ON THE FLEXIBLE NIVA
TEXT / ANATOLIY KARPENKOV, ANATOLIY FOMIN
PHOTO / ALEXANDER POLUNIN
The irresistible desire of Russians to emphasize their individuality is very often found expression in their cars. This is especially noticeable among the owners of the Niva VAZ 2121 3 and its modifications. Let us leave alone “kenguryatniks”, plastic body kits and other well-known gadgets. We’d better talk about wheels, because a good half of the Niva drives by no means on their standard VlI-5 and VlI-10 tires, but on completely different ones.
The running-in shoulder is largely determined by the design of the front suspension (Fig. 1). The negative shoulder provides more stable movement during acceleration and braking, especially on roads with different grip under the wheels (the so-called “mixed”). The running-in shoulder can be precisely determined only by the assembly drawing of the front suspension of the car. However, this is not required. It is enough to know its change, which can be calculated by the size of the tire and wheel.
The most important parameter in this case is “wheel overhang” (usually denoted by ET). The method of its independent measurement (for wheels with symmetrical side flanges) is shown in Fig. 2. The smaller the ET, the greater the displacement of the wheel to the outside, and the running-in shoulder to the positive side. At Niva, it is already positive, so an increase is not at all desirable - the handling of the car suffers.
FROM THEORY TO PRACTICE
We decided to illustrate the theory with examples using the editorial test. The wheel carrier was the VAZ 2121 4 with a 1.7-liter engine and GM single injection. The vehicle mileage at the start of work was 4650 km. The test used four wheel options (in automobile jargon - disks) with tires, the dimensions of which are given in table. 1. These combinations were chosen as the most common and, moreover, not requiring alteration of the hub units and suspension elements.
READE SET GO!
The measurement results (Table 2) confirmed our assumptions. A significant improvement in dynamics is one of the reasons for installing "small" wheels. The second, rather psychological - the speedometer readings in this version become very “optimistic”. Maximum speed in all cases was achieved in fourth gear. In the base (VLI-10 tires and steel wheels) engine speeds at a maximum speed of 126.2 km / h reached only 4800 rpm. In other cases, they ranged from 5300 to 5400 rpm. Thus, in the factory configuration, the engine does not reach the maximum power speed. In addition, with a decrease in the diameter and mass of the wheels, the braking efficiency increases, but most importantly, you feel the brake pedal well.
Many Russian drivers are very ambitious on the road, and here the installation of "small" wheels, among other things, does not require the cost of boosting the engine or interfering with the transmission. We add the psychological effect of a noticeably oversized speedometer, so convincing to return to the standard will not be easy at all. So, on smaller and lighter wheels, the car accelerates faster. And if the tires are also imported, highway, with low rolling resistance and high grip properties - is this not a triumph of “home” tuning?
POORULIM - WE LIKE …
The use of wide low-profile tires on wheels with a standard take-off value (in our case 205 / 55–70 instead of 175/80) almost does not change the running-in shoulder. But the “low” tire profile has a positive effect on handling and stability. Indeed, a car on 16-inch alloy wheels (ET 58) with a low-profile tire (205/55) responds more quickly to steering and better road holding. At the same time, on such tires you will not really train on broken asphalt. The ground clearance is less, and the ability to withstand chips and potholes is worse. There is one more thing to keep silent about. Wide low-profile tires mounted on a narrow 5Jx16 rim in a bend do not work optimally. For them, a rim of 6 or even 61/2 inches wide would be preferable. But then you have to reduce the departure … And it affects the behavior of the car much more noticeably. From this point of view, the 14-inch wheel from the GAZ 24 (ET 0) is the worst option. A running shoulder with a 205 mm wide tire is significantly larger compared to the base case (which has a 58 mm overhang). How does this affect the driver?
When maneuvering in cramped conditions (leaving the parking lot, parking), the effort on the steering wheel increases, which is also great with the standard Niva. Off-road driving, especially with deep ruts, also causes a lot of problems. At the same time, “blows” on the steering wheel during the passage of transverse furrows or shallow ditches become stronger - take care of your fingers.
