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Towing with lifted truck


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I have 2003 1500 hd with a 6 inch lift and 305/75/16 I towed a 6500 pound tow hauler around motorcross racing question is I have stock 3.73 gearing I have looked around but what gearing should i be running. i may put 315/75/16 on in the future I dont what to run to may rpms would 4.10 ,4.56 , 4.88 work the best i do us it for a daily driver also

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Here's my 2 cents A 31 inch tall tire with a 3.73 is stock.(on yours) Ok for towing OK for gas mpg Putting a 33" tire raises your effective gear ratio to a 3.50ish which is worse for towing but better fo mpg. A 35" tire raises you to a 3.30ish gear. This is not good for towing but pretty good on gas exspecially if you do alot of highway. To get your truck back to overall stock gearing as your trans sees it it would take a 4.56. Now considering the 3.73 is an ok gear ratio for our trucks, your truck would drive close to stock. Of course the tires weigh more so that takes a bit o power from you but not much. A 4.88 would give you an effective ratio of 4.10's which should give you back the little you lost from the added weight of your tires. the difference in RPM between the 4.56 and 4.88 would be about 230 at 65-70 mph. or 2000 instead of 1750. I will be installing 4.56's in mine when I get the chance, but if I had a toy hauler it would be 4.88's just to be in a better rpm range for towing.

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35" tire 3.73 = 3.30ish 1400rpmat 65 estimate

35" 4.10 = 3.50ish 1580rpm at 65 estimate

35" 4.56 = 3.73ish 1750 rpm at 65 estimate

35" 4.88 = 4.10ish 1930rpm at 65 estimate

 

Now this assuming a 31" tire factory with 3.73

 

Hope this is clearer than above

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  • 2 weeks later...
If I get the 4:10 gears, would 35s be okay if I tow? Or should I still go with 4:56?

 

 

 

 

 

4.56 minimum here with possible 35's. Even 31's with a 3.73 is not a good towing combo for heavy loads with a small block and should be 4.10 to start with. If you tow a lot and are going to 35's some day, go 4.88 and you will not be disapointed and MPG will be fine when not towing too with OD. There is a lot of misconception out there on cruise RPM in a SUV and most small block engines are most efficent at about 2500 RPM and above in lbs of fuel burned per HP hour developed which you must consider with you add big draggy tires and increase wind drag too from a lifted truck it takes more power to cruise with it than a stock one so you need to do more than just match RPM's of stock setup.

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