#Performance vs suspensions

10 / March 2022
Performance vs suspensions

Seletron Performance

Car suspensions and chip tuning

If you are reading this, you may already know that our followers chose some of the recent topics we covered, and others were even chosen by survey. In fact, in the last few weeks, we have been talking specifically about how Diesel injection systems with electronically controlled rotary injection pumps work. Then, we about the later radial piston injection pumps and related chip tuning, and about the PDE (injector-pump) system, the more modern common-rails, and related chip tuning for increased engine power and torque. We then moved on to topics related to chip tuning for gasoline engines and more.

Among the topics you have asked us about, some installers and mechanics have asked us for some advice and some explanations regarding the link between chip tuning units and car setup. Stated differently, some installers, who regularly use our CHIPBOX chip tuning and our PEDALBOOSTER chip tuning modules, are asking for some clarification on the necessity or advisability of changing the car setup as a result of electronic tuning through the installation of chip tuning manufactured by SELETRON. Let's shed a little light on this topic as well.


Car setup, what happens physically while driving.

In automotive jargon, "setup" refers to the set of components that make up the suspension system of the car. Such a system is composed of a number of elements, which we are going to look at individually:


Car suspension coils.

These are the elements that actually support the weight of the vehicle, and each wheel has a suspension element. There are not only coils (although they are absolutely the most common) but also steel leaf springs, torsion bars ( seldom used), and air springs, i.e., elastic elements held under pressure. These elements represent the system used to have variable height trim and are present (as standard or optional) on several cars.


Shock absorbers.

They are fundamental elements for proper grip on the road, serving to dampen spring-induced oscillations as they pass over bumps and depressions in the road surface. Each spring stress generates an accumulation of energy (during spring compression) that must be released (during spring extension). In the absence of shock absorbers (or with discharged or failed shock absorbers), the vehicle would begin to oscillate along the vertical axis to the point of triggering actual "jumps" of the wheel on the road, an extremely dangerous situation as it leads to the cancellation of the vehicle's grip and directionality.


To simplify as much as possible, shock absorbers are elements composed of a stem (piston) connected to the wheel and the cylinder it slides into that is connected to the vehicle frame (the position can also be reversed in many cases). A series of valves manage the flow of oil, creating a damping effect that absorbs some of the energy as the spring extends, damping the suspension travel. Much of the damping energy is converted into heat as a result of compression of the oil, which is forced to circulate in narrow passages. Some shock absorbers have a gas-operated section that allows for greater effectiveness and ride comfort. Other shock absorbers have electronically controlled valves to adjust the damping effect, which are used in variable stiffness setups.


Anti-roll bars.

These are elastic steel bars connected between the two wheels on the same axle. They are used to contain the rolling movements, that is, the rotation of the vehicle around the longitudinal axis. In practice, the elastic steel elements are attached to the chassis in the central part of the bars themselves and to the wheels (through articulated arms) at their ends. During curves, these bars oppose (partially) the difference in travel of the two suspensions of the same axle, precisely limiting the roll effect resulting in less load transfer and thus more stability. In almost all cases, there are two anti-roll bars, one mounted on the front axle and one mounted on the rear axle.


Unsuspended masses in cars.

Unsuspended masses are all those element masses that are not part of the vehicle, understood as a body or chassis. Unsuspended masses are tires, rims, brake discs (or drums were still employed), springs, arms, and shock absorbers. On a theoretical level, if we leave out some secondary aspects related to comfort, the lower the suspended masses (in terms of overall weight), the greater the road holding. To understand why, let us imagine two road surfaces, one perfectly smooth and one bumpy. On a perfectly smooth surface, the unsuspended masses have practically no influence on road holding (except from the point of view of inertia resulting from the overall weight and acceleration inertia for the rotating masses, thus tires, rims, brakes, and any axle shafts).

On an uneven surface, any change in the height of the surface (bump, roughness, etc.) causes an upward thrust of the wheel ( unsuspended mass formed by the weight of the tire, rim, braking elements, and part of the elastic suspension and damping elements), this thrust generates an upward acceleration, i.e., of subsequent departure of the tread from the road surface. The greater the overall mass of the unsuspended elements (which should faithfully follow the road profile), the greater the inertia of the wheel, with a subsequent longer time required to restore grip on the ground. Still, entirely theoretically, an unsuspended mass of zero kilograms would provide maximum road holding on uneven surfaces

Many years ago, Alfa Romeo developed a distinctive rear suspension system (on Alfettas, for example) that involved mounting the rear brake discs on the differential block and not inside the wheels. Although this system has since been abandoned, it allowed the weight of the braking elements (discs, calipers, pads) to be shifted from the unsuspended mass group to the suspended mass group, resulting in reduced inertia of the wheel assembly and optimized road grip on rough road surfaces. Today, many manufacturers use (at least on mid-to-high-end cars) light-alloy elements to precisely make the suspension reduce the overall weight of the unsuspended masses.


Helpers in car suspension.

I apologize if I mention this as well, but we were on the subject of road grip on uneven pavement. Have you ever heard of helper springs? To improve traction on uneven pavement (mainly in rallies), in some cases, additional steel spring elements formed by short springs with a rectangular cross-section are inserted between the main springs and the suspension spring plate. These additional springs, known as helpers, have the function of making the suspension "soft" for small excursions. They are precisely useful for improving traction on uneven surfaces.

Now back to us. To summarize, springs support the weight of the car and already have their own anti-roll and anti-pitching effects. Shock absorbers restrain the excessive oscillations that are triggered by any change in road surface profile, and anti-roll bars (also called stabilizer bars) limit load transfers, i.e., transfers of mass that pass from one side of the vehicle to the other in turns.


Why are load transfers a problem?

