Jay Johnson
Can a 6th-Gen Bronco Run 40-Inch Tires?
Yes, but 40-inch tires move a 2021+ Bronco into a completely different class of build.
A 35-inch tire is close enough to what Ford engineered around on Sasquatch that you can make relatively modest changes and keep the truck feeling factory-like. A 40 is five inches taller than that nominal 35. The tire radius grows by roughly 2.5 inches, the tire is usually much heavier, and every steering, braking, gearing, clearance, and driveline decision starts carrying more consequence.
That does not mean 40s are a bad idea. It means I would stop thinking in terms of “What lift fits 40s?” and start asking, “What system makes the whole Bronco work correctly on 40s?”
| Area | What 40s change | What the build needs |
|---|---|---|
| Ground clearance | Larger tire radius raises the wheel center | Enough body and suspension clearance at full lock and compression |
| Gearing | Taller effective gearing | Regear or portal reduction |
| Steering | More leverage and rotating mass | Correct offset, alignment, inspection, stronger parts where needed |
| Braking | More rotating mass to slow down | Healthy brake system and realistic stopping-distance expectations |
| Drivetrain | More torque demand from the larger tire | Gearing correction and controlled throttle |
| Spare tire | Much more weight on the tailgate | Proper carrier or reinforcement |
| Calibration | Tire size changes indicated speed and shift behavior | Correct tire-size calibration |
| Width | Wheel offset and portals can increase track width | Check tire coverage, trail width, garage clearance, and scrub radius |
Why Are 40-Inch Tires Hard on a Bronco?
The problem is leverage.
A larger tire gives the ground a longer lever against the steering, wheel bearings, axles, differential gears, driveshafts, and brakes. It also raises the effective gearing, so the engine and drivetrain have to work harder to create the same force at the contact patch.
Then there is mass. A 40-inch off-road tire and appropriately sized wheel can add a lot of rotating and unsprung weight compared with a factory setup. That extra weight has to accelerate, stop, steer, and move with the suspension every time the truck does.
This is why I would not call a Bronco on 40s “done” because the tires physically clear the fenders in the driveway. A build is only convincing when it clears at full steering lock, clears under suspension compression, tracks correctly, brakes predictably, keeps the drivetrain in a usable ratio, and survives repeated trail use.
How Much Lift Do 40s Need?
There is no single correct lift height for 40-inch tires on a Bronco.
A number like “4 inches of lift” tells you almost nothing by itself. A tire can clear at ride height and still destroy a fender liner, crash into the body mount area, or contact suspension components when the wheel is turned and the suspension compresses.
Wheel offset matters. Fender shape matters. Bump-stop position matters. Suspension travel matters. Whether you are willing to trim bodywork matters.
I would build for the minimum suspension height that gives the tire the clearance it needs through its real range of motion. Raising the body higher than necessary does not increase differential clearance. The tire diameter does that. Extra suspension height mostly raises the chassis and center of gravity.
That distinction is the reason portal axles become interesting once you get into 40-inch territory.
Why Do Portal Axles Help With 40s?
A portal moves the wheel hub lower than the axle output. The axle itself sits higher while the wheel stays on the ground.
Turn Offroad's Bronco portal system adds 4.75 inches of lift at the axle. That is very different from simply adding 4.75 inches of suspension lift. You are creating clearance underneath the axle and differential instead of only moving the body farther away from them.
Pair that with a 40-inch tire and the ground-clearance gain becomes substantial. Compared with a nominal 35-inch tire, the 40 adds roughly 2.5 inches of clearance from tire radius alone. The portal adds another 4.75 inches at the axle. Those two changes attack the part of the Bronco that normally hangs lowest without requiring the body to be lifted by the same amount.
This is the main reason I like portals as a 40-inch strategy. A giant suspension lift can make room for the tire, but it does not move the differential away from the rock underneath it. Portals do.
Do 40s Need Regearing?
They need some way to correct the gearing problem.
As tire diameter increases, the effective final drive becomes taller. The Bronco travels farther with each wheel revolution, which sounds good until you realize the engine has lost mechanical advantage at the tire.
Going from a nominal 35-inch tire to a 40 is about a 14% increase in diameter. Without gearing correction, you feel that in low-speed response, crawling control, acceleration, transmission behavior, and the amount of load being pushed back through the drivetrain.
Traditional axle regearing is one answer. Portal reduction is another.
Turn Offroad uses an 11% reduction inside its Bronco portal boxes. The reduction happens at the wheel end, after the ring and pinion and much of the upstream drivetrain. Turn Offroad's stated goal is to bring effective gearing back toward the range the Bronco was designed around while reducing load on the ring and pinion, transfer case, and driveshafts.
