Tire size/mpg

[Gunnyart]

I'll be buying tires in the next couple weeks.

The stock size for my '06 F-150 2wd 4.6 with 355:1 ratio is 255/65/17 Which my regular tire guy (Sardis Tire in Mansfield) doesn't have in stock.

I don't want to kill my mileage (in fact I'd like to improve on it) so will changing sizes slightly be a significant difference?

With my "middle of the road" gear ratio and mostly highway driving it stands to reason that a little taller would be better.

Your input is appreciated.

[oktx]

My son went up one tire size. He lost 1 mpg and is running almost 2 mph above what the speedometer says at 70.

[Gunnyart]

Not dramatic. Did the 1 MPG loss take into effect the increased speedo reading?

[oktx]

Not dramatic. Did the 1 MPG loss take into effect the increased speedo reading?

I don't think so. Bigger tire equals more rubber equals more weight to pull.

[Gunnyart]

I don't think so. Bigger tire equals more rubber equals more weight to pull.

True. I was thinking perhaps I could find narrow tire to offset some of the weight of a taller tire.

[oktx]

True. I was thinking perhaps I could find narrow tire to offset some of the weight of a taller tire.

You may be able too. My sons tires were just taller with the same width. The tread pattern made them look wider.

[lodgepole]

I went from 275s to 305s. No milage loss and no speedometer change.

[esp]

More aggressive tread patterns will decrease your mileage also.

[Bowtech32]

weight of the tire is the biggest reason you would loose MPG

[Gunnyart]

Found what should be a good option... we'll see.

Ended up with a tire the same weight as stock but two inches taller and a less A/T more highway tread.

I'll get the speedo re-calibrated and start running a tally to see.

[oktx]

Found what should be a good option... we'll see.

Ended up with a tire the same weight as stock but two inches taller and a less A/T more highway tread.

I'll get the speedo re-calibrated and start running a tally to see.

Let us know. My son didn't recalibrate his speedo. No tickets....yet.

[Bill]

My son went up one tire size. He lost 1 mpg and is running almost 2 mph above what the speedometer says at 70.

Assuming he really knows he's going 72 when the speedometers reads 70 (like with a gps reading out true mph), then 72/70 is about 3% high, which is the ratio of his new tire diameter to his old. The vehicle simply goes farther for each turn of the axle which the speedometer is calibrated for.

He'd need to multiply his new gas mileage by 1.03 to compare it to the old tires. I don't believe the increase in the tire's weight is a factor in mileage, it's a tiny percentage of the weight of the truck.

Your mileage may vary!

[Gunnyart]

Assuming he really knows he's going 72 when the speedometers reads 70 (like with a gps reading out true mph), then 72/70 is about 3% high, which is the ratio of his new tire diameter to his old. The vehicle simply goes farther for each turn of the axle which the speedometer is calibrated for.

He'd need to multiply his new gas mileage by 1.03 to compare it to the old tires. I don't believe the increase in the tire's weight is a factor in mileage, it's a tiny percentage of the weight of the truck.

Your mileage may vary!

It may be a tiny percentage of vehicle weight but it is un-sprung weight and is directly opposing the engine rotational force.

[TexMax]

I went from 275s to 305s. No milage loss and no speedometer change.

That's the width so it wouldn't change your spedo

Found what should be a good option... we'll see.

Ended up with a tire the same weight as stock but two inches taller and a less A/T more highway tread.

I'll get the speedo re-calibrated and start running a tally to see.

That ought to be fine. Rolling resistance from a/t or m/t tread is a killer

It may be a tiny percentage of vehicle weight but it is un-sprung weight and is directly opposing the engine rotational force.

Yep. Unsprung weight makes a big difference also

[oktx]

Assuming he really knows he's going 72 when the speedometers reads 70 (like with a gps reading out true mph), then 72/70 is about 3% high, which is the ratio of his new tire diameter to his old. The vehicle simply goes farther for each turn of the axle which the speedometer is calibrated for.

He'd need to multiply his new gas mileage by 1.03 to compare it to the old tires. I don't believe the increase in the tire's weight is a factor in mileage, it's a tiny percentage of the weight of the truck.

Your mileage may vary!

Too much math!