I own a bike and a car. I’ve wondered this for some time, when I am doing 120km/h the car gets around 3k revs and the bike easily 6k.
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The difference is gearing. The car has a lower gear ratio so at a given speed, the engine can turn slower in the car vs the motorcycle. The reason for the difference is the amount of power each engine makes. The motorcycle probably makes less power at the same RPM as the car engine. Each speed take a certain amount of power to propel a vehicle. So the motorcycle engine needs to spin faster than the car to maintain that speed.
It’s how they squeeze the horsepower into a smaller engine. More bangs per rev means more power per rev (ish)
However making a motor that revs higher for a reasonable price involves making tradeoffs. The main one is using shorter and wider pistons than you would normally use on a car. That makes them easier to run at higher RPM. Since the piston head is travelling a shorter distance up and down it’s linear velocity and acceleration end up lower.
It is however less fuel efficient, offset by being on a really lightweight bike, and the high RPMs tend to mean shorter engine life and more frequent maintenance per mile, offset by people not driving bikes nearly the same amount of miles they do cars (usually).
The smaller an engine is the higher it can rev. Motorcycles usually have small engines, up to a liter (1000cc) of total displacement, which is about 125 – 300cc per cylinder. They’re also usually more performance tuned than cars, because you’re not as likely to care much about fuel economy on a bike.
Cars start at about 300cc for small economy cars, which won’t rev high because they’re tuned for efficiency, and the more performance oriented cars have large cylinders with 500cc or more.
Now for why they do this, it’s better to have a slow engine for fuel economy and wear, but bikes simply can’t fit a humongous 3L V6 twin turbo between your legs, so they make tradeoffs. Plus it’s tradition at this point, sportsbike buyers want their engine to sound and feel a certain way, so the manufacturers keep that in mind.
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