A dually truck needs tires whose dual load rating, not single rating, covers the rear axle’s GAWR — and the door-jamb placard sets the size and pressure.
One wrong load rating on a dual-rear-wheel pickup can put the rear axle over its legal and structural limit before the truck even looks loaded. The placard in the driver’s door jamb, the rear GAWR on the certification label, and the dual load index on the sidewall decide whether a tire is legal, safe, and fits.
Start With The Door Jamb, Not The Tire Aisle
The driver’s door-jamb placard is the authority on tire size and recommended cold inflation pressure, so read it before shopping. Every dually ships with an OEM size and pressure spec for front and rear that the manufacturer matched to the axles.
Two numbers on the certification label matter after that:
- GAWR (Gross Axle Weight Rating) — the most weight each axle is rated to carry. Match tire capacity to this, not the truck’s total GVWR.
- OEM tire size and load range — the baseline the truck was engineered around. Changing size changes clearance, speedometer accuracy, and load capacity at a given pressure.
Write the rear GAWR down. That figure, divided across the rear tires, is the target the dual rating must beat.
What The Slash On The Sidewall Means
Light-truck tires often carry two load indexes separated by a slash: the first is the single-tire rating, the second the dual-tire rating. Goodyear’s load index guidance explains this split exists because the same tire can serve as a lone rear tire or as half of a dual pair.
The dual rating is deliberately lower. When one tire in a pair fails or loses pressure, its partner must absorb load the pair was sharing, so the tire is certified more conservatively for dual service. Treating the single rating as your rear-axle number is the most common and most expensive mistake in dually tire shopping.
| What To Check | Where To Find It | Why It Decides The Purchase |
|---|---|---|
| OEM tire size | Door-jamb placard | Sets fitment, speedometer accuracy, clearance |
| Recommended cold pressure | Door-jamb placard | Load capacity is only valid at the rated pressure |
| Rear GAWR | Certification label | The axle load the dual rating must cover |
| Single load index | Tire sidewall | Applies to the front axle, not the dually rear |
| Dual load index | Tire sidewall | Governs rear-axle capacity |
| Load range / ply rating | Tire sidewall | Indicates sidewall strength and max pressure ceiling |
| Construction type | Tire sidewall | Radial and bias-ply cannot be mixed in one dual pair |
Matching A Dual Set Without Creating Heat
A dual pair must match in size, construction, and rim width, and the two tires must never touch under load. Pirelli’s load index reference and Toyo’s load inflation tables both assume duals share load evenly — a mismatched pair breaks that assumption.
The rules that keep a dual set safe:
- Confirm the tire shows single/dual ratings appropriate for a DRW truck.
- Keep both tires on a pair identical in size and construction. Never mix bias-ply with radial in one dual assembly.
- Use the same rim width on both sides of the pair.
- Measure actual clearance between inner and outer rear tires with the truck loaded. Contact between sidewalls builds heat, scuffs rubber, and can end in a blowout.
- Set cold inflation to the placard spec, and check all six tires monthly plus before and after any towing trip.
If you have settled on the common 235/85R16 size for a dual-rear-wheel setup, our tested comparison of 235 85r16 dually tires breaks down which models hold their dual ratings under load.
Toyo’s application of load inflation tables is the reference for adjusting pressure to a specific axle load instead of the placard figure.
Where Dually Tire Shopping Goes Wrong
Most bad purchases trace to three shortcuts: reading only the single load index, which overstates rear capacity; buying a mixed pair because the shop had one tire and a near-match; and ignoring cold pressure because the truck “looks fine” — underinflation turns a marginal clearance problem into sidewall contact.
Two limits: this applies to dual-rear-wheel pickup trucks, not passenger cars or single-rear-wheel trucks. And current prices, model names, and version numbers change often enough that any figure here would be stale — check the tire maker’s current spec sheet and your own placard.
FAQs
Can I run the same pressure in the front and rear tires of a dually?
Not necessarily. Dually trucks often specify higher rear pressure than front because the rear pair carries more load, and the placard lists both figures separately. Use the placard’s front and rear numbers. If you changed tire size or load range from stock, work from the tire maker’s load inflation table.
Why is the dual load rating lower than the single rating on the same tire?
The dual rating assumes each tire may have to carry more than its share if its partner loses pressure or fails, so the tire is certified conservatively for that scenario. A tire rated comfortably for a single rear application can fall short when its single number is used to judge a dually.
Do both tires on a dual pair have to be identical?
They need to match in size, construction, and rim width. Mixing bias-ply with radial, or running two different sizes on one side, makes the tires fight for load and generates heat. Mismatched duals wear unevenly and can fail at the sidewall where they rub.
References & Sources
- Toyo Tires. “Application of Load Inflation Tables” Source for adjusting cold inflation pressure to a specific axle load.
- Pirelli. “How To Read The Tire Load Index” Explains how load indexes work, including dual-fitment ratings.
- Goodyear. “Tire Load Index” Confirms the single and dual rating split on light-truck tires.