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Gearing Question

Radon

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Radon Enthusiast

Radon

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I just got new tires and have heard a lot from the forum about rear end gears and how the bigger tire size lowers them. I personally have 3.23 (or im 99% sure). What I want to know is what the rear end gear numbers mean and what it means for my truck having the lowest gearing GM offers.

svensk Senior Enthusiast

svensk

Posted
Posted

Well honestly, your not going to win many drag races especially with a trailer hooked up. GM puts these passenger car type ratios in a select number of trucks to get better fuel mileage numbers. There is great discussion about whether or not this even gets you better mileage because in affect you are having to use more throttle to get moving. If you get new tires keep the stock size because if you go any bigger you'll be regretting it. You probably want to run a 245 and no larger.

thecraft Senior Enthusiast

thecraft

Posted
Posted

Higher gear ratios (lower numbers like 3.08) will give you better economy on the highway while lower gear ratios (higher numbers like 4.10) will give you better off-the-line and towing performance. Running larger tires will increase your gear ratio while smaller tires decrease it.

 

You're running 265/75R16 tires now, right? If you're planning on running bigger tires than that, you should definitely look into getting your gears changed... unless your truck never leaves the highway.

 

Go to http://4lo.com/calc/gearratio.htm and punch in your information. Your transmission ratio is 0.7:1 in OD and your transfer case ratio is obviously 1:1. If you're getting close to or over 2000rpms at 70mph in overdrive, you're in the sweet spot. Your truck will be able to tow moderate loads with ease and still get respectable mileage on the highway.

Radon Enthusiast

Radon

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Dumb question, is the tire size 265 or ~31.5. Both entries give me funny numbers. And since my truck is 2wd, what do I put in the transfer case ratio?

svensk Senior Enthusiast

svensk

Posted
Posted
Dumb question, is the tire size 265 or ~31.5. Both entries give me funny numbers. And since my truck is 2wd, what do I put in the transfer case ratio?

Just keep it 1:1 since you don't have a T-case.

thecraft Senior Enthusiast

thecraft

Posted
Posted
Dumb question, is the tire size 265 or ~31.5. Both entries give me funny numbers.
31.5

 

I'm getting 1688.2rpms, is that what you have?

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