Rims and MPGs

One of the teeth-aching disconnects of our time is the feigned obsession with MPGs on the one hand – and the very real obsession with huge wheels (and tires) on the other hand.

The two together amount to weight loss on the Burger King Plan.

Not that there’s anything wrong with big wheels as such – if that’s what you like. Just as there’s nothing wrong – as such – with Whoppers. What makes the teeth ache is people who talk about losing weight  . . . and eat Whoppers.

Also people who talk about saving gas . . . who buy cars with big “rims.”

Just as a diet of Whoppers adds to your waistline by adding calories to your diet, larger wheels and tires hurt fuel efficiency because they add weight and increase rolling resistance.

But people seem to like the look – and as a result, even minivans now come with 17 and 18-inch wheels. Bigger (larger diameter) wheels than exotic high-performance cars such as Ferraris used to come with.

On Ferraris and other cars like them, there’s a solid functional reason for large-diameter wheels. Ferraris and such are performance cars – and people who buy performance cars value  . . . performance. This includes faster steering response and firmer handling. Large-diameter wheels enhance all that by making possible the use of comparatively short and so stiffer sidewall tires, which flex less.

And having a wider contact patch enhances traction, which increases lateral grip threshold (how fast you can corner the car before it begins to lose traction and slide out of the corner) and improves straight-line acceleration by putting the power to the pavement – rather than up in smoke.

But there’s a price to be paid for all of that – just as there’s a price to be paid (at your waist – and possibly, your cardiologist) for dining on Whoppers every day.

Short sidewall tires result in a firmer ride, which has to be counteracted by suspension tuning. And there’s no counteracting the more rapid wear – and increased vulnerability to damage – which is part of the deal when you have a car with tall – and wide – rims fitted with short-sidewall tires.

Your car will also use more gas than it would if it were wearing smaller-size wheels and tires. See above point about weight and rolling resistance.

Which you’d think would be an important consideration to people buying cars that aren’t Ferraris.

To economy car buyers, at least.

But, nope.

Most new economy cars come standard with at least 16 inch wheels – the same diameter wheels that Z28 Camaros and Mustang GTs came with back in the ’80s. And all new hybrids come standard with at least 15-inch wheels, the same diameter as the wheels that came with my ’70s V8 muscle car, the Orange Barchetta (1976 Carousel Red Pontiac Trans Am).

Most new hybrids offer as optional equipment wheels as large as 18 inches, which is almost as silly as fitting a new Ferrari with 15 inch wheels.

It runs contrary to the point of the thing.

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