Cyclocross - frame size

I am looking into buying my first cyclocross bike and need to know what size I need if I happen to find a good deal somewhere other the the LBS. I am 5' 10" and have a 31" inseam. I am not planning on doing any real cyclocross racing, just love the design of the bikes. Thanks for the help!

Brusheda: Look out for a firestorm of advice that will range from a 52cm to a 64cm bike and plenty of dogma. IMHO, cross bikes ridden for non-race situations should fit like your other bikes. If you have another bike that fits well, get the same size / geometry. If you have never had a bike fit well, then you are in for some trial and error and even more conflicting advice.

Is it true that if I make sure the standover height is not too big then the frame size isn't too big?

In my opinion, not true at all. However, your proportions make it more likely that you will have a comfortable fit without handlebars that are too low. People with long legs and short reach have a harder time getting a good fit. What types of bikes do you currently ride and what size are they?

Typically if you are a road riding you'd look for whatever size frame has about the same length of top tube as your well fitting road bike.

But I'd think that you're looking for a 50 cm cross bike myself.

test ride as many different brands in different sizes that you can. but 50 sound like a good starting point. smaller than 50 is probably going to feel cramped.

I would think that 50cm would be tiny. Isn't that about the smallest frame size available? I'm not one of those Rivendell fit guys, but that seems darn small. A 56cm top tube seems like a better starting point.

I am relatively new to cycling and all the bikes I have had are free from neighbors who no longer wanted them. I have never had a bike that fit. I am going to try to find an affordable bike at the LBS but I may find a used bike online and I don't want to regret my first bike purchase- especially since I am planning on using whatever I get for many years.

IMO a 50cm bike would be tiny for a 5'10" person. That is about the smalles size that is made for road bikes and Brusheda isn't a small person. I would start with a bike that has a top tube in the 56cm range and work from there either bigger or smaller. Bigger bikes would mean that the handlebars could be raised higher and a smaller bike means a shorter reach. It's mostly trial and error and very personal.