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v to our past article we discussed how to force automobile to drive more rapidly, improving driver (you!). In this article we will be immersed into some technical details, which are concerned the suspension: as why she forces your automobile to go more rapidly.
One of the reasons, on which we selected BMW instead of Camaro or Corvette - this importance for us grow prettier controllability. At least, 4 for this I hope. And one of the things, by which are good BMW - this is actual controllability. But if then, why people similar to me or Karl bukland do always change their suspension in order to obtain the best controllability?

To volume there are two reasons: to go more rapidly and to obtain more than pleasure. Although they indicate that the races are won on the straight lines, all aspects are approximately equal in reality. The automobile, which passes zigzags only more rapid, will place shorter time on the circle. Concerning pleasure, many of us love the autopilot with the rapid response, who is obtained as a result of the stiffening of suspension. We simply consider that this machine to it is more interesting conduct.

You will ask: however, that not so with the standard plant suspension on my M3?. Good question. The engineers, who developed your automobile, had to consider many factors and dostich' many purposes in the realization of project.

For the beginning, automobile must be safe. Since BMW cannot force you to return the driver test before the purchase of your solar M3, them it is necessary to assume that not all their clients - excellent drivers. Thus they embed in the construction of small understeer so that, if you fall into unpleasant position, automobile would be more we govern.

In the second place, automobile must be comfortable. Therefore relatively soft springs and shock absorbers are established on it, in order to preserve convenience in the ride.

Thirdly, automobile must have competitive price, so that them is necessary to select this project of suspension and its component, which stand not excessively dearly.
Furthermore, there are many of other factors: from the size of motor section to the clearance, simplicity in the maintenance, longevity of tires. All this must be takeed into account with the final layout. It stands to reason, this project is a compromise.
V this year BMW sell 100.000 automobiles, and majority of them so will drive on plant suspension 10 for years later. So that, nevertheless, something BMW it makes correctly. However, some of us it is desirable to optimize construction for achievement of some specific purposes. This is - that moment, when we begin to modify our machine by certain complex method.

Each time, modifying your suspension for an improvement in the controllability, you conclude certain "transaction". You will decrease the height of suspension, and your clearance will be lowered. As a result sufficiently soon you detach any terrifically expensive piece of plastic away from the bottom of automobile. Increase the hardness of shock absorbers, and the softness of trip will depart into the window. Five miles of poor road - and your back will be ill as after 58- hour seat on the stool.

Another thing, which it is worthwhile to consider, starting for the modernization of the components of suspension - this is precise idea about the changes, which you want to feel in the behavior of automobile after the end of work. But changes will without fail be. Machine can begin to be governed better, and can and it is worse. Read any article either letter about the modified automobile, and there the author without fail bears delirium about the obtained best controllability, stability in the turning, predicted oversteer, and so forth extremely rarely they report to you that their automobile began to go as truck, heeling for entire elongation of way, or to plough by nose road as pig. All these things are possible and even they are probable, if you begin to substitute the random parts of the suspension without understanding of that how and why it is necessary to make this.

One of the fundamental phenomena with the passage avtomobil'nem of turning - redistribution of weight. In essence tires external with respect to the turning obtain large load, and internal - smaller. Tires can maintain these or other transverse loads exactly proportsonal'no to vertical load on them. Thus, the transfer of weight to the outer side means that the corresponding tires can better hold machine on the road in the turning. Unfortunately, with the internal tires - situation opposite. Moreover the loss of the ability to retain lateral force by the unloaded wheels is more than an improvement in this ability in those loaded. Thus, as a whole the redistribution of weight leads to reduction in the lateral friction of tires this BADLY.

Despite the fact that many do not believe to this, there are only two things, which can be made for changing the transverse redistribution of weight. It is possible either to increase interwheel distance or to lower the center of gravity of automobile. The value of the redistribution of weight - function of the dimensions of the triangle, drawn between these three points from the front and from behind of automobile (i.e., before and back they can have different properties of the redistribution of weight; this is - the crucial point, up to which we still will return more lately). You can to a certain limit increase interwheel distance it zaschet passage to wider rubber, but usually the dimensions of body do not make it possible to substantially increase this parameter (therefore Porsche it made once such "fatty" 911, and therefore Ferrari - are so wide). The easier method to improve gold triangle lies in the fact that to lower automobile, after lowering thus the center of gravity.

As you can lower the center of gravity? As a rule you place shorter counters. This in turn decreases the motion of suspension, decreases clearance, and, on some types of suspensions, increases negative disintegration, which IS GOOD, until it becomes is too great - and then this will be BADLY. Furthermore, since the motion of wheel was reduced, counters must be more rigid in order to avoid shorter suspension from the frequent impacts into the limiter.

After reducing the redistribution of weight, we increased the maximum transverse load, which they were capable of maintaining our tires. Thus, we increased the maximum theoretical speed, with which the automobile was capable to pass turning. In the turning with a constant radius the automobile with the smaller redistribution of weight will begin lateral slide with the larger speed. This automobile is called that having the best transverse balance.

