Civic VX - which tires is better to use for MPG
 

I know that the factory size is 165/70/13 but will 155/80/13 give me better MPG. When I bought my VX it cames with some new tires and I thought they were 175/70/13. Upon inspecting it, I found out that they were 185/70/13. I'm trying to purchase some new tires for it and I was debating between the 165/70/13 and the 155/80/13. Do you guys think I will be fine with some 175/70/13? What is best for MPG (92 civic vx FED Model).

I would suspect that the 185/70 would do best, if you could find them.

Between the 165/70 and 155/80 it's a toss-up. The 155/80 is a little taller but the 165/70 is a little wider. My research indicates that, counterintuitively, wider is better for fuel economy.

Is your driving more city or more highway?

By far better than any of these for increasing MPG would be to get a set of 14" wheels and get the 165/65/14 Bridgestone Potenza RE92 tires used on the Insight-I. I installed them on my car and their rolling resistance is well below that of any of the 175/70/13 or 165/70/13 tires that I've had on my car over the years.

Actually I have the 185/70 on my car right now. I guess since it's a toss up between the 165 and 155 than I might just go with the 165. I drive 30% city and 70% hwy.

If that's the case than I have always wanted to put my HX rims on. I'll see what's up. Thanks for the info.

Quick question? Could you point me in the direction of the study that says wider is better for fuel economy. Thanks, Jim

There is a severe lack of good data and complete studies on rolling resistance.

In my sig, there is a link to my thread on tire width where I placed an excessive quantity of my thoughts and research. In short, I can't prove that either narrower or wider is better for fuel economy.

What I do have is an understanding of some underlying principles that don't get much thought in general.

• At a given pressure and load, contact patch is expected to be the same regardless of width. What changes is its shape; a narrow tire has a longer, narrower contact patch, which requires more sidewall deformation to make that contact patch. Sidewall deformation for making a contact patch is a major component (possibly the largest contributor) of rolling resistance.

  * I believe that I am correct about all that, but I have doubts. Some data shows that modern automotive tubeless tires' contact patches don't adjust quite that way, unlike (for example) bicycle tires.

• A tire that holds more volume of air has a higher load capacity at a given pressure. Using less of a tire's laod capacity (again, at a specific pressure) means reduced rolling resistance. A wider tire holds more volume of air.
  
  
• One person's study: https://priuschat.com/forums/prius-te...rc-4-data.html
  
  Quote:

  Originally Posted by that study Michelin Tiger Paw AWP P225/60R16 at .00683 - a 25lb tire. On both these model lines, the smaller/lighter/narrower the tire gets, the higher its RRC/4.

There's also these issues, which may be less important:

• Aerodynamic drag - narrower tire is better.
• Keeping your momentum around turns - wider tire is better.

Both would have a tiny, immeasurable effect on your fuel economy.

Additional issues:

• Circumference/diameter - A taller tire will raise your effective gearing, lowering your RPM. Although the sizes in question are nominally similar in diameter, they are a little different.
  
  
• Tread life vs. price - IMO, this is the most important issue to consider. If you save $20 in gas over the life of the tires but have to buy tires more often then you've lost.
  
  
• Pressure - Check the maximum pressure rating of each tire you're considering. I'd rate this as second most important.

the holy cow, Could you give a size comparison to wrap my thoughts around. Thanks, Jim

What sizes would I compare?

I really can't quantify the possible gains. It's all theory, there's barely any data out there.

the holy cow,
All the data is out there. Here is a good place to start: https://www.tirerack.com/about/techcenter.jsp

Another good source is common sense. Does anyone think that a vehicle manufacturer for one second would try to get a lessor mpg rating by using a tire that would produce less. Think again. Read it, study it, and understand that their are hard cold facts about tire size, rolling resistance, and MPG...
Jim

ps: This is a much better tire size converter than the miata site example, https://www.wheelsmaster.com/rt_specs.jsp

That wheelsmaster tire size calculator is my favorite. I've had it in my sig on another forum for a few months. It gives you a lot more data than others and it's more browser-friendly.

I have plenty of tirerack links in my width and pressure posts. Tirerack doesn't provide data from studies, they just provide opinions and common knowledge...and some of it is conflicting, too.

Manufacturers do not have MPG as their highest priority. Higher priorities are price, liability, noise, longevity, warranty costs, speed, power, comfort, emissions, and general marketing. They meet the minimum MPG requirement goal that they have set for the vehicle and continue to refine the other things.

When trying to guess what their motivation was for a configuration (tire width, exhaust diameter, whatever), you have to guess which of those motivations went into that thing. Tire pressure, for example; they specify the lowest pressure that covers them from liability, so that the car will ride soft. The marketing department sets tire pressure specification after checking with the lawyers, the engineers don't get much say.

As for tire width...I'm not sure which motivations would come into play.

some of your conculsions are incorrect.

https://www.everytime.cummins.com/***...Whitepaper.pdf
there are sections on tires and other interests that crossover to cars and pickups

Thank you! I'm always happy to get more information. I'll have to give that a thorough reading.

Well, there's not much about tires in there, and the only thing I could find that contradicts any of my conclusions is where it says that tread is responsible for 60-70% of rolling resistance, and that worn tread reduces rolling resistance. There's no data to back it up, just like there's no data for much else about rolling resistance. :(

Tread on big rig tires comes 14/32 to 30/32, according to a quick look at Goodyear's commercial tire specifications. Passenger tires (except snow tires for pickups) rarely exceed 12/32 and tend not to have block/lug tread. However, I'll concede that in brand new tires, tread may often have a more significant effect on rolling resistance than I usually suggest.

