OKZCC Technical Notes & Tips

When vehicle manufacturers select a tire size for a vehicle, they evaluate the vehicle's gross axle weights, the anticipated use of the tire, and the tire diameter and width. Adjustments to these factors give the manufacturer a way to improve handling and appearance. This is especially true for performance tire sizes. The size selected is rarely limited to only one capability (i.e. carrying the vehicle's weight).

The tire usually needs to have additional load capacity as well. This extra capacity is important because without it all of the tire's performance would be used up just carrying the weight of the vehicle and little would be left for durability at high speeds or responsive handling. For all vehicles produced since 1968, the original tires sizes and inflation pressures (including the spare) are listed on a vehicle placard. This placard can be located on:

The driver-side door or door jamb (Ford vehicles on the rear passenger door jamb)
Glove box or console door
Fuel filler door
The engine compartment

Additionally, some manufacturers also list the original tire pressure in the vehicle's owner's manual. If a car's inflation pressure has varied from that which was recommended by the manufacturer, it's likely that the tire's wear and performance characteristics have also changed.

Under-inflation

If your vehicle's tires are under inflated by only 6 psi it could lead to tire failure. Additionally, the tire's tread life could be reduced by as much as 25%. Lower inflation pressure will allow the tire to deflect (bend) more as it rolls. This will build up internal heat, increase rolling resistance and cause a reduction in fuel economy of up to 5%. You would find a significant loss of steering precision and cornering stability. While 6 psi doesn't seem excessively low, remember, it usually represents about 20% of the tire's recommended pressure.

Over-inflation

If your tires are over inflated by 6 psi, they could be damaged more easily when running over pot holes or debris in the road. Higher inflated tires cannot isolate road irregularities well causing them to ride harsher. However, higher inflation pressures usually provide an improvement in steering response and cornering stability up to a point. This is why participants who use street tires in autocrosses, track events and road races, run higher than normal inflation pressures.

Effects of Time and Temperature

Tire inflation pressures change due to time and temperature. Tires lose about 1 psi per month due to air escaping through the rubber as it stretches. If you were to check your tires only every six months, it would not be uncommon to find them under inflated by as much as 6 psi. Tire inflation pressures also fluctuate with changes in the outside air temperature. This occurs at a rate of about 1 psi for every 10°F (plus or minus). So the tires you set correctly with an 80°F ambient temperature will be under inflated by 6 psi at 20°F.

If you add the variations of time and temperature together, it is easy to understand why a tire's inflation pressure should be checked frequently. Improper inflation can cause tires to wear irregularly and can void manufacturer's warranty.

Another advantage of checking tire pressure frequently is that it allows a slow leak to be found and repaired before it permanently damages a tire. Tire pressures should be checked once a week, preferably before the vehicle has been driven. Spending about two minutes a week will help you get the optimum performance your tires can offer!

These tires are airless and are scheduled to be out on the market very soon.

The bad news for law enforcement is that spike strips will not work on these tires.

This is what great R&D will do, and just think of the impact on existing technology:

A. no more air valves...
B. no more air compressors at gas stations...
C. no more repair kits...
D. no more flats...

These are actual pictures taken in the South Carolina plant of Michelin.

(From GIZMAG) Michelin has showcased a potentially disruptive technology with significant ramifications for the future for mobility: an airless, integrated tyre and wheel combination dubbed the TWEEL (i.e. Tyre/WhEEL) . The Tweel promises performance levels beyond those possible with conventional pneumatic technology. The first commercial applications of the Tweel will be in lower-speed, lower-weight vehicles such as the iBOT mobility device and Segway's Concept Centaur. Designed by Segway-inventor Dean Kamen, the iBOT mobility device has the ability to climb stairs and navigate uneven terrain, offering mobility freedom impossible with traditional wheelchairs. Additionally, Segway's Concept Centaur, a prototype that applies self-balancing technology to a four-wheel device, has also been equipped with Tweel to increase its performance potential.
Beyond these first real-world applications, Michelin has additional projects for Tweel on construction skidsteers and a variety of military vehicles.

Historically Significant

"Major revolutions in mobility may come along only once in a hundred years," said Terry Gettys, president of Michelin Americas Research and Development Center in Greenville, S.C. "But a new century has dawned and Tweel has proven its potential to transform mobility. Tweel enables us to reach levels of performance that quite simply aren't possible with today's conventional pneumatic technology."

The most intriguing application may be Michelin's early prototype Tweel fitment for passenger cars. The mobility company released video of promising Tweel performance on an Audi A4.

"The Tweel automotive application, as demonstrated on the Audi, is definitely a concept, a stretch application with strong future potential," said Gettys.

"Our concentration is to enter the market with lower-speed, lower-weight Tweel applications. What we learn from our early successes will be applied to Tweel fitments for passenger cars and beyond."

Benefits of the Tweel

The heart of Tweel innovation is its deceptively simple looking hub and spoke design that replaces the need for air pressure while delivering performance previously only available from pneumatic tires.

The flexible spokes are fused with a flexible wheel that deforms to absorb shock and rebound with ease. Without the air needed by conventional tires, Tweel still delivers pneumatic-like performance in weight-carrying capacity, ride comfort, and the ability to "envelope" road hazards.

Michelin has also found that it can tune Tweel performances independently of each other, which is a significant change from conventional tires. This means that vertical stiffness (which primarily affects ride comfort) and lateral stiffness (which affects handling and cornering) can both be optimised, pushing the performance envelope in these applications and enabling new performances not possible for current inflated tires.

The Tweel prototype, demonstrated on the Audi A4, is within five percent of the rolling resistance and mass levels of current pneumatic tires. That translates to within one percent of the fuel economy of the OE fitment.

Additionally, Michelin has increased the lateral stiffness by a factor of five, making the prototype unusually responsive in its handling.