Alloy wheel size and fuel economy
Discussion
http://www.caranddriver.com/features/effects-of-up...
Interestingly, as well as the fuel economy being better they also recorded the best acceleration times on the smallest wheels with the narrowest tyres, and not by a tiny margin either.
Interestingly, as well as the fuel economy being better they also recorded the best acceleration times on the smallest wheels with the narrowest tyres, and not by a tiny margin either.
vikingaero said:
There's been a few motoring shows who have tested a standard car v. a standard car with stupidly phat alloys where the standard car is nearly always the fastest.
Another classic one is some people elect to remove either brand new or still perfect condition exhausts bin them and put on another exhaust- Fabia vRS diesel springs to mind which it gives zero benefit and countless other cars too. Too much money
Or another one drilling holes into OEM air boxes with the thought that they get more power... Sadly not so ruined a perfectly good part and made the car slower to boot? Go figure.
Snowboy said:
I'm guessing the OP is asking about if it was the same width and same tyre circumference.
Exactly the same outer dimensions.
Just a bigger wheel and thinner tyre.
The bigger wheel is still likely to be heavier. If it's the same overall rolling radius, width and weight I see no reason to believe it will make a difference. Exactly the same outer dimensions.
Just a bigger wheel and thinner tyre.
Okay let's just say you were running 185/60 r14s which had, approximately a rolling circumference of:
Wheel: 14 x 25.4 = 355.6mm
Tyre: 185/100 x 60 = 111mm x 2
Total diameter 577.6
Circumference 1814.8mm
If you then decided you wanted 15" wheels and went for 185/55 r15 , the circumference would be:
Wheel: 15 x 25.4 = 381mm
Tyre: 185/100 x 55 = 101.75 x 2
Total diameter. 584.50
Circumference. 1836.5mm
My point being, even with the rough figures I've used above, a change in wheel size can not always be completely allowed for in reducing the tyre profile, as for every revolution of that wheel on the larger wheel covers an extra 22mm (ish, theoretically) so the change is gearing and hence fuel economy is obvious.
Over 1km travelled, there would 7 fewer revolutions required from the larger wheels, so the wheels are travelling less, but the engine may be expending more power turning them.
Wheel: 14 x 25.4 = 355.6mm
Tyre: 185/100 x 60 = 111mm x 2
Total diameter 577.6
Circumference 1814.8mm
If you then decided you wanted 15" wheels and went for 185/55 r15 , the circumference would be:
Wheel: 15 x 25.4 = 381mm
Tyre: 185/100 x 55 = 101.75 x 2
Total diameter. 584.50
Circumference. 1836.5mm
My point being, even with the rough figures I've used above, a change in wheel size can not always be completely allowed for in reducing the tyre profile, as for every revolution of that wheel on the larger wheel covers an extra 22mm (ish, theoretically) so the change is gearing and hence fuel economy is obvious.
Over 1km travelled, there would 7 fewer revolutions required from the larger wheels, so the wheels are travelling less, but the engine may be expending more power turning them.
kambites said:
http://www.caranddriver.com/features/effects-of-up...
Interestingly, as well as the fuel economy being better they also recorded the best acceleration times on the smallest wheels with the narrowest tyres, and not by a tiny margin either.
Interesting. Amazing that there's no advantage for a 235 tyre over a 225 tyre on a standard Golf. I assume the average suspension and brakes are offsetting the potential advantage in grip over a 225 tyre? Interestingly, as well as the fuel economy being better they also recorded the best acceleration times on the smallest wheels with the narrowest tyres, and not by a tiny margin either.
M4cruiser said:
It's more complicated than that: bigger wheel = less rubber (in theory). Alloy may weigh less than rubber, so the larger wheel may actually weigh less in total when fitted with a tyre. 
That's what the alloy wheel retailers would have you believe anyway.
Of course, but in my experience that is never actually the case, unless the wheels are made of completely different materials which on mainstream cars they generally aren't. I doubt there is a car on sale at <£40k where the smallest wheel option isn't the lightest (I'm intrigued to know if anyone has any counter examples?). That's what the alloy wheel retailers would have you believe anyway.otolith said:
Where cars are offered with the option of larger alloy wheels, is it not typical that they are wider as well as larger diameter?
I guess it varies. It's not, for example, the case with our Octavia which it was available with 225/45R17 or 225/40R18. The 18s are over 5kg a corner heavier though (running Eagle F1s Asymmetrics)!
kambites said:
M4cruiser said:
It's more complicated than that: bigger wheel = less rubber (in theory). Alloy may weigh less than rubber, so the larger wheel may actually weigh less in total when fitted with a tyre. That's what the alloy wheel retailers would have you believe anyway.
Of course, but in my experience that is never actually the case, unless the wheels are made of completely different materials which on mainstream cars they generally aren't. I doubt there is a car on sale at <£40k where the smallest wheel option isn't the lightest (I'm intrigued to know if anyone has any counter examples?). That's what the alloy wheel retailers would have you believe anyway.Gassing Station | General Gassing | Top of Page | What's New | My Stuff