Ram TRX Tire Guide: All-Terrain vs. Mud-Terrain, Load Range & Winter Ratings

Tires are the single most consequential purchase a Ram 1500 TRX owner makes. They are the only thing between six-thousand-plus pounds of supercharged truck and the ground, they change how the truck rides, steers, stops, and sounds, and — unlike almost every other modification — they wear out and force the decision on you again every few years. The good news is that the choice is far more structured than the marketing suggests. Once you can read a sidewall, compare load ratings honestly, and tell the tread categories apart, the shortlist gets short fast.

This guide is about which tire, not what fits. For the mounting numbers — the 6x139.7 bolt pattern, the 77.8mm hub bore, offset and backspacing, and what clears at what lift — start with the TRX wheel & tire fitment guide, then come back here to pick the rubber. For new tires and tire-adjacent hardware, browse the wheels & tires category; for factory takeoffs and used sets, the eBay Motors buttons below are the right rail — takeoff TRX wheel-and-tire sets are one of the most active used listings on the platform, because owners swap them off almost immediately.

Start by decoding the factory sidewall

The TRX ships on 325/65R18 tires on 18x9-inch wheels. That string is not a product name — it is a set of measurements, and being able to convert it is the whole foundation of shopping tires:

• 325 — section width in millimeters (the widest point of the inflated tire, sidewall to sidewall).
• 65 — aspect ratio: sidewall height as a percentage of section width. 65% of 325mm is about 211mm, or 8.3 inches, per side.
• R — radial construction.
• 18 — wheel diameter in inches.

Add it up — 8.3 + 8.3 + 18 — and the factory tire stands roughly 34.6 inches tall and about 12.8 inches wide. In other words, the TRX comes from the factory on what the aftermarket calls a 35-inch tire, which is exactly why this truck needs so much less work than a normal half-ton to look and perform the way owners want.

That matters when you cross-shop, because the off-road world quotes sizes two ways. Metric sizing (325/65R18) is what the truck wears. Flotation sizing (35x12.50R18) states diameter and width in inches directly. They are close but not identical, and two tires both called ”35s” can differ by half an inch or more in real diameter, which shows up as speedometer error and clearance you did not plan for. Convert everything to real inches before you compare.

Load index and load range — the number you must not go down on

This is the specification that gets skipped and should never be. A tire’s load index is a coded number for the maximum weight it can carry at its rated pressure. Load range (C, D, E and up, the modern successor to the old ply-rating language) describes how the carcass is built and the pressure it is designed to hold — C being the lightest of the three commonly seen on trucks, E the stiffest and heaviest-duty.

You will also see LT versus P-metric construction. LT (light truck) tires use tougher carcasses and higher pressures for load and puncture resistance; P-metric tires ride softer and weigh less but carry less at a given size. The TRX is genuinely heavy, genuinely wide, and genuinely fast, and it is frequently loaded further with a bumper, a rack, gear, or a trailer.

The rule is simple and non-negotiable: the replacement must carry at least as much weight per corner as the factory tire, at the pressures printed on your door-jamb placard. Read the load index on the sidewall of what you are buying, compare it against the original, and never trade down for a lighter or cheaper carcass. Everything else in tire shopping is a preference. This one is a safety floor.

Speed rating: the spec a fast truck can’t ignore

Most truck-tire buyers never look at the speed rating letter. On a TRX you should. This is a supercharged truck capable of sustained speeds that many aggressive off-road tires were simply never built for, and speed ratings on deep-lugged mud-terrains are often noticeably lower than on the highway-biased tires the same shop sells.

The mechanism is heat. A heavy vehicle flexing a tall, soft, heavily-voided tread block at speed builds temperature in the carcass, and heat is what separates belts. Desert running compounds it — high ambient temperatures, sustained speed, and sand or gravel that keeps the tire working. Match or exceed the factory rating unless you are consciously accepting a lower ceiling, and keep pressures where the placard says, because under-inflation is the fastest route to a heat failure.

The three tread families

All-terrain (A/T) — the right default

Moderate tread voids, reinforced but street-friendly carcass, useful bite in dirt, gravel, sand, and light snow, while staying quiet and predictable on pavement. All-terrains generally offer the best wet braking, the longest tread life, the highest speed ratings, and the lowest noise of the three families. Given that a TRX spends the overwhelming majority of its miles on the road — and that its off-road mission is high-speed desert running rather than crawling — this is where most owners should land, and it is what the truck wears from the factory for exactly that reason.

