How much would wheel weight affect fuel consumption?
Discussion
Taken from another forum -
"Well, going from 16" alloys with 195/45 R16 tyres to winter steelies with 175/65 R14 tyres I notice about a 10% difference in fuel consumption."
Given that the rolling radius of both tyres is the same, so gearing pretty much unaffected, would the extra weight of an alloy wheel give worse fuel consumption, and would it be 10% different?
NB the above is getting better fuel consumption on the smaller wheels, as they are lighter.
I'd find it unlikely that the difference in wheel weight would make that much of a difference to fuel economy - would it be more likely to a subconscious change in driver style with winter tyres on?
"Well, going from 16" alloys with 195/45 R16 tyres to winter steelies with 175/65 R14 tyres I notice about a 10% difference in fuel consumption."
Given that the rolling radius of both tyres is the same, so gearing pretty much unaffected, would the extra weight of an alloy wheel give worse fuel consumption, and would it be 10% different?
NB the above is getting better fuel consumption on the smaller wheels, as they are lighter.
I'd find it unlikely that the difference in wheel weight would make that much of a difference to fuel economy - would it be more likely to a subconscious change in driver style with winter tyres on?
doogz said:
The change in unsprung mass, and the extra torque required to get those larger heavier wheels turning would make a difference.
10% though? I don't think so.
The torque argument is the one being used for this difference, but I can't see it in a million years. If it was that easy, all cars would come on steelies as standard for CO reasons alone.10% though? I don't think so.
At a steady speed, with the same radius, the weight of the wheels has no influence. So it would be down to rolling resistance, and 10% seems very high.
Accelerating, extra weight of wheels and/or tyres would cause extra fuel consumption, but 10% seems very high.
Maybe he didn't have the correct tyre pressures. Or forgot to take the handbrake off?
Accelerating, extra weight of wheels and/or tyres would cause extra fuel consumption, but 10% seems very high.
Maybe he didn't have the correct tyre pressures. Or forgot to take the handbrake off?
Ford quite nicely provide fuel consumption figures for their cars with various sized tyres. The extra urban figures for my ST220 is 35.x MPG on 225/40/18, and 38.x MPG on 205/55/16 - on the flip size the urban cycle is negligible. Having used both tyre sizes, I would agree with Ford; the cars also much faster on the 16" alloys.
Car and Driver did an interesting feature on that:
http://www.caranddriver.com/features/10q1/effects_...
http://www.caranddriver.com/features/10q1/effects_...
Kolbenkopp said:
Car and Driver did an interesting feature on that:
http://www.caranddriver.com/features/10q1/effects_...
Good read, cheershttp://www.caranddriver.com/features/10q1/effects_...
My A6 came with cheap RS copy wheels 18" 235/45 tyres. I got rid of them for genuine 16" with 205's. The 18" were a bigger circumference meaning a higher ride height and much heavier. Over the week after fitting the stock wheels the computer changed from 24mpg average to 26mpg. Ride height has a significant impact of efficiency as does rolling resistance. I presume they were the important changes to improve mpg - they are variables BMW alter in that manner on the efficient dynamics cars.
I also experienced a similar (10%) improvement in consumption when I went from Michelin PS3 225/45/17 to Pirelli SottoZeros 205/55/16. I did as much research as I could and noted that in all the reviews the Pirellis come out very well for rolling resistance. I put it down to that... The difference in weight between the two alloy designs was pretty negligble. The 16s weighed 18kg and the 17s 20kg (with tyre), I know because I sold them on ebay and had to weigh them for shipping.
Herman Toothrot said:
My A6 came with cheap RS copy wheels 18" 235/45 tyres. I got rid of them for genuine 16" with 205's. The 18" were a bigger circumference meaning a higher ride height and much heavier. Over the week after fitting the stock wheels the computer changed from 24mpg average to 26mpg. Ride height has a significant impact of efficiency as does rolling resistance. I presume they were the important changes to improve mpg - they are variables BMW alter in that manner on the efficient dynamics cars.
But the trip computer wouldn't have known that the wheel rolling circumference changed, so I would have thought one of the readings would have been inaccurate (ie. the one the computer had not been calibrated for), the speedo and distance readings would be wrong too.For a given distance traveled the smaller wheel is rotating more times so the trip computer will see better mpg since it is counting the number of rotations per unit of fuel used, rather than distance per unit of fuel.
seagrey said:
A couple of years back I read an article in a bike mag where they were trying to make an R6 as quick as an R1 without any power mods,the biggest increase in performance came from fitting lighter wheels.
When I was racing, the single biggest improvement to lap times were by fitting lighter wheels and wheel nuts.I saved 7.5kg per corner and the overall effect on the car was night and day.
Apparently unsprung weight is bad, rotational weight is also bad! So unsprung rotational weight is the worst of the worst!!
