I want to build a stand of some kind to get some cardio in in my garage.

I was thinking about uses Uni-strut (C channel or w/e) and All-thread, or 2" angle iron or clamps and just have a wheel of some kind rub against back tire for resistance.

Anyone make one before? I think it would be neat to rig up an alternator or something to power a 12v car battery, that power a car stereo and speakers and amp & subwoofer if I decide to get carried away with it