Why are two slimmer wheels paired on each side of the axle in buses and container carrying vehicles, instead of a single large broader wheel?
In: Engineering
The big reason is so that tire companies can make a smaller amount of standard sized tires. A truck that needs 4 tires versus one that needs 6 can use the same tires, just with the truck that needs 6 using more of them. If you started making a significant amount of different tire widths, you create even more specific products in the market, and make it that much harder for a store to keep a relevant amount of stock.
Beyond that, there are going to be other issues like the inside edge of the tire traveling a significant different distance than the outside edge over a turn, which is going to cause uneven wear on the tires.
Dual wheels distribute loads better on the tire itself than one individual wheel/tire.
Dual wheels can afford to have a flat and still be drive-able.
Dual wheels have lower risk of load shifting in the event of a flat.
There are technical and commercial aspects of this
1. Technical
— better weight distribution ( two tires lead to better distribution of load on the surface, limiting the extent of pressure exerted on tire)
— higher safety factor (in case of air pressure loss, the other tires can still support the load, providing higher reliability),
— Stability (provides better grip and stability when turning, on when on uneven surface, avoids tipping over)
2. Commercial
— a single wider tire will lead to higher cost in terms of production, installation, maintenance, and repair
Hope it helps. Feel free to ask questions or connect.
Thanks
AbhyuK
you’d have to have a massive tire to equal the load capacity of two smaller ones, which would decrease fuel efficiency and maneuverability.
Two wheels can actually carry more weight than one wheel that is 2.5x the width.
The wider wheel needs to have much stiffer sidewalls and thicker tread to support that weight, otherwise the middle of the tread would buckle and the tire would collapse. There is also more flex in the tire tread that increases wear. By having 4 supporting sidewalls instead of 2, the individual tires do not need to be as strong to support the same weight and flex less. This leads to lighter tires that last longer and give you better fuel economy (all else being equal).
Another reason is redundancy. These tires generally do a lot of work and are put under a lot of stress, so they are more prone to failure. A single wide tire failing would immediately disable your truck and potentially cause a crash, but one of two narrower tires failing generally allows you to keep driving safely enough that you have some time to make it to a safe location.
Some dump trucks that frequent quarries use the single broad tires you describe. The benefit to them is the dually tires often pick up a rock between them, and after a few miles of driving, it can ruin both tire sidewalls.
The benefit to duallies is that if one tire goes flat, you can usually still drive a short ways to get to a safer place.
There is actually a type of tire called a ‘Super Single’ that’s just a very wide single tire instead of two thinner tires. With the super single there’s actually less overall tire width than two thinner tires resulting in slightly better fuel mileage. The combination is also lighter than duals resulting in a higher cargo capacity. Downside is if you blow you you can’t limp off the road and they aren’t great in snow or mud.
There are “super singles”. The problem is that they are more expensive than a pair of regular duallys. Also, tires are strongest when the section width (widest part of the tire) is just wider than the sidewall height. This gives a more round shape to the internal structure and is the strongest design. Having a single wide tire either requires a wider shape or wheels too small to fit brakes inside. There is also a logistical benefit to only having a single spare since the fronts are usually the same as one of the rears.
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