I will be replacing tires in near future. I want to know how much better fuel mileage might be as tire size increases and how big you can go on stock aluminum wheels,suspension.

 

Actually I do not think you will have a fuel milage increase by changing tires to a larger size. I am running 285/75/16 and my milage is about 15 with the winter fuel. Even though you will be changing your final drive ratio ( I think I figured mine at about 3.97) you will still have more wind resistance and weight with the new tires.

 

You can go to randy's ring and pinion web site and play with their gear/rpm/tire size calculator. If I remember right I would have had to gone to a 315 series tire to get close to a rpm range the equalled the 3.55 gear and my present 265 tire. I ended up going with a gear swap as I do use my truck to pull the race car and raising it more wasn't an option. So far I'm very happy with the change.

 

I have the 4:10 rear end and 285/75/16 tires. Works great. I am not sure you can get anything larger than the 285 in the spare tire space. It's real tight with the 285.

 

Heres a good link to help you out

Calculator

I've seen 315s on the stock rims.

I personally would think you would pick up mileage with larger tires. As, with 4.10s your Rs are very high when cruising on the highway.

Also, for your reference, the tranny ratios are as follows in OD

6 sp is .73
5 sp is .75
Auto is .69

 

I have 4:10's and 285's and the best fuel mileage I see is 13.5 empty no matter what. Gets as low as 9 empty in the winter. POS!!!

 

Are you guys with 285's figuriing speedometer error when you calculate mpg?

 

Try using this to calculate the change.
http://www.1010tires.com/tiresizecalculator.asp

 

Nope not using the corrected mileage. I did it once and it was like 10% Barely made a difference. Corrected maybe 14.5 mpg but still too low for me.

 

I know this is old,but I was browsing... I am running 12.50x35 tires w/4.10 gears and am getting between 15 and 17 depending on the driving.bigger the better,thats what I say.

 

I had the 3.55 rear end and put a set of 315s on my 02 4X4 and lost about 1.5 mpg., it looked GREAT, but never seemed to be in the right gear at the right time after adding the bigger tires

 

One option is more gears.

I have a us drive gearsplitter on my 97 with 4.10 gears. in double overdrive i am turning 1750 rpm at about 60."rough guess" The point is with the extra gears you can really control rpm. Plus you can tow with the unit on.

 

My truck came with 265 -75 -16 they were 33" tall went with 315 -75 -16 they are 35" tall. Fuel mileage increased 2mpg. From 16 to 18. I run freeway alot (85%)and am empty with cruise on. My speedo was off about 4-5mph after tire change. Now that I got the hypertech I was able to adjust for the increased tire size. Now instead of my truck governing out at 106mph it will register 116mph! And as silly as this seems my mileage seems to have went up also about 1.5 mpg! Yes 19.5 mpg. Now if I program it for the power stages it seems to go down about 3mpg. But I can't seem to keep my foot out of it when I tune her in like that. I figure that black cloud behind me is where those 3mpg go.

 

i have the stock 245s right now on the gasser but here soon iam goin to change out the tires on her and was goin to go with the 235 85 16s with the 4.10 rear end i should see no loss? the tire size differnce is very little even though iam goin to a bigger tire

 

33-12.50-16.5 and 15 mpg in town.