Except for a friction drive, which drives the outside diameter of the wheel at a certain speed (not rpm as a sprocket drive does) which would be friction wheel RPM multiplied by it's circumference. So the tire tread tavels a certain feet per second,not revolutions per second. And since the tread is connected to the ground, it then travels at the same feet per second.The rear wheel size does matter...a little, a 24" wheel will have a slightly lower overall speed at any given rpm than a 26".
You're right too! It started out as a sprocket question, and somehow I ping-ponged into friction drive...my fault!My mistake. I didn't read the whole thread. I thought the discussion was about sprockets. You are correct that on friction drives, the diameter of the spindle determines the speed.