Piston Slap: Design Weak: Big Ass Wheels

Mike writes:

Sajeev, what ever happened to 14-inch wheels? I mean, seriously, does the Caliber really need to be shod with 17-inchers? Why does my dad’s new half-ton pickup have 17-inch wheels? His old one had what used to be the industry standard 235-75R15. He about had a coronary when he found out new tires would be over $100 each. Perhaps if I put on my tinfoil hat, I’d say the tire companies are behind this. So really, does the average family sedan or minivan really need anything bigger that a 15-inch wheel/tire?

Sajeev replies:

Of course the Caliber doesn’t need 17-inch wheels: they can’t possibly fix Chrysler’s rolling abomination. But let’s think about why every modern car has big wheels.

Speaking from an Engineering Standpoint: wheels over 15-inches provide space for bigger brake rotors (and calipers) and a shorter profile tire in the same tire diameter. The benefits are better braking in extreme conditions, like mountain roads or any form of towing. Shorter profile tires provide more road feel and tread grip, completely changing a car’s “turn in” during the act of corner carving. In theory: most cars lose these benefits above 18” wheels, as more unsprung weight and rubber band tires make things worse.

Furthermore, modern cars/trucks are heavy, straddled with more gizmos, bigger (and taller) cabins and more rigid bodies. When you add more weight, you need more stopping power.

Speaking from a Design Standpoint: styling is a major factor in the mass-acceptance of larger wheels. By the 1980s, both the downsized American icons and Japanese entrants required a certain passenger volume without resorting to the bulk and shocking overhangs (front and rear) of previous decades. Which required a taller DLO (Day Light Opening) for more trunk space—among other things—and created a taller car in the process. And, in general, taller cars naturally look better with “taller” wheels filling out their wells.

And big wheels were here to stay when Ford sold Explorer SUVs like buttered popcorn, making everyone ride tall in the saddle. Hence the need for taller profile wheels and bigger brakes merging with America’s insatiable need for sleek sheetmetal since the 1950s.

Maybe 15” wheels can make a comeback, but vehicles need to ditch their platform shoes and go on a serious diet. I’m not holding my breath.

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