What if you can't spin?

Seems I can't manage anywhere near the gearing everyone seems to run. I worked out I ran 71 gear inches last night and my knees are killing me today. Generally I try to select a gear lower than I think on my normal road bike and like to be at a cadence of 100-110 or so. Looks like I want about 58-60 gear inches which looks to be 48/21 or 44/20 and seems nuts compared to you all. Maybe I should just stick to gears.....

You will easily be able to feel the difference of even 2 gear inches. What is the size of you chainring?