Unfortunately, the car didn't have an onboard computer.
Herman Toothrot said:
My A6 came with cheap RS copy wheels 18" 235/45 tyres. I got rid of them for genuine 16" with 205's.
205s with what section? The rolling radius should have remained close enough to the same overall, the ride height only being altered by that difference. A significantly reduced radius would throw your speedo out to misread both instantaneous speed and distance travelled, which in turn would result in skewing the MPG readout as displayed by the OBC. 235/45 R18 gives a radius of 334.35mm. 2.1008m rolling circumference. 761.6rpm at 60mph
205/60 R16 would be 326.2mm (-2.4%). 2.0496m rolling circumference. 780.64rpm at 60mph (2.5% error at 60mph)
205/65 R16 would be 336.45mm (+0.006%). 2.114m rolling circumference. 756.86rpm at 60mph (0.006% error at 60mph)
So assuming 205/65 R16, your ground clearance (ride height will technically be the same as your springs or dampers haven't got any shorter) will be 2.1mm higher (leading to worse, not better economy), but the 60mm decrease in overall tyre width and therefore frontal area/CdA I would have thought would contribute to a greater extent to any fuel economy improvements. With such a marginal error at that size, I'd expect the OBC to remain fairly accurate, bearing in mind that any tyre loses 5.4-6.4mm of radius from new down to 1.6mm wear indicators, which is why speedos, odometers and OBCs aren't able to be as accurate as they could theoretically be, they're a best average. As you can see, 2.5% error doesn't sound like a lot, but over a typical 150k mile life of a modern car, you've lost (or gained if it were the other way) 3,750 miles from your odometer reading.
The mass of the wheels themselves is almost incidental to such considerations, what that will affect however is steering torque (as will the decreased tyre area in contact with the ground as a result of the narrower tread width, so one may offset the other) and handling by either increasing or decreasing the load on the wheel hubs and therefore the control arms etc. and to an almost immeasurable and imperceptible amount the acceleration and braking of the vehicle as a result of higher or lower overall vehicle mass (which in itself has implications for economy).
Edited by Zwoelf on Saturday 1st October 10:07
Mr Sparkle said:
Herman Toothrot said:
My A6 came with cheap RS copy wheels 18" 235/45 tyres. I got rid of them for genuine 16" with 205's. The 18" were a bigger circumference meaning a higher ride height and much heavier. Over the week after fitting the stock wheels the computer changed from 24mpg average to 26mpg. Ride height has a significant impact of efficiency as does rolling resistance. I presume they were the important changes to improve mpg - they are variables BMW alter in that manner on the efficient dynamics cars.
But the trip computer wouldn't have known that the wheel rolling circumference changed, so I would have thought one of the readings would have been inaccurate (ie. the one the computer had not been calibrated for), the speedo and distance readings would be wrong too.For a given distance traveled the smaller wheel is rotating more times so the trip computer will see better mpg since it is counting the number of rotations per unit of fuel used, rather than distance per unit of fuel.
Rollcage said:
Taken from another forum -
"Well, going from 16" alloys with 195/45 R16 tyres to winter steelies with 175/65 R14 tyres I notice about a 10% difference in fuel consumption.
Given that the rolling radius of both tyres is the same, so gearing pretty much unaffected, would the extra weight of an alloy wheel give worse fuel consumption, and would it be 10% different?
NB the above is getting better fuel consumption on the smaller wheels, as they are lighter.
I'd find it unlikely that the difference in wheel weight would make that much of a difference to fuel economy - would it be more likely to a subconscious change in driver style with winter tyres on?
"Well, going from 16" alloys with 195/45 R16 tyres to winter steelies with 175/65 R14 tyres I notice about a 10% difference in fuel consumption.
Given that the rolling radius of both tyres is the same, so gearing pretty much unaffected, would the extra weight of an alloy wheel give worse fuel consumption, and would it be 10% different?
NB the above is getting better fuel consumption on the smaller wheels, as they are lighter.
I'd find it unlikely that the difference in wheel weight would make that much of a difference to fuel economy - would it be more likely to a subconscious change in driver style with winter tyres on?
Kolbenkopp said:
Car and Driver did an interesting feature on that:
http://www.caranddriver.com/features/10q1/effects_...
http://www.caranddriver.com/features/10q1/effects_...
GaryST220 said:
Ford quite nicely provide fuel consumption figures for their cars with various sized tyres. The extra urban figures for my ST220 is 35.x MPG on 225/40/18, and 38.x MPG on 205/55/16 - on the flip size the urban cycle is negligible. Having used both tyre sizes, I would agree with Ford; the cars also much faster on the 16" alloys.
So 10% is quite feasible. Weight, width, rolling resistance, and drag. Could be around £20 a month for many.Gassing Station | General Gassing | Top of Page | What's New | My Stuff