tire size impact on gas mileage

[Broncosaurus!]

I run 33" muds right now and I need a set of street tires, I have a great deal on some 33" BFG ATs or 31" ATs, or some 235/70? I think Green Diamond snow tires. I'm just wondering if anyone knows how much impact the gearing change by bigger tires helps gas milage, and how much the increase in weight of larger tires affects mileage. Are the differences too minor to care about, will I always be stuck with 10-11 mpg no matter what tires?

 

[1982 bronco lifter]

yes because you go from a 33 to a 31 the 31 takes less power to turn because there is less rubber, go from 31 to 33 there is more rubber to turn with takes more power. only one or two mpg diffrence.

 

[Yardape]

Yep you can expect a whooping 12-14 MPG increase. Think of the $$$$ you'll save.

 

[swampthing]

im running 4.10s with 36's right now and 20 dollars worth of gas at 2.05 a gallon gets me about 150 160 miles..which is great compared to first bronco i built that only got about 6 mpg

 

[Broncosaurus!]

but bigger tires will let the engine run at lower rpm

 

[swampthing]

yes..but i personally dont really care about that cause i dont run highways..fastest i usually go is 55 60...i'm upgrading to 38's during the winter

 

[1982 bronco lifter]

i was told it will only get one or two miles per gallon diffrence

 

[firelt90bronco]

I switched from 31s to 33s and get about 2 mpg less than before. Now I get a whole 6 mpg!!!!! Use this link to calculate tire sizes from standard to metric.

 

[BLADE262US]

Its not really the weight of the tire thats the factor , You have to think of it like gearing . The bigger the tire the more area it will travel in one rotation a 35 inch tire will travel 9.16 feet in one rotation now if you put 44 on it now youll go 11.51 feet in one revolution . Now look at it like this if you have 4:10 gears and 35 inch tires your drive shaft will turn 4.1 times to move you9.16 feet now take the same gearing with 44,s you go farther on the same revolutions of the drive shaft BUTTTTTTTT you have lost the mechanical advantage of the gearing which is harder on all compoments of the drive train . With the 44,s and 4:10 you will go farther in one revolution but the motor is working its ass off to make up for the lack of mechanical advantage . This is why when you build a truck or whatever you must think ahead as to what you are really going to do with it . Like if you put 5:88 in to gear for 44,s then decide when its all done your going to run 31,s It will be a tire smoking machine because of the mechanical advantage but try running down the highway and youll pop the motor or have it wound up way past its peak power RPM so either way you loose . For those that dont know to figure out how far youll go on one revolution of the tire its the diameter of the tire times 3.14 divided by 12 to convert to feet . /emoticons/[email protected] 2x" width="20" height="20" />

 

[firelt90bronco]

Well put blade. Its not just the gearing, but the momentum it takes to get tires up to speed.

 

[Broncosaurus!]

Exactly, that is why I was wondering if the gearing advantage of 33s would make up for the extra weight of tire and the extra rolling resistance. These will be my hwy tires and I would like better economy(and yes I know it will still have 302 cubic inches to feed)

but all in all, for my scenario, stock size tires will give me better fuel economy right? Plus the green diamonds are badazz snow tires (and free for me /emoticons/[email protected] 2x" width="20" height="20" /> ), I recommend them for anyone who actually needs snow tires, they are the best. www.greendiamond.com I had some on my 84 honda crx and I could not get it stuck, and I lived about as far north in upper michigan as you could do.

 

[seawalkersee]

What gas milage did you guys have to start with? Before I lifted mine up, I got 17mpg (more than once) on the highway, but averaged about 13. That did not matter with the 351 or the 289. Now...with the new 351, better carb and 4 spd, I am hoping to lean er out to get 12-14.

Chris

 

[swampthing]

when i first got my bronco it was about 12-13 mpg...once i put my 302 in i was getting about 8 driving normal...driving hard about 4-5....i went through a full 32 gallons in about 2 hours

 

[BLADE262US]

HMMMMMMM did it by chance have a 351 in it before your 302 ? /emoticons/[email protected] 2x" width="20" height="20" />

 

[swampthing]

straight 6....the 302 was out of a 13 second stang..i put a slightly bigger cam in holley 550 classic nascar dual feed double pumper carb..it had power and went through fuel like crazy