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Discussion Starter #1
i have a 3.42 in my 2011 5.3 liter silverado z71 . Now I am wishing i got the 3.08 gear for gas mileage. How does changing tire size effect axle ratio? can i get a tire size that make my truck act like I have a 3.08 gear in it. my last truck was a 2wd 5.3 liter with a 3.08 and got much better gas mpg. I know having a 4x4 crew cab vs a exted cab 2wd will effect mpg. but not that much. any thoughts?
 

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Using a little algebra and this formula, you should be able to figure out what you want:

original tire diameter in inches x gear ratio = new tire size x new gear ratio

so, if you start with a 29" tire with 3.08 gears, and you want to move up to a 32" tire, what's the new gear ratio needed to keep the ratio.

29 x 3.08 = 89.32

89.32 / 32 = 2.79, so that's the new adjusted gear ratio assuming the gears did not change in the axle.
 

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If you do go with a taller tire make sure you get the trucks computer adjusted for the larger tires so the trans will shift properly.
 

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as stated above the speedo and stuff will be off with bigger tires, but also realize by going to a larger tire for a higher effective gear ratio you will lose some of the performance but you should see some increase in highway mileage due to lower rpms.
 

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Maybe I'm a little confused here, but I can't see how a larger tire will do anything to help fuel mileage. Larger tire/more rotating mass = mpg loss.
 

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Maybe I'm a little confused here, but I can't see how a larger tire will do anything to help fuel mileage. Larger tire/more rotating mass = mpg loss.
you will see that more city wise (starting in traffic etc), but if its a nice highway tread tire wont be too bad on the highway and could help. at that point has a lot to do with the tire as well. going with a larger high void off road type tire will just bog down the truck and less mileage.
 

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i have a 3.42 in my 2011 5.3 liter silverado z71 . Now I am wishing i got the 3.08 gear for gas mileage. How does changing tire size effect axle ratio? can i get a tire size that make my truck act like I have a 3.08 gear in it. my last truck was a 2wd 5.3 liter with a 3.08 and got much better gas mpg. I know having a 4x4 crew cab vs a exted cab 2wd will effect mpg. but not that much. any thoughts?
For what your going to spend in tires, I would swap out the gears!! :party: What is your mileage now?

I had 3.23 gears in my 08, changed them out to 4.11's.

I get about the same in town as before - 14-15mpg....if I take it easy I have gotten as good as 16mpg. Highway I got an average of 18 on a trip from tucson to L.A.

I still have the 3.23's if anyone is interested. 10 bolt 8.5
 

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I am looking to just go with a bigger tire on the same rim. So yes there would be more mass but not much more as with rims and tires. If i did all my math right I have 265 60 r18 on the truck now, thats a 31" tire and a 285 75 r18 is a 34.8" tire and would give close to a 3.10 gear which is close to what i want. But its hard to find a tire that size that doesn't cost too much.



And i dont not want to change the axle the truck is to new for that.
 

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I am looking to just go with a bigger tire on the same rim. So yes there would be more mass but not much more as with rims and tires. If i did all my math right I have 265 60 r18 on the truck now, thats a 31" tire and a 285 75 r18 is a 34.8" tire and would give close to a 3.10 gear which is close to what i want. But its hard to find a tire that size that doesn't cost too much.



And i dont not want to change the axle the truck is to new for that.
To new for gear change but not for tires? Ok- I guess you could always sell your other tires to off set the cost. What kind of mileage are you trying to achieve...maybe you should be looking at other options.
 

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I am looking to just go with a bigger tire on the same rim. So yes there would be more mass but not much more as with rims and tires. If i did all my math right I have 265 60 r18 on the truck now, thats a 31" tire and a 285 75 r18 is a 34.8" tire and would give close to a 3.10 gear which is close to what i want. But its hard to find a tire that size that doesn't cost too much.



And i dont not want to change the axle the truck is to new for that.

IF you could fit those tires, your mileage will suffer all the way around.
 

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IF you could fit those tires, your mileage will suffer all the way around.
why would it?

---------- Post added at 02:33 PM ---------- Previous post was at 02:31 PM ----------

the truck is getting around 12 in the city and 15 highway. my old truck would get 15 city and 20 highway
 

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why would it?

