What would tires look like on a super-Earth with 2.5 G surface gravity?

A super-Earth has 2.5 G of surface gravity, as opposed to the Earth's 1 G of surface gravity. Some folks on it drive wheeled vehicles, and the wheels on said vehicles have tires on them. These tires are modern-style pneumatic tires built with the same technology and materials as today's tires.

What would these tires look like compared to real-life tires designed with 1 G in mind? Would they be thicker, wider, under higher internal pressure, etc.? I imagine the proportions wouldn't be the same, I'm just not sure how.

• I'm not exactly sure what you expect. A Škoda Fabia weighs about 1,100 kg. A Ford F-150 Lightning weighs 2,900 kg, about 2.6 times as much. Look at the pictures and try to articulate the difference between the external aspect of their tires. (Both are round, both are black, both come in different variants with different heights and widths.) Apr 23, 2023 at 11:53

They would look no different compared to tires we use today

On Earth I might have two trucks.

1. A half-ton pickup carrying 1,000 pounds, like the circa 1972 1/2-ton truck pictured below (courtesy How Stuff Works).

1. A 1-1/2 ton pickup carrying 5,000 pounds, like the gorgeous 1947 Ford 1-1/2 ton truck pictured below (courtesy Mecum Auctions).

On your super earth, that mass weighing 1,000 pounds on Earth would require the 1-1/2 ton truck. Meaning for the same mass that four-tire light-duty axle and drive train 1/2 ton pickup can haul on Earth, your super earth requires the six-tire heavy-duty axle and drive train of the 1-1/2 ton truck.

Tires aren't the issue. The actual difference would be (using trucks of today to make the point) the maximum mass you can carry on your super earth.

Let's take the Hitachi EH5000AC-3, believed to have the greatest payload in the world today (image courtesy Hitachi).

This bad boy can haul 326 tons here on Earth. In point of fact, it can only haul 326 tons on your super earth. But what does that mean?

The formula we'll use is this:

$$weight = \frac{(0.224809)mg}{2,000}$$

• m = the mass of the payload in kg.
• g = local gravity. 9.8 for Earth, 24.5 for your super earth.
• 0.224809 is the conversion from Newtons to Pounds.
• 2,000 is the conversion from Pounds to U.S. Tons.

What do we learn? Using the same truck...

• Max payload on Earth = 295,953 kg.

Meaning any truck on your super earth can only carry about 40% of the payload (measured in kg) that it could on Earth — but nothing else changes.

Conclusion

Tires don't change. The maximum payload per vehicle weight class is the real difference. And that involves more than just tires.

If the way you want to interpret what I just explained is, "beefier tires, more of them," that's fine. But all you're really saying is that you need a heavier truck to haul the same load.

• Wouldn't we also have to account for the heavier truck? The tires on the 1.5-ton truck w/2.5 tons (5,000lbs) load are carrying 5 tons, total. On super-earth the truck weights 4.5 "standard" tons with 0.5 standard tons left over which is only 400 super-earth pounds carrying cap (if my math is right). The Hitachi seems worse -- weights about 400 tons, carries total (truck+load) of about 700, which means it can't even carry itself on super-earth. Apr 23, 2023 at 21:29
• @OwenReynolds Yes, we would. It would have the effect of lowering the payload reduction below 40%. Remember, the truck is rated for the specified payload in addition to its own weight. And you're completely correct that the bigger the truck, the more this is an issue. But it doesn't change the premise of my answer in relation to the OP's specific question: tires won't change. They aren't the problem. Realistically vehicles will need better material science, but their basic shape and operation won't change.
– JBH
Apr 23, 2023 at 22:00

If you have ever had or seen a flat tire, you should have realized that:

• the tire is not full: it has compressed gas inside
• the tire alone barely holds its own weight

The load bearing capacity of the tire is granted by the compressed gas and its pressure, the tire is, so to say, barely an excuse to have the compressed gas stay compressed.

Based on the above, what might change is just the inflation pressure for the tires in exercise. The rest can stay the same.

• You might need to make the material thicker in order to avoid it bursting under the extra pressure. Apr 23, 2023 at 23:59
• @PaŭloEbermann Possibly not as much as you might think. What matters is the difference between internal and external pressure. So a tire designed for 35 PSI at 1G should be fine inflated to roughly 20 PSI over atmospheric pressure no matter what atmospheric pressure is. Whether that’s good enough for the vehicle it would be used on is another question though. Apr 24, 2023 at 1:43
• @AustinHemmelgarn I think that multi-tire setups like in semi-trucks or tired-armored vehicles would be more common since 2.5G also means 2.5x "heavier" vehicles, aka more load on the tires. But yes, the difference would likely be negligible for regular cards Apr 24, 2023 at 7:44
• @AustinHemmelgarn the issue is that the vehicle is 2.5 times as heavy, so you'll need higher (relative) pressure, or a different type of tire at all. Apr 24, 2023 at 20:50

Thicker Tires to Resist Extra Wear

With more Gs of normal gravity on your world, tires would be subjected to greater amounts of wear due to the increased weight of your world’s vehicles. This means that tires should be built thicker, with thicker treads to counteract the additional wear these tires would be subjected to. Wider tires wouldn’t likely hurt either for better load bearing. Since force of gravity is 2.5 x greater on your world, you could look at the tires used on trucks and/or heavy equipment that are designed to carry two times or more the load of an average vehicle to get a good real-world example of what an average vehicle would likely use on your world. Heavy equipment tires on your world would likely have to be yet thicker than that.

Higher Pressure Tires May Need to be Thicker

Many modern tires have maximum PSI ratings, and inflating above their maximum ratings could cause tires to fail. So thicker tires designed for higher pressure gas inside likely would be required. Since these tires should be thicker for the extra wear on them anyways, it shouldn’t really make much difference by itself.