I would not describe an 11% portal reduction as magically erasing every effect of a 40. The tire is still bigger and heavier. But it corrects most of the gearing change between a 35 and a 40 without opening the differentials and installing a much deeper axle gear.
Are Portals Better Than a Big Lift?
For a Bronco whose actual goal is 40-inch tires, I think portals solve the more important problem.
A suspension lift is useful when you need body and tire clearance. You may still need some suspension work with portals depending on the tire, wheel, fender, and intended travel.
What I would avoid is trying to get every inch of clearance from suspension height alone. That stacks compromises: steeper CV and control-arm angles, a higher chassis, a higher center of gravity, and no equivalent increase in differential clearance.
A portal build moves part of the lift to the wheel end. That lets you use suspension height for tire travel and geometry rather than asking the suspension to create all of the truck's clearance.
There is a tradeoff. Portals add parts, width, unsprung mass, gear oil, seals, bearings, and maintenance points. They are not a free lunch. But if the target is a Bronco on 40s that still drives like a complete vehicle instead of a stack of unrelated modifications, I would rather solve clearance and gearing deliberately than just keep adding lift.
Will 40s Break the Steering?
They can expose weak steering choices very quickly.
The tire has more leverage against the tie rods, steering rack, ball joints, and wheel bearings. Aggressive wheel offset can make that worse by moving the tire contact patch farther away from the steering axis.
This is one reason I would not automatically pair 40s with the most negative-offset wheel that fits. The wide stance might look right, but extra scrub radius adds steering effort and leverage exactly when the tire is already increasing both.
A safer 40-inch build starts with wheel fitment that clears the portal or suspension hardware without pushing the tire unnecessarily far outward. Then align the truck at its final ride height and tire setup.
I would also inspect steering components regularly, especially after hard trail use. A 40-inch Bronco should not be the truck where a worn tie rod, loose wheel bearing, or damaged ball joint gets ignored because “it still drives straight.”
Do Portals Reduce Steering Stress?
They help with drivetrain torque load, but I would not sell them as a magic steering fix.
The portal reduction means upstream components do not have to create all of the torque multiplication required at the tire. That is valuable for the axle gears, transfer case, driveshafts, and related drivetrain components.
The steering still has to turn a 40-inch tire. The wheel bearing still supports it. The ball joints still locate it. Offset still changes leverage.
That is an important distinction if you are building this truck for longevity. Portals solve some of the biggest 40-inch problems, but they do not cancel physics everywhere else.
Do 40s Need Bigger Brakes?
At minimum, they need a braking system that is in excellent condition and a driver who understands that a heavier rotating package can increase the work required to stop.
I would not make a blanket claim that every Bronco on 40s requires one specific brake conversion. Total wheel-and-tire weight varies, driving speed varies, and portal systems themselves can change the brake hardware at the wheel end.
Turn Offroad's current Bronco portal system retains factory ABS and parking-brake function and includes J-hook front rotors, brake-line extensions, and the electrical extensions needed for the system.
Even with upgraded hardware, I would test the finished build deliberately before treating it like stock. Bed the brakes correctly, confirm there are no ABS faults, test repeated stops in a controlled environment, and leave more following distance until you know exactly how the truck behaves.
What Wheel Offset Works With 40s?
The right answer is the offset that clears everything through steering and suspension travel without creating unnecessary poke.
This is not the place where I would pick wheels from a photo and hope.
Portals can increase track width. Low-offset wheels can add even more. By the time you stack both, a Bronco can become dramatically wider than stock. That affects scrub radius, steering leverage, fender coverage, garage clearance, trailer width, and how the truck fits on narrow trails.
Before ordering wheels, I would get the portal manufacturer's exact wheel-clearance and backspacing requirements for the system being installed. Then choose the least aggressive outward position that still clears the portal box, brakes, steering, and suspension.
More poke is not automatically more capable.
Will 40s Rub on a Bronco?
They can, even on a tall truck.
The places I would check are full-lock steering in both directions, the rear of the front wheel opening, fender liners, flare edges, control arms, body mounts, and anything the tire approaches as the suspension compresses.
The only useful clearance test is dynamic. Cycle the steering. Load the suspension. Articulate the truck. Check again with the tire aired down if that is how you wheel.
A tire that misses by half an inch in the garage can touch once the sidewall bulges at trail pressure or the suspension compresses diagonally.
I would rather trim a known interference point cleanly than add another inch of suspension lift just to avoid touching plastic.
Do 40s Need a Spare-Tire Carrier?
