Engine size. Car vs bike

[The Dude]

Hi all. This is probably a dumb question but i'll ask it anyway. Lately my brother has been asking me the difference between a car and a bikes engine. Example. If you had a 1000cc bike and a 1000cc car. The bike does around 180mph tops and the car does 90mph tops. If the car is say 3 to 4 times heavier than the bike, why doesn't the bike go 3 to 4 times faster than the car taking into account power to weight differences? Help me explain it to him as if he was a 4 yearold.

[Milo]

It's sunday so I can't be arsed to explain it well...but because of air resistance (drag) and friction you need about 4 times the power to double the speed.
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[1cyl]

Car's are slow.
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[Silver]

A car that weighs 640kg? I think the weight difference will be much bigger.

And, as Milo says, bikes are very un-aerodynamic. They have a similar drag factor to a transit van.

[Bendy]

Also, a 1000cc car engine and a 1000cc bike engine are very different beasts, so they're really not comparable.

My old 1 litre Micra was listed as weighing about 660kg. Newer small cars are probably going to be heavier though, with all the safety gumph they stick in them.

[Davo]

I have often wondered a similar thing, I own a Hayabusa and a Ford Ka they both have the same size engines. What I want to know is that the suzuki engine can develop approximately 180bhp, so how come ford can only get sixty ponies out of their engine.

180bhp in a Ford Ka, that'd be fun (for a car).

[Silver]

[1cyl]

bike engines don't need much torque, so they can have more bhp, a car engine needs a lot of torque to get it to go anywhere, so the sacrafice the horses (i might be wrong).

You might also notice that your bike engine redlines at around 13,000 and your car at around 6'000. bike engines are built stronger and to a higher performance spec than your average ford ka's lump.

I stand by what i said earlier.
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[mrchips]

Just spend 5 grand on an Sierra RS500 that will get you there quicker.

[Spiral]

170bhp cbr1000rr
13bhp cbr125r

Now i don't know why the cbr1000 does'nt go 15 times faster than the cbr125r look at it like the cbr125r top is 80mph that would make a cbr1000 do 1200mph which would just be silly.
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[Scotty]

I'd say alot of cars arn't tunned to make the bhp. more the reliability , saftey and fuel consumption.
Also parts are alot heavier in the engines.
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Regards
Scott

[Bendy]

Bingo.

If car drivers had to do the amount of servicing that bike owners (certainly sportsbikes) do, they'd have a fit.

[loply]

Bike = 160kg

Car = 1500kg



Air resistance skyrockets as your speed increases, as does friction. Hence why the bike doesnt do 600mph or whatever.

[The Dude]

I think you've missed the point a little Spiral. I wasn't asking why a 1000cc bike doesn't do 1200mph. Of course thats silly. I was asking what the difference was between a 1000cc car engine and a 1000cc bike engine

[loply]

Bike engine has the following advantages:

Ligher parts (more expensive)
Higher stressed parts (servicing more)
Revs higher (noise and fuel and reliability burden)
Sporty power curve (would make cars frustrating to drive)
Generally tuned higher (noisy/revvy/unreliable)
All the above makes the engine a lot more expensive.


Hence why theyre more powerful.

[Robby]

Its all to do with the revs.

Bike and car engine can deliver similar torque, in fact the bike can often be making more - Offhand a 4 cyl litre class sports bike should be making about 80 lb/ft of torque, against a 4 cyl litre class small car making about 60 lb/ft of torque AFAIK.

Car engine are in a softer state of tune to last about 4 times as long with service gaps 2 or 3 times that of bikes.

Car engines typically redline at about 6k rpm, whereas bike ones are redlining at around 12-14k now.


Remember torque is not the feeling of low down power - that is quite simply low down power. A twin does not make more torque than a four, it makes similar torque or less, just develops useable power lower down.

Power = torque x revs.


A bike engine also runs dirty compared to a car engine - only now are bikes having to run power robbing catalytic converters with fuel injection, which cars were doing 10 years ago.

Drag is less of a factor because bike drag is awful. The problem is weight and power holding cars back in comparison to bikes.

[Spiral]

[The Dude]

Thanks dudes. Like i said, it was my bother thats been asking.

[hugo-a-gogo]

double the power doesn't equal double the speed

the power/speed graph is a curve

you need 4 times the power to double your speed (roughly)

and it's all about the drag and rolling resistance, weight doesn't affect top speed so much, just acceleration
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clicky 4 bikey

[Gazdaman]

[Kickstart]

[stryker]

Ever wondered why a 1000cc car engine is so much bigger than a 1000cc bike engine?

One word, "stress". A car engine has to be prepared to lug around 1500kg of car plus say 4 passengers. A bike engine, even on a large bike only pulls around a couple hundred kilos. Hence a car engine has heavier cams, bearings, crank shaft etc.

The materials used and design of your typical family car engine are designed to deliver smooth torque through the rpm range. Sports bikes are designed to carry more torque at the higher range of revs.

Interestingly enough, the reliant robin engine is happy up to 9k revs, at which point the shaft to the dizzy shatters and drops into the engine The people who race with those engines can do a few mods though to get round that. However the reliant 850cc engine carries a very light car round hence its particularly small size and inherent high rev range.
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Now what?

[stryker]

[Jebus]

yeah, bike engines often have very short strokes compared to ccar engines, shorter stokes let engine rev more

[Robby]

The limiting factor is piston speed, so a long stroke at 12000 rpm would have to have its pistons moving faster than a short stroke at 12000 rpm.

So yes, shorter stroke = higher revs. Longer stroke = more torque, and more time to burn to more efficient.