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.

 

[Youare]

That gas milage is about right for that truck. My mother had the same set up and that is in the range of what she got for milage.

As far as the difference in gas milage between the 225 and the 215 width tires there may be a slight difference depending on the tread style on the tire. A more aggressive tread increases the rolling resistance of a tire. The narrower tire will have less rolling resistance when fully inflated if both tread patterns are the same. The narrower tire will give you better traction in some cases unless the ground is soft like sand or mud where the wider tire will floatation.

The more the tread wears off a tire the better the gas milage will be.

I just got a new set of tires for my Tacoma which came with 225R75-15's. The tire store tried to talk me into 235R75-15's saying there were a more popular tire used on SUV's. The wider tires take more fuel to turn and give less traction in the snow. A man I work with had wider tires on a
Toyota T-100 and he said that in the snow the truck was all over the place in the slush.

Randy

 

[cp1969]

The more the tread wears off a tire the better the gas milage will be.

I wonder if this is not due to odometer error. The smaller dia. a tire gets, the more miles it will record on the odometer. The truck's not actually getting better mileage; it just appears to be because the odometer is racking up more miles per tank.

 

[BTDT]

I think when Dakota's first came out, they sold them with larger tires to get them a 1/2 ton rating (marketing ploy).

 

[Boomerang1]

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

Where do you get a width of 6.3" from a 215 tire? and 7" width from a 255?
215 is the width in millimeters. 215 mil. = 8.471" and 255 mil = 10.047"
The actual dimensions for the 215 X 75 - 15 is 8.471 wide X 27.7065 tall.
The 255 X 70 - 15 is 10.047 wide x 29.0658 tall. In my first post, I rounded off the numbers to make it easier to figure the numbers.
P.S. Millimeters X .0394 = inches.

 

[Dmace]

Where do you get a width of 6.3" from a 215 tire? and 7" width from a 255?

SIDEWALL buddy, that means the distance from the rim to the top of the tread. I know what the width is and those numbers aren't listed.

 

[billbill1]

Thanks for the input guys, I won't change out the tires before they are worn out. I just wondered if changing would get me a couple of more mpg which wouldn't take too long to pay for them.

 

[KICK]

Toyo Recommender



this page tells you what will fit certain vehicles etc...

generally one size up wont hurt a thing

 

[jayhaitch]

LT215/75R-15=

LT=light truck P=passenger car

215mm in tread width (the width of tread touching the ground)

75=75%=aspect ratio= the ratio of the sidewall height to the tread. Put a yardstick against your wheel/tire, measure the vertical distance from the top tread (not the squished part against the ground) to where the wheel rim starts. Divide this by the tread width=aspect ratio.

R=radial

15=wheel rim diameter in inches.

So how tall is this tire? 75% of 215=161.25. Multiply this by 2 as there are 2 sidewall parts to the vertical measurement. Add the wheel diam.

161.25mm=16.125cm x2=32.25cm. 2.54cm/inch. 32.25/2.54=12.7inches. 12.7+15=27.7 inches tall.

 

[billbill1]

I read the inside of the door but didn't look closely at the tires, the tires on my pickup are 255 70R 16 and it second option for my truck is 255 65R 16. I guess it's not as far off as I thought. Thank you for the help. The door does say 215 75R 15