Which tire/wheel size for better fuel economy?

[on2]

I have a dilemma. I have a 2013 Honda Accord Sport. From the factory, it is equipped with 18x8 wheels that weigh in at a hefty 29 lbs. each. The OE tires are 235/45/18 Michelin Primacy MXM4 and are 26 lbs. each for a total of 55 lbs. per corner.

For better fuel economy I plan on changing the wheels to some much lighter weight wheels.

Cost aside, my questions are...

1.) Which wheel diameter uses less fuel between 18" and 19"? The 18" and 19" wheels I am looking at are both around 19 lbs. Assume both wheels have the same width and aerodynamics and the tires fitted are the same weight (which they really are to my surprise I checked the specs on tirerack.com).

2.) Which tire size uses less fuel between 225/45/18 (possibly 225/40/19) or 245/45/18 (possibly 245/40/19)?

The 225 section width tires weigh less at 22 lbs. each, have less rolling resistance due to less section width, but is effectively a lower gear ratio thus increasing the engine revs at cruising speed.

The 245 section width tires weigh more at 25 lbs. each, have more rolling resistance due to more section width, but is effectively a higher gear ratio this decreasing the engine revs at cruising speed.

So which combination of benefits is better for fuel economy?

I know that 17" wheels or less is the best in terms of weight for fuel economy but that size looks to small on this car. There are 18" wheels that weigh only 16 lbs. each. Equipped with 22 lb. tires that's a total of 38 lbs each corner a savings of 17 lbs. each corner for a total of a whopping 68 lbs!

Thank You

[CapriRacer]

Tire size is of minor importance. What is important is differences between tires. That difference can be HUGE - up to 60% difference in rolling resistance.

I talk about it more here:

Barry's Tire Tech

[mcrews]

Welcome.
there are numorous threads on this.....did you even search?

tire size - Google Search
ignore the truck threads.

[on2]

Originally Posted by mcrews

Welcome.
there are numorous threads on this.....did you even search?

No I didn't. Sorry. I know... I know... first rule of fight club is...

Funny thing is, in most of those threads I read, you pop up and say the same thing you said to me. "Did you search?"

So after reading some threads on the first and second page of search results and the link CapriRacer posted...I have came to answer my questions in following manner. Correct me if I'm wrong.

1.) The larger of the two wheels of the same weights is less FE because the weight is farther from the center thus using more energy to get going. Once up to speed the difference is negligible, especially since I'm looking at wheels of the same weights.

2.) The wider tire (245) is better because it actually has less RR. My previous thinking that wider tires have more rolling resistance is wrong. It is actually the opposite. The wider tire is less aerodynamic (barely) but is more than made up with the lesser rolling resistance. The wider and taller tire is also effectively a lower gear ratio thus increasing FE. The increased weight (2-3 lbs.) of the wider tire 245 compared to the narrower 225 will use more energy when accelerating, but once up to speed the difference is again negligible.

Thanks for the help. I'm going with the 245/40/19's. Better looks and better fuel economy to boot.

According to the tire specifications. The new tire is 0.4" taller effectively making my car 0.2" taller. (Will be 57.9" tall, stock is 57.7") This is great because this also means a 0.2" reduction in wheelwell space which is good for aerodynamics and aesthetics, but is also bad because it makes my car 0.2" taller which is bad for aerodynamics and aesthetics. Since I was already planning on lowering my car (20mm) for the handling benefit, I will also benefit from a lower car (will then be 57.1", stock is 57.7") and even less wheelwell space (reduction of 1") which is both great for aerodynamics and aesthetics.

Coming from a performance oriented mindset to an ecofriendly mindset, I'm finding that there is a lot of similar shared benefits to both performance and fuel economy. This is so FULL OF WIN!

[PaleMelanesian]

1. When it comes to wheels, lighter weight is better. Smaller diameter can help with this.
2. The specific tire design matters more than size for mpg. Look for LRR tires like Bridgestone Ecopia or Michelin Energy Saver. TireRack has an option for LRR in its search criteria.

[mcrews]

Good job!
1. Depnending on amount of freeway driving.....larger diameter is better. When it's all citty...not so much.
taller tires have always worked for me on the 2002 Q45 and the 07 Kia Sportage.
2. As Barry says....look for a composition that offers lower rr.
3. If there is room go w/ the taller tire (after judging #1)
4. While a taller tire is moving a small amount of the weight farther out, the real concern is when someone wants to increase rim size to get to a taller tire.
5. Need to be taller by at least 5% to have a noticeable gain in mpg.

on the issue of weight:
1 lb static is worth 4 lbs moving(rolling) so more weight is bad. Mainly because of the increased wear on the suspension parts and brakes.
Lowering weight for better mpg is not really effective.
Foe example: remove your spare and check your mileage against having it in the trunck. Bet you $1 there is no difference......and the spare is 40-50 lbs. or 10lbs a tire.......

Now maybe on a truck.......but not on a car.
think about it....how much smaller diameter do you have to go to gain a 10lb reduction????
Now look at the rpms at the smaller diameter.

[PaleMelanesian]

Yes, but you can go smaller on the wheel, and upsize the tire's sidewall to maintain the diameter. Just like my Fit is offered with 15" wheels or the top trim has 16's.

An example from my Fit. The lightest wheels at Tirerack are the Enkei RPF1's. 15" (base model size) weighs 9.5 lb. 16" is 13.7 lb.

Yokohama Avid Ascend tires in those sizes (both 185 width, 60 vs 55 sidewall) are both 19 lb.

Combined weight: 15" = 28.5 lb, 16" = 32.7 lb.

[mcrews]

Pale,
absolutely agree.
Just wanted to clatify: A reduction in overall diameter just for a coiple of lbs will show no gain.
The u;timate win/win is as you explained. a lighter, smaller rim and a larger diameter tire!!

[RedDevil]

Tire width does not help with rolling resistance imho. It may seem like so if you run the narrow and wide tires on the same pressure (especially when that's quite low) because the narrower tire would have to flex deeper.
To compensate for the narrower thread you have to increase the pressure to the same ratio to get a fair comparison. Then you'll see the narrower tire win hands down.
Narrower tires are less prone to aquaplaning too; as the risk of aquaplaning rises with higher pressure it is tricky to raise the pressure on tires that wide.
Narrower tires will allow for far higher pressure before losing traction.
As increasing tire pressure is the one mod that effects FE most, go as narrow and up the pressure as high as you dare.

My Insight is sensitive to side wind, but that effect has almost gone away since I raised the pressure from below OEM to way above.
My Insight is at 175 width winter tires now. The Accord would need to weigh over 2 tons to get the same thread pressure as mine if you go for 245 mils. I'd rather go for 205's... but I'm not you.

[wmjinman]

I just checked the Tire Rack site for LRR tires for my Swift (13"), and it showed nothing. Then I checked the "optional" sizes 14" and 15", and it STILL showed NOTHING (in LRR). What's the deal? What do other Metro/Swift/Firefly owners do for tires???