If you followed the build of our Mighty Car Mods "240Z" you would have seen that we bought a classic 1975 Nissan/Datsun S30 240Z Fairlady off the internet. Then we flew over to Japan to service it, throw it on a race track and then and imported it back to Australia. Due to Australia’s import laws relating to asbestos, we couldn’t easily keep the original 2 litre engine so with the help of some mates we installed a turbocharged RB26 engine from a Nissan Skyline GT-R, and replaced pretty much every piece of drivetrain, suspension and braking componentry to ensure the vintage machine could handle having more than three times its original power. Our final power figures came out at around 330kw at the wheels in a car that weights around 1100 kilos. To put this into perspective, the power to weight ratio is similar to that of a Bugatti Veyron.
A large part of this upgrading process was replacing the Japanese tyres with modern high-performance Bridgestone Potenza RE003 rubber. Although the bias ply tyres which came on the S30 looked to have decent road-legal tread depth, the age of it made it necessary to install some new rubber.
We also got a good look at just how far tyre technology has come in the last 45 years when we discovered the Zed’s original spare wheel in the boot, which was still wrapped in the original Bridgestone Super Speed-5 bias-ply tyre! The Super Speed-5 is the same model of tyre which was fitted to the highly desirable Z432 high-performance variant of the S30 Fairlady when it was launched at the 1969 Tokyo Motor Show, and is a thoroughly out-dated piece of equipment today thanks to evolutions in tyre construction that make tyres safer and able to handle higher power and speeds.
While the first commercially successful pneumatic tyre appeared in 1888, and the first pneumatic car tyre was released in 1895, the largest leap in tyre technology happened in 1946 with the development of a new type of tyre construction, called the radial-ply. Traditionally car tyres had been made using bias-ply (or cross-ply) construction, which offered smooth ride but wore out faster and were more prone to sudden, catastrophic blow-out failures.
The key difference between how a radial or cross-ply tyre is made comes from how the piles of cord in the tyre’s carcass are arranged. The cords give the tyre carcass form, and radial tyres run their cord at 90-degrees to the direction of travel to provide lower rolling resistance, improving fuel efficiency. Radial tyres also feature woven steel belts as part of the carcass, to help strengthen the whole tyre.
While the radial tyre was quickly picked up in Europe, the UK and Asia by the 1950s, American automobile manufacturers resisted until public pressure peaked in 1968 to switch over to the safer, better-performing radial tyres.
Bridgestone had launched its first radial tyre, the RD10, in 1967, although many Japanese cars still featured cross-ply tyres if they were being sold into the American market. This is why it is highly likely the Super Speed 5 tyre found on the MCM 240Z’s spare wheel is the original item.
While it may be tempting to fit a vintage tyre for 'period correctness' the reality is the rubber will have dried out and be unsafe to use at speed, risking a blow-out occurring. After all the hard work we put into our classic Fairlady, we’re definitely not going to risk destroying it for the sake of one old tyre! The RE003s have worked brilliantly on the road and on the track with so many of our cars, and with the power available from the RB26, we might need some wider ones soon!
Marty & Moog
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