I'm getting ready to swap from 3.73 to a 4.30 . I'm running 37 in tires any of you guys done this yet? If so did it help your mpgs ? To put back into stock rpm range and help trans shift correctly? I'm just worried it may kill my mpg

 

If you are running 37's and you want to bring it up around stock 3.73 gear performance go with 4.10's and that should be about right. The 3.73's you have in it now are putting you around 3.50 gearing, give or take so any gear changes you do (as in putting in lower gears) is going to cost you fuel mileage. As the gear changes affects low end, it will be your "around town" mileage that will suffer. If you drive mostly highway, the swap will not be as bad but either way, the mileage will be less than what you have now. I run 3.73's on 37's so my rpm's stay very low on the highway and I save fuel. The trade off is that I burn more fuel on short stop and go's around town getting the truck up to speed.

I don't tow much of anything anymore so it's not a big deal. If I towed stuff on a regular basis, I would put 4.10's in mine and even though the fuel mileage would suffer, it would pull better. Right now you are probably pulling 1600-1700 rpm at 65 mph, if you go with a lower gear, you will back up to 2000 rpm or more at the same speed so there goes the fuel mileage. It's all a trad-off, do you need more pulling power or better fuel mileage.....

 

38s and 4:30 gears are as close as you can get to equalling the factory 3:73s with different ratios. So with that being said I'm with Dan and 4:10s unless you tow a lot or heavy.

Joey runs 37s and 4:56s and iirc said mpgs didn't change much. Keep in mind every truck is different.

 

My son with 35 tires and 4.56 gears brings his truck right to 4.10 ratio what mine is. And I run stock tires so 4.30 gears and 37 should bring you right around 3.73 gears. Freeway driving should be okay but sometimes around town your mileage will go down. So much stop and go with the lower gearing in the lower gears. But to me that would make your truck more useable all around.

 

Looking for mpgs I don't do much highway and towing slim to none I'm getting around 13 mpg now guesstimate since speedo is off. At 50 I'm doing 60 but at 30 I'm doing 30 . Biggest thing is I don't want to hurt trans and dont want to be in single digits with mpgs I drive average 36-45 miles a day to and from work . I read bringing rpms back to stock would help mpgs so I'm looking for some real info on someone who has already done this and this page has never let me down yet lol

 

What will help a lot too is getting your speedo calibrated so your transmission shifts like it should when it should.

 

Which begs the question:

Why did you put large tires and a lift on something you drive every day? Park the pickup and drive a car if you're worried about fuel economy.

36-45 miles per day while is a TON of around-town driving.


I'm not saying that it is wrong or stupid to lift a vehicle and put larger than stock tires on it (hell, I built a 1995 CC/LB from stock to 20" of lift with 49" Iroks when I was in college), but you have to be realistic and have realistic expectations when you make the vehicle less aerodynamic and more strenuous to move down the road.

 

I run 37's on my e99 and wanted to go to 4:30's to put it close to stock, I got talked into going with 4:56's. I wish I has stuck with my math that told me 4:30's was the correct choice, my mileage did go up around town but on the highway the 4:56's runs the rpm too high.

 

Yeah that's what I keep getting 4.30 but this guy keeps telling me 4.56

 

You've got 5 guys here over ruling "this guy"..... Just pointing out the obvious

And "this guy" is he buying the gears?.... Just call me "tips"

 

If I was towing heavy all the time, or even once a month I'd go 4.56 but your not. 4.30 should be good. My sons 4.56 and 35 tires turns the same RPM's on the highway as my stock dually with 4.10's so that should tell you something.

 

Yeah he builds racecars but he's got the twin to my truck and he tows . He's also has everything to set up the gears so it wouldnt make sense for me to buy them when he's not going to charge me much on labor otherwise I would put them in myself

 

Many gear charts will show that the 4.56 is a good medium between MPG and performance with 37's; however, if you recalibrate the speedo that will fix the shifting issue and as you don't tow, I recommended the 4.10s as they will give you a little more torque without a bigger hit in MPG. I don't follow charts too much as the individual driving style will far outweigh any type of mileage gains from a chart JMHO

 

Ok I called my Buddy he's going to recalibrate speedo next week . Last time we did it for some reason it didn't save and I've been busy since then . Also what is this AE program I see posted in here a lot ? Is it a tuner or program for a laptop ? Besides being able to make adjustments is it like a reg MODIS snap on scanner? Any difference between the 2 besides being able to make adjustments? Can someone send me a link to where I can buy one? I'm having some other issues but I'll make a new post for those if I can't figure it out

 

How do you recalibrate the Speedo?

My truck is getting older and losing its sack, still pulls good but running 285s at 65mph cgvw of 15000lbs this things slows to 50-55 and down shifts. if im doing 70 it will pull hills all day long, and never down shift. I was thinking of going to 410s that should give me 200? rpm about where I need to be.

I hardly ever drive faster than 70 so I think the 410s and 285s towing will be a good combo.. maybe even 305s because sometimes they are cheaper..