IT’S hard to find cross-ply tyres these days because tyre manufacturers simply don’t make them for cars anymore and there is a very good reason for it; performance.
Today’s entry-level family cars can cruise at 140kph without a second thought, and many can clock 200kph if pushed.
To put that into perspective, at the start of the steam locomotive era, the general understanding was that speeds in excess of 30kph is really unsuitable for human beings and anything that goes beyond 60kph was thought capable of inducing general mental instability and madness.
What we now accept in terms of family car performance parameters were sportscar numbers from four or five decades ago.
With increasing speed, the quality and capabilities of tyres become ever more critical to the level of safety that the car can afford the driver and occupants, since most cross-ply tyres have a speed rating of 100km/h or less.
Cross-ply tyres are still used in heavy duty vehicles that work in rough areas because they have a more rigid sidewall construction and can resist heavy loads better.
Cross-ply, bias-ply or radial-ply are terms used to describe tyre construction.
At the heart of every tyre is a series of fabric and metal belts that are laid in some fashion to create the size and determine the strength of the tyre.
In cross-ply tyres, the fabric belts are laid down in a criss-cross around the tyre and they form part of the side wall. This continuous coverage from tread to sidewall create a strong and rigid tyre, an important consideration in the early days of pneumatic tyres.
Rigidity is good to a point, but as cars became faster, the rigidity of the tyre reduced its ability to respond to steering inputs. The heavy construction also meant higher heat build-up.
Tyres deform slightly at the point of contact with the road due to the weight of the car.
At high speed, the constant rubbing between the plies generate a lot of heat; constant 100kph driving was enough to cause blowouts.
The rigid sidewall meant the tyre itself resisted directional change due to the mechanical forces interacting between the tyre and the road and this made them unsuitable for high-speed driving.
However, early radial-ply tyres were known to suffer from weak sidewalls, the softer sidewall which allowed for more subtle steering inputs was also its main Achilles heel.
When Michelin introduced the radial-ply, it was first used on the Citroen 2CV, a car that is commonly used for farm implements than family cars we see today.
On the low-speed, low performance 2CV was fine, but on bigger and more powerful cars, manufacturers had to find a solution for the weak sidewalls.
When Lancia needed a radial-ply tyre for their legendary Stratos, Pirelli took a year to work out the problem. The power of the Stratos chewed up radial tyres in less than 10km due to the ultra-wide nature of the rubber.
Today, you can find cross-ply tyres made by specialty manufacturers for classic cars. If you want absolute faith in recreating the driving feel of cars from the 1970s or earlier than these, older tyre designs are a must.
They don’t offer any form of performance advantage and the driving pleasure is slightly better, thanks to taller sidewalls that have a bit more give than shorter radials.
But the main reason for choosing cross-ply for your classics is that it offers bragging rights for those who want absolute faith in specifications.
Radial tyres and their soft sidewalls do make some veteran motorists feel nervous, thinking that the tyres are slightly under inflated, so there is a small visual advantage to cross-ply rubbers.
Dunlop and Goodyear still offer cross-ply tyres for classic cars in limited production and there are several specialist manufacturers that cater to the vintage and classic market.
If you are a serious concourse competitor, a set of cross-ply is absolutely necessary for shows and you can keep a set of radials for actual driving because radials last longer due to greater tread stability and lower heat build-up that result from the construction method.