The medium-duty world is dominated by the rental and leasing sectors and the pickup and delivery sector, at least in terms of the Class 5-7 trucks using 17.5- and 19.5-in tires.

What they wanted dictated what the tire makers delivered. And until recently, that crowd wanted a bulletproof tire would last forever, could be retreaded several times, and would handle the rigors of life on the mean city streets.

Over the years, tire makers delivered the tires industry wanted -- and was prepared to pay for. It's a very price-sensitive market, and that has historically limited innovation. And historically, fuel economy wasn't even on the radar screen.

Those days are behind us now, and the labs and engineers at most every major tire maker in the world are hard at work developing more fuel-efficient tread designs and compounds, because a tremendous market has just opened up for that kind of tire with the new federal fuel-economy regulations.

The biggest push in this new direction is coming from the original equipment manufacturers, who have few options at their disposal to meet the new GHG reduction mandates.

The heavy-duty guys have about six model inputs to play with to meet the limits on greenhouse gas emissions related to the overall vehicle, including aerodynamics, the ability to limit vehicle speeds, engine modifications, etc., and including using low-rolling-resistance tires.

In the medium-duty market, however, and especially the vocational segment, the variables in the EPA's Greenhouse Gas Emissions Model (GEM) model suddenly drop to essentially two: steer and drive tire rolling resistance improvements and the downsizing the engines. All the aero improvers seen for on-highway Class 8 trucks have limited application for most medium-duty trucks.

And no longer do medium-duty customers want just the cheapest and the longest-wearing tire they can get. When UPS announced that they wanted their entire fleet to be as efficient as possible, that sent a very strong signal to the tire industry.

Today's product development programs focus on producing a tire for an urban setting with lower rolling resistance, but with the same damage-mitigating performance attributes as before.

The urban nature of the segment does bring a few challenges. It's a more abusive environment with concerns about curbing, scrubbing, etc.

If tire makers use low rolling resistance compounds, they can't afford to give up the tread qualities that let the tire stand up to the harsher environment.

Manufacturers have improved manufacturing processes, and made big gains in materials. Today, some steer and drive tires could have as many as two to four different compounds in the tread area to minimize trade-offs. It's becoming the case for medium-duty tires as well.

So you see how OE demand is driving tire design for 17.5- and 19.5-inch tires in Class 5-7. Even with four of the largest fleets in the land (with more than 100,000 trucks between them) calling for a design change in the standard tire, what will the guy who owns a bakery and a couple of trucks to get his product to market think about the change?

Some users might wind up buying an extra set of tires over the life of the vehicle, perhaps two, which would consume in cash whatever savings accrued from improved fuel consumption. You have to look at each unique case and do a value calculation that takes into account miles to removal, retreading, and all the rest versus what you can measure in fuel savings.