Low profile tires, fuel economy benefits?

RoadWarrior's picture

Hi folks,

I was just reading an old blurb about Pirelli introducing a 65% Aspect ratio tire and claiming F.E. benefits due to reduced sidewall flexion etc, over a 85% tire. Now they said something about 65% being "ideal" but I dunno if at the time it was thought possible to go much lower.

So I've been wondering if the modern low profile tires such as 40% aspect ratio are even better in this regard or not.

I realise there's a bit of a problem in comparison, since when you go up a couple of wheel sizes you're usually getting fatter tires too, so likely to go from say a 175/65 to a 225/45. But I was thinking that if one was careful and found the right wheel and tire combo, i.e, as skinny as possible, while being as large as possible, whether the reduced rolling resistance would pay off over the width penalty.

So, anybody ever upsize the wheels and get an MPG benefit without changing overall wheel diameter significantly? Or find higher mpg after your 5% (or whatever) mileage loss or gain was calculated in?

Road Warrior

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Low profile tires, fuel economy benefits?

RoadWarrior's picture

Was reading through that .pdf report that has been posted in a couple of links below. There is some hint of lower profile tires being more efficient in that but only indirectly. It has one graph showing 16 inch tires being a few percent more efficient generally than other sizes. Now, since at the time of testing it had become mmmore popular to oversize the wheels on cars sold new even, then that might have meant that in general they were lower profile.

However, the practice of giving the profile by percentage, kind of makes things hard to figure. I imagine that what we really want to know is efficiency versus actual sidewall depth. Since a wide 65% tire will have a taller sidewall than a narrower 65% tire.

Probably the savings with buying a new set of upsized wheels with low profile tires, a minimum of $500 if you take advantage of a package deal, is going to take years to pay off in mpg savings. I'm just trying to get it figured out, because once in a while one will come across a very good deal at a yard sale or in classifieds, for a hundred for a set or something. So I'm trying to get everything figured out so I can take advantage of any steals like that, if something comes up in a suitable size.

Road Warrior

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Low profile tires, fuel economy benefits?

ETAmax's picture

I would expect that lo-pro tires would have a positive effect on mileage in only a few instances, and a minor one even then.
Considering that:
Lower profiles allow for tires to be wider at a given rim size and wheel diameter to "improve handling" which means a larger contact patch and thus higher rolling friction. Or they allow for a larger rim diameter, mostly aesthetics. Bigger wheels are heavier wheels, which constitutes more rotational inertia. Plus when they wear out, you get to pay a premium price for replacements.

I say keep the rims small and the sidewall tall.

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Low profile tires, fuel economy benefits?

RoadWarrior's picture

Actually the contact patch area with a more rigid lower aspect ratio tire often ends up pretty much the same, only it's wide from side to side instead of long from front to back. For a mental picture of that, think of the large supersized sidewalls on swamp buggy or sand tires that roll more like caterpillar tracks than wheels. That effect increases the taller the sidewall. It's why you need to keep tire pressures up, to stop wasting energy flexing the sidewalls.

Also I think that for the same overall external diameter, the extra inch or two in the alloy wheel is actually lighter than the extra inch or two of steel belting and rubber that the tire makes up. Plus the extra air required at 30 psi or actually weighs something too, probably about another pound. Of course if you go silly and put 10 inch wide rims on a vehicle that had 5 inch wide rims stock, then there would be a weight gain (Unless you spend insane money for custom titanium rims or something). However, keeping it modest, like to a 16" 6.5 inch rim, then it's likely that the overall combo will weigh a bit less than stock 14" 5.0 steelies.

So, if we had some data on profile vs rolling resistance vs mpg, then we might be able to make some educated decisions about where the sweet spot is.

Manufacturers these days are supplying cars with larger rims and lower profile tires, for example the 2005 Toyota Matrix comes with 205/55-16 as standard equipment. With CAFE requirements to meet, you'd think they would offer the skinniest tallest tires on the smallest wheels as standard, if that got better economy, and give attractive deals on alloys to upgrade if they were desperate to get the younger customer on looks.

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Low profile tires, fuel economy benefits?

ETAmax's picture

All right, good points. LP tires are definitely harder, higher pressure, lighter with alloy rims.

Then again, if the stock suspension was designed to work with sidewal flex, handling and ride may suffer at the extremes.
I guess I look at the mileage champs; Insight, Prius, Metro, Euro-cars, '80s civics...
Seems they all tend to have wheels the smaller side.

I could do better, but I think I'll stick with my 185/7x-14s for the ubiquity and value! :D

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Low profile tires, fuel economy benefits?

DragonDon's picture

Something else that wasn't mentioned...unsprung weight. I'm guessing that many of the benefits will be offset with heavy rims.

I can attest to the handling benefits as with swapped springs and low-pro ties in my neon, the car stays _very_ flat when autocrossing, starts and stops with very little rocking. Now, the bumps on the road are felt pretty good.....but it handles well.

I just want a more confortable ride now.

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Low profile tires, fuel economy benefits?

RoadWarrior's picture

Well I might be finding something out, got a great deal on a set of 15" alloys that fit the van. Not sure what tires I'll get on them yet. Choices are 205/65 215/65 215/60 or 225/60, I've got 205/70/14 on right now. 205/65 don't seem to come in high enough weight rating, neither does 215/60. 215/65 seems a little tall (about 1.5% out I think, the 215/60 is about the same amount short) and 225/60 seems hard to get hold of at a decent price.

Edit: you know what though, seems decent rubber has gotten expensive all round, Won't see much change from $400 it looks like for 4 reasonable tires fitted and balanced. So maybe those $500 all-in deals for 16 or 17 inch alloys with tire on the internet are a better deal than sourcing even real cheap rims locally.

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Low profile tires, fuel economy benefits?

fuelmaxaman's picture

not sure whether the air pressure in the tire has more affect of fuel economy or if the sidewall size has more effect, but i can tell you that I have a 99 Grand Am gt-1 with the ram air 3400 HO and it has 225-55-ZR16's on it and it's mileage is a painstaking 22Mpg right now. Car runs and drives like it should and then some, but at least it gives me a nice low starting mileage to increase hopefully to appx. 50mpg!!!!!!! I'll definately post pics and have a place where people can see a power point presentation of a mileage test.

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