Tyre test 2008: Test 3 - Dry slalom (July 2008)

Wheels Tyre Test 2008: Tyre Test 3 - Dry slalom

Wheels Magazine
June, 2008

WHAT WE MEASURED
Our circle tests (tests one and two) quantify outright grip once the car and the tyre have settled into a state of continued, hard cornering. A slalom does exactly the opposite by never letting the car settle. It's a bunch of entries to, alternating with a bunch of exits from, corners defined by cones.

Relevance to the real world? Plenty - think about those times when the unexpected happens, and a sharp swerve is required. There are dozens of variations on this theme, ranging from kids running onto the road to drivers backing out of driveways without seeing you approaching, cars (and trucks) parked just over blind crests and oncoming drivers drifting into your lane. And there's always the old faithful - Skippy in the middle of the road, circa 3am.

There are three parts to a slalom - and its somewhat more serious counterpart in the real world. Perversely, many people consider only two of them - the first two. These are the 'swerve' and 'avoid' phases. What's often overlooked is the 'recover composure' part of the deal. It's not especially flash if you swerve and avoid Skippy, only to snot the huge river gum at the roadside. Our slalom exercise tests all three parts of the deal, six times in a row.

HOW WE DID IT
It's certainly true that Skippy (and other real-world obstacles) don't generally line up six-deep at regularly spaced intervals. We contrived the test this way, however, to give us a longer set of events to measure.

One swerve is hard to control and too brief to measure; six swerves take longer and offers a more meaningful set of transitions from left to right and back. And because the recovery from one swerve is followed immediately by the start of the next (on the opposite direction) there's no opportunity to overcook one swerve, and produce an artificially good result at the expense of on-exit composure.

We took six cones spaced at 20 metres, then put a pair of cones 15 metres back from the start of the slalom to mark a constant point for our standing start. That meant the car was already up to speed when it encountered the first infrared timing beam, positioned in line with the first cone. The second timing beam was positioned 10 metres beyond the last cone, which meant McKay had to keep the last exit tidy if the run was to return a good time.

After three runs, we downloaded and looked for consistency - ideally two runs within 0.1 seconds, or about 1.5 percent, of one another. If we got that, we ran with the best time. If not, McKay went back for a second go, which only happened once, funnily enough.

DRIVER IN THE DARK
To ensure perception didn't engineer performance, our driver McKay was kept in the dark about which tyres he was driving on during each test. McKay didn't see a list of the tyres, either, and we didn't even run them in alphabetical order.

We also ensured consistency by double-checking that each set of tyres was run at the placard-recommended pressure of 39psi for the Commodore (the high-speed recommendation) and 32psi for the Mazda (which didn't specify a high-speed pressure on its placard).

It's certainly true we could have mucked around optimising tyre pressure combinations for each of the tyres, but the test would have ballooned to weeks. In the real world most drivers inflate their tyres to the recommended pressure, so that's where we tested 'em.

ROAD TO NO WEAR
It's not possible for us to assess the relative wear rates of the tyres we test - doing so would take tens of thousands of kilometres of controlled driving.

Anyway, there are three factors other than tyre construction and compound that have a far more profound impact on tyre wear:

» Tyre pressure
Under-inflation contributes hugely to the profits of tyre companies. Owner's manuals advise checking tyre pressure every two weeks, and hey, compressed air from the local servo is still free.

» Wheel alignment:
Biffed a kerb lately? Get your wheel alignment checked. Tyres that aren't running true scrub out - it's that simple.

» Driving style
Nothing in life is free. If you drive it like you stole it your tyres won't last even half the distance that they could. Just ask a car company press-fleet manager...

☆ WINNER: 195/60R15 - Bridgestone Turanza ER300
It's interesting how the Mazda 3 on the Bridgestones out-slaloms the Commodore on every 235/45 we tested. It's right up there on the Pirellis, too, compared with the Commodore.

The smaller car's lower mass means less inertia - less resistance to directional change, which is what a slalom is all about. The Mazda's smaller footprint also means it fits between the cones a little more easily than the bigger Commodore.

And after that? The disappointing end of the field is more than six percent off the pace in elapsed time through the beams, which equates to something like 13 percent less cornering load. That's a significant disadvantage with the family aboard and a big, fat red kangaroo in the headlights.

☆ WINNER: 235/45R17 - Falken FK 452
The verdict? The Falken may have taken the gold and the Goodyear the silver, but the rest of the field pretty much came equal last. Just five hundredths of a second separated third place from seventh, with less than 0.2 seconds - a spread of 2.5 percent - right across the field.

There are two ways of looking at this. The first is that 2.5 percent isn't much - at least if you're driving in the real world and not motor racing. The second is that swerve-and-recover ability matters, and an extra 2.5 percent could make all the difference in extreme situations.

A remaining consideration is that as with the constant cornering measured in tests one and two, the slalom time measured relates to the speed of the car. And that 2.5 percent spread means the winner actually carries about six percent more cornering load.

Intro:  Let's roll ...	Test 5: Dry braking ...
Test 1: Dry cornering ...	Test 6: Wet braking ...
Test 2: Wet cornering ...	Test 7: Hot lap & summary ...
Test 4: Wet slalom ...

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