joshF

This mite be a stupid question but does anyone no why motorbikes rev so hard?

generally interested?

cheers

Remko GT

Because all the engine components are much lighter and smaller than in car engines and because they hardly make torque (compared to a car) everything can spin faster and doesn't need to be as strong..... I think.

Chip

iTrader: (3)

The simple answer is because they are trying to make lots of BHP from a small engine.

BHP = Torque * RPM / 5252


So only TWO possible routes to more power:
1) more torque
2) more rpm

They are already fairly good for torque for the size engine that they are to be fair (despite what people say to the contary), so the only option for big power is to design them to rev a lot harder.

This is done by short stroke's to keep piston speeds down, and a lot of valve area per CC of displacement, along with of course the required mechanical strength of components.

foreigneRS

you're always quote that formula

it's simply power = torque * rotational speed

it's only the 5252 bollocks if you want to calculate BHP (old fashioned imperial unit) using torque in lb.ft (another old fashioned imperial unit).

why don't we get with the modern world in this country and talk Nm for torque and PS (only a metric close equivalent of BHP) or better still kW for power?

foreigneRS

typical reply from a backward northener

alistairolsen

because everyone still uses bhp, and most wouldnt have a fucking clue what a KW is. same with "torques"