Load capacity
The maximum weight that is allowed to be carried on the boot.
It is definitely not worth exceeding this parameter — even if the structure does not break immediately, this can happen at any time due to off-design loads. And ideally, you should have some margin for carrying capacity — this will give an additional guarantee in case of emergency situations (like hitting a wheel in a hole at speed).
Also note that the weight of the intended load must be supported not only by the boot itself, but also by the crossbars on which it is installed (if this installation option is used, see above). Moreover, the weight of both the cargo and the boot falls on the crossbars, which requires an even greater margin for load for them.
As for specific carrying capacity indicators, in general, the indicator
up to 50 kg is considered relatively low,
51 – 75 kg — average,
76 – 100 kg — above average, and in the most "heavy" models, the permissible load weight
exceeds 100 kg.
Internal capacity
The internal volume of the closed boot — boxing (see "Type").
Along with the load capacity (see above), this parameter determines the amount of cargo that can be placed in the boot. At the same time, we note that more load-bearing models generally have a more extensive interior space; however, products of a similar "weight category" may differ markedly in this indicator. And here it is worth proceeding from the fact that with the same allowable weight, a more voluminous boot is better suited for light and/or bulky goods, but it will have more weight, dimensions and price, and also (with a high probability) create additional resistance during movement, especially at high speed.
As for specific values, most modern boxes have a capacity in the range of
400 – 500 liters. A volume of
300 – 400 liters or
less is considered relatively small,
more than 500 liters — large.
Skis number
The number of pairs of skis for which the luggage rack is designed.
Note that such mounts are available not only in specialized models (see "Type") —
boxes are also available with the possibility of transporting skis. As for the number of clamps, the skis take up relatively little space, so
up to 4 inclusive is a relatively small number of pairs of skis for a modern boot. Models for
5 – 6, or even
7 – 8 pairs are noticeably more common, and in some products this number may
exceed 8.
External dimensions (LxWxH)
Boot dimensions in working position; usually indicated for open models and boxes (see "Type"). The capacity of the product directly depends on this parameter, in particular, its suitability for transporting large items. And in the case of boxes, dimensions also affect aerodynamics: increasing the height or width increases drag and fuel consumption. At the same time, it should be noted that the aerodynamics of the container also largely depends on its shape.
For open boots, the height is most often not indicated — after all, its actual value usually depends not on the dimensions of the structure, but on the size of the cargo being transported.
Weight
Net weight of the boot in working (fully assembled) form.
The light weight contributes to fuel economy (especially during long-term use) and also makes it easier to transport the boot outside the car (for example, from storage to the car and back). On the other hand, lightening the product leads either to a decrease in its strength and load capacity, or to an increase in cost. So in certain situations, a relatively heavy boot may be the best choice; and when choosing a light model, you should pay special attention to the claimed load capacity.
