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HD trucks are available with 4.10, the 1500s can get 3.92
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It's the front differential that's the hang up for going lower than 3.92. With the Gen4 body trucks, you could get lower gears for 2010 and older front difs. People would swap those into newer trucks, I think you had to use the CV shafts also. Not sure if it's possible to retrofit one into a Gen5 truck.
The first two gears of the 8HP75 are 5.0:1 and 3.20:1, that should get you moving with 35s unless you plan on towing.
The first two gears of the 8HP75 are 5.0:1 and 3.20:1, that should get you moving with 35s unless you plan on towing.
KKBB
Senior Member
If you are putting 35s on, I would go with 3.92
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You are buying a Hemi. Why would you want it run like a V6 
Just saying.
youtu.be
Just saying.
Find Your Effective Gear Ratio With This Equation
Ian shows you how to find the effective gear ratio on your vehicle when you upgrade to bigger tires with this equation on a PowerNation Extra tech tip. It ca...
youtu.be
REDNECK28871
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I have a 2021 Warlock 5.7 witth 3.21s with 35's I tow a 26 ft 7800 lb camping trailer with no problem . Wasnt sure how well it was giong to work but with the 8 speed tranny no problem at all.
Minotaur 013
Member
I have a 2016 Ram Minotaur running 35" tires, 3.92 gearing and 8 speed auto. This is a very good combination for performance and power. Would recommend the gear change if it's within budget.
Devin Taetsch
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The truck I’m purchasing has 3.21’s bummer… Lol, not sure I plan to lift this one though. Probably going to be an old fart and run it on the stock 22’s.
ASPLR
Junior Member
2019 Ram 1500, 5.7 HEMI, 4X4, 3.21 rear end. I'm pulling an rv at about 3500 pounds loaded. I know it's sufficient but I'm thinking of upping to 3.92. Will my rpm's decrease with a different rear end? I run the hell of rpm's when traveling. 3000 plus! Would I have to change anything up front because of 4X4? I put the truck in 4WD Auto if it's raining. Thanks for your input. I'm happy to provide more information if needed.
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Your rpm's will theoretically increase if you change to 3.92. I suspect your rpm problems are caused by your transmission shifting to lower gears to keep rpm's in the power band. So changing to a shorter rear gear could decrease your rpm's if the trans doesn't down-shift as much. Yes, you would also need to change the gearing in your front dif to match the rear. The gear ratio needs to match front to rear.
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I have to wonder if that's a lack of copy-n-paste as those are the gear ratios for the 8HP70. The 8HP75 has a wider gear ratio spread from 1st through 8th, the 4.71 first wouldn't contribute to that.
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I used this calc when I was in the Jeep world. You put in new size, old size and it will give you the the current "effective" end ratio (gears + tire size). Then in the New Ratio it gives you what gears that you would need to keep the same performance of old tires.
www.4lo.com
This one gives you what the engine rpm at an entered speed. Do one with stock, then with new setup and compare. IF you can figure out what the top gear ratio (od) is then change the Transmission ratio to that. Or just leave at 1:1 and see the gear differences.
Tire Size Change Calculator
The last year model suburban available with a manual transmission.
This one gives you what the engine rpm at an entered speed. Do one with stock, then with new setup and compare. IF you can figure out what the top gear ratio (od) is then change the Transmission ratio to that. Or just leave at 1:1 and see the gear differences.
Engine RPM / Engine Speed Calculator
Crawlpedia's RPM and Engine Speed Calculator will find your engine RPM at any speed given your transmission ratio, ring and pinion gear ratios, and vehicle speed.
www.crawlpedia.com
