Lower gas mileage with larger tires

[thejackyll]

I put some larger tires on my Insight recently and it is registering lower fuel economy. Mathematically is it possible that the mileage is not actually lower but only seems that way because the computer is calibrated to calculate mileage according to revolution of a tire with a smaller diameter?

If this is the case, is it possible to recalibrate the computer?

[Eli]

Yes, tires of a different size will affect the MPG reading.

No, it's not possible to recalibrate the computer.

However, as we all know, any tire other than the Bridgestones will lower fuel economy.

You'll be able to tell when you do some fillups. The FCD in the Insight overall is very accurate, but I still go by actual fillup numbers and not the FCD.

[gilbertguy]

The problem is that even if you fill up and put lets say 10 gallons in the car in order to do the math correctly you need to know the correct number of miles driven. With the bigger tires your reading will be off because of the tire size. So unless you are on an interstate and can go by mile markers it will get you in the ball park but will still leave you wondering if it is right.

[ackattacker]

Find an online tire calculator such as:

Tire Size Calculator - tire & wheel plus sizing

Plug in the stock tires into #1 (165/65/R14)
Plug your new tires into #2 and hit calculate

It will show you the difference in speedometer/odometer accuracy and revs per mile.

[DBHope]

Originally Posted by thejackyll

I put some larger tires on my Insight recently and it is registering lower fuel economy. Mathematically is it possible that the mileage is not actually lower but only seems that way because the computer is calibrated to calculate mileage according to revolution of a tire with a smaller diameter?

If this is the case, is it possible to recalibrate the computer?

Hi .. what size larger fit your car? I have an insight 2001 that needs new tires. I'm looking to maximize my mileage.

[Eli]

Originally Posted by DBHope

Hi .. what size larger fit your car? I have an insight 2001 that needs new tires. I'm looking to maximize my mileage.

If you're looking to maximize your mileage, you have one choice; the Bridgestone RE92 165/65R14.

[DBHope]

so putting 185/65/14 won't increase mileage?

[jdstew]

Originally Posted by DBHope

so putting 185/65/14 won't increase mileage?

This might give better milage - I've got to figure out how to fit them under my skirts... Eli, you know this would help your milage...

[kennysmith]

You can imagine, this is a very old discussion around here and sometimes people get tired (so to speak) of answering this same question repeatedly. The fuel economy winner is clearly the original tires Bridgestone Potenza RE92s in the correct size. It has been demonstrated numerous times around here. Spend a little time searching and you'll find lots of posts. Aftermarket wheels, too have proven to hurt mileage as most are heavier and generate turbulence. No one around here would encourage you to buy anything but the RE92s.

[Eli]

Originally Posted by DBHope

so putting 185/65/14 won't increase mileage?

No, doing such a thing will decrease your mileage, probably considerably.