Today we all know that radial tyres give longer tread life, better handling, and a softer ride at medium and high speeds. They are of course far superior to the older style bias or belted-bias tyres. The radial tyre has the carcass plies laid across the circumference of the tyre from bead to bead. Two or more belts are also laid under the tread. This tyre construction gives strength to the sidewall and greater strength to the tread.
Because there are different types of tyre designs, handling characteristics of each design will differ. The suspension set-up is crucial to how a car performs on the road and around corners. And Radial Tuned Suspension was one that had been specifically designed to suit the handling characteristics of the radial tyre.
When the 1977 - 1978 Holden HZ sedan was introduced, there was plenty to celebrate with the new model. Arguably the most important new feature was Radial Tuned Suspension (RTS), which created a revolution in Aussie big car design. Until the Holden HZ, Australian motorists had become used to grappling with the understeer characteristics of many big sedans driven in Australia. It was the Radial Tuned Suspension system which helped tame the large Holden sedan, giving it precise and predictable handling.
The car’s suspension was tuned to ride on radial specific tyres. RTS offered such technology as anti dive geometry, stabilizer bars front and rear and a panhard rod rear end. Having the car suspension set up for using a specific tyre design is a safe way of ensuring that the handling remains as sharp as possible. Until the HZ, Australian motorists had become used to grappling with understeer on every country drive, but the Radial Tuned Suspension system tamed the large Aussie sedan, endowing it with precise and predictable handling. The fact that all other local car manufacturers were forced to rush handling modifications into their cars proved just how right GMH got it.
RTS was also fitted to the TD Gemini and LX Torana. With the introduction of the UC Torana/UC Sunbird range came phase two of the General's RTS suspension programme. We've covered RTS changes in other articles on this site, suffice to say that GM improved an already good handling car even further. But while the car may have been better, sales never reached expectiations leaving the good folk at Fishermens Bend somewhat disappointed.
Press Release from Holden on Radial Tuned Suspension
"All components are carefully engineered to increase Holden's confident handling."
The design of modern automotive suspension systems has reached a high degree of sophistification in Holden vehicles. Through the use of advanced computer simulation and technology, improved manufacturing materials and design, and highly skilled automotive suspension engineers, GMH was able to develop Radial Tuned Suspension. Each suspension component - even the frame and body it'self - had to be examined in detail and re-engineered as required in order to create RTS as a complete system. Neutral handling behaviour is the most important benefit of RTS, this means, in essence, that Holden will do what you want it to, and nothing unexpected will occur.
By relocating the front upper control arm bracket for positive castor, we reduced understeer. In addition we increased static camber and decreased dynamic camber and toe change reducing the tendancy of cars to "plough" toward the outer edge of the corner. The front and rear stabiliser bars reduce body lean and are synchronised to transfer cornering load for neutral handling behaviour. RTS permits smooth ride without sacrificing good handling. Deeper four-coil suspension contibutes smoothness and improved road-handling, while larger front compression bumpers reduce dynamic suspension travel and improve ground clearance. The re-tuned, larger diameter shock absorbers have less fade, retaining effectiveness over rough terrain. As a result, tyres maintain contact with rough road surfaces, the ride is smooth and the driver stays in control.
High response steering results from the reduction of compliance, or "flex", throughout the system. Holden's steel belted radial tyres fitted on wide rims hold the tread to the road surface while cornering, rather than rolling under as do conventional cross-ply tyres. Front and rear suspension bushings are less compliant in cornering, while retaining longitudinal softness for smooth ride in normal driving. High cornering force ultimately results from the degree of tyre adhesion to the road. This is increased by the use of steel-belted radial tyres, and the rest of the RTS system is designed to get the most from them. For one thing, the wheel rims and tyres have a revised offset giving Holden a wide-track. Larger diameter shock absorbers help keep the tyres on the road when it is rough. And again, the re-engineered castor and camber retain the proper wheel geometery to get the most from the steel belted radial tyres.
"Anti-dive" controls the amount of front end diving while braking for a greater feeling of control. Reduced body roll (or "lean" in corners) is accomplished by front and rear stabiliser bars working togther with re-engineered 4-coil suspension. Maximum straight-ahead stability is the result of several RTS suspension components. Steel belted radial tyres, for example, are best in this characteristic. Where conventional cross-ply tyres will tend to pull the car to the right or left in tram tracks or pavement edges, the radial steel plies in Holden's tyres tend to retain straight-ahead direction. Positive castor and negative camber also help keep the wheels straight ahead without driver effort. And all of these characteristics help retain straight-ahead stability in a sudden gust of wind, or the buffering from a passing truck.
A few more benefits of RTS are worth noting. Our tests indicate that Holden's steel belted radial ply tyres increase the kilometer per dollar investment ratio in each tyre by 47%, and the fuel economy by 5% over the biased ply tyre. The durability of the suspension system has been increased. Road noise and vibration has been further reduced. And optional power steering has been redesigned for improved on-centre feel and more predictable driving control.
But it is all the components working togther as one system, which have made today's Holden the best handling cars and wagons we have ever built.