Does light alloy wheels improve gas mileage?

[mechtech]

You'll see greater gains around town, or suburban driving, than at steady highway speeds.
A lightweight wheel or tire is much easier to accelerate[or brake].

It is in the right direction, but don't expect miracles.

 

[m2200b]

If you want better gas mileage from the wheels / tires on your Echo - take a hard look at the rims, size and tires used on Prius as Toyota was trying for max mpg on those.

 

[eljefino]

If your echo uses, say, 4x100 rims, there are years and years with that pattern.

Some cars unpopular enough they're all junk now.

I have seen rims on ebay for $1 ea, which would make sense if you could pick them up locally.

Junkyards can and do simply melt them down so if you can beat the melt value it might be worth it.

PS, I have alloys on my saturn and they leak air more than steelies. 3 out of 4 are moderate leakers. IDK if it's bad mounting, bad valve stem sealing, porosity, but if you're not absolutely on top of things that low pressure would cut your mileage.

 

[johnd]

I won't comment on alloy wheels per se but a "lighter" wheel will improve the sprung/unsprung weight ratio and thus improve the car's ride.

 

[H2GURU]

I think there is some advantage to a rim up-grade. How about turning the clock back to 1966. Didn't any of you have Cragars on the rear and Slotted on the fronts?

 

[Ken4]

I did a test on my '00 Camry 2.2L:

1. With 17" Enkei Aegis rims & 215/50/17 tires, weight 19.5kgs each (tire + rim), 0-100kph in 12.65secs.

2. With 15" Factory Steel rims & 205/65/15 tires, weight 18.3kgs each (tire + rim + hubcap), 0-100kph in 11.65secs.

3. With 15" Sprinthart CP-035 & 205/65/15 tires, weight 13.5kgs each (tire + rim), 0-100kph in 11.2secs.

Never tested for fuel economy though. I was more interested in straight line performance. The 15" CP-035s are ultra light weight forged alloy rims which weigh only 4.6kgs each, paid S$600 per piece. In comparison most 15" cast alloy rims weigh around ~7kgs. And I've weighed some 15" alloy rims that are even heavier than my steel rims! And of course if you upsize to 16" or 17" rims, you will lose performance bcos they are even heavier, and give a more uncomfortable ride, and more braking effort required. Unless all you're interested in is cornering performance.

 

[Jim Spahr]

Then there is a disadvantage in going to a larger diameter wheel and tire. You increase the 'flywheel effect' at each wheel. Braking force is reduced. To counter that, you would have to increase the rotor size and caliper size. This increase in rotor size would be allowed by the larger diameter wheels, but now you have significantly increased the unsprung weight, when REDUCING unsprung weight is one of the main advantages of going from steel to alloy wheels. I shudder when I see the 22" wheels in vogue on the streets. They have ruined the braking and probably the ride and handling as well. Notice also that alloy wheels are usually not rated as high for towing as steel wheels are.

 

[Kestas]

OEM cringes when they see people modifying their cars with huge rims, for the reasons Jim and Ken just mentioned. Rubber is lighter than metal. Although they do improve cornering, huge rims just aren't as safe when it comes to braking.

 

[PRND3L]

quote:

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Originally posted by sifan:
Are alloy rims typically stronger than steel ones? Do they get bent more easily the steel ones?

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generally, no and yes.

 

[XS650]

quote:

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Originally posted by Gurkha:
The point is if you size up say from a 205-70-15 to a 235 or 245 16 tire, the additional weight of the bigger steel rim can be compensated by the lighter same size alloy wheel thereby putting less load on the suspension which was originally designed for the smaller and lighter tire/rim combo.

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Unless you are careful what you buy and willing to spend a fair amnount of money, alloy wheels can end up weighing more than steel wheels.

I doubt that 1 in 100 alloy wheel buyers could tell you what their alloy and previous steel wheels weighed.

 

[sifan]

That is an excellent point. With so many hidden facts I can see how easily a consumer could blindly fall into buying alloy rims due to their aesthetic appearance.

 

[TooSlick]

Jim,

That flywheel effect is directly due to the increase in angular momentum from oversized and heavier wheels/tires and is exactly what I was referring to. It takes more energy to spin heavy wheels/tires up to speed and more energy to stop them as well.

TS

 

[Dave H]

TooSlick,

I believe the ratio for non-rotational mass to rotational mass on wheels is approx 3:1. This means that for each 1 pound reduction in rotational mass (lighter rims/tires), it's like taking approx 3 pounds out of the inside of the vehicle.
For mileage concerns, I'd bet any increase in mileage from going to lighter rims could easily be made up just by modifying driver style.

Dave

 

[XS650]

quote:

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Originally posted by Dave H:
TooSlick,

I believe the ratio for non-rotational mass to rotational mass on wheels is approx 3:1. This means that for each 1 pound reduction in rotational mass (lighter rims/tires), it's like taking approx 3 pounds out of the inside of the vehicle.
For mileage concerns, I'd bet any increase in mileage from going to lighter rims could easily be made up just by modifying driver style.

