When you own a half-ton truck, finding the right rubber for your factory rims matters more than you might think. The factory setup for a 2020 Ram 1500 wearing 20-inch wheels typically relies on a 275/55R20 tire size, measuring roughly 31.9 inches in overall diameter. Whether you're replacing worn-out original equipment or searching for a meatier stance, understanding exact dimensions, load ratings, and clearance limits prevents costly rubbing and speedometer errors.
Upgrading your 2020 Ram 1500 20 inch tire size requires looking past basic aesthetics. You need to balance daily highway comfort, towing capacity, and clearance tolerances, especially if your truck features factory air suspension or a leveling kit. This guide breaks down factory specifications, popular aftermarket upgrades, clearance boundaries, and maintenance habits to keep your truck tracking straight.
Factory Specifications and OE Fitments
The fifth-generation Ram 1500 (DT chassis) introduced a 6-lug pattern (6x139.7mm), marking a major shift from older models. Trim levels like the Big Horn, Laramie, Longhorn, and Limited frequently leave the factory floor with 20-inch rims.
The original equipment tire size for these 20-inch rims is standardized across most trims:
- Size Code: 275/55R20
- Section Width: 275 millimeters (approx. 10.8 inches)
- Aspect Ratio: 55% (sidewall height is 55% of the section width)
- Wheel Diameter: 20 inches
- Overall Diameter: 31.9 inches
- Standard Load Index / Speed Rating: Typically 113T or higher
Some Classic body style trims from 2020 (which retained the older 4th-generation 5-lug platform) use a 275/60R20 tire, which is slightly taller at 33 inches. Always check your driver-side door placard to confirm your exact door-sill specifications before ordering new rubber.
Popular Aftermarket Tire Upgrades for 20-Inch Rims
Drivers frequently want a more aggressive tread pattern or a slightly larger footprint without hacking up their wheel wells. Because the wheel wells on the fifth-generation Ram 1500 are remarkably generous, you have several strong upgrade paths.
Staying Stock Height: The 33-Inch Jump
If your truck sits at standard factory height, you aren't restricted strictly to the factory 31.9-inch tire. Many owners step up to a true 33-inch tire, such as a 275/60R20 or a 305/55R20, on stock suspension.
- A 275/60R20 all-terrain tire adds a bit of sidewall cushion, smoothing out rough job-site roads without causing inner liner rub.
- A 305/55R20 gives you a wider, beefier footprint (about 12 inches wide), though you should verify that your offset doesn't push the inner edge into your upper control arm.
Adding a Leveling Kit
Installing a 2-inch to 2.5-inch front leveling kit alters the geometry just enough to clear wider setups. A popular combination is a 20x10-inch wheel with a -18 to -25 offset paired with 33x12.50R20 tires. This creates an aggressive, flush-to-fender look without requiring a full suspension lift.
Moving to a 3-Inch Lift
If you want to run true 35-inch tires (such as a 35x12.50R20) on your 20-inch rims, plan on installing at least a 3-inch suspension lift. Trying to stuff 35s onto a stock-height truck will cause severe rubbing on the plastic inner fender liners and sway bars during tight turns.
Air Suspension Versus Standard Coil Springs
Your choice of tire size is heavily influenced by how your truck handles suspension travel. Ram offered two distinct setups on the 2020 model:
- Coil-Spring Suspension: Standard steel springs offer predictable, fixed ride heights. They tolerate slight tire size increases well, provided you stay within clear articulation limits.
- Four-Corner Air Suspension: This system automatically adjusts ride height for aerodynamics, entry/exit, and off-road clearance. Trucks equipped with air suspension have tighter clearance margins in "Entry/Exit" mode. If you push past a 33.2-inch overall diameter on an air-suspension truck, you risk contacting the composite fender liners when the truck drops down.
Common Mistakes to Avoid
Upgrading truck tires involves a few hidden traps. Avoiding these missteps saves you from premature wear and annoying dashboard lights.
- Ignoring Load Ratings: Half-tons work hard, and putting passenger-rated (P-metric) tires on a truck used for heavy towing creates excessive sidewall flex. Look for XL (Extra Load) ratings or LT (Light Truck) metric ratings with appropriate load indexes if you regularly tow trailers or haul heavy payloads.
- Neglecting Speedometer Calibration: Moving from the stock 31.9-inch tire to a 35-inch tire throws your speedometer and odometer off by roughly 10%. Your truck will log fewer miles than you actually travel, and your transmission shift points may feel sluggish until you recalibrate the computer using an OBD2 programmer.
- Overlooking Wheel Offset: Wider aftermarket wheels with deep negative offsets push the tire edge outward. While this looks aggressive, it increases the scrubbing radius and forces the tire edge directly into your front bumper valance or rear fender liner.
Frequently Asked Questions
Can I fit 35-inch tires on a stock 2020 Ram 1500 with 20-inch wheels?
No, true 35-inch tires will rub significantly against the upper control arms and inner fender liners at stock height. You need a minimum 3-inch lift kit or careful trimming to clear 35-inch rubber cleanly.
What is the widest tire I can run on a stock 20-inch Ram wheel?
You can safely mount a 12.50-inch wide tire (like a 33x12.50R20) on a stock 20x9-inch Ram wheel, but verify that the specific tire manufacturer approves a 9-inch wide rim for that tread width.
Does changing my tire size void my factory warranty?
Changing your tire size doesn't automatically void your entire vehicle warranty under federal guidelines like the Magnuson-Moss Warranty Act. However, if a larger, heavier tire or improper offset damages your wheel bearings, ball joints, or suspension components, the dealership can deny warranty coverage for those specific broken parts.
How do I check my current tire size and load index?
Look at the sidewall of your current tires. You will find a alphanumeric string starting with a letter like P or LT, followed by numbers such as 275/55R20 113T. You can also consult the official Ram Trucks Owner Manuals or the tire placard sticker located on the driver-side door jamb.
Will larger 20-inch tires ruin my fuel economy?
Yes. Moving to heavier all-terrain or mud-terrain tires increases rotational mass and rolling resistance. Expect a drop of 1 to 3 miles per gallon depending on how aggressive and heavy your new tire choice is.
