The comparison between 7, 8 or 9 ratios in a car and 20+ on a cycle is really irrelevant.
With three front chain rings and anything between 5 and 10 on the rear (I don't think 3 x 11 has been done) means that you have a very wide spread between small front ring and big back cog and big front ring and small back cog though with quite a few duplicate ratios in between. For instance on my old 21 speed hybrid (3 x 7) I usually use the middle ring on the front and the 3rd, 4th, 5th and 6th cogs on the rear though if I select the big front ring then I find that the 3rd cog on the rear is a very similar ratio to the middle front ring and the 5th rear cog.
My road bike has two front rings and nine rear cogs (2x9) and seems to have fewer similar ratios though 18 ratios in total are still more than necessary. I use to road race, time trial and hill climb with five ratios on the 70's.
With the advent of 11 speed rear hubs there is a move to again only use one front ring so you have 11 useable ratios with added lightness an simplicity.
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