The installation of wheels with a reduced overhang enhances the tendency of the car to the effect of "biting". Having hit one of the front wheels on a surface with great rolling resistance (loose soil or heavy snow), the car abruptly tends in this direction. Moreover, the force on the steering wheel increases jerkily, in addition, unexpectedly for the driver. In this case, it is rather difficult to maintain a given direction of car movement.
Even with normal braking, the car on wheels that increase the running-in shoulder (especially with ET 0) pulls strongly towards the front wheel, which has a high coefficient of adhesion or rolling resistance on the road surface. What can we say about the emergency stop. Explain the numbers …
When braking from 70 km / h on the “mix” (the wheels of one side on dry, the other on wet surfaces), the standard car was able to be kept in a given corridor with an effort on the brake pedal of up to 200–250 N. “Niva” on 14-inch wheels with a reduced overhang (ET 0), under similar conditions, it remained within the limits indicated by the cones with an effort on the brake pedal of not more than 100–150 N. The braking distance increased by 16–18%.
With increasing speed, emergency braking on a slippery road with a heterogeneous coating can result in a loss of trajectory stability of the car, followed by a deep skid of the rear axle and uncontrolled rotation.
Any production car is a kind of balance of design solutions for given operational requirements. Or, if you like, a compromise. Therefore, insignificant, it would seem, interference in the design leads to the improvement of some, but the deterioration of other characteristics. The only question is whether it meets the safety requirements and how much the result is acceptable to the consumer.
WHAT WILL THE FACTORY SAY?
Our findings were confirmed by AvtoVAZ specialists. Cars of the VAZ 2121 3 series at the factory are equipped with 5jx16 wheels with a 58 mm rim offset. Reducing the diameter of the wheel or increasing the width of the rim without changing the offset will cause the rim to touch the upper lever of the steering knuckle. On vehicles of the VAZ 2121 3, VAZ 2120, VAZ 2131 family, it is possible to install 5jx15 wheels with a 45 mm offset and 6jx15 wheels with a 35 mm offset The use of wheels with a smaller overhang is unacceptable in terms of controllability and stability when braking. The use of 14-inch wheels is not permitted. Please note that with 15-inch wheels tires of this dimension should be used, the outer diameter of which is close to the diameter of the tire 175 / 80R16, adopted for the VAZ 2121 3. For example: 195 / 80R15, 205 / 70R15, 205 / 75R15.
"GIFT" FROM STSI
Fans of "home" tuning need to know that on December 7, 2000, Order No. 1240 of the Minister of the Ministry of Internal Affairs of the Russian Federation was signed, which regulates the traffic police. One of the sections of the order relates to the conversion of vehicles in use. In accordance with this document, making changes to the safety of traffic in the design of a production car is possible only with the permission of the traffic police on the basis of the conclusion of the manufacturer or organizations accredited in the GOST R Certification System. But this is a separate conversation.
The VAZ 2121 was originally conceived for driving on poor roads. That is why he has high ground clearance and a short base. To increase ground clearance, the first Niva prototypes used M-51 diagonal tires measuring 6.70-15 with a profile height of about 100%. However, the controllability of the short car in this version was unsatisfactory - the high tire “developed” in the corners. Therefore, I decided to use 16-inch tires with a reduced profile height (VlI-5 - about 80%). Radial VLI-10 with an all-weather tread pattern appeared after a good decade, but their proportions (175 / 80R16) are far from modern ideals. The size chosen by VAZ specialists is largely dictated by the layout of the Niva, according to which the spare tire is placed exclusively under the hood - and there is no alternative to the "standard" size.
EDITOR THANKS PROMA WHEELS OF EASY ALLOYS LLC FOR THE PROVIDED
ON THE TEST OF WHEELS AND THE "RALLY CLUB" FOR THE PROVIDED CAR AND ACTIVE PARTICIPATION IN TESTS.
175 / 80R16 VLI-10 ET 58
205 / 65R15 Voltyre VS-20 ET 35