1.15. About parallelism of bridges of the car and trailerFor everyone engaged in operation of trucks is not a secret that exact centering of the operated axis increases service life of tires, increases stability of the movement of the car and facilitates management of it. Two important reasons because of which it is necessary to maintain parallelism of the leading bridges of the car and axes of the trailer are also well-known: service life of tires and fuel consumption. But there is also the third factor to which sometimes do not pay attention, but it, maybe, the most important. This factor, safety is.
Every time when coaxiality of any detail is broken, regardless of whether there is it in the engine, transmission or a suspension bracket, there can be unsafe traffic conditions. Besides, there is an increasing possibility of "folding" of the road train at the movement on dangerous roads if dual axes of the trailer are nonparallel. If all axes of the road train are parallel, then it will make rectilinear movement along the road. But if axes of the trailer are not perpendicular a longitudinal axis of the road train, then the trailer will tend to move in that direction to which its axes are perpendicular. It complicates driving and causes side slipping of tires in addition to advance. There is a premature wear of back tires and additional wear of lobbies. Of course, this slipping of tires caused by not parallelism of bridges will be the cause of increase in fuel consumption.
It is undoubtedly much heavier to drive the car with nonparallel bridges on dangerous roads. If not parallelism is rather big, then the car can become dangerous even on the good road as the driver has to fight against a tendency of such car to turn constantly.
Parallelism of dual bridges has to be checked every time when the car comes to a workshop for maintenance of a suspension bracket. Such check has to be made no more than through 50 thousand km of a run of the tractor, and the trailer – from 160 thousand to 200 thousand km on the corresponding equipment.
Need of the following centering of axes can come before the expiration of 160 thousand km of a run. It can be caused by small blows (when moving through curbstone or blow about an angular rack) or damages at collision. Even usual wear of plugs of jet bars of a suspension bracket on one party of the car can cause not parallelism of bridges.
At left-side driving of a wheel of the right board perceive more shock loadings, than a wheel of the left board as they move on roughnesses at roadsides more, and also as a result of redistribution of mass of the car on boards because the majority of roads has slightly convex profile. Usual wear of plugs or replacement of a jet bar can cause not parallelism of dual bridges. It is undoubted that check of parallelism of bridges at any repair work has to become the rule.
Tires with a radial cord are more sensitive to not parallelism of bridges, than tires with a diagonal cord for all types of axes and suspension brackets. Symptoms of wear of tires with a radial cord often appear after 16–32 thousand km of a run, and at tires with a diagonal cord – after 80–92 thousand km of a run.
Wear of humeral zones from the internal and external parties is characteristic of the tires with a radial cord installed on the operated axes. At turn of edge of a protector seek to rise as unlike the tires installed on the leading bridges in this case there is no force keeping the plane of contact of the tire with a roadbed. This wear usually does not influence durability of the tire, so it is observed only on the first 0,79 mm of width of a protector.
Not parallelism of bridges usually results in cross wavy wear of the tire. If bridges are nonparallel and the trailer tends to move from a longitudinal axis of the road train aside, there will be an uneven wear of the internal and external tire at a dual busbar or internal and external parts of a protector at an unary busbar. It causes slipping of the tire and its wavy wear very similar to wear of the tire installed on the operated axis. Result of such uneven wear of a protector can become "skalpirovany" tires.
Forms of wear of the tire with a radial and diagonal cord are various. For example, at the first of them both the too big, and too small pressure of air brings besides to the wear of a protector about an internal and external humeral zone. At the second at the elevated pressure of air wear of the central part of a protector increases, and with the lowered air pressure – internal and external edges of a protector. This wear is found in tires with diagonal usually quicker, than with a radial cord. The unary wide-profile tire has the same spot of contact with the surface of the road as both dual tires of a usual profile.
The wear caused by not parallelism of bridges probably will not appear on unary wide-profile tires also quickly because they wear out on turns less, than dual tires of a usual profile. Nevertheless they are more expensive so check of parallelism of bridges at installation of unary wide-profile tires is obligatory.
At new trailers it is necessary to check parallelism of installation of their axes. However it is necessary to remember that this adjustment will not be the last. There is a period of grinding in of details, especially at application of a four-spring suspension bracket.
After the small run of the chassis it has to be checked as some shift to the right because of gaps in earrings is possible. Usually the shift of a longitudinal axis of the chassis (concerning a bridge axis) increases during trailer service life. The more the trailer run, the bigger wear arises in the directing devices of a suspension bracket or earrings.
While the wear of tires and fuel consumption depending on preservation of parallelism of bridges can be defined, the traffic safety which is even more important factor, to measure not so easily. Regular checks and adjustments of parallelism of bridges only for safety considerably reduce the additional expenses connected with damages, accidents and idle times of cars.