how does one properly size a bike
 

I heard there were different methods for road bikes vs. mountain bikes. I want to buy a used bike from craigslist or ebay, and since most bikes tend to get sold very quickly from those places I dont think I have time to mess around. I'd like to know right off the bat before I even drive to the person's place if the bike will fit me. Anybody have any tips?

Stand over the bike and lift it up until it touches the dangly bits. If you have 2" to 3" on a mountain bike (1" to 2" on a road bike), you are almost ready to go. Any less than that on a mountain bike and you have to decide how much value you place on the dangly bits:D

Once you get a size range that fits, it's pretty standard. You could go to a shop and see what fits but that would be kinda rude...I mean you aren't planning on buy from them. Check your buddy's bikes. If you have a friend about your size, you should ride a similar sized frame.

The 'almost' bit? Get up on the pedals and see if the top tube is too long or too short. If you feel like you should be ringing bells in Paris, it's too short. If you feel like a giraffe drinking water, it's too long. Adjustments can be made in the stem length and the saddle position but only a few inches. Thankfully, most bikes fall into similar ranges for similar sized frames.

And ride it. If it doesn't feel right...it ain't!

so is there no ready-made formula to use just to estimate the right frame size without actually sitting on a bike first?

Nope, they're kind of like shoes in that respect. You can get a rough idea with the numbers but until you try them on you won't know if they fit comfortably.

I'm no expert on MTB fitting myself, but one odd thing I have noticed, is that if one looks at the riders' size and the bikes they ride from sites like CyclingNews.com, I notice most pros seem to ride bigger bikes in terms of top tube lengths than what you might see on road bikes for the same riders. Example: Chris Eatough's Trek Top Fuel: rider 5'10" on a 62.8cm top tube. Is this normal? Same size guy on road bike would be on like a 55 to 57 likely. Not even close to a 62!


In my case my road bike is a 57cm top tube and my Titus Racer X is actually very close to that (measured 'virtual' or level). It feels fine to me. I run a 120mm stem though.

There are formulas and tables all over the place. http://www.google.com/search?hl=en&q=bike+sizing

Be aware of a fundamental difference between road bikes and mountain bikes, though. Mountain bikes have sloping top tubes, while road bikes have level or nearly level top tubes. This means that for the same effective size, the mountain bike will have smaller stated size because it has a shorter seat tube (the usual basis of measurement for the stated size).