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Gearing for 37's?

LongrangeLauber

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LongrangeLauber Senior Enthusiast

LongrangeLauber

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I think I will probably go with the 4.56's just so I can get a little bit of power back, hopefully get better mpg's around town, and at 80 mph on 37's it will sit right at 2500 rpm's

Prokopchuk_9 Senior Enthusiast

Prokopchuk_9

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I think I will probably go with the 4.56's just so I can get a little bit of power back, hopefully get better mpg's around town, and at 80 mph on 37's it will sit right at 2500 rpm's

exactly, 4:56 gives you the best of both worlds i think...

Badass69 Senior Enthusiast

Badass69

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4.88's........ you have a 60E and a 5.3. It needs more help than less. Revving to the moon......... Lol. When you have .7:1 overdrive with that big of a tire it will not. With the convertor locked 4.88's comes out to 2482 ( or 2500 rpm) at 80 mph. I run 30" tires with 4.10's and am about 300 rpm higher rpm at 80 mph..... and get your mileage with a loaded to around 7500 lbs 1500HD with an LQ4 and 4L80E.

 

You will be better off with 4.88's...... don't fear gear reduction lol.

blackout07 Senior Enthusiast

blackout07

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4.88's........ you have a 60E and a 5.3. It needs more help than less. Revving to the moon......... Lol. When you have .7:1 overdrive with that big of a tire it will not. With the convertor locked 4.88's comes out to 2482 ( or 2500 rpm) at 80 mph. I run 30" tires with 4.10's and am about 300 rpm higher rpm at 80 mph..... and get your mileage with a loaded to around 7500 lbs 1500HD with an LQ4 and 4L80E.

 

You will be better off with 4.88's...... don't fear gear reduction lol.

 

Agreed. The difference between 4.56 and 4.88 is minimal when it comes to rpms. Why spend the money to undergear? Any chart will place you at 4.56 for 35s based on tire height alone. Then you need to factor in the weight of your tires, the weight of the wheels, and the overall rolling resistance of the lifted truck. If you tow that's another consideration. Poke around on GMFS. There's a lot of gearing knowledge there and guys who actually have geared trucks. Seek out experienced advice on the matter.

LongrangeLauber Senior Enthusiast

LongrangeLauber

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Its only a 200 rpm difference at 80 mph. Which will give me better fuel economy around town? That's the one I'll go with then haha



Badass69 Senior Enthusiast

Badass69

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Its only a 200 rpm difference at 80 mph. Which will give me better fuel economy around town? That's the one I'll go with then haha

 

 

 

Exactly...... it's only 200 rpm. The one that works the truck the least in a stop and go situation will net the best mileage....... which would be the 4.88's. If you want mileage put it back to stock, lol.

LongrangeLauber Senior Enthusiast

LongrangeLauber

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Exactly...... it's only 200 rpm. The one that works the truck the least in a stop and go situation will net the best mileage....... which would be the 4.88's. If you want mileage put it back to stock, lol.

 

It would probably cost more to put it back to stock than it would to switch the gears haha... I guess 4.88's will make the cut then.

 

Im guessing 2500 rpm's is optimum for about 80 mph? That's what I'm collecting from this...

Badass69 Senior Enthusiast

Badass69

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It would probably cost more to put it back to stock than it would to switch the gears haha... I guess 4.88's will make the cut then.

 

Im guessing 2500 rpm's is optimum for about 80 mph? That's what I'm collecting from this...

 

Depends on the vehicle. Something aerodynamic, low to the ground and overall more efficient would benefit from less rpm. But your truck is absolutely none of that, no offense, neither are mine even sitting stock. You have low cruising rpm now with your 3.73's at 80 mph and those tires...... and look at the mileage you get lol.

 

People will argue with you all day long on optimum rpm for mileage...... which is great for stock stuff with aerodynamic consideration. I doubt your highway mileage will increase from what you get now...... but it won't go down either. That's why I always say leave it stock if you want mileage because this whole lifted big heavy tire mileage talk is absolutely a joke.

 

You will have power you thought not possible with the 37's with 4.88's.... and a reasonable cruise rpm lower than a lot of stock combo trucks. I mean I am over 2700 rpm at 80 mph with either or my two trucks rocking 245/75R16's and 4.10's..... but the 80E's overdrive is only .75:1 as well. Leave it at that.

Prokopchuk_9 Senior Enthusiast

Prokopchuk_9

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I was just sayin from experience a truck I owned before had 4:88's and it was too much I thought...I always wished I had 4:10's or 4:56's instead. I know it's only couple Hun rpm but hey, my old 1500hd the difference between 1900 rpm and 2100 rpm was a couple mpg almost...

Prokopchuk_9 Senior Enthusiast

Prokopchuk_9

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I get what nota member is sayin too. Lifts/trucks and MPG don't go together. If you run bigger tires say good bye to ur fuel mileage doesn't matter what you do. You are driving a land yacht...I've never complained about fuel economy with a truck, it is what it is...

Badass69 Senior Enthusiast

Badass69

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I was just sayin from experience a truck I owned before had 4:88's and it was too much I thought...I always wished I had 4:10's or 4:56's instead. I know it's only couple Hun rpm but hey, my old 1500hd the difference between 1900 rpm and 2100 rpm was a couple mpg almost...

 

Different trans, different ratios in said trans and I don't know what you had for tires nor does it matter. He has a deeper overdrive than the 80E does so it lets you run a little more gear while keeping the revs down slightly. Like I said it's all moot in the end worrying about fuel economy lol. I get maybe 12-13 mpg in either of mine and honestly couldn't possibly care less.

Carder09 Senior Enthusiast

Carder09

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This is all but confusing lol, not to high-jack the thread but I was wanting 4.56 gears but I am not increasing tire height but rather width, to hopefully 305's so I am not sure of what route I should go with it either.

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