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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