This chassis tuning allows specific handling problems to be cured by changing one or more shocks. Adjustable shocks can offer adjustments in rebound only or for bump and rebound double adjustable. Tuning can be accomplished by adjusting the shock absorber, most often while still on the car. In any case, changing the valving of shocks overall, in bump only or in rebound only, can change the handling of the car and improve lap times.
For the most part, tuning with shocks is considered a fine-tuning adjustment once the chassis is setup and tuned. If a shock bottoms or reaches full extension under load, handling can change dramatically and damage to the shock can occur. Bump stops on the shaft of the shocks reduce this and some chassis builders use rebound travel limiters to keep the shock from reaching full extension.
Full extension is usually less of a problem. Shocks dampen by using friction, which causes heat. Heat buildup can affect the rate of the shock, always softening it. Dissipating heat always helps shock performance.
Bumpy tracks create more heat than smooth tracks. It is best not to cover shocks, and even to duct cool air to the shocks. Aluminum shocks dissipate heat faster than steel bodies. For coil-overs, threaded body shocks cool better than smooth body shocks with thread spring perches over the body for the coil-over adjusters. In the middle of a race, you are running just behind the race leader.
He is pulling away slightly, and the place on the racetrack where he seems to gain is going into the corners under braking. If you go in that hard, you pick up a small push. The car is great everywhere else and you can run with the leader.
Your cars are identical and on the same tires, so where could his advantage be? The key to this situation is probably a shock absorber. Similarly, shocks will not cure a big handling problem, though they can cause handling problems if they are bent, bind or too stiff or soft. The shock controls how fast weight is transferred. The valving for low shaft speeds is the primary controlling factor for weight transfer. This affects the load on a tire and can change the handling balance while weight is being transferred.
Once all weight has been transferred, the shock no longer influences handling. In general, rebound damping controls how fast weight leaves a tire while bump controls how fast weight goes onto a tire. Stiffer valving causes a shock to react more quickly.
Softer valving slows the reaction of the shock. Stiffer valving gets the load to change more quickly. Stiffer rebound valving gets the load off a tire more quickly and onto an opposite tire faster. Stiffer bump valving gets the load onto that tire faster. When going into a corner, as long as the driver is moving the steering wheel or the brake pedal, the shock has an influence on tire loading.
Braking causes weight to transfer forward, compressing the front suspension and shocks, extending the rear suspension and shocks. When cornering, the weight transfers from the inside to the outside, extending the inside suspension and shocks while compressing the outside suspension and shocks. When both braking and cornering take place, as they nearly always do going into a turn, both effects occur. In a left turn, the right front, which is compressing from roll and pitch, and the left rear, which is extending from both factors, are moving the most and will have the biggest influence.
The left front and right rear are receiving opposite movements from roll and pitch, reducing their movement and therefore their influence. This is a very transitional stage and the shocks contribute significantly in this phase of the turn. Note the difference in velocities. On the right it shows each corners max velocity achieved in compression and rebound during this one lap.
Figure 7 Rough Track Histogram. A shock histogram shows the percentage of time the shock spends at each velocity a history of its velocity on paper…histogram…kind of funny. Velocity is across the bottom, percentage is on the left. Figure 6 is from a smooth slick track. When the shocks are valved incorrectly the histogram looks radically different and does not have the preferred normal distribution and bell shaped curve you see in this diagram.
This is called the low speed boundary. The low speed is what the driver feels and the high speed is what affects the chassis when it hits a bump. This is due to the roughness of the track and the fact that shocks are tuned many times for platform control chassis attitude or the car's position. Since the car is racing in a circle and symetry is not needed in our setup, the car is offset to the right.
The top histogram is from a slick track and the shock had more compression in the right front FR , more rebound in the left front FL and low compression in the right rear. Note the use of "FR" for right front because that is how the Motec graph and F1 race engineers reference it. Most likely, that notation started in Europe where their language puts the noun first, then the verb. The percent of time the shock spends in rebound and compression above and below the low speed boundary is shown on the graphs across the top of each corner of the car.
Observing the velocity plot shows that on corner entry, the LF and LR see some pretty high numbers due to the winged down effect. This effect is much higher on slick tracks than on wet tracks. When we change the valving on the shocks, the histograms change significantly.
