How to Choose the Right Tire Size for Your Rig

Reading Tire Sizes: The Basics

Before you can choose a tire size, you need to understand what those numbers on the sidewall mean. There are two common sizing formats, and knowing both will save you confusion when shopping.

Metric Sizing (e.g., 265/70R17)

• 265: Section width in millimeters — the tire is 265mm wide from sidewall to sidewall
• 70: Aspect ratio — the sidewall height is 70% of the section width (265 x 0.70 = 185.5mm)
• R: Radial construction
• 17: Wheel diameter in inches

To calculate overall diameter: (section width x aspect ratio x 2 / 25.4) + wheel diameter. For 265/70R17: (265 x 0.70 x 2 / 25.4) + 17 = 31.6 inches.

Flotation Sizing (e.g., 33x12.50R17)

• 33: Overall tire diameter in inches
• 12.50: Section width in inches
• R17: Radial, 17-inch wheel

Flotation sizing is more intuitive — you can immediately see the tire's diameter. It is most common on larger off-road tires (33 inches and up).

Stock Size vs One Size Up vs Two Sizes Up

Here is a general reference for popular truck and SUV platforms. Your specific vehicle may vary, so always verify fitment:

• Stock: Typically 29-31 inches depending on vehicle. Fits with no modifications.
• One size up (32-33 inches): Usually fits with a leveling kit or 2-inch lift. May require minor trimming of fender liners or mud flaps. Minimal impact on gearing and fuel economy.
• Two sizes up (34-35 inches): Requires a 2.5-3 inch lift minimum, likely fender trimming or body mount chop, and regearing is strongly recommended. Noticeable impact on acceleration, fuel economy, and transmission behavior.
• Three sizes up (37+ inches): Requires significant lift (4+ inches), extensive body modifications, regearing, possibly aftermarket axles and drivetrain components. This is competition/dedicated build territory.

Gearing: The Hidden Cost of Bigger Tires

This is the factor most people underestimate. When you increase tire diameter, you effectively change your gear ratio. A larger tire covers more ground per revolution, which has the same effect as running a taller gear. The result: slower acceleration, higher RPMs needed to maintain highway speed, and a transmission that hunts between gears because the factory shift points no longer match.

Here is the math. If your stock tire is 31 inches and your stock axle gear ratio is 3.73:1, going to a 33-inch tire gives you an effective ratio of 3.73 x (31/33) = 3.50:1. That is a 6% reduction in mechanical advantage. Go to 35 inches and it drops to 3.30:1 — a 12% change that you will feel every time you press the throttle.

When to Regear

General guidelines:

• 1-2 inch increase in tire diameter: Most vehicles handle this without regearing, though you may notice slightly lazier acceleration
• 3-4 inch increase: Regearing is recommended, especially for automatic transmissions that hunt for gears under load
• 5+ inch increase: Regearing is mandatory. Your vehicle will be unpleasant and potentially unreliable without it

Common regear targets:

• 33-inch tires with stock 3.73 gears: regear to 4.10 or 4.30
• 35-inch tires with stock 3.73 gears: regear to 4.56 or 4.88
• 37-inch tires: 4.88 or 5.13 depending on platform

Regearing is expensive — $1,500-$3,000 installed for both axles. Factor this into your tire budget. A $1,600 set of 35-inch tires becomes a $4,000+ investment when regearing is included.

Speedometer Calibration

Larger tires make your speedometer read slower than your actual speed, because the tire covers more distance per revolution than the factory calibration expects. A 33-inch tire on a vehicle calibrated for 31-inch tires will cause your speedometer to read about 6% low — you will be doing 64 MPH when the dash says 60.

This also affects your odometer, trip computer, fuel economy calculations, and (on some vehicles) transmission shift points and ABS calibration.

Correction options:

• Programmer/tuner: Devices like the Superchips Flashcal or Hypertech Speedometer Calibrator plug into your OBD-II port and correct the speedometer signal. Simple and effective ($100-$200).
• Dealer recalibration: Some dealers can update the tire size in the ECU. Availability and cost vary.
• GPS speed verification: At minimum, use a GPS device or phone app to know your actual speed. Not a fix, but it keeps you from getting tickets.

Trimming and Cutting for Tire Clearance

Larger tires may rub on fender liners, bumper corners, mud flaps, or the pinch weld at full steering lock or full suspension compression. Before cutting anything, do a thorough clearance check:

1. Turn the wheels to full lock in both directions and check for rubbing
2. Compress the front suspension (drive onto a curb or have someone push down on the bumper) at full lock
3. Check rear tire clearance at full suspension compression (load the bed with weight)
4. Check clearance with the wheel offset you plan to run — more offset means more outward clearance but less inner clearance

Common Trimming Areas

• Fender liner: The most common modification. The front fender liner can usually be trimmed or pushed back with a heat gun. This is reversible and low-risk.
• Pinch weld: The folded metal seam at the bottom of the fender opening. Flattening or trimming this provides significant clearance. Apply seam sealer or paint after cutting to prevent rust.
• Bumper corners: Some aftermarket bumpers require trimming at the corners where they meet the fender. Alternatively, aftermarket high-clearance fenders solve this more elegantly but cost more.
• Body mount chop (CMC): On certain trucks (notably Toyota Tacomas), a cab mount chop — trimming the sheet metal above the rear cab mount — is necessary for 33+ inch tires. This is a common and well-documented modification but is irreversible.

Lift Requirements by Tire Size

These are approximate guidelines. Actual fitment depends on vehicle, wheel offset, and how much trimming you are willing to do:

• 32-inch tires: Leveling kit or 1-2 inch lift, minimal trimming
• 33-inch tires: 2-2.5 inch lift, moderate trimming likely
• 35-inch tires: 3+ inch lift, significant trimming, UCA correction recommended
• 37-inch tires: 4+ inch lift, extensive modifications, regearing mandatory

For lift kit guidance, see our lift kit guide. And remember: a 33-inch all-terrain on a 2-inch lift will outperform a 35-inch tire at stock height that rubs at every bump. Fitment matters more than size.

The Practical Approach

For most overlanding builds, the sweet spot is one size up from stock — typically 32-33 inches. This size provides meaningful improvement in ground clearance and obstacle capability, fits with a modest lift and minimal trimming, does not require regearing, and has minimal impact on fuel economy and drivability.

Going to 35 inches is a significant commitment — not just in tire cost, but in the cascade of supporting modifications. Do it if your terrain demands it. But do not do it because the internet told you bigger is always better. Choose the tire size that matches your actual use, your budget for supporting mods, and your tolerance for trade-offs.