Which tires for best Fuel Economy? 2001 Corolla CE.

[morkys]

Looking at keeping my steel wheels with their winter tires and getting 14" alloy rims. I'm looking at the FAST Static 14" x 6" alloy rim as it is lighter than the stock steel 14" wheel. The tires I am chosing from are:

175/65-14
185/65-14
195/60-14

So, any advice as to the tire size and which model? The 175/65 and 185/65 can both be found in the common Michelin Harmony/Destiny. The 195/60-14 is not available in that model, so I need suggestions.

thanks,

[theholycow]

My research indicates that, contrary to popular belief, a wider tire will have less rolling resistance. The 185/65-14 is the tallest among the three listed sizes and will give you a slight gearing advantage.

Generally, I recommend buying long treadwear tires and not worrying about rolling resistance too much. You can be sure a long treadwear tire will save money. You can't be sure of rolling resistance numbers.

[morkys]

Originally Posted by theholycow

My research indicates that, contrary to popular belief, a wider tire will have less rolling resistance. The 185/65-14 is the tallest among the three listed sizes and will give you a slight gearing advantage.

Generally, I recommend buying long treadwear tires and not worrying about rolling resistance too much. You can be sure a long treadwear tire will save money. You can't be sure of rolling resistance numbers.

I heard the 'gearing advantage' has caused some to experience reduced fuel economy. Not sure how that works. In some ways, you'd think lower rev's = less fuel used, but, maybe taller gearing equals a higher load on the engine? Interestingly, many Corolla's came with 185/65-14's with no change in speedo calibration. I think the LE and sport had 185/65-14's. Anyways...a taller tire won't be as resistant to flex, so I believe it would use more fuel. The 175/65-14 and 195/60-14 are almost totally identical in height.

I have been doing some research, and just recently, after I posted this question, I found some people saying that narrower tires have an aerodynamic advantage. I suppose the best choice would be a 175/65-14 in terms of frontal area aero-dynamics. So, it's kinda tricky to figure it out. I'd love to buy two ot three identical sets of rims and run a bunch of sets of wheels and calculate fuel economy...but hey, I can't afford that science experiment...heheh...

thanks for the feedback,

[theholycow]

Certainly, the benefit of taller gearing through taller tires is limited to cars that don't come with the best gearing for fuel economy. A Corolla may already come with the best gearing for fuel economy, and changing it in either direction might reduce fuel economy. I think most cars probably come adjusted for better acceleration instead, at least a little bit.

It's my guess, based on my research, that the aerodynamic difference is miniscule but the rolling resistance difference (if you expect one) is worthwhile.

Again, the most sure way to save money in the long term is to get long-lasting tires.

[morkys]

People are saying BMW did some research about aerodynamics of tires. I find it hard to believe that a 2 cm difference in tire width would make much difference. The wider tire has a larger contact patch, but since it's not higher, it shouldn't make much difference. I am torn between the two tire sizes that are nearly identical in height. I am trying to decide between 175/65 and 195/60. I'll flip a coin.

[theholycow]

The 195 will deliver more fun cornering, in addition to what I believe would be lower rolling resistance.

[JanGeo]

The Goodyear low rolling resistance tire is rated for 51psi max and has a narrow than usual tread for the same size conventional tire. TireRack also says that a taller tire has MORE rolling resistance than a shorter tire but by how much is not stated so there may be some small gearing / rpm advantage to a slightly taller tire. I am contemplating that right now along with some 9.9lbs mag wheels to lighten up the stock 19lbs steel rims on my 06xB. 185/60R15 vs 185/65R15 for a little taller profile.

[morkys]

Why would the 195 have lower rolling resistance? I'm not sure I understand that. I admit that other Corolla owners have said that switching from their 185/65-14 to the 195/60-14 caused no drop in fuel economy. I just thought a narrower tire gives you lower rolling resistance. Maybe that's not true, as you say. I just wonder why.

[theholycow]

Well, there are a number of theories and few measurements. The theory I continue to use until proven otherwise is as follows:

• Given an inflation pressure and a load, the contact patch will be a certain size. For example, at 10 pounds per square inch inflation with a 100 pound load, the contact patch will be 10 square inches.
• A major component of rolling resistance, probably most of it, comes from deformation of the sidewall to produce the contact patch.
• If the contact patch size doesn't change with the width of the tire, then its shape must. As you make it narrower, it gets longer; that means more deformation of the sidewall. If the contact patch is going to be 10 square inches and your tire is 2 inches wide, then the contact patch will be 5 inches long. If the tire is 4 inches wide, the contact patch (and required sidewall deformation) will be 2.5 inches long.

That is definitely true of bias ply tube-type tires as found on bicycles. It is possible that something about modern automotive tubeless radial construction fundamentally changes that effect. However, without good data to tell me for sure, I have little reason to doubt it.

There are other issues that make me think that a wider tire would have lower rolling resistance, but that is the largest and easiest one.

[morkys]

Yeah, I guess it's totally impossible to decide what will be the absolute best in the end. The stock steel wheel I have is 5.5" wide x 14" and from most sources, weighs about 18 LBS. The replacement rim I intend to use is a FAST 'Static' rim at 6.0" x 14" and 13.6 LBS. I have asked what the weight of the 15" rim is but so far haven't heard back.

The stock tire I have is:

175/65-14

The common upsize is:

185/65-14

but this is both significantly taller, at close to 1/2" AND also wider.

The other options are:

185/60-14 (slightly shorter than stock 175 by 1/4" or 5 mm)
195/60-14 (slightly taller by about 5 mm)

or

185/55-15 (essentially identical in height to stock size...but an oddball size and a heavier wheel (6.5" wide x 15"))

Not sure what to do....

I wonder which is worse for Fuel Economy vs stock 175/65-14...Taller and wider 195/60-14 or shorter and not as wide 185/60-14?

I agree you guys and others have found little difference in MPG when going with a slightly wider tire, but some have found the Cd goes up noticabley. I guess it's possibly only significant when you go up more than 2 cm in width.