What are the main limitations of conventional double-wishbone suspension systems?
In essence, a tyre that is held in optimum contact with the road will have its tread used in uniform shear and so withstand the greatest possible loading and provide the highest possible grip. It is obviously therefore vitally important that optimum contact is provided whenever maximum grip is likely to be a requirement and particularly during acceleration/braking and/or cornering. But it is precisely during these modes of operation that the footprint of a conventional double-wishbone suspension system becomes compromised.
The almost universally adopted unequal-length double-wishbone design can achieve quite effective camber correction when in roll (cornering) by means of its shorter upper wishbones and the tighter arcs that they describe. However, this direct link between camber change and suspension movement obviously can't be miraculously broken when the vehicle starts to travel in a straight line. As a result, unwanted camber changes occur as the suspension compresses under acceleration or braking that inevitably compromise grip. The way to reduce these unwanted camber changes has traditionally been to inhibit suspension movement by substantially increasing spring rates and/or building in further geometric compromise. Both methods, in themselves, having negative implications for grip with ride quality being an early casualty on all but the smoothest of surfaces.
Alternatively, a double-wishbone suspension system that has parallel arms of equal length is clearly capable of providing an excellent footprint with the road when the vehicle is traveling in a straight line. Cornering performance however is certain to be severely compromised due to the adoption of adverse camber when in roll. Similarly, the only solution is to try to eliminate body/chassis roll (not helped by the very low roll centre provided by such a system) and with obvious consequences for ride quality and ultimate grip.
The Camber Compensation & Anti-Roll front suspension system of the DAX Tojeiro (Jaguar XJ40/X300 - based).
What does the CC&AR system do that a conventional double-wishbone suspension system doesn't?
The CC&AR system essentially ensures that the best possible contact is provided between tyre and road regardless of whether the vehicle is accelerating/braking and/or cornering. No longer is it necessary to sacrifice performance in one mode of operation in order to maximise that in another.
In particular, braking/tractive performance and general predictability/control (even at and beyond the limits of adhesion) are all noticeably enhanced when compared to a conventional unequal-length double-wishbone design.
Springing can be kept softer with additional benefit to both grip (particularly on uneven and/or wet surfaces) and of course to ride quality.
Roll is effectively countered (again without loss of ride quality) due to the system's naturally high roll centre and by making use of the forces generated during cornering. Further details of this and other CC&AR system benefits can be seen in our 'How It Works' section.
An example of a CC&AR front suspension system with inboard coil-over dampers – as featured at the front end of Duncan Cowper's latest DAX Rush MC Hayabusa turbo.
Do the wheels of a vehicle using the CC&AR suspension system always remain upright, even when cornering?
It depends. In a rear application of CC&AR, the system would normally be configured to keep the wheels perpendicular to the tarmac at all times. For a front application, however, the system can usefully be configured to provide different camber in different modes of operation.
The CC&AR systems designed for the front of the XCS 427, DAX Rush and Tojeiro, for instance, are configured to provide a small and unchanging amount of negative camber when traveling in a straight line which is supplemented on lock through the interaction of caster and KPI. No anti-roll bars are fitted or required as is the norm for CC&AR equipped cars.
Visitors to our site may be interested in clicking on the following two links. Both will take them to YouTube and some motion footage, posted by DAX Rush owners, of the CC&AR systems fitted to the front of their DAX Rushes. One is of Jason Baker's Honda S2000-powered Rush and the other of a French gentleman's Hayabusa-powered Rush MC.
Does the CC&AR system provide perfect contact in every situation?
No, it is obviously impossible for any suspension system to take account of every imperfection in the road surface but CC&AR will naturally provide a predetermined average that is hugely closer to the ideal than any conventional suspension design.
Clearly, one of the greatest strengths of the CC&AR system is its innate ability to provide the best possible geometry (and footprint) on all occasions where maximum grip may be required – i.e. during acceleration/braking and/or cornering. In fact, it is only during the lesser event of one-wheel bump that the CC&AR system is not able to improve upon the geometry of a conventional double-wishbone design. And as the inputs here are by definition momentary and invariably of much lower magnitude, it is perhaps not surprising that this has not been found to be of consequence.
Indeed, those racing CC&AR equipped cars will invariably make special mention of the superior grip and composure provided over rumble strips – in part due to the much softer springing allowed by the system. (See the link provided in the answer below.)
The spring rates used on a typical CC&AR track car can appear unusually soft. Whatever the benefits, doesn't this make the car more difficult for the driver to control?
Surprisingly for those unfamiliar with CC&AR, the answer is no.
Even when softly sprung the CC&AR system will always provide a notably constant footprint and a low level of roll. Good composure, predictability and control are all natural and strong system characteristics and it is unnecessary (and, for obvious reasons, counterproductive) to follow the usual practice of fitting springs with ultra high rates for track use.
You may like to click on the following link. It will take you to YouTube and some in-car footage recorded over a couple of laps of the Bedford Autodrome circuit aboard Duncan Cowper's Hayabusa turbo Rush.
In fact, it was one of these laps on a still damp track that secured Duncan the top spot on the MSV ‘How Fast’ leaderboard in October 2015 with an amazing time of just 1minute 14.593seconds. An incredible achievement for a road-going sports roadster - albeit one with 340bhp on tap at 1.1bar of boost!
Of particular relevance to the viewer here are the softness of the springing, the lack of roll (no anti-roll bars fitted) and the general level of composure provided – especially over rumble strips.
Can CC&AR be fitted to any car as an alternative to a conventional unequal-length double-wishbone system?
Yes normally, but the upright used must meet specific requirements to be suitable for use in a CC&AR suspension system and the geometry of the system itself obviously differs from application to application and needs to be established for each. There must also be sufficient room for the system’s cross-links to be accommodated – but this is rarely a concern.