if a vehicle has more than one rear axle ,and they don‘t steer. it must mean that wheels in at least one rear axle are sliding side wise?is it really like this ? and if so ,what are the consequences of this effect.
An axle is the device that connects the vehicle to the ground. For larger commercial type vehicles the axle is a 2 part system. First it allows the weight hauled to be spread out evenly along the entire length of the vehicle. This is important when crossing bridges, off-highway applications and is much easier on the road way as it does less damage. The second application axles supply is rubber to the road which is used in braking. In a small car 4 wheels are sufficent to stop a car weighing 2-4 k lbs. Commercial tractor trailers in the US can weigh 80k for the standard combo, and even more with permits. The more axles you have, the more brakes on each axle become available and the easier the vehicle is to effectivley stop.
On normal highway driving the steering input is really small. In sharp steering,however, you can see the effect and you are right, a vehicle with more than one rear axle is difficult to steer. In some designs there are options to make the extra rear axles free to steer to negotiate adverse situation such as met in city driving.
Almony: Sliding is not a huge problem. Wheels on multiple fixed axles, e.g. on an over-the-road trailer, track more or less along a straight or curved path, depending on the path of the tractor. If the rear wheels are on a trailer hitched to a tractor by a pin (pintle), the trailer wheel path is dependent on the movement of the tractor hitch. This simple but ingenious invention allows the tractor to maneuver the trailer to move into tight spaces. For long trailers, however, it can make negotiating right-hand turns at many urban intersections difficult. For this reason, many firefighting ladder trucks have independent steering for the trailer. Civil engineers should carefully consider the design of intersection corners and other sharp curvature in designs that will be used by trucks. Road design criteria typically contain templates showing tractor and trailer wheel paths for design purposes. Software such as AutoTURN can assist in the design process.
