Civic VX - which tires is better to use for MPG

[GasSavers_viperguy]

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).

[theholycow]

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?

[basjoos]

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.

[GasSavers_viperguy]

Originally Posted by theholycow

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?

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.

[GasSavers_viperguy]

Originally Posted by basjoos

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.

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.

[astroturf]

Originally Posted by theholycow

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?

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

[theholycow]

Originally Posted by astroturf

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: http://priuschat.com/forums/prius-te...rc-4-data.html
  

  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.

[theholycow]

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.

[astroturf]

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

[theholycow]

What sizes would I compare?

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