Tire size vs gearing


Boyelroy2000

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My 1997 2wd has the 2.3 , 5 speed, and 3.73 rear end gears. I plan on leveling it and fitting larger wheels and tires.As of right now it is sitting on 225/70/R14 tires. If I make the switch should I move up to the 4.10 rear end gearing? I'm considering moving to a 235/75/15 or 245/75/15. I'm leaning towards the 4.10 gears but I don't want to completely axe my gas mileage. I just want a second opinion on this.
 


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ericbphoto

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Bigger tires and changing ride height, which affects aerodynamics will have a slight negative effect on gas mileage no matter which gears you run. Driveability is what you get by changing gears. Being able to keep your engine in a decent rpm range while going uphill or towing is something most of us like.

Go to the "how to tech" page and follow the links to articles about gear ratios, tire sizes, etc. There is a cool chart there that gives good comparisons of engine rpm vs gear ratio and tire size. That will give you a good idea of what gear ratio will keep your engine rpm in the right range. You don't have to guess.

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ericbphoto

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delete
 
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Boyelroy2000

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Bigger tires and changing ride height, which affects aerodynamics will bigger have a slight negative effect on gas mileage no matter which heard you run. Driveability is what you get by changing gears. Being able to keep your engine in a decent tomorrow range while going uphill or towing is something most of us like.

Go to the "how to tech" page and follow the links to articles about gear ratios, tire sizes, etc. There is a cool chart there that gives good comparisons of engine room vs gear ratio and tire size. That will give you a good idea of what gear ratio will keep your engine rpm in the right range. You don't have to guess.

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I understand the fact that my efficiency will be slightly downgraded by larger tires and differing aerodynamics, but I was really hoping to find some info on the gas mileage I could expect with such a change. If I opt for the 235/75s the truck would essentially act like a 3.45 (3.41 was the true ratio) which is perfectly driveable in my experience (My buddy has an 89 Ranger with 225/70/15 with a 3.45 rear end and it does fine). If I go to the 245/75 then I'll definitely opt for the 4.10 gearing. Thanks for the help though man!
 

RonD

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Go here: http://www.therangerstation.com/how-to_pages/gears_needed_after_adding_larger_tires.shtml

Plug in your numbers

If you need diameter in inches go here: https://tiresize.com/calculator/

Yes your tire choice would set 3.73 actual ratio at 3.45, a change to 4.10 would put you back at actual 3.82 so Performance and MPG would remain "close", as would speedometer, the larger tires are 1" wider, so more friction and heavier which drops MPG a bit, also harder on the brakes so slow down heavier wheels
 

ericbphoto

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gas mileage numbers are the hardest to estimate. It doesn't sound like your proposed changes will result in what I would consider a large change in mpg. It might not even be enough to notice unless you have some really accurate way of collecting exact data.
 

kimcrwbr1

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You should be OK i believe you can get a different gear for the speedo senser to avoid the blue light special?
 

Boyelroy2000

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gas mileage numbers are the hardest to estimate. It doesn't sound like your proposed changes will result in what I would consider a large change in mpg. It might not even be enough to notice unless you have some really accurate way of collecting exact data.
Well that's a good thing. Economy is important on my tight college budget haha.
 

Boyelroy2000

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You should be OK i believe you can get a different gear for the speedo senser to avoid the blue light special?
I'm definitely going to have to check because I don't want a speedo reading 10 mph off lmao
 


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