Normal cars have two axles and four tires. There is no load transfer in static situations (stationary car or car in uniform, straight motion on perfectly smooth pavement). Each tire adheres to the ground with a weight that will be about 25% of the vehicle's mass. This at least applies to cars with perfect weight balance, meaning equal weight at the rear and front. Many cars have a preponderant weight balance on the front, usually around 55-60%. Returning to the example of perfect weight balance in static conditions, we assume that each tire has an equal grip on the ground. During braking, since the center of gravity of all cars is in a higher position relative to the ground (slightly higher on low-slung super sports cars, much higher on SUVs and tall vehicles), there is a transfer of load from the rear to the front resulting in more load on the front tires and less on the rear tires.

This is why the front brake discs/calipers are always oversized compared to the rear ones (although in some cars, the diameter of the front discs is the same as that of the rear discs, the calipers are always oversized on the front end). As a result, the setup no longer has the same stability as the static situation during more powerful braking. The same happens around curves when the outside wheel receives a load transfer relative to the wheel inside the curve. The inside wheel will have less grip and, therefore, less road grip and braking capacity. In summary, a car braking on a curve has a heavy load transfer to the front wheel outside the curve itself, a situation that is not optimal for road holding, stability, or containing yaw effects (rotation of the vehicle around the vertical axis).

Increased stability and road holding are achieved with a lower center of gravity and stiffer spring elements, at least in the presence of perfect ground. This is why car setup is always a compromise between safety, driving pleasure, and comfort. A low and stiff setup allows excellent road holding (on perfect ground) and few load transfers. Conversely, a very stiff setup provides little feedback on approaching the limit of longitudinal (under braking) and transverse (cornering) grip, so it is more suited to driving experts.

Though not in all conditions, a more supple setup provides (though not in all conditions) greater comfort and more leeway in understanding when one is close to the limit of grip. Just think of the roll during a curve. When raised, it alerts us to the excessive speed with which we are approaching the curve. Then there are aspects related to transitability on certain rough roads. A vehicle with a high and relatively soft stance can traverse rough terrain (see off-road) without any problem. A vehicle with a very low stance, perfect on the track, can run aground on rough terrain, curbs, sidewalks, and steep garage ramps. As you can see, it is always a compromise that must be adapted to the type of use of the vehicle.

Obviously, cars with trim height adjustment and shock absorber stiffness are better suited for more conditions. In general, consistent with the type of car desired, cars with a low center of gravity are always preferable (which does not necessarily mean a low setup, see, for example, the difference in center of gravity between an SUV, a minivan, and a sedan). 

Setup and chip tuning.

Here we go back to the topic of this article, which is what needs to be done to the car setup when installing a chip tuning additional unit. In general, you don't need to do anything at all. Let's start with a few simple examples. A car that has 150 horsepower and is upgraded to 175/180 horsepower with the installation of a chip tuner will be perfectly suited (also in terms of trim) to handle the difference in power. The biggest differences after the installation of a chip tuner are in acceleration and pickup ability; top speed, however higher, is certainly not a problem.

To give an example, a sedan that reaches 215Km/h with original power, after electronic tuning, might reach 225Km/h or perhaps 230Km/h, values not far from the original version. In fact, the percentage increase in power is by no means related to the same percentage when it comes to top speed. To stay with the example just now, reaching the speed of 260Km/h might take four times more power increase than the +25/30 hp provided by the chip tuner.

Another example: a BMW that is limited to a 250Km/h standard and on which a chip tuning additional unit will be installed that brings an increase of +40hp. It will not need to change its setup because the top speed (being limited to the maximum speed) will remain the same. Moreover, the standard setup is already suitable to handle high performance. To summarize, installing a chip tuning module or installing chip tuning for the accelerator pedal (the PEDALBOOSTER) does not require an adjustment of the car's setup.

If you want to intervene in this aspect as well to further improve road-handling and driving pleasure, this can still be done. In this case, we want to leave you with some advice:

- Use only quality springs and shock absorbers; they are critical elements for safety, don't skimp by using cheap parts!

- While it may be advantageous to replace just the shock absorbers with sportier ones, we do not recommend doing the opposite, that is, replacing just the springs while leaving the original shock absorbers in place. This is for two reasons; first of all, the length of the shock absorbers may not be suitable for the lowered springs. Second, the released energy of stiffer springs may not be offset optimally by insufficiently restrained shock absorbers, and you would end up with a car that jerks too much when driving on bumpy roads.

- If you want a complete setup, look for high-quality and already proven spring and shock absorber pairings. To give an example, Eibach springs and Bilstein shock absorbers are a solid bet, and while they are definitely not the only brands, we can say from experience that you can't go wrong with these. Koni is also a very good brand for shock absorbers. When choosing shock absorbers, one should also pay attention to the length of the stem. For example, Bilstein provides shock absorbers called B6 that are also perfect for use with original springs (but make the setup much sportier), while for super-lowered springs, you need B8 shock absorbers that are shorter.

- As a general rule, however, we suggest replacing the shock absorbers if they are worn out or excessively loose; contrary to what one might think, stiffer (if not excessively stiff) shock absorbers do not compromise ride comfort in many cases (e.g., driving on roads with many curves) they can even improve comfort and safety because of the reduced boat effect given by roll and pitching. They also result in lower load transfers that make greatly improve braking and vehicle stability.

We do not think we have exhausted the subject related to car setup tuning with this article. It is a complex technical field based on physical laws. Nevertheless, we hope we have clarified a few points and given you some basic advice that may be useful if you are thinking of modifying your car's setup. We reiterate, however, that it is not necessary to modify your car's setup if you install one of our torque and power increase kits. Be sure to keep up to date and read our other technical articles, and if you like them, share them with friends and colleagues!


Come back and read more; we look forward to seeing you!


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