However, automobile can remain completely unbalanced longitudinally. In the ideal it is good to have rapredeleniye of weight 50:50 between the front and rear axles, and the plant standard M3 - is very close to this distribution. The replacement of counters does not change the static weight of automobile, therefore, even having lowered it, we let us preserve initial relationship 50/50. But as soon as your M3 enters into turning, weight distribution changes. In the project is placed understeer, you do remember? As it is designed by engineers BMW, you will feel the results of the longitudinal redistribution of weight, which is the function of differences in the lateral stability of front and rear it is bridge. The steadier end of the automobile will be able to transmit a larger quantity of weight to another end. Thus, if before machine harder than back, then back obtains a larger quantity of weight in the turning and, thus, better it is caught for the road. This is called understeer. ("is caught" - incorrect word, because in actuality the discussion must deal with the angles of slippage and the force vectors. In reality understeer - such situation, when the ratio of the angle of slippage to the angle of rolling for the front wheels is more than the same relationship for the rear).

Well as, you did already grasp idea?

Lateral stability depends on many things. Spring constant, shock absorbers and transverse stabilizer - here basic three factors. Furthermore, the geometry of suspension (angles of the slope of counters and the like.) they also play role. If you make rear axle more rigid relative to front (or you soften front relative to rear) automobile will experience less than understeer. In the theory "ideal" suspension must make an automobile neutral: this machine experiences neither understeer nor oversteer in the ideal curve. In the reality the racers love to tune automobile either into one or to other side (I think that I use the 3rd article in order to discuss - why).

Having this quantity of variable (spring constant, the height of the center of gravity, the dissipating force of shock absorbers (both to the tension and to the compression), the hardness transverse stabilizers... (4 he did not forget about the tires?), how it is possible to determine, how "magic" combination? Answer is such - there is NOT ONE (wait by 3- it article). Nevertheless, you can something undertake...

On this score there exists many different opinions. Some call to the installation of hard springs and and soft stabilizers. Others - for the soft springs and the thick stabilizers. I personally love in reality, when springs not are more rigid how they must be - i.e., they must be such that the suspension almost, but would not entirely reach limiter on the quite very strong pothole of this route. Springs are critical for guaranteeing the ability of tires to correspond to the unevennesses of road instead of jumping over through them. When your wheel find in air, it not at all has cohesions with the road. After you installed springs with the minimum hardness from all four sides, you regulate relative hardness between the front and rear suspension. Then you balance automobile with the aid of the selection of the hardness of stabilizers.

However, this only for the race. For the motion along the street, to you are necessary the springs not harder than it is possible to allow themselves on the roads, on which you usually drive. You remember also that the stabilizers of stability - also spring (torsion). The harder your stabilizer, the stronger the dependence of two wheels: when one of them starts up, another, it follows it.

One of the solutions of the problem (I it went to this) - the suspension, rise-and-fall. Usually these are the special supports of springs with the thread.

Such supports are useful for two reasons: a simple change in the clearance and the standardization of diameter and size of springs. As a result it is possible to find the springs of different hardness. All this makes with possible for the racing command to have a collection of springs for the different routes (in more detail about this - in by 3- it part). Some sets of supports make it possible to regulate height only on the front suspension; with others it is possible to regulate all four wheels.

Last more preferable, since this makes possible for you to lower both ends of the automobile independently, and to also regulate weight distribution over the angles. This - the process of balancing the automobile between the right front and left rear, between the right rear, and left front the wheels. The automobile, not balanced diagonally, will badly conduct precisely when least of all this wants you. This will also allow you to distribute weight for the specific tuning to the concrete route. Principle is simple: the lift of rear right angle increases the weight of left front, and vice versa. And so forth

all this leads us to conclusion 2-1 of article: how to us to solve, what to make? In you two selections. You can establish finished "packet", or develop it independently. Packet - complete suspension of certain firm, for example Dinan or some still. They select the combination of springs, shock absorbers and stabilizers for the concrete automobile, and they assure, that all this together will work well. Thus far your purpose in tuning of machine coincides precisely with the purposes, which they placed with the selection of this packet, this will satisfy you. Alternative - its own packet. You begin from the finished packet and change details, or simply you begin from zero itself you select springs, shock absorbers and stabilizers. This is dear, it is time-consuming and it is potentially dangerous with testing of new tuning on the route. The best method to independently tune suspension lies in the fact that to work just as the tyuningovye firms: ensure to itself as much as possible those tuned it is main. If in you the tuned transverse stabilizers stand, you can try different hardness without the need for always buying new stabilizers. In this sense shock absorbers Koni are better than Bilstein: they are tuned. Thus far still no one devised the tuned springs, but adjustable supports give very nearly the same effect. Usually they make it possible to increase or to reduce suspension with the sufficiently small step for the fine adjustment.

We envelopped here much material, and I hope that at least its part was useful. I think, to write all this me impelled partly the advertising declarations, which I saw in the periodicals and in the network apropos of different springs. Usually they are described in the terms of the decrease of the height of automobile (for achieving the desired exterior view!), what is sufficiently senseless measure. If you lower the center of gravity, this is certainly good... But if in this case you completely disrupt balance, or your springs prove to be too soft or rigid - this is bad.

We yet did not have a talk nevertheless about the adjustment of suspension and about rubber. Also we did not speak about why the automobile, which today ideally obeys, can become nightmare tomorrow. And why people are disturbed about the temperature of tires. I will try to describe about all this further.

John Browne
BMW CCA
BMW ACA Puget Sound Region
M3 LTW (PeeKay)
Suburban 2500 (Godzilla)
326 iX (Spunky the brave little car)

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