Thinking that your gearing is what limits your speed is a common error. Extending some observations someone made earlier, so they don't get lost in the deluge of replies:
The fastest and strongest bike racers spend very little time in their highest gears, which are generally used only in mountain descents and in end-of-race sprints.
Guaranteed: race against a decently strong bike racer, with you in your highest gear and the bike racer confined to using sprockets in the middle of the cassette, and you'll be left in the dust.
I was only a middle-of-the-pack racer, but I always enjoyed having some would-be racer out on the road pass me while he was lugging along in his highest gear, because that was license to kill (his dreams, that is).
Looking to build leg muscle? Use a leg press machine or do squats with free weights. It's impossible to apply much more than your own weight to the pedals of a bike, so riding in the hope of building muscle is a waste of time.
Proof: look at the guys who are dominating the Tour de France this month. They range in build from moderately muscular to skeletal - and one of the most skeletal is currently leading the race. Legs like pipe stems, arms like pipe cleaners. (Fun fact: Skeletal Guy won last year's Tour de France.)
If you're like most newcomers to cycling for fitness, you won't believe any of the above, and you'll continue to try to figure out how to get higher gears. Good luck.
Last edited by Trakhak; 07-08-23 at 03:41 PM.