Thread: Tire choices
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Old 07-26-2009, 07:19 AM   #8 (permalink)
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Originally Posted by Christ View Post

Hm. seems like the trailer tire is actually stronger? We can't really assume that, because I estimated the diameter of a trailer tire. It's been awhile since I've measured one.

As far as handling, braking, etc... yeah, those things actually are designed into trailer tires... trailers have brakes, my friend. They also have to maintain a course in a straight line behind the towing vehicle, which means that they have grip while cornering. It may not be the same handling characteristics as a car tire might have, since they're not designed to be car tires, but for a very small city vehicle, I still don't see a safety issue.
Ah ........ Mmmmmm ............. Where to start?

The load carrying capacity of a tire is determined by quite a few things - directly: the amount of allowable deflection - which is a function of the size of the air chamber, inflation pressure, and some factors to account for the type of service. Indirectly: the size of the air chamber is a function of the section width and the diameter.

The factors used to account for the type of service can be boiled down to:

The higher the speed, the less the load capacity.

The rougher the road, the less the load capacity.

The more sensitive the service, the less the load capacity. (Meaning if people are involved or a tire failure causes a major problem - like on an airplane.)

In the case of trailer tires, they aren't stronger. They are just allowed a higher load capacity because of the lower speed limitiation and the fact that they don't carry people, and a tire failure on a trailer wouldn't have as large an impact as one on a car.

BTW, a P175/70R13 Standard Load has a rated inflation pressure of 35 psi, while a 4.80-12 Load Range B has a rated inflation pressure of 60 psi. That's quite a difference!

One of the issues with higher inflation pressures is impact resistance. A tire's ability to absorb the energy (Force X distance) of a penetrating object is a function of its spring rate. Lower inflation pressures allow a tire to absorb more energy. While impact type failures are fairly rare, because they completely destroy the integrity of the tire, they need to be avoided if possible.

BTW 4.80-12's are mostly used in light trailer applications - boat and utility trailers - and those usually don't have brakes. Cornering? Well, not so much.

Overall, I could see these type of tires being used on an city type electric vehicle where the top speed is limited by the size of the electric motor. Sort like those golf cart type vehicles - which in fact use these types of tires.
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