Tire size + Gear change + MPG difference back to stock?

Ponyman460 · December 28, 2007

I know the tire size will affect the mpg that I attain. and I also know that a gear change from 3.73's to a different gear like 4.10's will do the same. However, I went from the stock tires to 30X9.5 (and will be 31x10.5 or 33x10.5 next time) and I am wondering of changing the gear to the 4.10's will actually increase mpg for me due to the larger tires.

I do a lot of HWY driving and put about 300 miles on the truck a week between hwy and in town.

just looking for some direction here. Thanks in advance.

Rick

sjr033 · December 28, 2007

With the same size tire a higher (lower number) gear ratio number will increase mileage. So with your 30" tires you will get better mileage with 3.73 vs. 4.10. A larger tire will effectively increase your gear ratio (lower the number). So in a perfect world putting a larger tire will lower you rpm at the same speed and increase your milage. Now I said perfect world. A larger tire weigh more and your truck will sit higher. So your wind drag will increase and you motor will have to work harder to turn the bigger tire. Also being that you increased the ratio (lowered the effective number) buy putting on larger tires you most lickly give it more gas and rev higher to acheve the same performance you had before. I don't know if this answered your question but I hope it gives you some help.
Last check out this site. You can put in different tire sizes and gear ratios to find out what your rpm will be at a set speed or find out how much your speedo will be off.
http://www.4lo.com/4LoCalc.htm

Ponyman460 · December 28, 2007

sjr033 said:
With the same size tire a higher (lower number) gear ratio number will increase mileage. So with your 30" tires you will get better mileage with 3.73 vs. 4.10. A larger tire will effectively increase your gear ratio (lower the number). So in a perfect world putting a larger tire will lower you rpm at the same speed and increase your milage. Now I said perfect world. A larger tire weigh more and your truck will sit higher. So your wind drag will increase and you motor will have to work harder to turn the bigger tire. Also being that you increased the ratio (lowered the effective number) buy putting on larger tires you most lickly give it more gas and rev higher to acheve the same performance you had before. I don't know if this answered your question but I hope it gives you some help.
Last check out this site. You can put in different tire sizes and gear ratios to find out what your rpm will be at a set speed or find out how much your speedo will be off.
http://www.4lo.com/4LoCalc.htm

yeah I get most of that, and i understand that the tire physically spins fewer times per mile with the larger tires, but doesnt the truck have to work harder to achieve the same performance? ...like you said. and if that is the case, wouldnt the 4.10's essentially make it "easier".....or just as if it were back to stock?

Thanks for the response!

Ponyman460 · January 2, 2008

in other words, if I lost some mpg by going to larger tires, would I get that back with the 4.10's, or lose more?

carlover · January 2, 2008

Youd get back some of the mileage but not all. Its not just the diameter of the tires that affects mileage its also the extra rotating mass caused by the extra weight of the tires.

Ponyman460 · January 2, 2008

carlover said:
Youd get back some of the mileage but not all. Its not just the diameter of the tires that affects mileage its also the extra rotating mass caused by the extra weight of the tires.

understood perfectly!! thanks!

manaen · January 2, 2008

Let me throw a wrench in the mix. The mileage increase with a lower ratio gear will only work to a certain point. The ideal RPM is in the lowest part of the torque curve for the vehicle. If you go too low you may actually harm your mileage by requireing the vehicle to downshift more and apply more gas to get the car rolling in the first place. Also in hills or passing situations a higher ratio gear may actually be more efficient since it takes less power to push the vehicle along.

All in all generally for highway mileage it will almost always yeild better results with lower ratios (smaller numbers). But getting the right gear for the job will always yeild the best results, and you can in fact go too low with ratio which will mess with shift points and the engines sweet spot in the power curve.

Does that make sense..

Ponyman460 · January 2, 2008

manaen said:
Let me throw a wrench in the mix. The mileage increase with a lower ratio gear will only work to a certain point. The ideal RPM is in the lowest part of the torque curve for the vehicle. If you go too low you may actually harm your mileage by requireing the vehicle to downshift more and apply more gas to get the car rolling in the first place. Also in hills or passing situations a higher ratio gear may actually be more efficient since it takes less power to push the vehicle along.

All in all generally for highway mileage it will almost always yeild better results with lower ratios (smaller numbers). But getting the right gear for the job will always yeild the best results, and you can in fact go too low with ratio which will mess with shift points and the engines sweet spot in the power curve.

Does that make sense..

yes it does..I do a lot of hwy driving, so I am not sure that I am going to get the gears unless I get the 31's....for fear it may harm my mileage.

Here in fl, hills are not a problem, but 80mph on the hwy from time to time while passing is common..thanks!

MountaineerGreen · January 2, 2008

Until you get up to 32's + for an explorer, I wouldn't bother with a gear change. (unless you have 3.27's or possibly 3.55) I had 3.73's and 32's, got pretty decent mileage. Went to 4.10's with the 32's, my mileage on the highway went down, and it went up in town. Changed to 33's, and its about right now, I get decent mileage in both.

storlied · January 2, 2008

This all has me kind of confused, what about 31's with 3.73? It'll act as if it were 3.55, correct? If so.. would that be better for gas mileage or worse? If it's better, it's at the cost of some power though correct?

manaen · January 3, 2008

it would be better once your up to speed, however in town the mileage (as MG stated) will probably be worse.

Incidentally, with my 4.10's and current stock 30's my trucks in town and highway mileage is pretty close 18/20 however if I start to push 80mph my mileage starts to drop, I usually cruise around 70mph on the highway up here. And even towing 5000lb I get about 14 to 16 so in these instances the 4.10's are really helping. Of course I will be going to 32 or 33's the next time around and then we will see what happens....

storlied · January 3, 2008

So city mileage will be considerably worse going from 29'' tires to 31's?... that's pretty lame..

manaen · January 3, 2008

I wouldn't say considerably worse, but you will be pushing the truck much harder to get to speed, so you will see a few mpg difference. It all comes down to how you drive your truck. I can go from 16 to 18 in the city, its all in how heavy my foot feels that day.

storlied · January 3, 2008

I'm quite heavyfooted... lol

Ponyman460 · January 3, 2008

I have a heavy foot too....

storlied · January 3, 2008

Ya think I'm gonna notice the power loss with my heavyfoot? =)

manaen · January 4, 2008

yes, you will notice a difference, if you drive heavy footed all the time and have the money for the gears, IMHO I would do it.

storlied · January 4, 2008

Even with my V8? I've read it makes up in the power loss a lot better than the 4.0 does.

Ponyman460 · January 4, 2008

I think i am going to do it later this year.

MountaineerGreen · January 4, 2008

5.0's are OK with up to 32's with no gear change, IMO. My 32's were fine with stock gears. 4.10's would be too low, IMO.

Tire size + Gear change + MPG difference back to stock?

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