What Drives Sizing - Tire Review Magazine

What Drives Sizing

ition of rim diameters, profiles, widths or even tire appearance in some time.

While attending a recent auto show, the wide variety of new tire sizes was impressive. As you might expect, futuristic concept cars, SUVs, and light duty pickups provided the most expansive array of new tire designs and sizes. Aggressive, macho and rugged are descriptions that come to mind for some of these futuristic models. With most of these prototypes, it’s all about style, bragging rights and marketing push, with vehicle manufacturers trying to outdo one another.

Production models, however, weren’t far behind. Bigger diameters, expanded widths and futuristic tread patterns were in abundance. Some models were fitted with 24-inch wheels, and production options of 20-inch wheels on sporty pickups are available now.

In many cases, the plus one and plus two upgrades from the standard tire/wheel packages, previously the turf of specialty tuners and high performance tire dealers, are now available by simply specing an option package.

Commercial truck tire sizes, on the other hand, evolve slowly and rely more on market pull-through from end users. Major tire changes don’t take hold unless one can prove the value of the design or size change in dollars and sense terms – maximize tire cost/mile while minimizing any investment cost associated with the change.

Consider the history. Tubeless designs became popular during the mid- to late-1970s, coincident with the move from bias to radial construction.

This wasn’t a monumental change for manufacturers, however, as most actually used the same molds (with different lower sidewall rings) to manufacture, for example, 10.00R20 tube-type and 11R22.5 tubeless sizes.

The next major change – low profile highway service designs ®“ came in the 1980s. The same 22.5- and 24.5-inch wheel diameters and popular 8.25-inch rim widths were maintained, but with slightly shorter overall height. The lowered ride height and reduced weight low profile radials delivered allowed fleets to increase payloads.

Still smaller diameter 19.5-inch tires and wheels were introduced to the line haul market about a decade ago. These smaller tires, however, have failed to expand beyond niche applications despite treadwear, casing durability and vehicle handling performance that is fairly equivalent to that delivered by 22.5-inch counterparts.

The increased cube capacity and lower unsprung weight typical of these smaller diameter tires would seem to be attractive to productivity conscious users. But the need for non-standard brake hardware and the lack of on-road emergency replacements are major stumbling blocks.

From fleet cost angle, these tire design or size changes can face another Catch-22. If fleets don’t seem interested in specing new fangled tires, retreaders won’t devote capital and plant space to retread the casings. And if a ready supply of retreads isn’t available, fleets aren’t likely to adopt the new tires.

Understand the Limits

Forecasting future commercial tire trends also requires an appreciation of limitations imposed by related axle-end and driveline hardware and an understanding of industry resistance to adopt new componentry without proven cost benefits and demonstrated long-term durability.

Some other key considerations are:

®′ Life cycle costs

®′ Required changes to driveline components (axle ratio, U-joints, clutch)

®′ Brake hardware compatibility

®′ Net change in dock height, overall vehicle height, and underside truck/trailer ground clearance

®′ Axle use interchangeability (steer/drive/trailer)

®′ Effect on fleet component standardization and maintenance costs

®′ Effect on vehicle trade/resale value

Today’s commercial trucks are products of considerable evolution, not just in basic design but also in many of the core components. These parts and systems are often sourced from numerous outside vendors and not from the vehicle manufacturer.

Therefore, the coordination of engineering, testing and compatibility issues tends to be more complex and time-consuming than with passenger vehicle manufacturers, which are more vertically integrated in their R&D programs and accustomed to model year changes that include major redesigns.

The new generation super wide single drive and trailer tires are an excellent example of this. To take full advantage of this new tire technology, fleets and OEMs had to consider the potential redesigns of wheels, hubs, bearings, axles, brakes, on-board inflation systems and other components. Much resistance was eliminated because the new super wides match popular low profile dual sizes, and because drum and disc brake packages used with current duals are compatible with the super wide wheels.

Justify Deviation

During any technology transition phase, whether its tires or engines, most end users want to retain as much of the time-proven componentry as possible to contain costs and protect vehicle resale value.

Modern over-the-road trucks utilize many components that are readily available from numerous vendors. This helps contain maintenance costs, minimize downtime and improve resale opportunities.

Any deviation from "popular spec" components needs to be justified. The changes must be either due to specific service requirements or because they provide cost benefits in an acceptable payback period.

An excellent example of this is the use of 19.5-inch tires on auto transporters. Non-standard brake packages, wheels, axle ratios and other components are required, but resale value is a low priority because these specialized vehicles have very long life cycles and have a limited resale market.

But without the shorter 19.5-inch tires, these transporters couldn’t handle taller SUVs and still allow the transporter to meet legal height and ground clearance requirements. The trade-off benefits favor the smaller tires.

Tire innovations for North American commercial vehicles are primarily end-user driven, based on productivity and life cycle cost needs. That’s a good thing since it helps control transportation costs, ultimately making our products more competitive in the world marketplace.

While slow to change, the trucking industry still relies heavily on innovative manufacturers to propose and deliver new technologies for evaluation.

Historically, nearly all successful, significant commercial tire changes came only after they demonstrated clear-cut economic advantages.

Just like back on the farm, the cream always rises to the top.

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