"What changes is its shape; a narrow tire has a longer, narrower contact patch, which requires more sidewall deformation to make that contact patch."

not true. low air pressure causes that nothing else.
https://www.tirerack.com/tires/tirete...e.jsp?techid=1

a narrower tire increases mpg. the contact patch is changed more by the diameter of a tire. a larger dia has more contact patch, the reason drag cars have taller tires on drive wheels plus wider. more contact area, more friction more traction.
lets reverse the thinking, which would give u shorter braking stopping distances, a narrow tire or a wider tire? the wider tire of course, more contact area.
u made reference to bicycles, do road racers use narrow high pressure tires or fat mountain bike tires to go fast with the least bit of effort?

There is no data supporting the contact patch shape not changing with width. Pressure definitely changes it, but at the same pressure, width is bound to change it too.

The theory, against which I've seen precious little data, is that you can calculate contact patch size quite easily from pressure and load. So, if you have 1000 pounds load and 100psi (that's Pounds per Square Inch), you're going to have 10 square inches of contact patch. If you make it narrower, it's going to be longer, but it's going to be 10 square inches.

Road racers use narrow tires for four reasons:
1. High pressure - traditionally, it has not been feasible to put 120psi in a fat tire; the tire would blow off the rim. Regardless of rolling resistance, you need a lot of pressure for safe high-speed cornering.
2. Aerodynamics - Extremely important for road bicycling. You wouldn't think it matters much at human-powered speeds, but it does matter very much.
3. Light weight - Road racing traditionally shaves every gram off the bike that can possibly be removed.
4. Ignorance/blind tradition/myth-following - Everybody assumes that narrower has less rolling resistance, it is in print in many places, so the myth lives on; but reality differs somewhat.

I have done much bicycling, much study of it, and I'm pretty sure there is data showing the issue quite clearly in that context.
https://www.analyticcycling.com/Force...esistance.html
That refers to width, not diameter. The data comes from Jobst Brandt, one of the world's foremost experts on bicycle wheels and tires.

if u are overloading a tire and/or with low air pressure u would be correct. but it seams if those too variables are not the case then narrow has a smaller contact patch.

https://www.google.com/#hl=en&source=...oq=&fp=1&cad=b

There's a large collection of data at https://www.performancesimulations.co...on-tires-1.htm (the first link in that search) showing that contact patch is NOT calculable from pressure and load, taking away the logic about contact patch length and leaving us with unexplained data from the study I posted earlier in this thread...drat, now I don't know why the narrower width in that study had more RR.

I have seen that link before and totally forgot about it. Thank you.

Edit: D'oh! It was already right at the top of my tire width thread, just before the aforementioned unexplained study.

https://www.physicsforums.com/archive.../t-330790.html

so it seams we were both half right.

my conclusion is two tires of the same OD and two different widths will basically have the same contact patch. As I had stated earlier, a larger OD will increase the contact patch. So to have the smallest contact patch a tire would have to be wide with a small OD. But according to the white paper posted and as most know aerodynamics reduces mpg the most at 50 mph and over, whereas wide would be bad.
It seams a balancing act is needed for the use of the vehicle and weather conditions one expects to see for the best mpg size tire to use.
Using a larger dia wheel so that the tire side wall is smaller will help reduce tread movement thereby increasing mpg.

I have Michelin Harmony tires size 175/70R13. They are quiet, smooth, have excellent grip in rain, snow, and dry conditions (outstanding performance in the snow due to open tread blocks on the outside of the tires, one of my prerequisites to buying a tire). After being on the car for nearly 20,000 miles, they show almost ZERO wear.

My bad... they're Michelin Destiny tires, not Michelin Harmony.

I paid $225 or so for them at Discount Tire. I have seen mileage soar into the high 50s to mid 60s with sensible driving with these tires.

Ah! I must have missed the part about diameter; I had assumed we were talking about the same diameter, where we only change the width.

I totally agree that a balance is the best idea.

As for low-profile tires...Common knowledge has been that upsizing (same OD, larger wheel, smaller sidewall) results in increased RR (and decreased MPG), but I'm not sure that I've seen any data. I think I also haven't seen any logic to explain it in either direction, so I can't really say if one way or the other is better.

Larger wheels almost always reduce mpg even if the total OD of the tires is the same as the old wheel/tire combo. Often it's the city mileage that takes the worst hit because it requires more effort for the engine to get larger wheels moving compared to smaller wheels. There might be some exceptions though where the larger wheels are significantly lighter (eg. made of magnesium) than the older smaller wheels made from a heavier material.

not true. look at the white paper I posted. Any thing that can reduce tread movement helps mpg. a shorter stiffer sidewall works. Too big and wide of a wheel whereas the unsprung weight goes up too much, then I would agree.
I biggest pet peeve is these hwy depts that groove the hwys, this increases tread movement lowers mpg but increases the states fuel tax revenue as a result.

Which highway department grooves a highway? The only grooving I've ever seen was during construction and was temporary (as well as dangerous for motorcycles).

Hoping these will do the same for me. I was lucky enough to get the $70 rebate, so $225 was the net total mounted and balanced. They do look like an awesome tire, especially for the $$$.

should have been more clear, the rain grooves some hwys have esp calf., u can feel the vehicle moving side to side. I guess some clown thinks because tires have tread grooves that the hwy should also, IMO it just holds the rain on the hwy.

Interesting. Can you find any pictures of it? Here on the other coast, I don't think I've seen anything like that.

THC,
have been to calf. on business trips, I'm south of u in jersey.:)

remember smaller height tires change your mileage readings, if changed from stock size... so be ready to do some serious mathematics if you plan on calculating your mileage on a regular basis.. :):eek:

The math can be quite simple. All you have to do is figure out your multiplier (which will never change as long as you have those tires) and multiply your miles before figuring them in. So, for a 10% difference, you'd just multiply your miles driven by 1.1 before dividing by gallons.