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Gearing for 37's?

LongrangeLauber

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Chris Senior Enthusiast

Chris

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4.10's

 

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LongrangeLauber Senior Enthusiast

LongrangeLauber

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4.10's

 

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Agreed. If not increasing height then it will have the same rotational speed. 4.56 is for 35's or above if you want the stock rpm's from what I've learned in this forum

LongrangeLauber Senior Enthusiast

LongrangeLauber

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Now if I have my 3.73's on 35's right now, wont that give me better highway fuel mileage since the rpm's are lower due to the increase in the circumference of the tires over stock? Im still going to swap gears, I was just wondering...

Badass69 Senior Enthusiast

Badass69

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Now if I have my 3.73's on 35's right now, wont that give me better highway fuel mileage since the rpm's are lower due to the increase in the circumference of the tires over stock? Im still going to swap gears, I was just wondering...

 

Aerodynamic drag from the lift and greater rotating mass negates any of that. If that were the case we would all have 2.73 gears and 40" tires lol. Look at it this way..... you want your cruise rpm somewhere in the general vicinity of what the truck would have been with the stock tires and gear set. I say general vicinity because you are offsetting more drag and weight now than when the truck was stock. Personally I like more gear than the factory offerings..... or at least the deepest I can get. My last half ton was a 2000 5.3 powered reg cab long box and it was rocking 30" tall tires and 4.10 gears stock........ That truck had more gear than you will with 4.88's and your 37's.... so let me explain.

 

Truthfully 4.56's is slightly less mechanical advantage with the 37's than 3.73's with 245/75R16's were....... and you were 9" lower to the ground with a tire combo that was smaller and probably 60 lbs lighter lol. This stuff all eats gas mileage...... and why you continue to talk about mileage with a 9" lifted 4X4 with 37's is just funny.....

 

4.88's is a slight performance edge with a 37" tall tire over what 3.73's with a 30" tall tire was. A truck with 4.10's from the factory and the stock 245/75R16's as a half ton ( like my 2000 was) still has more gear than you will with your 4.88's and 37" tires...... Funny how that works lol. It's all just ratios. To equate to a 4.10 geared 30" tall tire equipped truck you would need 5.13's with your 37" tall tires...... which is the deepest gear you can get with the 8.25" IFS diff.

 

Stop worrying about gas mileage lol.

 

So to all those goobers out there that cringe at 4.88's and whatnot I just laugh. 4.88's with a 30" tall tire is a steeper gear....... but add 7" and like 60 lbs of rotating mass to that and get back to me.

 

Once again if it doesn't hit home, 4.88's and 37" tall tires bascially gets you the same effective final drive ratio as what you were at with 3.73's and a 30" tire. Only now you are 9" higher up and have way heavier tires to turn......

LongrangeLauber Senior Enthusiast

LongrangeLauber

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I was just curious, that's all. I know im gonna get crappy mileage anyways but rather have the questions answered. Plus if I get half a mile per a gallon better, it all adds up real quick. And my truck actually came stock with 265/75r16 tires. Not sure why but it did.

And all this does make since. Thanks for going into detail about it for those of us (including me) who don't fully understand it

yukon25008.1 Senior Enthusiast

yukon25008.1

Posted
Posted

Im going to run a 36/37" tire when i get the lift installed, So I am now debating between the 4;56 and 4;88 I have a 5 spd allison and 4;10,s rite now.. I was running 305 70 16,s and just temporarily switched to 265 75 16,s and i felt a diiference! so i definitly want to have the right gear/s in place when the big tires go on..

blackout07 Senior Enthusiast

blackout07

Posted
Posted

 

Aerodynamic drag from the lift and greater rotating mass negates any of that. If that were the case we would all have 2.73 gears and 40" tires lol. Look at it this way..... you want your cruise rpm somewhere in the general vicinity of what the truck would have been with the stock tires and gear set. I say general vicinity because you are offsetting more drag and weight now than when the truck was stock. Personally I like more gear than the factory offerings..... or at least the deepest I can get. My last half ton was a 2000 5.3 powered reg cab long box and it was rocking 30" tall tires and 4.10 gears stock........ That truck had more gear than you will with 4.88's and your 37's.... so let me explain.

 

Truthfully 4.56's is slightly less mechanical advantage with the 37's than 3.73's with 245/75R16's were....... and you were 9" lower to the ground with a tire combo that was smaller and probably 60 lbs lighter lol. This stuff all eats gas mileage...... and why you continue to talk about mileage with a 9" lifted 4X4 with 37's is just funny.....

 

4.88's is a slight performance edge with a 37" tall tire over what 3.73's with a 30" tall tire was. A truck with 4.10's from the factory and the stock 245/75R16's as a half ton ( like my 2000 was) still has more gear than you will with your 4.88's and 37" tires...... Funny how that works lol. It's all just ratios. To equate to a 4.10 geared 30" tall tire equipped truck you would need 5.13's with your 37" tall tires...... which is the deepest gear you can get with the 8.25" IFS diff.

 

Stop worrying about gas mileage lol.

 

So to all those goobers out there that cringe at 4.88's and whatnot I just laugh. 4.88's with a 30" tall tire is a steeper gear....... but add 7" and like 60 lbs of rotating mass to that and get back to me.

 

Once again if it doesn't hit home, 4.88's and 37" tall tires bascially gets you the same effective final drive ratio as what you were at with 3.73's and a 30" tire. Only now you are 9" higher up and have way heavier tires to turn......

 

Thank you! This is what I was talking about. The charts are basic guides only and there are clearly other considerations.

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