Many hours have been spent revalving shocks to get the histograms to look the way they do in these graphs. With previous shocks, the histogram of the front shock looked flat, since the low speed valving was way off. Histograms are what all the advanced asphalt teams look to when they tune their shocks. This in combination with driver input are what is used to achieve the lowest lap times.
Shock Position A plot of each corners shock position is very useful to look at as it shows how the car is moving and when each shock is generally in compression or rebound. Before we look at these graphs, realize that, we race on dirt where conditions change all the time, we race on many different shaped tracks, the amount of traction in the track can be drastically different from top to bottom, we sometimes bounce off curbs and berms, and each driver has his own style.
These variables lead to position graphs that make it very hard to derive any generalizations. I have spent countless hours staring at these position graphs trying to come to some sort of true statements that I can make about what ours cars do and when. The top 4 lines are the positions of the 4 shocks. The next group of lines down shows the lateral roll angle of the car. As the car rolls right, the line moves down.
The roll angle is a simple math channel written based on the shock position and a few known static measurements. The next line down is the pitch front to back roll. The lower the line the more rolled to the rear the car is. The bottom group is the g-force, lateral and longitudinal.
Figure 9 shows how much the car rolls left on the bigger track, and for how much longer. It wings left so much that the right front shock is topped out. Using the shock dyno graph, shock position, g-forces, many static measurements, and formulas, math channels can be written to calculate the weight on each wheel as the car takes a lap.
Monotube Vs. Twintube Monotube shocks are also incorrectly known as gas shocks. Both monotube and twin tube shocks use gas pressure. Monotube shocks use high pressure gas nitrogen on the opposite side of a floating piston to keep a constant pressure and volume of oil in the shock body as the shaft adds and subtracts volume when the shock oscillates.
Twin tube shocks use a lower pressure gas in a bag to achieve the same result. Monotube shocks have an advantage of control, since their larger pistons displace more oil for a given stroke. This is especially true for the rebound stroke. The greater the amount of oil moving through a shock's piston, the easier it becomes to regulate the flow and thus control the dampening forces of the shock. Although fading is generally not a problem for micro sprints, monotube shocks also will not fade due to heat.
They stay cooler because the piston and oil are in direct contact with the outside wall of the cylinder allowing for better dissipation of heat. Monotube shocks also last longer because they have less moving parts to wear out.
Gas Pressures The nitrogen gas pressure in a monotube shock is required at all times for it to function properly. The gas pressure can be adjusted to suit various track conditions. Don't have time to search through all the pages in the printed catalogue?
Why not try our brand new online catalogue? It's quick and easy to use. Find a Dealer. Safety Specialist Log-in. Email address: Password:. Not a Monroe Safety Specialist? What do shock absorbers do? Despite popular belief, shock absorbers do not support the weight of a vehicle.
In more detail But it's nowhere near as complicated as it may sound. Types of shock absorbers Although all shock absorbers do the same job, different types of vehicles and suspension designs require different types of shock absorbers which can appear radically different. This is part of the black art of shock absorber tuning. There are a few different methods for controlling damping.
Very high-speed damping is often regulated by allowing maximum flow through the piston holes. For extra high-speed control, some units use remote reservoirs that add another set of pressure valves to the equation.
We refer to this as free bleed or bleed in a shock, it is the larges factor in making grip in a car. To much or to little will change everything in how the car performs.
Low-speed damping occurs when the shock absorber shaft speed is less than a few inches per second. This typically occurs during slalom maneuvers and initial turn-in corner entry.
The car might be moving quickly, but the suspension is moving up and down somewhat slowly. In dirt tack racing this is what gives a car attitude or holds the car in posture; it is also a large factor in grip and the level of grip. High-speed damping occurs when the shock absorber shaft speed is faster than approximately six inches per second. This is the damping that affects how a car reacts to surface irregularities—like expansion joints, potholes or the rough terrain of a rallycross or dirt track surface.
High speed can be overlooked in the fact that it needs to be there to support the low speeds ability to work. High speed gives strength to low speed and the balance of the two together becomes more important as the grip level of the track goes down. Look at the whole suspension as a package when choosing shock absorber valving. The final answer depends on a number of factors, including the suspension geometry, available grip, and weight of the car.
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