Bigger tires gave me better mpg..

[Musick17]

I stepped up from the stock 27" tire to 31" muds from treadwright. And since they are so much bigger I cant run in 5th gear anymore, so on the highway I keep it in 4th running about 3000 rpm doing 65ish mph.

With the 27's I would run about 75-80 mph in 5th at about 3000 rpm and could net about 22 mpg usually.

I filled up and drove 40 miles in town and then ran 120 miles down to my college and filled it up again so check what the difference was in mpg. I did the math to get the proper miles traveled with the difference size and then calculated it like you would normally. Came out saying I was getting about 26-27 mpg now....

I checked my math 3 times over and it was the same each time. I was expecting the exact opposite to happen with such a big bump in tire size. I suppose using the gears more and the throttle less is what is making the difference.

 

[Sunk]

Have you accounted for the increased tire size?

 

[Musick17]

I sure did.

I took "31/27" = how many miles I really traveled per each miles read on odometer
then
multiplied that number by how many miles were on my odometer = how many miles I really traveled
then
divided how many miles I really traveled by how many gallons of gas it took to fill back to to full from full

Im pretty sure mathematically that would be the correct way to do that conversion

 

[press 1 for english]

Your mileage increased by 4-5 mpg........that would be impossible.

 

[sblake01]

Wrong math. What you really would need is to compare is the difference in the tires' circumference, not diameter, since that would be the measure of the actual distance per revolution.

 

[triumphrider-1]

Wrong math. What you really would need is to compare is the difference in the tires' circumference, not diameter, since that would be the measure of the actual distance per revolution.

Different numbers yes, but they would give you the same ratio.

31"/27" = (31*pi)/(27*pi)

 

[sblake01]

Different numbers yes, but they would give you the same ratio.

31"/27" = (31*pi)/(27*pi)

Yeah, I realized that after I thought about my post. Circumference being a product of pi x d so pi just cancels itself out.

 

[Musick17]

Also, the new tires are a little skinnier than my old tires and alot more stiff. Both would help reduce rolling friction I guess.

 

[triumphrider-1]

That will affect it.

What was the old tire size, and what is the new one size?

 

[ES894x4]

I keep it in 4th running about 3000 rpm doing 65ish mph.

With the 27's I would run about 75-80 mph in 5th at about 3000 rpm and could net about 22 mpg usually.

^this is why. your not forcing a brick through the air at 80 mph. air resistance increases by factors and isnt linear to the speed. that drop in 10-15 mph is taking a large load off the truck as it tries to cut through the air allowing the motor to work less and save gas.

 

[Musick17]

I think the old tires were 27 inch in diameter and 8 inches wide. The new ones are 31 inch in diameter and 7 inches wide.

Either way, It definitely is getting better gas mileage. And its nice.

 

[cape_royds]

ES894X4 is right. The speed reduction, which disproportionately reduces the amount of drag, is the decisive factor in the mileage improvement.