http://www.drive.com.au/motor-news/skin ... 0qelg.html
Tyre design is blasting back to the future with car makers set to adopt larger diameter wheels with significantly skinnier tyres than most cars are running today.
Despite decades of tyres getting bigger and wider, there is a new trend towards narrower tyres with a large diameter.
The emerging trend towards skinnier tyres is being driven by a desire to reduce fuel use and carbon dioxide emissions.
Tyre companies, including Michelin (pictured) are experimenting with taller, narrower rubber.
Tyre companies, including Michelin (pictured) are experimenting with taller, narrower rubber.
"This is the new future," said Damien Hallez, Michelin's head of technical communications. "It helps to improve the energy efficiency [and use less fuel]."
Hallez said every centimetre a tyre increases in diameter there is roughly a 1 per cent reduction in rolling resistance (all things being equal), which is the tyres internal resistance that slows it as it rolls across the ground.
So increasing a tyre's diameter by 2 inches (tyre diameters are measured in inches, not centimetres) would reduce that rolling friction by about 5 per cent.
Having less rubber width also brings improves aerodynamics and further reduces rolling resistance.
"Increasing the diameter we gain in rolling resistance without losing all the security aspects of wet and dry grip," said Hallez.
"There's less deformation of the tyre in the compact patch [the part of the tyre that is touching the road at any time] and less deformation in the side walls so that helps to gain in energy efficiency."
He also said skinnier tyres were better suited to dissipating water, therefore reducing the chance of aquaplaning, or skipping across the surface of the water.
"It's like a boat, it's much more efficient [at going through water]."
Renault design boss Laurens van den Acker agreed wheel and tyre designs would continue to get larger in diameter but with skinnier, more energy efficient tyres.
"It is one of those things that is the best of both worlds," said van den Acker. "The designers want big wheel and the engineers and aerodynamicists want narrow wheels.
"It gives you good comfort, it's good for CO2 … because it has less resistance."
Van den Acker said the only potential negative was in braking performance, something that had to be monitored.
But he said the benefits far outweighed the negatives, particularly when it came to aesthetics.
"If the choice was between having large tyres that are a bit skinny or small tyres that are a bit fat I would still go for the large ones because from the side view it is undoubtedly better," he said.
However, because the skinny tyres are still relatively new – despite being similar widths to tyres sold 40 or 50 years ago – van den Acker said there were issues with supply of replacements.
"What's stopping us is not technology, what's stopping us is tyre manufacturers who are just happy to supply the same tyre and the clients who are feeling more comfortable that the tyre can be bought anywhere, so you have to create a market for these special tyres," said van den Acker.
BMW is one of the first manufacturers to use the new breed of skinny tyres in a production car with its upcoming i3 electric car.
The bulbous carbon-fibre-bodied hatchback gets wheels that are 19 inches in diameter – commensurate to the diameter of wheels used on many performance and luxury cars – but the tyres are almost half as wide as some tyres.
At the front the BMW i3's tyres are just 155mm wide, while the rears are 175mm wide.
By comparison the popular BMW 3-Series has tyres that are between 225mm and 255mm wide, while the Holden Commodore tyres range from 225mm and 275mm.
Various concept cars have also used the larger diameter skinny tyres, while Citroen's C4 Cactus uses 18-inch tyres that are just 155mm wide.
Michelin's Hallez said in many cases the contact patch of rubber on the road was similar to a smaller diameter, wider tyre, so grip levels were often not compromised.
Interesting article. Given I have changed my tyres / rims to wider sizes I also find the fuel efficiency claims interesting- as I can't say I've seen any worse economy....
) to get better fuel specs..... at least better on paper! 
But I disagree that you don't need bigger brakes. It's amazing how much better the Kizashi's acceleration and braking gets with 16" wheels. The torque created by a larger wheel does have a huge effect that imo needs changes in the brakes to still be safe.