Discussion
If car wheels were made about 3-4" bigger would a car with a standard gearbox and engine go faster/use less petrol,Obviously the car would have to be designed to accommodate the bigger wheels and the handling aspects would have to be considered.
If the outside circumference was bigger than it would travel further than a smaller wheel,May look stupid though.
If the outside circumference was bigger than it would travel further than a smaller wheel,May look stupid though.
If you could maintain the same engine RPM's, yes, it would be travelling faster.
But you've got the additional power required at lower RPM's (generally not desirable), an increase in unsprung weight from your huge wheels (spoiling the ride and handling), and significantly poorer acceleration.
But you've got the additional power required at lower RPM's (generally not desirable), an increase in unsprung weight from your huge wheels (spoiling the ride and handling), and significantly poorer acceleration.
Short answer: depends.
Long answer: what you're doing is increasing the gearing. If you are willing to re-engineer the car to suit your new wheels it'll be easier to just change the gearing instead, and not put up with needlessly huge wheels. Top speed may increase, or may become lower, depending on gearing, same with MPG. Gearing is a massive compromise and not always easy to improve on. Acelleration will be worse.
Long answer: what you're doing is increasing the gearing. If you are willing to re-engineer the car to suit your new wheels it'll be easier to just change the gearing instead, and not put up with needlessly huge wheels. Top speed may increase, or may become lower, depending on gearing, same with MPG. Gearing is a massive compromise and not always easy to improve on. Acelleration will be worse.
nickcowen said:
Always thought that bigger wheels would give a higher top speed but smaller one would give better acceleration
In theory, bigger wheels will give you a higher top speed in each gear but there are a couple of issues.Think about a small engined car, where fifth is just a cruising gear and you only have enough torque to accelerate in fourth. If you put sufficiently big wheels on, fourth gear would become the equivalent of fifth so you'd have to use third to accelerate. At that point you can only accelerate up to the top end of third, so you've actually reduced the top speed of your car.
I know that's an extreme example but it's valid, and even if that didn't present a problem the maximum speed of a car is generally dictated by power so large wheels won't help anyway.
Small wheels might make acceleration faster and probably won't affect your top speed, but it's not all win as they require you to upshift earlier when accelerating, which can counter the effect of faster in-gear times.
Moral of the story: it's never simple!
Bigger wheels (as in rolling diameter) have much the same effect as increasing the final drive ratio. Most cars would probably get less efficient if you just blindly increased the rolling radius because manufacturers have carefully tuned the final drive ratio for the standard size. Top speed would probably fall for much the same reason - very few cars are limited by the rev limited in top gear.
matthias73 said:
Captain Muppet said:
Krikkit said:
RPM's
Revolutions is already plural, no need to pluralise the entire unit.Also it's not a grammar thing, it's retarded use of engineering units.
If anything I'm from the engineering police.
blearyeyedboy said:
Captain Muppet said:
If anything I'm from the engineering police.
Just don't try that as a chat up line. 
Although "I have a house and disposable income" works nearly as well as "does this smell like chloroform to you?".
cindychops said:
If car wheels were made about 3-4" bigger would a car with a standard gearbox and engine go faster/use less petrol,Obviously the car would have to be designed to accommodate the bigger wheels and the handling aspects would have to be considered.
If the outside circumference was bigger than it would travel further than a smaller wheel,May look stupid though.
If the outside circumference was bigger than it would travel further than a smaller wheel,May look stupid though.
cindychops said:
If car wheels were made about 3-4" bigger would a car with a standard gearbox and engine go faster/use less petrol,Obviously the car would have to be designed to accommodate the bigger wheels and the handling aspects would have to be considered.
If the outside circumference was bigger than it would travel further than a smaller wheel,May look stupid though.
What do you mean by faster??If the outside circumference was bigger than it would travel further than a smaller wheel,May look stupid though.
Upping the wheel size will reduce rpm's for a given speed. If you are not labouring the engine, then it should offer better mpg, although dependant on pumping loses.
If you have the power (and aero) to run to the same engine rpms as before, then yes you'll be travelling at a high speed. Although likely with slower acceleration.
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