Spin bike vs. stationary, plus general exercise bike questions

[AndrewLB]

Hey,
apologies if this is the wrong forum.
I was wondering if someone who knew a lot about biking could explain to me the difference between normal exercise/stationary bikes, and these flywheel / spin bikes that I've read about.
I'm looking to get some cardio going in my bedroom when I can't wade through the giant snow drifts to the indoor track, and yeah, hoping to buy a spin bike or stationary bike on craigslist in the next week.


Also, could someone explain to me how to convert RPM to MPH on a stationary/spin bike? For example, what rpm would 20mph be? I'm a runner fundementally, but getting into the bikes and a bit of cross training sounds like a good idea.

Thanks in advance!

 

[[Focus]]

I don't know much about flywheel/spin cycles, but I have a stationary bike in my bedroom. I love the thing.

To convert RPM to MPH you first need to know the OD (Outside Diameter) of the wheel of the bicycle. The ratio will always be vehicle-specific. If the wheel on your bike is inaccessible, you won't be able to get at it with a tape or string measure, but even the extremely low-end digital-screen bikes usually come with both RPM and MPH displays.

All you need is the formula for circumference and a simplified conversion formula for MPH, as follows:

Circumference = (pi * OD)
MPH = ( (RPM * Circumference in feet * 60) / 5280), unless I've forgotten my gradeschool math.