40" Tires on 250 Series Land Cruiser - Is it Possible?

[BG]

I wanted to dive into a topic that's been debated: can you run 40" tires on a 250 Series Land Cruiser? The short answer is yes – it is possible, but there are some key considerations and potential limitations you need to be aware of.

First, the core ingredient here is the 74W portal axles. The portals can indeed make the 40" tires a reality on the Land Cruiser, offering the necessary lift and clearance to make it work and in theory, reduce the strain from the larger tires by 22%. In other words, the strain on the drivetrain should be similar to what we would see with a 32” tire because of the gear reduction. That said, a 40” tire is going to get more traction where a 32” tire may just spin or get hung up, so that cannot be overlooked - bigger tires tend to yield better results off-road. While the portals do reduce the strain on the drivetrain components, it's worth noting that the steering, link arms, axel housings, and potentially other components will feel the effect of the 40” tires due to the additional leverage from the 3.8” drop achieved at the hub.

As some of you might already know, Ben from Dissent did manage to snap a 74W axle shaft while running 40" tires on Fordyce, highlighting a key concern with this setup. So, the real question isn’t just whether 40" tires will fit, but whether they’re the best move given the added stress they place on the axles and other components.

The crux of the issue seems to come down to a few factors:

1. 74W Axle Shaft Strength: Does the axle housing need a stronger axle shaft to handle the added load of a 40" tire? In Ben’s case, the failure may have been a result of the increased stress from the 40" tires however he did have 38” tires on prior and did not have any issues with the factory axle shafts running Rubicon. In theory, he only went up 5% in tire size from the 38s but reduced the strain 22% with the gear reduction, and the new 74Weld axle shafts are made from 4340 air heat-treated chromoly and should be roughly 10-20% stronger than the factory axle shafts. By that math, we should actually see less chance of shaft failure with the portals and 40s than we would see with the 38s and factory axles. So, why did it fail? Was Ben simply asking too much of the 8.25 axle housing and shaft size or did he have a faulty part?
2. Axle Housing Upgrade: The 8.25 axle housing on the 250 Series Land Cruiser is fairly robust, but it might not be ideal for supporting such large tires in the long run. So, would it make more sense to upgrade to a larger axle housing to accommodate stronger, larger-diameter axle shafts? This could improve durability, but it comes with added costs - especially on the new 250 Series so early on in its release. A larger axle housing (such as the 8.5 or 8.75) would be better suited for handling bigger tires. The better or best upgrade would be a custom housing with a Toyota 9.5 diff or even the 10.5 found in the previous generation Tundra but this could get expensive. The other difficulty that one would face with such an upgrade is the lack of gearing options to match the factory front 3.58s diff gears which are honestly perfect for the 40” tire with the 22% reduction from the portals (3.583 250 ratio X 1.22 74W ratio = 4.36 final ratio). There is the possibility of upgrading to a complete rear axle from a gx550 which would likely be plug-and-play but you are looking at roughly a 6k upgrade.
3. Smaller Tires: Alternatively, you could opt to downsize to a smaller tire, but even with a 38.5" or 37" tire, there’s still a potential for similar issues - hard telling not wheeling with each and every setup on the same line at the same speed with the torque applied at each hub.

There are many factors involved here. Are 40" tires too big for the land cruiser? Is the axle not big enough? Are the 74W portal shafts not strong enough for 40" tires on the 8.25 diff?

At the end of the day, you can run 40" tires on the 250 Series Land Cruiser with the right setup and can run them quite well. After talking with Ben, he said the steering so far seems to be holding up well and the electric steering turns them with ease but they may not be the optimal choice for long-term reliability with an OEM rear end.

If you’re considering 40" tires, weigh the pros and cons carefully, as the cost of upgrading to larger housings might not justify the benefit of running such large tires, especially in more technical off-road environments.

At the end of the day, I would personally stick with 37" tires with the factory rear end on Portals. I am running the 74W Portals on my 5th Gen 4Runner and wheel some pretty hard trails out here in NorCal. I have not put my rig through Foryce but I hit Slick Rock three times, and Gold Lake/Snake Lake twice this year on Portals, 37" tires all on the same 8.25 rear end and didn't have failures.

It really sucks that Ben snapped a 74W shaft but the whole point in running these parts is to find their limits and 40" tires might just be the limit.

Ben will continue to build out his 250 Series. If you want to follow them closer, check out their IG: https://www.instagram.com/dissentoffroad/?hl=en

For more on 74W, check out their IG: https://www.instagram.com/74weld