1500 5.7hemi 3.21end increase gearing with smaller tires?

In reading through the posts, many are saying if towing close to capacity will put strain on the running gear, and its better to swap gears/rear end for higher gear ratio. Has anyone achieved higher gear ratio by installing smaller tires? My tires now are 275/60/20 and I am planning to install LT tires, what if I install 275/55/20 or 275/50/20? and have the speedometer reprogramed so it would show the actual speed. Will I have a better towing rig? Or maybe go to 17" wheels since there are more tire sizes available?

Don't waste the money with the 8speed your truck is more capable than a 6 speed 3.92 truck. My truck has no issues towing my TT thru the mountains or anywhere else it weighs in at 7500lbs.

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I did that, sort of, and for similar reasons. When I bought the truck used it had "macho" tires on 18" Ram wheels. The tires were almost 34" tall and rubbing on the front control arms. The stock size on the truck was 245/70-17 (2013 Tradesman 2500), that's over 3" difference in diameter. The speedo was way off, and the MPG (even after accounting for the low reading odometer) was pretty crappy. The truck is now on 265/70-17 which is a very common size giving you lots of options. Unloaded MPG got quite a bit better, it's also a tad quicker off the line but towing MPG still sucks

One thing I noticed with Ram is that they have somewhat widely varying tire diameters depending on options. The 2013 Tradesman 2500 had a 30.5" tall tire while on an SLT the standard size was 31.6". In 2014 the higher trim levels got a 33.2" tall tire on 18" wheels. All with the same engine and gearing. Some back of the napkin math shows that going from a 30.5" tire to a 33.2" tire is about the same as changing the gearing from 3.73 to 3.45. The reverse is obviously true as well.

Thanks Ohio for the feedback, I mostly saw posters say the 1500 will struggle going uphill, that is why I was wondering if it’s better to increase the gear ratio with smaller tires.

I am planning to replace the current P275/60R20 Wrangler SRA’s to LT tires for towing and even though the factory wheels are rated at 65psi max, I will keep the LT tires aired around 50psi.

Since I want to buy LT tires, I just thought about these sizes: the 275/60/20 height is 33”, 275/55/20 height is 31.9” and 275/50/20 height is 30.8” . If the smaller sizes do not affect alignment, they might even be better for lowering the center of gravity. Thanks Csuder99, I am still trying to napkin math decide.

I do like the ZF 8HP70 Transmission, with the 3.21 axle it has a 2.15 Overall Top Gear Ratio.

Geogee said:

Thanks Ohio for the feedback, I mostly saw posters say the 1500 will struggle going uphill, that is why I was wondering if it’s better to increase the gear ratio with smaller tires.

I am planning to replace the current P275/60R20 Wrangler SRA’s to LT tires for towing and even though the factory wheels are rated at 65psi max, I will keep the LT tires aired around 50psi.

Since I want to buy LT tires, I just thought about these sizes: the 275/60/20 height is 33”, 275/55/20 height is 31.9” and 275/50/20 height is 30.8” . If the smaller sizes do not affect alignment, they might even be better for lowering the center of gravity. Thanks Csuder99, I am still trying to napkin math decide.

I do like the ZF 8HP70 Transmission, with the 3.21 axle it has a 2.15 Overall Top Gear Ratio.


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I think most posts that say they struggle are people who don't own one and think the 3.92 is is the end all be all. Cruise set at 70-75 thru the smokies no issues. Also has no issue gain speed for inclines temps don't get out of control either.

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I'm sure it won't be a crazy performer now with the 35s and 120lbs on each corner compared to the 72lbs stock but I well. Weight is the big thing with these trucks not tire size

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The setup of the truck matters, the truck should tow just fine based on factory setup and following factory weight sticker. Adding running boards, people, tools, etc. to the truck reduce payload and maximum possible trailer weight. Of course running close to the maximum weight without weighing everything at scales can mean actually being overweight. Gear, food, drinks, plus options on trailer that were not originally included in trailer dry weight (awnings are not always included, for example) add up quicker than we think. At the end of it all, each rig is unique and no one's experience will substitute for your own diligence. Before you go spending money, load everything and get your individual axle weights and tongue weight. If properly set up you will not stress your gearing or truck at all, it will be doing exactly what it is designed for. Good luck.

I'm posting this about smaller tires. I know this is a little older but, I have a 1500 classic 5.7, with 3.21 gears and stock 275/60-20 tires. My trailer is only 5,700lbs loaded and I have no power issues towing.

When I had my hitch professionally set up it was suggested, when I needed to have my tires replaced I consider Pirelli scorpion 265/50-20 tires. It was suggested that they will handle much tighter, give me a little more power and slightly better fuel mileage. Yes, the speedometer will show a higher speed than actual.
My stock tires have worn out at only 27,000 miles, so I'm now considering these tires.

Gearjunkie said:

I'm posting this about smaller tires. I know this is a little older but, I have a 1500 classic 5.7, with 3.92 gears and stock 275/60-20 tires. My trailer is only 5,700lbs loaded and I have no power issues towing.

When I had my hitch professionally set up it was suggested, when I needed to have my tires replaced I consider Pirelli scorpion 265/50-20 tires. It was suggested that they will handle much tighter, give me a little more power and slightly better fuel mileage. Yes, the speedometer will show a higher speed than actual.
My stock tires have worn out at only 27,000 miles, so I'm now considering these tires.

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Why not 65/60/20? I really don't think ya need a 50 series tire... Why not just buy a better quality/grade of 275/60/20 tires?

06 Dodge said:

Why not 65/60/20? I really don't think ya need a 50 series tire... Why not just buy a better quality/grade of 275/60/20 tires?

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I'm starting to lean towards better quality 275/60/20 tires.

Go down one size. That's a reasonable way to tilt things in the right direction without affecting normal ride and handling.

Gearjunkie said:

I'm posting this about smaller tires. I know this is a little older but, I have a 1500 classic 5.7, with 3.21 gears and stock 275/60-20 tires. My trailer is only 5,700lbs loaded and I have no power issues towing.

When I had my hitch professionally set up it was suggested, when I needed to have my tires replaced I consider Pirelli scorpion 265/50-20 tires. It was suggested that they will handle much tighter, give me a little more power and slightly better fuel mileage. Yes, the speedometer will show a higher speed than actual.
My stock tires have worn out at only 27,000 miles, so I'm now considering these tires.

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If you changed the tire size and didn't tell the BCM, that explains why your gauges are f-ed. You can do this very easily in AlfaOBD.