Selecting the right tires for your truck or trailer is critical for safe and legal transport, especially when hauling oversize or overweight loads. Tire size affects everything from vehicle height to axle weight distribution and fuel efficiency. Incorrect tire data can lead to fines, bridge clearance issues, or permit denials.
We've created a clear, beginner-friendly guide to help you identify and interpret tire sizes, avoid mistakes, and prepare for DOT inspections. Read on, follow the steps, and use our tips to haul confidently!
Locating tire size is straightforward, with three reliable sources:
Tire sidewall. The most accurate method is checking the sidewall, where a code like 295/75R22.5 is embossed. This provides the exact data needed for permits and inspections.
Cab placard. Look at the sticker on the driver’s door frame or pillar, which lists manufacturer-recommended tire sizes, pressure, and load ratings.
Documentation. The truck or trailer’s owner’s manual or spec sheet details standard and approved tire sizes for steer, drive, and trailer axles.
If the sidewall marking is worn or the placard is missing, refer to the manual or contact the equipment dealer. For oversize loads, precision is crucial!
Tip. Photograph the sidewall markings and placard for quick reference during DOT checks.
Tire markings, like 295/75R22.5, consist of letters and numbers that describe the tire’s specifications. Here’s what they mean:
295: Tire width in millimeters (sidewall to sidewall).
75: Aspect ratio, the sidewall height as a percentage of the width (75% of 295 mm ≈ 221 mm).
R: Radial construction, standard for most modern truck tires.
22.5: Rim diameter in inches (the wheel size the tire fits).
Example. A 295/75R22.5 tire is 295 mm wide, with a sidewall height of about 221 mm, and fits a 22.5-inch rim—a common size for trucks. Record the markings for all tires (steer, drive, trailer) and ensure they match manufacturer recommendations. Mismatched sizes across axles can disrupt balance and violate regulations.
Tip. Write down each tire’s marking in a log or ELD to streamline permit applications.
Tire sizes vary by vehicle type and axle function. Here are typical examples:
Steer axle (truck): 295/75R22.5—standard for highway stability and maneuverability.
Drive axle (truck): 11R22.5 or 295/75R22.5—deep tread for traction.
Trailer axle: 255/70R22.5 or 11R24.5—low profile for stability under heavy loads.
Light trucks/pickups: 265/70R17—smaller rim, higher sidewall for versatility.
For oversize loads, confirm tires match the load’s weight requirements, especially for high load index ratings.
Tip. Check the permit to ensure tire sizes align with axle weight and load requirements.
Beyond size, tires have other critical markings:
Load and speed index. Example: 144/141M means the tire supports 2,800 kg (dual) or 3,000 kg (single) at a max speed of 81 mph (130 km/h). Ensure the index matches your load’s weight.
DOT code. Indicates manufacturer and production date. Example: DOT AB12 3419 means the tire was made in week 34 of 2019. Tires over 6 years old may be unreliable.
Regroovable/retreadable. Indicates the tread can be regrooved or retreaded, saving costs for commercial tires.
M+S or 3PMSF. M+S (mud and snow) or 3PMSF (mountain snowflake) denote suitability for winter conditions, required in states like Colorado.
Tip. Photograph all markings before a trip to provide proof for DOT inspections and permit applications.
Follow these steps to avoid errors:
Park the truck or trailer on a flat surface and secure it.
Clean the tire sidewall to clearly read the markings.
Note the code (e.g., 295/75R22.5) for each tire.
Check tires on all axles, as steer, drive, and trailer tires may differ.
Compare with manufacturer specs (manual or placard) and permit requirements.
Record results in a log or ELD for inspections.
Use a flashlight for low-light or dirty tires. If unsure, measure tire width with a tape measure to confirm sidewall data.
Tip. Use a laser distance meter for quick sidewall width checks on large fleets.
Tire size directly impacts oversize or overweight transport:
Vehicle height. Larger tires (e.g., higher aspect ratio like 75 vs. 70) increase load height, risking clearance issues under low bridges (standard limit: 13’6” without a permit).
Axle load. The tire’s load index determines axle weight capacity. For example, a 144 index tire supports up to 2,800 kg. DOT checks this at weigh stations.
Permit accuracy. Incorrect tire sizes skew axle spacing or weight distribution calculations for the Federal Bridge Formula (W = 500 × [(L × N) / (N - 1) + 12N + 36]), leading to permit rejections.
Fuel efficiency. Larger diameter tires lower engine RPM, improving fuel economy but potentially affecting speedometer accuracy.
Tip. Include precise tire sizes in permit applications—errors as small as 1 inch can trigger fines ($100–$5,000+) or delays.
Inspect before trips. Check tire sizes and record them to ensure compliance with load and state regulations (e.g., California limits tire width to 108 inches).
Store documentation. Keep the manual, placard photos, and tire markings in the cab for DOT checks or disputes.
Review state rules. States like Pennsylvania are stricter on axle weight, while Texas focuses on height. Check DOT websites or omnipermits.com.
Carry spares. Have spare tires with matching size and load index to avoid delays from flats.
Monitor tire pressure. Follow placard pressure recommendations to maintain load capacity and prevent blowouts.
Consult experts. If unsure about tire compatibility, contact omnipermits.com for guidance on permits and compliance.
Use certified scales. Verify axle and gross weights on CAT scales to confirm tire load ratings.
Check tire age. Avoid tires older than 6 years (per DOT code) for heavy loads due to reliability risks.
Document markings. Save sidewall photos in your ELD for quick reference during inspections.
Train your team. Ensure drivers know how to read tire markings and understand state regulations.
Related guides. Read our guide on Oversized cargo transportation at night: how to do it safely and legally for related safety tips.
Use navigation apps. Hammer or Trucker Path can help plan routes while considering tire and load restrictions.
Monitor tire condition. Regularly check for wear or damage, especially for oversize loads with high stress.
Keep DOT contacts. Store state DOT numbers for quick clarification of tire-related regulations.
With accurate tire size data and proper checks, your transport will be safe, legal, and cost-effective. Verify sizes, follow regulations, and hit the road with confidence!
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