Will slightly taller tires alter my mpg? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

TwoFiftyShifter · 02-07-2010, 07:19 PM

So since I got a tach and GPS in my truck, I've been checking the mpg alot, and at 60mph 2200-2300 tpm on highway I'm getting 14.5 mpg. City is 10-12. I currently have 245/75/16 tires on there, and I want something just a little taller, and was thinking of 235/85/16. They seem to be an inch taller, and would look a little better. This change is too small to negatively affect my mileage, right? I have a 87 V20 350TBI, 3.42 and a 4 speed.

Benelli · 02-07-2010, 07:55 PM

Gear ratio calculator says it should improve it by shutting off 100 or so RPM's.

I'm not sure if an inch is enough to cause worse gas mileage when your getting it roller.

Restrorob · 02-07-2010, 09:08 PM

Quote:

Originally Posted by Benelli

I'm not sure if an inch is enough to cause worse gas mileage when your getting it roller.

I wouldn't think a inch would make any difference with a stick but could fathom it would with a auto due to pre-set shift points.....

Benelli · 02-07-2010, 09:16 PM

I suppose.

Though since they are vacuum controlled, I don't see how they are pre-set.

Restrorob · 02-07-2010, 09:28 PM

A auto shifts when IT wants to, A stick shifts when YOU want to....

PhilaTruck · 02-07-2010, 10:14 PM

Make sure you don't increase width. That will certainly decrease mileage due to friction.

bikes&bowties · 02-07-2010, 10:28 PM

1 inch with the same tread and width may actually help flat highway cruising

James McClure · 02-08-2010, 11:10 AM

A 1" difference in height will be a 3" difference in circumference. If the tire covers 3 more inches with every rotation, every 4 rotations is a foot, so every 21,000 rotations is a mile that you wouldn't cover with the smaller tires and every 13 miles is a gallon of fuel. Over the life of the tires, the fuel savings will pay for the tires. Just something to think about. I'm bored, it's winter & I have nothing to do.

andrewmp6 · 02-08-2010, 02:27 PM

My brothers 02 f150 going from stock to a 31 he lost 1mpg but he went like 2 or 3 inch taller tires.

nzjkb5 · 02-08-2010, 02:54 PM

There is a little more to it than just the diameter. As somebody else mentioned, a wider tire generally will increase rolling friction somewhat, and if you really want to get technical, aerodynamic drag will increase too! But also the tread compound, possibly the tread pattern, inflation pressure - there are a lot of variables. I imagine when the 02 F150 went from stock to 31" tires, they also got wider and probably were made of a softer compound. Also, if the the F150 owner was relying on his truck's odometer for his mileage calculation, it would be off.

I won't bore everybody with my calculations, but ALL THINGS BEING EQUAL (which they probably won't be), I would expect you to see about a half mile per gallon increase on the highway when changing from your 245/75/16 to a 235/85/16.

02-07-2010, 07:19 PM	#1
TwoFiftyShifter Registered User Join Date: Nov 2008 Location: Gwinnett GA Posts: 1,803	Will slightly taller tires alter my mpg? So since I got a tach and GPS in my truck, I've been checking the mpg alot, and at 60mph 2200-2300 tpm on highway I'm getting 14.5 mpg. City is 10-12. I currently have 245/75/16 tires on there, and I want something just a little taller, and was thinking of 235/85/16. They seem to be an inch taller, and would look a little better. This change is too small to negatively affect my mileage, right? I have a 87 V20 350TBI, 3.42 and a 4 speed. __________________ 1982 K10 SWB 1987 V20 - Sold - Doh!

02-07-2010, 07:55 PM	#2
Benelli Watchin the rust grow Join Date: Oct 2008 Location: Western Nebraska Posts: 950	Re: Will slightly taller tires alter my mpg? Gear ratio calculator says it should improve it by shutting off 100 or so RPM's. I'm not sure if an inch is enough to cause worse gas mileage when your getting it roller. __________________ 1979 Chevy K10 (H/D Front end) - 350 w/ Holley Truck Avenger, Weinald Intake manifold, headers, bored .060 over, mild cam, Built up TH350 (TranStar Shift kit) with a part-timed NP203 t-case SOLD ($3,000) 1997 Chevy Silverado 1500 - 4.3 vortec, extended cab, 21 highway MPG, stock. "Red" SOLD ($3,000) 1987 Toyota 4wd Pick-up - work in progress, future DD SOLD ($1,850) 1998 Dodge Ram 2500 Cummins 5spd Quad cab - old 12 valve with some work done 2004 Chevy Silverado - Black, 4x4, 5.3L, stock for now Underneath that rust is a heart of gold

