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WHERE WILL THE CURVES TAKE OUT?

Wheel beating is a national feature of the Russian car. Employees at the wheel went to tire shops to see how they cope with this disaster there.

Mikhail KOVRIGIN, Roman SOLDATOV

There are two ways to calm the steering wheel twitching in your hands: to reduce the speed of kilometers to forty, when vibration is almost not felt, or to seek help from specialists. They are familiar with this phenomenon and its causes: power and mass tire heterogeneity, coupled with radial and lateral runout.

And how do you order an ordinary motorist to understand this zaum? The only thing that is clear is the imbalance of the wheel (the disk with the tire assembly), caused most often by the uneven distribution of materials in the tire.

It is customary to distinguish between static (Fig. 1) and dynamic (Fig. 2) imbalance. In the first case, it is possible to balance the wheel freely mounted on the axle: balance the heavy place with weights on the diametrically opposite side of the wheel. But for a modern high-speed car this is not enough - a statically balanced wheel may not be dynamically balanced. What this means is shown in fig. 2: if a heavy place is shifted to the distance l from the tire symmetry plane by a distance l, then its centrifugal force Rsb seeks to “overturn” the rotating wheel by the moment Rsb.l. This means that the balancing weight should be positioned so as to create an equal in magnitude moment in the opposite direction.

How important is balancing? Judge by a simple example. Suppose that in order to statically balance the wheel, weights 60 g should be hung on the rim. It is easy to calculate: at a speed of 100 km / h the unbalanced wheel “at 13” will hit the suspension with a force of 11.1 kgf with a frequency of 16 Hz!

Another factor that can cause vibration is the radial and lateral runout of the wheel due to deviations of its shape from the drawing. Many motorists forget about this, or maybe they don’t know. Let's turn to fig. 3 and 4. Rolling along the road, the “non-circular" wheel for each revolution either raises or lowers the body. Let's make a calculation for a special case. For example, the axis of rotation of a 15-kilogram wheel for one reason for one millimeter does not coincide with its own axis. This is equivalent to the fact that we “hung” a weight of 83 g on the rim of a perfectly balanced wheel! .. If you recall the previous example, the centrifugal force of such a weight at a speed of 100 km / h will be 15.4 kgf! It turns out that the negative effect of distortion of the geometry of the wheel can be even greater than that of the usual imbalance. By the way, speaking about the geometry of the wheel, do not forget about the bearing assembly on which it is installed. The wheel can hit due to defects in the hub, bending of the axle shaft, etc., and not just your own!

And finally, the third factor, the least known to motorists, is the power heterogeneity of the tread and sidewalls of the tire around its circumference (Fig. 5) - individual sections of the tire with different stiffness. If it happened to use a tire repaired after a cut, the effect of its local efforts with a rigid patch is well felt.

Nevertheless, it is useful for a motorist far from all this “science” to know: a real wheel, unlike an ideal one, certainly has the above-mentioned defects, but as long as they are within the limits defined by GOST, the wheels vibrate weakly and the driver does not feel any discomfort.

The mentioned power heterogeneity is on the conscience of the manufacturer (the owner of the tire and the balancing wizard will not do anything with it - it will shake), but they can overcome the remaining shortcomings in tire fitting. If they want to!

According to the rules, the process takes place in four stages: mounting the tire, checking the imbalance, optimizing the wheel assembly and final balancing. Optimization is the selection of such a position of the tire on the disk, when their mutual deviations from the geometric ideal are maximally compensated. But this method, which appeared not from a good life, is not suitable for alloy wheels (wheels) - their shape is close to ideal. Hence the conclusion: it’s hardly worth buying luxury alloy wheels for low quality tires. On the contrary, the worse the tire geometry, the more “crooked” the disc should be. Only with this combination can their disadvantages be mutually eliminated. But you won’t guess …

Every self-respecting tire fitting has a balancing machine. Today, even the simplest of them measure imbalance with high accuracy (up to 1 gram) and have special programs for alloy wheels. More complex devices are able to perform optimization. The equipment of the 21st century is the American "Hunter GSP 9700". It imitates the operation of a wheel under load and measures radial and lateral runout with an accuracy of hundredths of a millimeter, revealing also the force heterogeneity of the tire. Remembering the parameters of the disk and tire, such a machine will best fit them to each other. However, due to the high cost, such equipment has not yet taken root in us. We managed to find one "Hunter" in the capital company "Eurosiv".

