A 31x10.50R15 or 33x12.50R15 all-terrain in Load Range C is the right tire for the overwhelming majority of early Broncos. It has real dirt and wet-road grip, it stays quiet enough to drive four hours to the trailhead, and — the part most buyers miss — it is light and soft enough that a 4,000-pound truck with a small V8, a manual steering box, and possibly front drum brakes can still stop, steer, and accelerate. The 33 is the sweet spot. Go bigger only when the terrain genuinely demands it.
The early Bronco is 92 inches of wheelbase and roughly 3,600 to 4,200 pounds depending on hardtop, engine, and how much steel armor is bolted to it. That combination is why the truck wheels so far above its tire size — the approach and breakover angles are enormous, and there is very little mass to push through a mud hole. It does not need a giant tire to be capable, and every inch of diameter you add costs you somewhere else.
The costs on this chassis are steeper than on a modern truck, because the early Bronco has no power assist for most of what a big tire loads up:
Steering. A large share of these trucks still wear the factory manual box, and many "power" conversions are a Saginaw box with modest assist. A 33 in a soft compound is noticeably heavier at parking speeds than a 31; a 35 is a different vehicle entirely. If your Bronco is manual-steering, treat the 33 as the practical ceiling until you address the box — see the power steering conversion guide.
Brakes. Early Broncos left the factory with front drums through 1975. Drums plus a taller, heavier tire is a measurable stopping-distance penalty, not a theoretical one. If you are running 33s on four-wheel drums, the front disc conversion is a higher-priority purchase than the tires.
Gearing. Factory ratios are 3.50, 4.11, or 4.57. A 31 on 3.50s is livable; a 33 on 3.50s is lazy and hunts on grades; a 33 on 4.11s is well-matched. Read the gear ratio guide before you buy, not after.
An all-terrain sidesteps most of this because it is the lightest and lowest-rolling-resistance tire that still carries usable trail tread.
These numbers match the dedicated tire sizing reference — use that guide for the full matrix and this card for the buying decision.
Backspacing matters as much as lift and gets ignored more often. The early Bronco runs a 5x5.5 inch (5x139.7) bolt pattern, and the target for a 15x8 wheel is about 3.75 inches of backspacing. The factory wheel is deeper than that and tucks a wide modern tire straight into the radius arm, where it grinds the sidewall at flex — a contact point out of sight from the driver's seat and unfixable by fender trimming. The backspacing guide has the full explanation; the short version is that you settle the wheel before you order rubber.
Before committing to a size, mount one tire and cycle the truck: jack the axle to full bump with the tire on, turn the wheel to full lock both directions, and look for contact at the rear of the front fender opening, the radius arm, and the frame rail. One tire proves the fit. Then order five.
This is the most common mistake on a classic 4x4. Tire shops default to Load Range E because it is what half-ton and three-quarter-ton trucks take, and E-rated tires are marketed as tougher. On an early Bronco, E is the wrong call.
An E-rated 33 carries a 10-ply-equivalent casing designed to hold up a 6,000-plus-pound truck. A 4,000-pound Bronco cannot deflect that sidewall, so the tire rides harsh on the road and, more important, refuses to air down usefully on the trail. At 15 psi an E-rated tire under a light truck barely bulges, which throws away the single biggest free traction gain available to you.
E casings also weigh roughly 8 to 12 pounds more per tire than the C version of the same size. Across five tires that is 40 to 60 pounds of unsprung and rotating mass added to a truck with modest brakes and a small engine.
Load Range C in a 33x12.50R15 is rated in the neighborhood of 2,000 pounds per tire. Four of those carry an early Bronco with a wide margin, even loaded for a week out. Buy C, and spend the difference on a fifth matching tire so the spare still works behind a locker.
Reference weights are worth internalizing: a 31x10.50R15 all-terrain runs roughly 44 to 48 pounds, a 33x12.50R15 around 55 to 60, and a 35-inch mud-terrain 68 to 75. That spread is why a 33 all-terrain and a 35 mud-terrain feel like different trucks from behind the wheel.
BFGoodrich All-Terrain T/A — the long-standing default. The KO2 is being superseded by the KO3, and both are offered in the classic 15-inch sizes early Broncos want. Tough three-ply sidewall, long tread life, predictable in wet. The most expensive of the mainstream options.
Falken Wildpeak AT3W — the value pick and hard to argue against. Close to BFG capability for meaningfully less money, quieter on the highway, strong in snow. The tire many builders land on after pricing the KO2.
Cooper Discoverer AT3 XLT — quiet, long-wearing, good on-road manners. The better choice for a Bronco that spends most of its life on pavement and graded fire roads.
Toyo Open Country AT3 — a solid middle option with strong wet and winter performance and a reputation for even wear.
All four are offered in 31x10.50R15 and 33x12.50R15, which is the real constraint worth checking. The 15-inch light-truck market is smaller than it was, so confirm current availability in your exact size before you settle on a wheel diameter.
Tires age out before they wear out on this truck. A Bronco that covers 2,000 miles a year will reach ten years on a set with most of the tread intact. Rubber does not care about tread depth. Read the DOT date code on the sidewall — the last four digits are week and year — and plan to replace on age somewhere between six and ten years regardless of how the tread looks. A 50-year-old truck on 12-year-old tires is a highway blowout waiting for its moment.
The spare is a real problem to solve. A 33 will not stow the way the factory spare did, and it is heavy enough that a tailgate-hung carrier stresses the hinges over time. Decide the carrier before the tires land — see the rear bumper and tire carrier guide.
The speedometer will read slow. The early Bronco's speedometer is cable-driven off the Dana 20 transfer case, so the correction is a physical drive gear swap, not an electronic recalibration. Moving from a factory-diameter tire to a 33 leaves you roughly 10 percent optimistic on both speed and odometer. The gear is inexpensive and the fix keeps the mileage on the truck honest.
Air down and mean it. The whole reason to run Load Range C is that it will deform. On a light truck, 15 to 18 psi transforms the footprint on rock and sand. Carry a gauge and a way to air back up — that is the cheapest capability upgrade in this entire guide.
A realistic all-in for a set of 33s on an early Bronco is $1,450 to $1,950 before wheels. If the budget forces a choice between 33s now and the front disc conversion, take the 31s and the brakes — the truck will be better in every measurable way. Step up to a mud-terrain only when your terrain is genuinely rock and deep mud, and go in knowing that tire drags lift, fender work, and a regear behind it.
| Part | Vendor | Est. price |
|---|---|---|
| All-terrain tires, set of 5 (31x10.50R15, Load Range C) | BFGoodrich KO2/KO3 / Falken Wildpeak AT3W / Cooper Discoverer AT3 XLT | ~$1100 |
| All-terrain tires, set of 5 (33x12.50R15, Load Range C) | BFGoodrich KO2/KO3 / Falken Wildpeak AT3W / Toyo Open Country AT3 | ~$1450 |
| Mount, balance, and new valve stems (per tire) | local tire shop | ~$35 |
| Dana 20 speedometer drive gear (recalibration) | Wild Horses 4x4 / Bronco Graveyard | ~$30 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.
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