If you look in a race car you'll see a whole variety of things that can be adjusted. Foremost in any current car will be the variables in the engine management system - there are literally hundreds of different factors that can be changed to allow the engine to better develop power. And the adjustments to the aerodynamic trim are also many and varied. But let's look at something a little less esoteric - the suspension. A sedan-based race car usually has adjustment for the ride height, spring rate, bump and rebound damping rates, front and rear sway bar stiffness, and - if it's counted under "suspension" - the front/rear brake bias. While some of these are set by the mechanics in the pits, the sway bar stiffness and brake bias are normally driver-adjustable.
When I interviewed an Australian 5 litre V8 SuperCar driver a few years ago I commented on the long, boldly detented levers that were mounted on the transmission tunnel. They were made so that a gloved hand could swiftly but surely make changes to sway bar stiffness in the turmoil of racing. What was the go with these levers? I asked. Were the bars adjusted as the tyres went 'off' or as the fuel load changed during the race? Yes, said the driver, but I also change the sway bar adjustment from corner to corner!
Gulp!
That idea has stayed with me - the optimal set-up of the car varies, depending on the exact nature of the corner being negotiated. And that seems to make sense. So why do such few road cars - even highly modified ones - have any in-cabin driver adjustment of the cornering balance? Surely it would be A Good Thing?
And it definitely is good! Those of you who have read
my story
on the torque split controller than I developed for my Skyline GT-R will know that I have on-dash control that determines how much torque goes to the front wheels when cornering. At position '0' on the 10-point scale, the back will arc out in first and second gear power slides, while at higher knob numbers the front will pull the car straight, letting full power be put down while the car remains neutral in attitude. Too high a setting on the dial will result in much power understeer.
The first version of the torque split controller had a round adjustment knob on the centre console. However, I found that quick changes on the move weren't possible - I had to look away from the road to see what setting I'd made after twiddling it. The second version mounts the knob much closer to the driver, and also uses a knob design whose setting can be worked out by feel alone. That means that I can confidently reach down, change the torque setting, and then place that hand back on the wheel knowing what change I have just made.
And after nearly a year of driving the car like that, guess what - I often change the control to suit the approaching corner! If it's a very tight hairpin I dial in less front wheel torque. The car turns in better and a touch of power oversteer cancels any front-end push. And it's not just different corners that use changed settings. If it's a hot day - as with any turbo car - the GT-R's power is noticeably down. That means that there isn't the same urge to kick out the tail on roundabouts and the like, so again I dial in less front torque. With the setting left as for cold days the car noticeably understeers. And - obviously - when it rains I set the car to be very much in four wheel drive.
There are other subtleties too. As the tyres wear, more and more front wheel torque is needed to keep the car balanced. Fit new tyres, and immediately the knob comes back 4 or 5 positions. The reasons for all of this are a little more complex than they first appear - the 4WD system detects variations in front/rear tyre speed (amongst other factors) and shuffles the torque around accordingly. So it's not just lateral grip that is affecting the handling balance, but also the tyres' torque transmission to the pavement.
OK, so the GT-R is an unusual car in its drivetrain. But I reckon that driver-adjustable front and rear sway bars on a conventional FWD, RWD or constant 4WD car would make changes to the car's handling in much the same kind of way. And even if you're an enthusiastic driver, I reckon that you might end up changing those bar settings a lot more frequently than you might first think...
So how are sway bars (or anti-roll bars, or anti-sway bars, or stabiliser bars!) made adjustable? Typical in a race car applications is the use of blades. These are flat pieces of bar that connect the ends of the sway bar to the suspension (or bodywork), forming the levers that twist the sway bar. The flat blades can be rotated, all the way from the flat part being parallel to the ground right through to the blade being at right angles to it. When the blade is orientated so that its edge is vertical, it acts as a very stiff link to the sway bar - the anti-roll affect
is high. When the blade is positioned so that its flat is parallel to the ground, the blade is more flexible, so the anti-roll affect isn't as great. Rotating the blade therefore adjusts sway bar stiffness.
Another way of changing sway bar stiffness is to have a number of holes drilled in the arms of the bar. The link that connects the bar to the body can then be connected at different positions along the "lever" portion of the sway bar, changing its effective stiffness. This is fine when there's the time and inclination to get out the spanners, but it doesn't allow on-the-move driver adjustment.
Another approach is to use a collar that slides along the lever portion of the bar. The set-up shown here doesn't actually use that approach (the collar is bolted into place) but you can clearly see that the collar could be moved along the bar by an appropriate screw and thread acting on it.
So that's how it can be done - but what about on a road car? The answer to that is that all of the quoted techniques don't lend themselves well to on-the-move changes when the mechanism must also be absolutely reliable, endure dust and water, be effective, and be cheap! So if you've developed an adjustable sway bar approach suitable for a road car (or know of a commercially available system) I'd love to hear from you.
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