Friday, May 30, 2008

Using the suspension to set up F1 car


A Formula One car is almost infinitely adjustable so that it handles according to the demands of the track, conditions, and the driver. The set-up of a car refers to particular settings: wing settings and suspension. The necessary balance between cornering downforce and straight line speed is determined by wing settings (see the section “Wings and underbodies”, earlier in the chapter). But this is only part of the set-up. The more complex part is that of suspension.
In general, the suspension set-up is determined by balancing two aims which are frequently at odds with each other: the need to adequately support the cornering and braking force of the car and the need to achieve the necessary responsiveness of handling. A circuit generating high aerodynamic loadings, for example, generally demands stiffer springing, but this can cause problems in slower corners where the suspension needs to be more supple in order to enable the car to brake well and to ensure good direction-changing response to the wheel. Achieving a good set-up invariably involves finding the best compromise. Achieving maximum grip is obviously important, but getting the best handling balance is even more so.
Driven to its limit, any car will surrender its grip at either the front or the back. There is no such thing as a car with unlimited grip, and any racer worth his salt soon finds where the limit of grip is. This is where the handling balance takes over. Handling balance refers to whether the car runs out of grip at the front first and understeers (that is, tries to run straight-on when asked to turn) or surrenders grip at the rear first and oversteers (turns more than asked). A very narrow window of neutrality exists between these two states, where both ends of the car surrender their grip at the same time, and the car drifts, but this state is rarely seen with modern cars. Driver preferences and the timing monitors determine the best handling balance for a given car and track at a given time. In terms of wing settings, oversteer can be tamed by using more rear wing or less front. Understeer would be countered by more front wing or less rear. But playing with wings is the easy – and usually less efficient – way out of a handling imbalance, because it involves screwing up the ideal downforce/straight line speed trade-off So for a given wing set-up, the handling is usually fine-tuned with the suspension. The suspension components that are used to determine handling balance are the following:
  • Springs: A spring that’s not stiff enough under cornering doesn’t properly counteract the car’s tendency to roll, moving its centre of gravity outwards and quickly overwhelming the outer tyre’s ability to keep a grip on the road. A spring that’s too stiff slows the transfer of load from the inner to the outer tyre too much; as a result, the outer tyre isn’t being loaded enough to achieve its potential before the corner is over. However, the spring rate that’s just right for one corner on the track may be wrong for the next one, because of the corners different shape and speed. To further complicate matters, the difference front to rear must be considered as well. If the spring rate at the rear is just right, both toostiff or too-soft at the front produces understeer. If the front rate was just right, both too-stiff or too-soft at the rear produces oversteer. The driver and his engineer need to find a compromise over the many and varied corners of the track; this compromise may involve surrendering some grip from one end of the car to get the desired balance. At circuits with a wide variation of corners, variable rate springing may be used to give a relatively soft spring at low speeds but a stiffer one at high speeds.
  • Dampers: Dampers don’t determine a car’s grip as much as they determine how much of the grip the driver can access. The dampers offer a very effective way for drivers to fine-tune the car’s handling in the limited time of a practice session. The damper is adjustable in the bump phase of its progression (as it absorbs the initial bump) and in the rebound phase. These adjustments can be made in two ranges – low speed and high – to give four-way adjustment. The damper is also adjustable within the overall range of frequencies in which it works, although this involves fitting different internal valves – not normally something done during practice. A driver might soften the bump rate if the car’s trajectory is being affected by bumps in the braking or cornering zones or if he wants to use more kerb without being thrown off line. Softening the damper’s bump rate allows the spring to smother more of the bump’s effect. A driver may increase the damper’s rebound setting in order to keep the nose of the car down after he has finished braking to help him get the car turned into the corner. In addition dampers include “blow-off valves”. These valves enable the damper to ignore any out-of-range inputs so that, for example, a severe kerb can go undamped beyond a certain range and so not compromise the settings needed on the rest of the track.
  • Arms: The linkage formed by the suspension arms and how they interact front to rear have a direct bearing on the overall handling characteristics of the car. The geometry of the wishbone linkages determine the roll centre of the car. The roll centre is an imaginary, but accurately defined, point on the centre-line of the car around which the car rolls on its suspension. The roll centre can be high off the ground, low, or even underneath the ground (it’s only imaginary, remember). A line connecting the rear suspension roll centre with that of the front is called the roll axis. If the axis runs nose-down, the car tends to oversteer. If the axis runs nose-up, the car tends to understeer. These linkages are intrinsic to the car’s design and can’t be changed during a race weekend, but some adjustment can be made to the car’s ride height (the height above the ground of the car’s underside) via the suspension’s pushrod. The closer to the ground, the more grip but the less the car can tolerate bumps and kerbs. The camber of the wheels can be altered by adjusting the wishbones so that the highly-loaded outer wheel becomes upright under cornering and uses more of the tyre’s width rather than just the outer edge. (Here, camber refers to when the wheels aren’t perfectly upright, but run at an angle to the road surface, usually with the bottom pointing in slightly.) The downside of altering the camber is that it makes the car less good under braking.
  • Roll bars: Roll bars have a big effect on the car’s handling, particularly in the first part of a corner as the driver turns in. The bar’s primary function is to keep roll under control, but the way it does this also results in cornering load being transferred from the inner tyre to the alreadyloaded outer tyre. If the spring rates aren’t too stiff, this detracts from ultimate grip. Taking grip away from the front or the rear by increasing the stiffness of the roll bar gives the driver another tool in adjusting the car’s handling balance.

2 comments:

Dante Mallet said...

Handling is one of a car's many factors that should take notice. Negligence of this can bring a driver to life-threatening incidents, most especially with quick cars like in the F1. This has been proven many times before and road accidents are the proof. It proves that even professional drivers can crash in a blink of an eye. So average drivers like us should always take extra care when driving.

Dante Mallet

Dwayne Charles said...

The suspension is one of the great tools for setting up and F1 car. I think that the formula one can run faster and smoothly with the best suspension installed.
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