Airless tires have been getting lots of press over the last few years, with Michelin’s “Tweel” being touted as the most amazing bit of tire tech since the invention of the radial. Except that it really isn’t, because a very similar airless-tire concept was under development in the 1930s and ‘40s.
James Vernon Martin was a legendary aircraft and automobile inventor in the early 20th Century, developing everything from retractable aircraft landing gear, to cars with weird rubber cord suspensions to this: an elastic spoke tire.
Actually, James V. Martin has his name on quite a few patents for airless elastic tires: the Lightweight Resilient Tire, the East Biding Tire, and then there’s the Elastic Tire.
The concepts were all the same, though: Martin wanted to develop a lightweight, easy-to-manufacture, “easy riding” tire that wasn’t prone to puncture, could conform to uneven terrain, and would give a vehicle better control at high speeds over bumps.
These design objectives would have made Martin’s tire perfect for use on military vehicles, and that video above–which seems to definitely over-dramatize the difference in performance between the airless tires and the standard pneumatic tires (look at that windshield flopping around)—is likely a bid for a U.S. military contract.
How The “Elastic Spoke” Tires Work
The concept behind Martin’s Elastic Spoke tires is fairly elaborate; Rubber is cured to a number of parallel flexible metal hoops to comprise the outer tread section of the tire. Martin says in his Elastic Tire patent that using multiple small-diameter spring-steel tubes as hoops to stiffen the tread is a much better idea than just using one big metal hoop, saying:
To put the required strength in one hoop or tread portion produces so much stiffness and rigidity that the metal tends to hammer itself to pieces and crystallize.
That hoop then “yieldably [suspends]” an inner hub via a number of elastic spokes, which are connected to that hoop via lugs. The inner side of the spokes attach to the metal wheel (the center portion that connects to the hub) via a number of special crossbars, whose job is to allow “the spokes on the bottom of [the] tires to move inwardly toward the wheel center without carrying compression loads to the axle.”
In other words, this design uses a stiffened tread hoop to carry the axle’s load in tension via a bunch of elastic spokes. If that sounds familiar, it’s because Michelin’s hot “new” Tweel uses a very, very similar design. Like the “spring steel” hoops that stiffen the tread portion of Martin’s tire, Michelin also uses a similar concept:
And like Martin’s design, which uses elastic spokes to carry the load in tension, Michelin’s Tweel uses “poly-resin” spokes to hang the load from the top of the wheel structure.
So yes, this airless, elastic-spoke tire concept is hot and exciting. But it was also hot and exciting in the 1930s and ‘40s. Whether it will ever catch on in applications other than low-speed landscaping machinery remains to be seen.