Mud-terrain (M/T) — specialist rubber

Big blocks, deep voids, tough sidewalls built to shrug off sharp rock, and self-cleaning tread that keeps biting in deep mud. If your driving genuinely includes slow technical trails, rock, clay, or wet mud, nothing else works as well. The costs are real and constant: noticeably more road noise, faster wear, softer wet-pavement grip, more unsprung weight, worse fuel economy on a truck that already drinks, and frequently a lower speed rating. Buy them because you use them, not because they photograph well.

Rugged-terrain / hybrid — the middle ground

A newer category that pairs mud-terrain-style shoulder blocks with a tighter center tread. You get more off-road bite and a more aggressive look than an all-terrain with less of the noise and wear penalty of a full mud-terrain. It is a genuine compromise in both directions — better than an A/T in the dirt, not as good as an M/T; quieter than an M/T on the road, not as quiet as an A/T. For owners who wheel occasionally but commute daily, it is often the honest answer.

Winter and cold-weather: M+S vs. 3PMSF

Two symbols show up on truck-tire sidewalls and they do not mean the same thing.

• M+S (“mud and snow”) is a designation a manufacturer may apply based on tread geometry — void ratio and block shape. No standardized performance test is required. Most all-terrains carry it.
• 3PMSF (the three-peak mountain snowflake) is earned by passing a standardized snow-traction test. It is a measured claim, not a design claim.

If you drive a TRX where it actually snows, look for the snowflake, not just M+S. And be clear-eyed about the limits: even a 3PMSF all-terrain is not a dedicated winter tire, whose compound stays pliable in deep cold in a way that an all-season truck compound does not. Owners in serious winter climates often run a second set of wheels with true winter tires — which is also the cleanest way to protect an expensive summer-tread set, and the reason a spare set of TPMS sensors belongs in the budget.

The other cold-weather detail nobody mentions: pressure falls as temperature falls. A tire set correctly on a warm afternoon will read low on a cold morning, and a truck this heavy is unforgiving of under-inflation. Check pressures with the seasons, not with the oil changes.

Sizing up: what changes when you leave 35 inches

Because the TRX starts on a 35, going bigger is an option far earlier than on other trucks — but “it fits” is not the same as “it is free.” Moving to a 37 or beyond changes several things at once:

• Effective gearing gets taller, dulling acceleration and shifting where the transmission wants to live.
• Rotating and unsprung mass goes up, which is felt in braking distance, ride quality, and driveline load.
• Speedometer and odometer read low until they are corrected.
• Clearance depends on wheel offset and backspacing as much as on lift — the wrong offset rubs even with height added.

None of that is a reason not to do it. It is a reason to plan the whole package — tire, wheel offset, suspension, and correction — instead of buying a size and hoping. The wheel & tire fitment guide covers the offset math, and the lift kit buyer’s guide covers what actually creates the clearance.

A short pre-purchase checklist

Before you commit to a set, confirm each of these:

1. Real diameter and width, converted to inches, versus the factory 325/65R18 — not the marketing size.
2. Load index at or above the factory tire, at your door-jamb placard pressures.
3. Speed rating matched or exceeded, or a conscious decision to accept less.
4. Tread family chosen for the driving you actually do, not the build you admire.
5. 3PMSF if winter is real where you live.
6. TPMS sensors accounted for if this is a second set of wheels.
7. Offset and clearance verified against your exact wheel and suspension if you are sizing up.
8. Date code and storage checked on any used or takeoff set — rubber ages whether or not it is driven.

Buying new vs. used

New tires are the straightforward path, and the wheels & tires category plus the tire-size searches below are the place to start. But the TRX has an unusually strong used market for one specific reason: a large share of owners pull the factory wheel-and-tire package almost immediately for something more aggressive, which puts low-mileage takeoff sets on eBay Motors constantly — often with the TPMS sensors already installed. If you want to return a truck to factory spec, keep a stock set for road trips, or replace one damaged corner with a matching tire, that is where to look. Inspect the date code, ask for tread-depth photos across the width (uneven wear tells you about the previous alignment), and confirm the sensors are included.

Once the tires are sorted, keep the rest of the truck on schedule with the TRX maintenance schedule & parts checklist — rotations and alignment are what turn an expensive set of tires into a long-lived one — and check the year-by-year fitment guide before ordering anything model-year sensitive.