02-07-2010, 09:16 PM	#4
Benelli Watchin the rust grow Join Date: Oct 2008 Location: Western Nebraska Posts: 950	Re: Will slightly taller tires alter my mpg? I suppose. Though since they are vacuum controlled, I don't see how they are pre-set. __________________ 1979 Chevy K10 (H/D Front end) - 350 w/ Holley Truck Avenger, Weinald Intake manifold, headers, bored .060 over, mild cam, Built up TH350 (TranStar Shift kit) with a part-timed NP203 t-case SOLD ($3,000) 1997 Chevy Silverado 1500 - 4.3 vortec, extended cab, 21 highway MPG, stock. "Red" SOLD ($3,000) 1987 Toyota 4wd Pick-up - work in progress, future DD SOLD ($1,850) 1998 Dodge Ram 2500 Cummins 5spd Quad cab - old 12 valve with some work done 2004 Chevy Silverado - Black, 4x4, 5.3L, stock for now Underneath that rust is a heart of gold Last edited by Benelli; 02-07-2010 at 09:17 PM.

02-07-2010, 09:28 PM	#5
Restrorob The One And Only !!! Join Date: Jan 2007 Location: Hole in the woods Florida Posts: 4,567	Re: Will slightly taller tires alter my mpg? A auto shifts when IT wants to, A stick shifts when YOU want to.... __________________ 93 Jeep XJ 88 Buick La Sabra Toys; 88 TA-GTA in the works.... 97 GMC Ext. Cab 502 Crate 5 Spd......Sucks Gas But Haulz Azz ! The primary function of an Engineer is to make it difficult for the Fabricator and impossible for the Mechanic. *"Why go out preserved when you can go out beat up, worn out, sliding in sideways screaming, Holy Sh!t What A Ride" !!!*

02-07-2010, 10:14 PM	#6
PhilaTruck Right on the line, baby! Join Date: Oct 2003 Location: Phila, PA 19130 Posts: 1,486	Re: Will slightly taller tires alter my mpg? Make sure you don't increase width. That will certainly decrease mileage due to friction. __________________ 83 GMC 406 th400/3.73 Eaton Truetrac posi, headers, x pipe, & racePros. Tubular control arms, lowering rear springs, caltracs. Still ugly, but getting built right, although slowly Click and scroll down for site vendors! Subscribe here!

02-07-2010, 10:28 PM	#7
bikes&bowties Registered User Join Date: May 2009 Location: Washington Posts: 663	Re: Will slightly taller tires alter my mpg? 1 inch with the same tread and width may actually help flat highway cruising

02-08-2010, 11:10 AM	#8
James McClure One shot, one kill. Join Date: Dec 2007 Location: Saratoga Springs NY Posts: 859	Re: Will slightly taller tires alter my mpg? A 1" difference in height will be a 3" difference in circumference. If the tire covers 3 more inches with every rotation, every 4 rotations is a foot, so every 21,000 rotations is a mile that you wouldn't cover with the smaller tires and every 13 miles is a gallon of fuel. Over the life of the tires, the fuel savings will pay for the tires. Just something to think about. I'm bored, it's winter & I have nothing to do. __________________ 1984 K20 350M engine with 465,000 miles. Well, it's finally done!! Almost 2 years of work, but it was really worth the effort. Little stuff left to do is mount winch, wet sand & buff out and build belly pan\running boards. Body work takes lots and LOTS of beer!!!! God, Guts and Guns made America and God, Guts and Guns will preserve it! The worst thing you could do is get into my sights, but that don't matter, you'll never know it, cause you'll never hear the shotJim or Paladin whichever you choose.

02-08-2010, 02:27 PM	#9
andrewmp6 Registered User Join Date: Jan 2009 Location: Louisville,Ky Posts: 5,811	Re: Will slightly taller tires alter my mpg? My brothers 02 f150 going from stock to a 31 he lost 1mpg but he went like 2 or 3 inch taller tires.

02-08-2010, 02:54 PM	#10
nzjkb5 Registered User Join Date: Jan 2010 Location: East Tennessee Posts: 3	Re: Will slightly taller tires alter my mpg? There is a little more to it than just the diameter. As somebody else mentioned, a wider tire generally will increase rolling friction somewhat, and if you really want to get technical, aerodynamic drag will increase too! But also the tread compound, possibly the tread pattern, inflation pressure - there are a lot of variables. I imagine when the 02 F150 went from stock to 31" tires, they also got wider and probably were made of a softer compound. Also, if the the F150 owner was relying on his truck's odometer for his mileage calculation, it would be off. I won't bore everybody with my calculations, but ALL THINGS BEING EQUAL (which they probably won't be), I would expect you to see about a half mile per gallon increase on the highway when changing from your 245/75/16 to a 235/85/16. __________________ -Keith http://classiccarfinancingandloans.com/ http://classiccarpricestoday.com/ http://autowindowrepairs.com/



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