube (which is accurate). It also said that I needed 5.5 to 5.9cm of saddle setback. Now who’s going to do the trigonometry for me to get that measurement from the few listed geometry charts available?
This actually became a dealbreaker because my femurs are too long to fit on most 49cm/50cm road bikes. Even with a 30mm offset seatpost clamp and saddle slammed all the way rearward, I was exceeding what was deemed “safe” on my saddle rails.
So I needed another frame and wasted some money.
A good LBS will put you on the bike, and measure your knee and hip angles to get everything in line. It’s definitely the safer option, and cheaper if you don’t luck out the first time (as in my case). Even when you do receive the bike and set it up in the range that the calculator spits out, it’s still a range. Will you know if 5mm forward or 5mm rearward on your saddle is good or bad unless someone tells you? It all goes back to fit.
If you get into cycling enough, you’ll get to a point where you know your measurements well enough that you could buy a bike sight unseen, but until you can rattle them off the top of your head, I’d probably stick to trying before you buy.
Of course, you can just ride it and deal with the consequences, but I value the fit of a bike more than any component I have hanging off that frame.
My personal experience with bike shops has been less than stellar. If you can find a good shop (the kind that will actually change out the stem right there when you want to try a bike out), then you can’t beat that. Be careful of shops that offer “fit” programs that will run you $100. If you are going to pay for fit, I’d go the UPMC approach that has been discussed in the past.
But, the last time I was shopping for a new bicycle, I found most stores less than helpful. In fact, I bought two bikes that didn’t fit (as I started to learn more about the topic. The first was an easy enough return, I bought it at REI (in Seattle, none the less!). The second, I kept for a few years and ended up selling it used because I rarely even took it for a ride.
I think it is important to be your own advocate and know what questions to ask. If you aren’t really vigilant with questions about fit, most local shops aren’t going to be vigilant in helping you find a good fit (they just want to sell what is in stock). I’m not speaking for Pgh as I’ve only bike shopped at a handful of stores here. I did have a great experience at Freeze-Thaw in StateCollege, but that’s a bit out of your market. My shopping experiences in both Seattle and Chicago have been anything but impressive.
So be your own advocate. Read as much as you can online. There are several different fit methods and it doesn’t hurt to be familiar with them (assuming that you have the time and interest).
The only way to know what works, mail order wise, is to know what works locally and find something with similar geometry (if it even exists).