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1997 Chevrolet Impala SS

  • Choosing a car at dealership. Thoughtful grey hair man in formalwear leaning at the car and looking away

A friend of mine whom I'll call Fran the Man was looking to

expand his already extensive car collection.

"I'm thinking along the lines of neat cars of the '90s," he

said on the phone the other day. "Ones that didn't do that well

in the market, but deserved to.

"Sort of noble failures, if you like. Gotta be black, of

course."

He mentioned the Mazda RX7, Toyota Supra Turbo, Toyota MR2.

"And I've always liked the Chevrolet Impala SS, the world's

fastest police car. By the way, do you know what its

trailer-towing capacity is? Everybody tows their race cars with

Suburbans or pickups; I think the Impala would be a cool tow

car."

So do I.

I mined the piles of press information kits littering my

office, but failed to turn up a definitive number for this car.

The regular Caprice sedan and wagon have a 2,000 pound (these

press kits are American; that translates into 907 kg) limit. A

trailer-towing package — consisting of heavyduty frame,

heavyduty suspension, lower final drive ratio, limited slip

differential and additional engine and transmission cooling –

raises the limit to 5,000 pounds (2,268 kg).

Affliction with these wheels is why GM does not offer factory

aluminum rims with three-quarter or one-ton pickup trucks

That's close enough for Fran the Man's requirements.

I checked the Impala SS's specs. Heavyduty frame. Heavyduty

suspension. Lower final drive ratio. Limited slip diff. Extra

engine and tranny coolers. Looks like it's all there.

But when I called General Motors of Canada, the product public

relations guy, Chris Douglas, said, "No. Impala SS is rated

2,000 pounds, like the base sedan."

The reason? The wheels.

Turns out the SS's lovely cast aluminum wheels are a potential

weak point. According to John Healy, a cheerful engineer with GM

Canada who, if he doesn't know it all certainly knows most of

it, too much load on aluminum wheels could pull the centres out

of them.

Healy says that's why GM does not offer factory aluminum

wheels with three-quarter or one-ton pickups (the 2500 and 3500

series). If you specify aluminum wheels on a quarter-ton pickup,

you may be cutting trailer towing capacity dramatically.

You gather up a new nugget of wisdom every day.

'Everything I know about alloy wheels tells me they're

stronger than steel wheels' says veteran wheel manufacturer

I asked Steve Kantor of Tiremag, one of Canada's premier

manufacturers and retailers of aftermarket wheels and tires. He

was surprised, too.

Kantor says the original design of the 17-inch Impala wheels

came from ROH and was rated at 2,100 pounds (953 kg) per wheel.

The look-alike production wheels are built by Superior and carry

a slightly lower rating of 1,500 pounds (680 kg).

Times four, that means the Impala's wheels could bear 6,000

pounds (2,722 kg). With the car itself weighing around 4,000

pounds (1,814 kg), that leaves about 2,000 pounds (907 kg) for

people and cargo. (We're talking round thousands here.)

Is that where the 2,000-pound trailer-towing limit comes from?

Not really; with a 2,000-pound trailer, the car itself isn't

carrying that much weight — it's just pulling it.

The only vertical load on the wheels is that applied by the

tongue of the trailer hitch, which is typically one-tenth the

trailer weight.

Kantor concluded that it seemed odd to him that aluminum

wheels would be the reason for Impala's low trailer-towing

limit.

"Everything I know about alloy wheels tells me they're

stronger than steel wheels," he said. "They pass more severe

tests, are better made, have higher load ratings."

Back to GM's John Healy. He agreed that in general, that's

probably true. But cast wheels do have a tendency to porosity

tiny holes embedded in the wheel's structure when the molten

metal is poured into the mould.

That could be the starting point of a crack if a sudden load

were applied. If a steel wheel mightily smites a curb, for

example, it will likely bend; an alloy wheel is more likely to

break.

What about aluminum wheels on big trucks? (They aren't the

ones falling off on Highway 401, by the way — those are

typically steel.)

Precisely because of concerns about porosity, aluminum truck

wheels are tested at several times the rated load, to ensure a

huge margin of safety, people in the business told me.

Aluminum wheels certainly can be made strong enough for any

application.

Healy also brought up the fact that it's not just the wheels.

Trailer-towing puts a lot of strain on the drive-train and

cooling system.

While the Impala does have the same heavyduty equipment as

the Caprice trailer-towing package, the SS engine is also

pumping out a lot more horsepower.

"We as a corporation have to be very careful about what we

recommend," he noted. "We have to err on the conservative side."

That's why trailer-hitch installers invariably say off the

record that you can tow way more than the carmaker suggests.

Then again, if your Geo Metro blows up as you're towing your

80-foot Riva powerboat, are you going to sue the hitch installer

or GM?

"We really do have very stringent standards," added Healy,

"and tests that ensure those standards are met.

"If the vehicle has not passed those tests maybe because

we've never submitted the vehicle to the tests in the first

place we aren't going to recommend anyone try it."

He said it was likely the designers of the Impala SS didn't

visualize anyone wanting to tow more than a lightduty trailer,

so they probably didn't even schedule the tougher tests.

Does that mean the Impala might be able to tow more than the

recommended 2,000 pounds?

Healy said with a smile, "You know I can't say that, Jim."

Yeah, I do.

Is the answer, then, to fit wheels from a Caprice with the

trailer-towing package to an Impala SS, drive gently and resolve

not to sue GM (or me) if something breaks?

That would seem to do it.

But of course, you'd be losing the visual and handling appeal

of the big Impala wheels, not to mention the big tires.

The alternative is a pit stop prior to each race meet: swap

the SS's regular wheels and tires for trailer-towing specials.

When you get back home from the race track, swap 'em back

again.

Or, Fran, you may just have to follow the crowd and buy a

Suburban.

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