Car and Driver Will Now Take Your Questions, Part Three

From Car and Driver

You have a lot of questions and occasionally we find ourselves with enough time and in a good enough mood to answer them. Joking aside, we strive to answer any and all of your question about our procedures, tests, or the mysteries of the automobile. We’ve actually been doing it in the print magazine for years. So, feel free to use this chance to broaden your knowledge or even settle a bar bet. And remember, there are no stupid questions—well, if they’re really stupid we won’t answer them.

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Voltage Warning

Your September articles describing the Fiat Chrysler (page 069) and the Mercedes (page 081) hybrid systems indicate that a 48-volt motor-generator also starts the gasoline engine. Unless these cars have a second starter operating on 12 volts, a jump-start will require a 48-volt energy source; how many roadside-assistance providers equip their trucks with 48-volt sources? Are there any 48-volt batteries suitable for keeping in the trunk for emergency use? The conversion from 6- to 12-volt electrical systems in the mid-1950s went smoothly (with the exception of some foreign makes), but that was an industry-wide transition.
—Stanley Kalemaris, Melville, NY

Modern hybrids—including those with the emerging 48-volt systems—retain a conventional 12-volt battery and starter for the initial ignition sequence. The 48-volt motor-generator then refires the engine during stop-start events. It also replaces the alternator, charging the 12-volt battery through a DC-to-DC step-down converter. Vehicle accessories continue to operate on 12-volt electronics as well. —Ed.

A Gripping Question

In the December “Snow Shoes” feature, you said that on dry pavement, the Corvette’s “big footprint was an advantage and not a detriment” compared with the 911’s contact-patch size. It’s not obvious to me why a larger contact patch would be a detriment on snow and ice. Can you explain, please?
—Bob Woolley, Asheville, NC

In winter conditions, the best traction is achieved by cutting through snow and ice in two directions: down toward the road surface and forward as the vehicle travels. A narrower tire acts like a sharper knife, whereas wider tires are more likely to plow through and float on the snow. Mounted on the same vehicle at the same pressure, different–width tires will have the same total contact-patch area, but the narrower tire’s longer contact patch improves longitudinal traction for acceleration and braking. —Ed.

The Weighting Game

In the “Show Boats” full-size-pickup comparison [January 2019], the Ram’s payload (990 pounds) is less than 10 percent of its towing capacity (10,600 pounds). Is this correct? How can this be safe?
—Aaron Voynar, Berea, KY

When towing with a conventional hitch, the trailer tongue should carry between 10 and 15 percent of the total trailer weight. As Voynar alludes, placing 10 percent of the max towing weight (in this case, 1060 pounds) on the receiver will exceed this particular truck’s gross vehicle weight rating (GVWR), the maximum total mass of the vehicle, passengers, and cargo the truck is designed to carry. And that would be unsafe if you were towing with a conventional hitch. But the math changes if you use a weight-distribution hitch. By adding vertical rigidity to the ball connection, a weight-distribution hitch shifts some of the load that would otherwise be carried on the truck’s rear axle to its front axle and—crucially here—to the trailer’s axles. The complex calculation is different for every combination of truck and trailer. It’s detailed in the industry standard for determining towing weights, known as SAE J2807, but in the case of our Ram, the limiting factor with a weight-distribution hitch becomes the gross combined weight rating (GCWR)—the max total weight of the truck, trailer, and all payload—rather than the GVWR. So, yes, our Ram 1500 could safely tow 10,600 pounds. Of course, to properly use a weight-distribution hitch, you’ll need to know the relevant instructions from both the truck and hitch manufacturers, and the easiest way to check that you haven’t exceeded the truck’s axle-weight ratings, GVWR, or GCWR is to weigh each axle of your rig individually. Or you could always buy a bigger truck. —Eric Tingwall

The G-Spot

I’ve been trying to find the lateral g’s for all Teslas, including the Roadster, but no one can give me an answer. Can you help?
—Ken Miller, Toronto, ON

You’re in luck, Miller. In addition to the Roadster, we’ve lapped the Model 3, S, and X on a skidpad. Here are the highlights:

Here are all the Tesla results from our skidpad tests.

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