 Trailer Tires
| 385/55 R 22.5 with a profile for long-distance transport here. |
One would rather assign different gripping profile to a drive axle, right? Not quite, as there are at least two different ones for trailers and semi-trailers, for regional and long-distance transport.
As so often, the direction of the profile lines seems to be decisive here. If it moves more like a zigzag across the tread, Krone, for example, describes this as coarser and suitable for regional traffic. With the profile grooves for
long-distance traffic, stable directional stability is more important. It therefore has hardly any lateral deflections.
| There are even trailer tires with a snow tire profile. |
The size 385/65 R 22.5 has emerged as a kind of standard. If you multiply the 22.5 inch by 25.4, this results in a rim diameter of 571.5 mm. If you now calculate 65 percent of 385 mm, this results in 250.25 mm. These accrue
at the top and bottom, so multiply by 2 and add them to the rim diameter 1072 mm.
| Of course, the running noise of the tire also depends on the type of tread. |
There is also the option of choosing a smaller cross-section with stroke 55 instead of 65, which then results in 211.75 mm instead of 250.25 mm. This lowers the chassis of the trailer by almost 40 mm. The reason for this is
the prescribed external height of 4 m, which is also specified by bridges, for example.
So if a certain internal height of e.g. 3 m is important, the diameter of the tire must be even smaller. Because the bottom of the platform, e.g. a trunk, must be flat and even, i.e. it must not have any indentations caused by the
tires. That leaves one meter minus ground clearance, required engine-to-body clearance and spring deflection.
The corresponding dimension is 435/50 R 19.5, which results in a rim diameter of 495.3 mm and thus an overall height of 930.3 mm. Just under 7 cm doesn't seem much for roof or ground height, required engine-to-body
clearance and spring deflection, but this strictly mathematical calculation does not take into account the possible flexing of the tires even at 9 bar pressure.
For even higher interchangeable platforms, there is, for example, the dimension 235/5 R 17.5, which then results in 444.5 plus 352.5 mm, i.e. 797 mm. So the chassis sinks here by half the difference, so about
twice that of the previously mentioned tire. Due to the now lower load capacity of the tire, dual tires are used here.
We have already mentioned that the so-called Last Index for twin tires is slightly lower for each individual, but with a difference of rarely more than 5 percent it is not very significant. For individual trailer tires,
the goal is a load capacity of 5 tons, which corresponds to an LI of 164.
It can be read off the sidewall along with the letter for the maximum speed limit. The first two tires mentioned with two axles and a load capacity of 20 tons would comply with the permissible 18 tons, as would the three-axle
models with the permissible 25 tons, with air suspension even 26 tons.
Of course, this in no way relieves the driver of the obligation to ensure that the load is always distributed in such a way that none of the permissible axle loads are exceeded. Recently, this can even be checked and, if
necessary, reminded by transmitting the data to the dispatch department.
With all of these influences, which can be described as complex, there is one that is very easy to check and has a really strong effect on consumption and of course also on the wear of the tire(s). If you hadn't heard of credible
stories, you wouldn't want to believe it.
A tire that is too hot can set the entire trailer or semi-trailer on fire. If this happens, an unnoticed, non-release brake is usually to blame. But there are said to have been cases where the cause was significantly too low tire
pressure. Although It can usually be called up in the cockpit.
But it would have to be corrected in good time, which of course is only possible when the tires are still cold. It is also said that an undamaged tire can lose up to 0.7 bar of pressure per month, more so in summer than in
winter due to the heat. It is also unfavorable that you can hardly gain any experience with the respective tires, e.g. by changing trailers.
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