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Coachwork - Package

Dimensional chains

What decides the size of the car which is to be newly constructed? Is it the length or maybe the even more important wheelbase? Sure, the new one must be slotted in somewhere, and it shouldn't encroach too much on the market of the next larger model.

Whereby it must be said, that very seldom are two models which lie quite close to each other, renewed in the same year. Should both deliberately be enlarged, then perhaps the earlier appearing model will reduce the distance quite a lot, before the larger of the two then moves away again.

The question is, how long can it go on this way? They are all getting bigger and from time to time, a new one is pushed in. One would think that one of those at the top would have to be taken out. That happens only rarely, because due to reasons of prestige, hardly any manufacturer can afford to retract his top model. Still, somewhere along the line, they have to make their contribution to the CO2 reduction by becoming leaner.

This brings us to the subject of weight. It can be seen in the new E-models: Even bold manufacturers like BMW cannot manage, to manufacture a relatively small series with a complete body made of carbon. The entire flooring is already made of aluminium. Although weight-saving is there, it is still somewhat limited.

One sometimes has the feeling, that in the specifications of a car, an ambitiously low weight is given. Basically however, all the alterations during the development phase have a negative affect here. A lot can possibly be done through a tacit agreement, e.g., between two departments, the weight however, still increases with almost every innovation.

Where does one start to apply the new measures? With the available interior, or rather the outside, which is certainly also determined by the design. We've now arrived at the so-called 'Package'. What has to be fitted into the new car? One might think, that space can always be found for small parts. However, be careful if these parts are high value components and are placed directly behind sheet-metal body-parts, which can easily be deformed by other road users. The insurance companies are quick to place the car in a higher tariff-class because of such unfavourable positioning.

The legislators are even more finicky. Lately, they want to do more to protect pedestrians. Thus the noses of the cars are now higher and somehow softer. Those who really want a larger interior, mostly mean the leg- room between the rear seats and the backrests of the front seats. Oddly enough, the more comfortable the rear seats are, the more space one seems to need for luggage.

So, we've finally landed with the box-form, at least from the windscreen onwards. Since of course, taller passengers on the rear seats shouldn't have to bump their heads on the ceiling. In addition, a 1/3rd- 2/3rd solution doesn't seem to be enough anymore, the rear set backrests must now have a 40/20/40 partitioning.

As far as the demands on the construction space are concerned, the needs of men (95%) are taken more into consideration than those of women, because the men are generally bigger. Indeed, have you thought about the fact that everything must still be reachable in these cars, for big men and for smaller women and that a laterally adjustable steering wheel can sometimes make a reasonably priced small call too expensive.

For the final determination of the measures, one goes out from the pedals. Even the otherwise variable transfer matrix platform of VW fixes the distance from here to the center of the front axle as the only measure which is not variable. From this point the further measures can be developed. E.g., the higher the seats are, the more length can be saved.

Low-lying motor cars require a lot of length. If the roof then falls away sharply to the rear, the only thing that helps, is if the seats are lower and have a higher bolster under the knees. The luggage compartment also suffers in low cars. If the boot-lid doesn't go far enough into the roof, then an opening right back to the bumper is not much use either.

A lot has been done up front, also in bread-and-butter cars. The strengthening sheet-metal (tailored blanks) for weight-saving, have also been introduced here. The front-end is less collapsible nowadays. Instead there are two-stage safety belts. Any sort of 'free-crumple-zone' is limited in front-wheel drives with a transverse engine anyhow.

By the way, it's quite fascinating, how certain compact cars, mostly of Japanese origin, have reduced the distance between the pedals and the centre of the front axle in such a way, that one has to ask oneself, where the rack-and-pinion of the steering is mounted. After all, the electric motor of the power steering then hangs on the steering column.

The already mentioned measures should, in the event of an accident, be as fixed as possible, to prevent the pedals from penetrating into the interior. The only deformation zone that really remains, is the space in front of the engine and its auxiliary components. Those who want more, will be better served by a top-notch sports-car with a straight mounted engine in the rear and a trans-axle construction.

Let's, for the moment, stay with the front-wheel drives, because with the flooring of the interior, it starts to get interesting. Even the height of the door-sills is important. It protects, together with the reinforcement in the doors, in the case of a side-on collision. The centre drive-shaft tunnel is actually, no longer needed, but for reasons of stability it has to remain where it is.

The question of the lateral- or cross-stability remains interesting. To achieve this, cross-braces would be necessary, they could, e.g., be placed underneath the front seats and because these can be moved back and forth, the passengers in the rear would have more room for their feet. On the other hand, cross-braces are exceptionally important because the opposite side of the vehicle is then also involved in the absorption of side impact forces.

This is also why the support which runs underneath the front part of the rear seat bench is so important. The fuel tank, mounted behind the support and undivided because there is no driveshaft, is protected. Thus, the rear axle can be a relatively simple construction, which altogether, makes itself noticed as a weight advantage for the front-wheel drive car.

The wheel housings become apparent when loading luggage into the boot and also by the amount of legroom (or lack thereof) in the front. Despite being quite narrowly built, the small car is at an advantage here because the wheel housings are not designed to accommodate really wide tyres. Unfortunately however, wide wheels are also a lucrative optional extra, not only for those selling the upper class cars. For this 'luxury' the customer pays the price of not having much freedom of movement to operate the pedals. 08/14

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