Jun 18, 2013 update to the Volkswagen Beetle TDi project car

Resistance is Futile

We finally located our VW Beetle’s wheel lock (it had fallen down inside the spare tire well, quite out of sight) and got our 18-inch BFGoodrich Super Sport AS tires mounted up. While we’ll be doing some track testing in the near future, the butt-meter tells us that the handling should be measurably improved with the new rubber.

But what cost does that additional grip come at? Would the additional rolling resistance hurt the fuel economy of our TDI diesel-sipper?

We devised a simple method to measure rolling resistance: We pointed a video camera at the dash and coasted from 60mph to 30 mph on a straight stretch of road. Then we could return to the lab, open the files in Adobe Premiere and measure the time that the car took to coast down to specific speeds. We did the test in largely windless conditions, but we did several runs in both directions to try and counteract any variables. We’ll publish the numbers in the next issue of GRM, but suffice to say that a quick look at the video shows a measurable difference in the two tires. The BFGs, with their wider footprint and grippier compound slowed the car faster than the stock Continentals, whose hard compound and narrow tread blocks were optimized for low rolling resistance.

How much of a difference this additional drag makes in mileage remains to be seen. We’re leaving for Orlando in a few minutes with a reset trip odometer. Stay tuned.

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