---------- Post added at 02:33 PM ---------- Previous post was at 02:31 PM ----------

the truck is getting around 12 in the city and 15 highway. my old truck would get 15 city and 20 highway
you mentioned getting 35" tires, which is why. 1 they wont fit without a 6" lift (I think Rancho says 35's with there 4") thats why. And yes going up to a 35" tire will kill your mileage. goes back to the weight. I had 3.73's in my truck and went from a 31 to a 35 with a lift and I switched to 4.10 gears and it is under powered in hills and city but maintained my 12mpg that I was getting pre lift(since I do 85% highway which is why I only went up to 4.10). If I would have left the 3.73 I would have been gutless so with you even taller gears your truck will really struggle with that size tire, and I have the 6.0 4l80e etc. In my previous posts I didnt realize you were trying to go that big.
 

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All other things being equal, increasing the width of the tire will reduce economy. Going taller will reduce engine rpms just like a gear change. But if you have to go wider to go taller, it will be a trade off. Also, raising the truck higher in the air by running taller tires will reduce economy too.

I would look at a custom tune, and possibly changing driving styles/habits to improve economy.

Your indicated MPG sound very very low for a half ton truck. Those are bad numbers for a 3/4 ton. Do you have a heavy right foot? How fast do you drive on the highway.
 

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Discussion Starter #14
you mentioned getting 35" tires, which is why. 1 they wont fit without a 6" lift (I think Rancho says 35's with there 4") thats why. And yes going up to a 35" tire will kill your mileage. goes back to the weight. I had 3.73's in my truck and went from a 31 to a 35 with a lift and I switched to 4.10 gears and it is under powered in hills and city but maintained my 12mpg that I was getting pre lift(since I do 85% highway which is why I only went up to 4.10). If I would have left the 3.73 I would have been gutless so with you even taller gears your truck will really struggle with that size tire, and I have the 6.0 4l80e etc. In my previous posts I didnt realize you were trying to go that big.
I know a guy that has 35 with just a leveling kit and he has now issues with them. Also with my last truck which was a extended cab with a 5.3 2wd it had 3.08 rear and it wasn't gutless. i do agree about the width of the tire cutting down on mpg.
I haven't had much luck find any tire that are not going to cost a arm and a leg to get.
 

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you mentioned getting 35" tires, which is why. 1 they wont fit without a 6" lift (I think Rancho says 35's with there 4") thats why. And yes going up to a 35" tire will kill your mileage. goes back to the weight. I had 3.73's in my truck and went from a 31 to a 35 with a lift and I switched to 4.10 gears and it is under powered in hills and city but maintained my 12mpg that I was getting pre lift(since I do 85% highway which is why I only went up to 4.10). If I would have left the 3.73 I would have been gutless so with you even taller gears your truck will really struggle with that size tire, and I have the 6.0 4l80e etc. In my previous posts I didnt realize you were trying to go that big.

That's why.
 

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i have tried but the mpg on this truck compared to my last truck is night and day. I could get 20 out of my 2wd truck on the freeway doing 75 to 80 all day long and if i babied it between city and freeway it wasn't bad. I just didn't the a 4x4 would be that bad and was thinking it had some to do with the 3.42 in this truck.
 

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I would maybe consider a custom tune for mpg over tires.
 

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I too bought a 4X4 crewcab 5.3 engine with 3:42 gears and came with 265/65/18 tires. I also have a 2wd 5.3 engine excab with 3:73 gears.
I really didn't expect the 4X4 to come close to the mpg the 2wd has. I wouldn't pay much attention to the EPA estimated figures either, they are garbage.
I did lift my 4x4 2 inches in the front and 1 inch in the rear and installed 275/65/18 tires with a more aggressive tread pattern plus the c.c is heavier.

I just drove my 4x4 from southwest Louisiana to Daytona beach FL and back (about 1600 miles) and got about 16.5 mpg. Thats about what I expected. Going from 2wd to a 4x4 and expecting similar fuel milage is pretty much a heart breaker. Too bad you already dropped the coin on the 4x4 to figure that out.
Good luck my friend.
 
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