Conventional machines are equipped with a taper clamp as standard. He holds the wheel by the central hole, and it may not coincide with the axis of rotation, giving a measurement error of up to 10 grams per side. Better is a special adapter - on it the wheel is fixed for the holes for the bolts. But the majority of tire fitting spending on it is considered unjustified …

… So, for his money, the client should get the “right” wheel with a minimum of balancing weights. And how is it really?

We bought several 13-inch domestic tires of the Nizhnekamsk, Yaroslavl, Moscow and Belotserkovsky tire plants and wheels for them. Arbiter - Research Institute of the Tire Industry (NIISHP). The wheels were assembled, optimized, so that, turning to the workshops, they could evaluate the quality of balancing in each of them, regardless of equipment. Each time, the results were checked twice: first, in the laboratory of the institute, and then alive - on the high-speed section of the Moscow-Kashira motorway. The “eight” became the experimental car, the sensitivity of the “sharp” steering wheel of which to the foci of the wheels is well known.

Conventionally, workshops can be divided into three groups. The most numerous are street ones. In trailers, containers, sheds, etc. The range of equipment is unexpectedly wide - from primitive to quite acceptable. Advantages - proximity to car owners and the lowest price for services.

The second group settled in tire stores and mid-range services. Here you can hope for a more serious approach to the process, sometimes for the same money as in the first group.

World-class tire service - with branded service centers. The equipment is appropriate, but the prices are 5-6 times higher! And, as they say, bargaining is inappropriate.

In all the workshops we visited, the attitude towards the client is respectful. It is understandable - competition! And the rest - who is what. Somewhere they will offer to wash the wheels themselves and clean the tread, and somewhere silently knock down a layer of adhering dirt with a hammer. A pleasant exception is tire fitting of the highest category. Upon entering, you think that you were mistaken by the door. Cleanliness, like in the operating room. Here they will wash and balance, but they will take a lot - at 4-5 dollars per wheel.

In street workshops, weights are sometimes not enough. Stock replenished removed from the old wheels. It happens that not those that are needed are hung, but those that are, and at the price of new ones. The old brackets do not hold well, and the dirt that accumulates in the cracks adds up to the weight of the weight (see photo). Poverty sometimes pushes the master to other tricks. If his machine does not have a program for balancing alloy wheels, he, without blinking an eye, leads the process using conventional technology. The result may be far from required.

Sometimes the quality of balancing between the “poor” and “rich” surprisingly coincides - the law of physics is one. The main thing is that it’s not customary to remember the word “optimization” in tire shops: who wants to, once they have assembled the wheel, check, disassemble again, reassemble and so on? Of course, we did not offer such a service anywhere. But the majority, as if by conspiracy, took to work those tires, the path of which is to dump. It can be seen by eye - a screw. For the sake of interest, pretending to be "suckers", we gave the curved wheel into balancing. And in all tire service except one, experts carefully clung weights to it! Have you ordered a fight? Paid.

We heard that among the masters there are also noble ones - from those who, having seen a crooked wheel, immediately indicate to the owner the senselessness of balancing. But we didn’t meet such people … And everywhere the wheels were mounted on a cone, we never saw the adapter. This means that a balancing error of up to 10 g (see above) is already guaranteed. Rearranging the wheel relative to the cone, they were repeatedly convinced of this.

Now about the guarantee. Only in one place were they given us a document valid for three days. And that is gratifying - you can check on the road. If it hits, you will need to do it all again, but for free.

Based on the results of our raid, we made up the final tables (1-3). For all workshops on wheels (“thanks” to the cone), the residual imbalance barely fell within 10 g. This was checked in the NIISHPA laboratory.

Now it was necessary to continue checking on the road. Most of the balanced wheels (and tested at NIISHPe) … continued to shake the steering wheel! Knock non-circular! Weights will not help. When measuring radial run-out, only three out of eight wheels fit into the norm! But they all went through the OTC! With such indicators, even after the Hunter, the car will shake the whole soul.

So we have uncovered the secret of that unknown force, in the struggle against which overseas balancing machines pass: their electronic brains are too expensive for our rubber of the first grade!

Well, what should a practicing motorist do if he drives at very high speeds of 90–100 km / h? About this - a conversation in one of the following numbers.

1. Static wheel imbalance.

2. Dynamic wheel imbalance.

3. Radial runout of the wheel.

4. Lateral runout of the wheel.

One of the most advanced balancing machines is the Hunter GSP 9700.

Measuring beats of a wheel rim.