Pickup (tire size) question

[billbill1]

I resently bought a Dodge Dakota Extended cab SLT pickup with the 4.7 V8 engine. The tires on it are brand new and are 255 R 70 15's. Inside the door it says the recommended tire size is 215 R 75 15's. How will this effect the fuel mileage? I get between 16 and 17 mpg driving through town or on the highway and feel that it should get better than that but I'm unsure and felt someone on here could tell me if the tire size might be causing some of the problem. Plenty of power, no problem there, what do you guys think? Thanks in advance. The truck is a 2001 at, 2wd, loaded with 77,000 miles.

 

[Bird]

Bill, I'm one who prefers to stay with original tire sizes, but what you have is an acceptable "optional" size for that truck. Keeping all tires properly inflated is the most important thing you can do, tire wise, for fuel mileage. Changing to the original size tires might help a tiny bit (I'm talking hundredths of a mile per gallon, and I'm not even sure it would do that). It won't help enough for you to tell it unless you keep detailed records for an extended period of time. Money wise, you're better off to keep and wear out those tires, then you can go back to original size, if you wish.

The Dakota are nice little trucks, but everyone I've talked to who had one complained about the gas mileage.

 

[cp1969]

If I did the numbers right, the 215 rotates 728 times per mile; the 225 rotates 736. Around a 1 percent difference...any fuel economy difference that might make is lost in the noise.

 

[Boomerang1]

The 255x70 are 10" wide and 29" tall.
The 215x75 are 8.5 wide and 27.75 tall.

 

[cp1969]

Well, as I said, "If I did the numbers right..." and I didn't. I used 225 numbers. Boomerang is right.

 

[Egon]

I'm like Bird. I go for original tire size. The bigger tires make for more unsprung weight and add to front end wear in my opinion.

 

[RobertN]

Check the manual. My '01 RAM2500 came with stock with tires one size bigger than listed on the door. They are listed in the manual.

Also, the mileage sounds about right. My wife has an '04 Ram1500 with the 4.7l. The best it ever ever ever got was 18mpg on a trip while I was really babying it.

 

[Dmace]

215 R 75 15
Sidewall: 6.3"
Radius: 13.8"
Diameter: 27.7"
Circumference: 87"
Revs/mile: 728

255 R 70 15
Sidewall: 7"
Radius: 14.5"
Diameter: 29.1"
Circumference: 91.3"
Revs/mile: 694



The smaller tires may wear out a little faster since the rubber is hitting the pavement more every mile but I highly doubt you will see much difference in mileage.

 

[bx23barry]

You might get alittle mileage by lowering it, putting tall skinny tires running 60+psi and installing a light cab high camper but it sure would look funny.

 

[RobertN]

215 R 75 15

Diameter: 27.7"

255 R 70 15

Diameter: 29.1"

The smaller tires may wear out a little faster since the rubber is hitting the pavement more every mile but I highly doubt you will see much difference in mileage.

2" increase in tire size will result in an overall higher gear ratio, and feel of less power. It will also throw the speedometer off.

From years in Jeeps and other 4x4's, this is like jumping from 31x10.50 tires to 33x12.50 tires. Threw the speedometer off by 7 or so mph. It felt like changing the axle gear ratio from 3.73 to 3.50. You colud definitely feel the change when switching tires.