Dave

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If you add rotational mass on the outer diameter of the tire, it's 2:1. If you add it anywhere closer to the center of the tires it's less than 2:1. People like to exagerate, some claim as much as 8:1, but they are just fuller of ** than your source.

There's a reason they are called Newton's Laws of Motion, not Newton's Good Ideas of Motion.

 

[ChrisW]

Forged (one-piece) wheels are the way to go for the benifit of both weight and strength. Though I have seen several cast al wheels that are very light.
Magnesium is another story.

But i say just buy some stickers. Adds HP, reduces aero drag, and they're cheaper than wheels.

 

[Gary Allan]

The ultimate mod! Just "Type-R" it. Outstanding results.

 

[DJ]

I have been researching rims for my slicks for drag racing my street car. Options I came up with are some 16lbs. 15x8s for $80 apiece or $200-300+ for 12lbs aluminum or billet aluminum. Takes a lot of aluminum to get the strength of steel so like others are saying you will spend a lot to get an aluminum rim that actually weighs less than steel be cause it will have to be a very high quality material and machining. My street tires are on 94-96 Impala SS rims 17x8.5" 5 spoke aluminums and weigh 29lbs apiece without the heavy 255/50ZR17 rubber, which pushes the total package to near 60lbs, snow tires are 215/75/15 on an alloy 15x7 about 40lbs total and you can definetely feel a difference in response.
For handling a heavy front wheel acts like gyro so reduced weight is good there.
Far as applying Newton's Laws think you need to calculate in DIAMETER and were in that diameter the weight is, everyone I know who dragraces has found reducing rotating weight to pay off pretty signifigantly, moreso with larger diameters and higher rpms.

Far as how all this plays into fuel economy

the results could not be meanigfully measured on the street and no way could it be worthwhile. Want to spend money to gain economy think O2 sensors, cleaning the MAF, plugs and wires, heck maybe even exhaust upgrades ro reduce pumping losses but that would not do much if anyting if you drive very moderately, I doubt if any current exhaust systems develope meaninful backpressure at low light acceleration flow.

 

[Gary Allan]

How's this tie into the evolution to a greater wheel to tire ratio? I've got the impression, that in addition to decreasing the sidewall deflection that could be a factor in handling, that the, properly made, larger alloy wheel would be lighter then the same cross section, with the required increased sidewall mass/strength, tire.

Any truth to my "impression". Otherwise having those 1.25" high sidewalls (apply appropriate number to accomodate 33" tires with 20+" alloys, as needed) with that low aspect ratio (or is it high

) are just bling.

I saved about 20lbs total with my OEM alloys over the steel counterparts. It was kinda a lost cause since I also added more then that in added tire height/width when going from 205/75r15 to 235/75r15. So, I exchanged the parachute effect when I let off the gas @70+ mph for the smoothness of a larger and heavier rotating mass(es) ..and spent the extra energy to move them.

 

[sifan]

Did the guy remove the muffler prior attaching the "Type-R" exhaust tip? If not, why the sound recording sounds so loud? I wonder if you have to rev the engine very high to achieve the added horse power. Since added horse power also means more fuel to burn, this is not a fuel saving device, isn't it?

 

[Master ACiD]

something that no ones really hit on is the fact that aluminum wheels just flat out ride better than steelies. you take a car with steel wheels and upgrade them to aluminum and re use the current tyres. once the tyres are rebalanced the car rides better. ill speculate here that its got something to do with the ammount of deflection that both steel and aluminum have when hitting small bumps, cornering, etc. not only that but aluminum wheels seem to be easier to balance on a machine, and they hold their balance longer. ive done alot of balancing with my uncles balancing machine. steelies typically require more weight and are back more often for a rebalance.

my car came with 14x5 steelies from the factory. the tyres are 185/60-14 and weighed 16.5 lbs each. the tyres whcih were weighed when new were 17lbs each. thats 134lbs for all 4 wheels/tyres.

i bought some konig helium's on ebay which weigh 10.2lbs each and are 15 inch. coupled with some 205/50-15 which weigh 18lbs, thats 112.8 total.

thats 21 lbs of savings. if you factor in that 2:1 theory thats 42lbs.

now of course i didnt buy aluminum wheels just to save 42lbs. i bought them to run slightly wider, low profile tyres. and because aluminum wheels just flat out ride better. plus they look great.

i didnt go with 16's or 17's etc because those are stupid for a car. too low profile means 1. expensive tyres 2. higher risk of damage from bumps 3. higher risk of theft 4. the wheels themselves cost more. 16's and up may be OK for a truck which has a bigger diameter tyre but for an average small-midsize car i think they are too small.