why do bikes rev high

[paras211]

why do bikes rev higher than cars? is it just coz the engine is small its easier to rev higher or is there more to it?

i mean even not so performance oriented bikes rev till 9k


one more question didnt want to start a new thread
what is different about avation fuel than normal fuel? i remmeber seeing gautam singhania putting some blue fuel or some thing like blue(not kerosene i am sure) in his lotus at the speed run a few years back. when it was held at bandra

[revtech]

ill answer the latter part for you.aviation fuel are mainly of three types

100 (green)
100 low lead(blue)
jet fuel (red)

they are of a slightly higher octane.most other high octanee fuels in india are with addiitives while these are pure.

[paras211]

so without additives is better??

[ananthkamath]

small-capacity bikes rev higher because they need to have higher specific power output in order to maintain decent driveability.

they can afford to have higher rev limits because they have a small stroke compared to most car engines and so the piston speed & acceleration is much lower at a given rpm.

[badri]

Higher RPM of a bike engine is due to

1) Small stroke ( piston speed is limited.Hence smaller stroke-faster rpm)
2) Lighter rotating internals ( like crank)
3) Lesser valve movement/spring rebound.Hence higher cycles per sec

If you get rid of valve springs ( by means of pneumatic valves), have smaller stroke and light interernals you can have a car engine revving as high as a bikes ( F1 engines by cosworth ran over 20000 rpm in the last race with Williams)

[veyron1]

Actually, any engine can have a high rev-limit, provided it has a low stroke, and the design specifications to support it (valve height, weight, roller specs, flywheel weight, etc.) . High performance Hondas have always been rev-happy, straight out of the showroom. Modded Skylines have been known to have 10K redlines, without reliability issues.

Litre class engines and upwards do not rev that high. It's just the 600cc sportsters that have been known to rev above 15K; like the new R6...

Originally Posted by ananthkamath

small-capacity bikes rev higher because they need to have higher specific power output in order to maintain decent driveability.

Actually, even though they have high specific outputs (most surpassing 150 bhp/litre), driveability/rideability is affected a lot by their torque curve. Most of the sportsters aren't that rideable below 5K (a big pain in city traffic), because of their peaky torque curves..

[Mpower]

Originally Posted by veyron1

Litre class engines and upwards do not rev that high. It's just the 600cc sportsters that have been known to rev above 15K; like the new R6...
..

..and 400cc inline fours rev even higher. 250 cc inline fours (kinda rare but do exist) take it up to another level. All driven by the same logic.

[kuttapan]

@paras - The primary reason for bikes to have high revving engines is lack of torque. The small capacity bikes make piddly amount of torque, so they need to rev high to produce decent power. power is a function of torque and rpm.

If you notice, Bullets don't rev high(less than 6k rpm), as they have oodles of torque, but still produce the most power(among Indian bikes). There are other reasons why a Bullet does not rev high, but that's not relevant here.

Another thing is, high revving engines usually have shorter stroke, compared to the lazy engines. Also, push rod engines generally rev lower than OHC engines.

[ajitkommini]

Originally Posted by revtech

ill answer the latter part for you.aviation fuel are mainly of three types

100 (green)
100 low lead(blue)
jet fuel (red)

they are of a slightly higher octane.most other high octanee fuels in india are with addiitives while these are pure.

Aviation fuel for piston engined aircraft is high-octane petrol with a low flashpoint. Jet fuel (Aviation Turbine fuel) is a kerosene based fuel

[paras211]

flashpoint=ignition point??