Dodge Ram 35 inch spare tire

Cooper STT PRO 295/65R20 (35.4″), ready to winch under a 2017, fourth generation Ram/Cummins 2500.

Question: How much spare tire can you fit under your truck?

Answer: It depends.

This post is about squeezing a large (35.4-inches) tire into the stock location on a late-model, fourth-generation, Dodge Ram Cummins pickup.

Both my Ram 2500 trucks (2014 and 2017) have had the tailpipe heat shield removed to facilitate winching a much larger tire into the factory spot. Obviously a bigger tire sits closer to the tailpipe. Only you can decide if it’s too close for you and your application. This Cooper Tires STT PRO is only about one-inch from the tailpipe; close!

35.4″ Cooper STT PRO spare is close the factory tailpipe on this 2017 Ram/Cummins.

For several years I have carried oversized rubber in the factory location on my fourth-generation Ram/Cummins trucks, mostly tires that were 34.8-inches tall. The 295/65R20 Cooper Discoverer STT PRO is substantially taller.

This 2017 Ram has plenty of clearance for the rear-axle track bar.

My 2017 has less room overall than my 2014, as the factory trailer hitch receiver is still in place. (It was removed on the 2014.) There are also steel plates on the inside of the frame to mount the Hillsboro 2000-Series aluminum flatbed. The 3/8-inch plates, one on each side, consume 0.75-inches.

3/8-inch steel plates inside the frame are part of the flatbed mounting.

There are advantages to choosing 35-inch or smaller tires on late-model, heavy-duty trucks instead of the popular 37-inch versions, particularly if they will fit in the factory spare location. These include, but are not limited to, not needing an additional tire carrier or pushing a truck camper further aft to fit a spare in front of the camper (which increases rear-overhang, tail-swing, and impacts weight distribution). Unless your rig is geared low—and most new vehicles have tall gearing—the taller overall gearing that results from fitting larger diameter tires is often a negative, as it results in less torque at the wheels.

Many should ask themselves if they really need the extra clearance provided by 37-inch rubber, or are they just following the crowd, and potentially making unnecessary compromises. There are positives and negatives for nearly every modification and upgrade choice. Generally we need to give something to get something. Everyone should decide for themselves if the juice is worth the squeeze.

35.4″ Cooper STT PRO stuffed under a 2017 Ram/Cummins 2500.

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James Langan

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Cooper Tires STT PRO truck camper MPG test

Attempted to establish a baseline for fuel economy/mpg at 65 mph, with the 35.4″-tall, 295/65R20 Cooper STT PRO tires under a heavy Hallmark flatbed truck camper outfit. There was too much wind for this to be a true baseline, but efficiency was still good for this not-aerodynamic configuration; just under 13 mpg. I probably will revisit this in the future.

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James Langan

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Cooper STT PRO 295/65R20 low psi flexing

Recent photoshoot (June 2020) with Cooper Discoverer STT PRO, 35.4″-tall, 295/65R20 tires. My 2014 Ram crew cab with Cummins Diesel and stock-height suspension was the model. Pressures were 27 in front, 17 in the rear.

Disclaimer: As with all things, proceed at your own risk, only you can decide what is appropriate given your training, experience, knowledge, the conditions, etc.

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James Langan

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Cooper Discoverer STT PRO 295/65R20 first look

Mount and balance, and first look at the 35.4-inch tall, LT295/65R20 Cooper Discoverer STT PRO tires I’m running on my diesel truck(s). There will be more in the weeks and months ahead, here, and also @RoadTraveler on Instagram (typically extra content in Instagram stories).

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James Langan

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Centramatic Big Wheel And Tire Balancers

This video introduces using Centramatic 400-409 balancers designed for DRW trucks with 16-inch wheels, on SRW pickups with 20-inch wheels. These balancers have 16-ounces of balancing media!

Article about the possible performance advantages of 20-inch wheels over 18- or 17-inch wheels on heavy outfits: 20-inch vs. 18-inch Wheels and Tires

Prior video regarding the basic design and function of Centramatic wheel balancers for light-truck applications: Centramatic Wheel Balancers Introduction

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James Langan

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Banks Differential Cover

Banks Ram-Air Differential Cover

Backgrounder: I have installed, used, and liked Banks Power products in the past, and I respect the engineering that goes into everything they do. However, I watched Banks’ YouTube videos regarding the purported inferiority of flat-back, high-capacity, aluminum replacement differential covers while they developed their own aftermarket differential cover.

Their target was obviously the original, and arguably still the best with the most features, Mag-Hytec. Obviously Banks needed to offer more than a rounded rear aluminum cover, as Ram already makes one of those for their trucks, and maybe other OEMs do as well.

Cut-away Mag-Hytec and Banks Ram-Air Differential Covers. 2019 SEMA Show.

Banks says their new Ram-Air Differential Cover “…cools 5X better than flat-backs by directing cool air through its break-away ram-air scoops. Increases fuel economy and extends lubrication life by utilizing proper fluid dynamics”.

Smoother, proper fluid dynamics, I won’t argue with. The theoretical fuel economy improvement is understandable, though I’d like to see a real world test and a measurable increase on a truck actually rolling down the road. For the tow-rigs and hot-rodders that never leave the pavement, the Banks cover might be a great accessory. However, what I noticed and what concerned me in the prototype videos on YouTube I confirmed with my own eyes at the 2019 SEMA Show: the low-hanging “break-away ram-air scoops”.

Solid axle differential housings are generally the lowest chassis component on pickups. Dragging them down the center of a rutted track or caking them with slime on a farm or ranch is not uncommon. During more technical off-road driving, getting hung-up on a differential does happen, which must be why the cooling scoops are “break-away”. During on-road winter travel in our part of The West, we often have a snow/slush mix that gets slung everywhere, and can freeze into a solid mass. Maybe the grimy wintery mix will increase cooling?

Forward-facing, wide and low-hanging cooling scoops are potential anchors and debris catchers.

Some don’t care about all-season or off-pavement performance, and this Banks differential cover might be perfect for them. Because I actually use my four-wheel-drives in rough and sometimes sloppy real-world conditions, the wide, low-hanging cooling scoops are a deal breaker, I’d rather run the stock cover. That’s me, and the Banks Ram-Air Differential Cover might be what you need and want. At press time Banks’ site listed a retail price of $439, with a pre-order sale price of $395.

A version of this article was also published in the Turbo Diesel Register magazine, as part of my 2019 SEMA Show coverage.

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James Langan

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