Why do you many cafe racers only carry a speedometer gauge and remove the tachometer gauge

I see it in a lot of cafe racers how do you know when to switch gears do you just base it off the feel of the ride? via /r/CafeRacers https://www.reddit.com/r/CafeRacers/comments/8ktrw0/why_do_you_many_cafe_racers_only_carry_a/?utm_source=ifttt