Yes, I would plan for one.
A 40-inch spare is not only larger; it is usually dramatically heavier than the factory spare assembly. Hanging that mass farther away from the tailgate creates more leverage on the carrier and tailgate structure.
A reinforced carrier or bumper-mounted solution should be part of the build budget from the beginning.
This is the kind of cost people forget when pricing 40s. The first four tires get the attention. The fifth tire can become a tailgate problem if the truck was never designed to carry that weight in that position.
Do 40s Need Speedometer Calibration?
Yes. Any major tire-size change should be calibrated so the vehicle knows how far it travels per wheel revolution.
That affects indicated speed and can influence how the powertrain and electronic systems interpret vehicle speed.
Turn Offroad says its 11% portal reduction helps correct speedometer function when running larger tires. I would still verify actual indicated speed against GPS after the finished tire and portal combination is installed rather than assuming the math is perfect for every 40-inch tire brand.
The sidewall may say 40, but real rolling diameter varies.
Should You Start With Sasquatch?
Sasquatch is a good starting point, but I would not call it a requirement.
Its lockers, off-road hardware, and factory 35-inch setup mean the truck is already closer to the type of build that eventually ends up on 40s.
Portals change some of the normal calculus because the portal reduction lets the factory axle ratio stay in place. Turn Offroad states its system fits 2021–2026 2-door and 4-door Broncos, Sasquatch and non-Sasquatch, but not Bronco Raptor.
If I were starting from scratch specifically to build a portal Bronco on 40s, I would care more about having the trim features I really want — lockers, interior, transfer case, armor — than paying for factory parts I already know will be replaced.
What Does a Safe 40-Inch Build Need?
I would not install the tires until the rest of the plan is written down.
At minimum, I would want the final wheel and tire dimensions, the portal or axle-gearing strategy, suspension travel and bump-stop plan, steering clearance, brake configuration, spare-tire solution, calibration method, fender coverage, and alignment targets decided first.
Then I would have the finished truck aligned professionally and do an early reinspection after the first few hundred miles and the first serious trail day. Recheck wheel torque, portal fasteners, fluid level, brake lines, steering joints, tire contact marks, and anything that moved during break-in.
The safest version of a 40-inch Bronco is not the one with the longest parts list. It is the one where every modification has a reason and the systems still work together.
Are Portal Axles Worth It for 40s?
If your goal is genuinely 40-inch tires, that is where portals make the strongest argument.
Turn Offroad's system is designed for 37- to 40-inch tires, adds 4.75 inches of axle clearance, uses an 11% portal reduction, retains the factory axle ratios, and keeps factory ABS and parking-brake functions. The manufacturer also uses a four-gear portal box with 7075 aluminum housings, hardened steel gears, and increased oil capacity.
That is a much more complete answer to 40s than “add enough lift until they fit.”
It is also not cheap. The Turn Offroad Bronco portal system we carry is a serious drivetrain upgrade, and I would only recommend spending that kind of money if the build goal genuinely needs what portals do.
Turn OffroadPortal Axles
$11,999.99
View part
For a Bronco staying on 35s or mild 37s, portals can be more system than you need. For a Bronco whose end goal is 40s, difficult trails, real differential clearance, and a truck that still has to drive on the highway, the math starts making a lot more sense.
Can You Run 40s Without Portals?
Yes. People have done it with suspension, trimming, stronger steering, deeper axle gears, and careful wheel fitment.
I would not write a portal article that pretends portals are the only way. They are one way to solve the problem, and an expensive one.
The reason I prefer the portal route for a serious 40-inch build is that it solves two problems that otherwise require separate compromises: it raises the axle itself and reduces gearing at the wheel.
A conventional build can absolutely work. You just need to account for the same problems somewhere else in the system.
Are 40-Inch Tires Worth It?
For most Bronco owners, no.
That is not an insult to 40s. It is the reason they are interesting.
A Bronco on 40s gives you huge obstacle clearance, a larger contact patch when aired down, and the ability to roll over terrain that stops smaller tires. It also costs more, weighs more, stresses more parts, takes more room, and demands more maintenance.
If you are choosing 40s because 37s “do not look big enough,” I would stop and price the entire build before ordering tires.
If you are choosing 40s because your trails, terrain, and build goals genuinely benefit from them, then build around the tire from the start. In that case, I would seriously compare a portal setup against the cost and compromises of suspension lift, axle regearing, steering upgrades, trimming, and the other work needed to make a conventional 40-inch Bronco behave correctly.
For more context on what happens before you reach 40s, our 37-inch Bronco tire guide explains how quickly the supporting-mod list grows even one step down.