Tyre test 2008: Test 7 - Hot lap & summary (July 2008)

Wheels Tyre Test 2008: Tyre Test 7 - Hot lap

Wheels Magazine
June, 2008

WHAT WE MEASURED
Eastern Creek's skid circuit is hardly Silverstone or the Nürburgring. It's just Eastern Creek. Basically it's well under 1km of very wrong concrete corners jammed together to form a figure of eight. With an average speed in the 50-60km/h range, it's ideal for driving road cars on the limit all day without killing them.

Another handy characteristic, for tyre testing, is the absence of straights in the skid circuit. Tyres don't do much in straights except wait for the heroic braking effort at the last moment. This is why lap times on racetracks largely reflect power-to-weight and brake performance - which is interesting, but not if you're testing tyres.

Basically, Eastern Creek's skid circuit combines steady-state and transient cornering in a series of worst-case combinations you might face one day in the real world - it's a little bit of slalom, and a little bit of circle, but off-camber and tightening up, with crests and dips. It's like driving dosed-up on Midazolam, on a circuit designed for Lilliputians.

HOW WE DID IT
This was the simplest set-up of the whole test. All we did was mark the apexes at the crossover of the figure of eight with cones. The purpose of this was twofold. Firstly it took corner-cutting off the menu. Secondly, it's impossible to see the apexes from the driver's seat when you'd really like to, thanks to crests in the concrete on approach. The extra 450mm in height of the cone - and of course the fact that it's fluoro orange - allowed McKay to get missile lock on the apex just that much earlier than otherwise. It removed lingering ambiguity from the process.

All we did then was place one infrared timing beam across the track and told Pete to drive three laps, the data from which was then downloaded and checked for consistency before we trotted off to the tyre bay for a new set of hoops. For scoring purposes we ran with the best lap time of the three.

What was interesting, apart from the differences in times across the field, was the differences in 'racing' lines - tyres really do make a profound difference to the entries and exits and the car's on-limit behaviour generally, which you can pick if you trainspot enough back-to-back laps.

If anyone has any bright ideas about how we can quantify those differences objectively and report them, please send us an email, because frankly, it's got us stumped. It's there, and it's happening, it just appears to defy measurement.

SAVING SPACE, SANS GRACE
Space-saver spare tyres are no less common now than they were two years ago when we put one to the test on a Volkswagen Golf during the 2006 Wheels tyre test. We found the car's cornering capacity dropped by 20 percent, while stopping distance from 80km/h (the space saver's rated maximum speed) grew by half a car length.

Another space-saver drawback surfaces if the car's full of kit and people, and you get a flat - where do you stow the full-sized flat tyre?

Space savers are usually more expensive to replace than full-sized tyres, too, and generally last less than 500km owing to the soft tread compound used in an attempt to redress the grip imbalance brought about by a reduced footprint.

Car companies don't necessarily see any of this as a disadvantage, however. Mazda's Alastair Doak went on the record a few years back citing space savers as a net customer benefit: "They give you the benefit of a larger boot and cargo area," he said, adding, "there's also a safety benefit in using a space-saver tyre as it does help in rear-end crash protection."

SIDEWALL GLANCES
Never really understood how tyre sizes and specifications work? Ponder no longer.

For 235/45R17 94Y:
235 is the maximum section width (not the tread width) in millimetres, with the tyre at its notional operating pressure.

45 is the tyre's 'profile', 'aspect ratio' or 'series' - they all mean the same thing. It's just the sidewall height divided by the section width.

R means 'radial', which all road tyres are these days. The cross-ply is like the VHS cassette and the dodo - dead.

17 is the rim diameter. Despite metrication almost four decades ago, it's still measured in inches, across the bead seats

94 is the load index rating. You must fit tyres that meet or exceed the load index on the car's tyre placard. That applies to 'plus one' and 'plus two' upgrades as well.

Y is the speed rating. The common ones are H (210km/h), V (240km/h), W (270km/h), Y and Z (both 300km/h).

☆ WINNER: 235/45R17 - Goodyear Eagle F1 Asymmetric
It's monotonous, seeing the Goodyear and the Falken in front again. Still, it's a fair old indication that there are two tyres in this pack that walk a little taller than all the rest. Almost a full second per lap separated first from last in this competition. In racing, that would be the difference between on the pointy end of the grid and back to the blackboard, scratching one's head and wondering where it all went so horribly wrong in development.

One second per lap - just by changing tyres - is the kind of gain real race teams can only dream about. Once everything is optimised, if you can tweak something and come away with a few hundredths, it's been a great day. On the road, maybe the difference isn't so profound - but it's still 3.6 percent more safety margin, or more fun, depending on how you look at it.

THE ENVELOPE PLEASE
In summary? Premium rubber was the real winner on the day.

Never forget that premium tyres are a form of insurance. Pay maybe $30 more per corner and you could avoid a traumatic brain injury - surely one of the better insurance deals around.

With that in mind, it's almost impossible to go wrong when you shop for tyres. If everyone went into their local tyre retailer and selected only from a 'premium' list, without being distracted by the discount specials from Eastern Europe, India or China (and checked the pressures once a fortnight) the roads would be safer. Here's the list (in alphabetical order): BF Goodrich, Bridgestone, Continental, Dunlop, Falken, Goodyear, Michelin, Sumitomo, Toyo, Pirelli, Yokohama. It's that simple.

In a sense, what we're doing here is splitting hairs. There's a little less than five percent separating the six 235/45R17 contenders, and just over three percent separating the 195/60R15s. A big deal in racing; less so on the road. It means they're all good tyres, and infinitely better than any cheapies or retreads.

Me? I'd opt for the new Goodyear Eagle F1 Asymmetric, despite its significant price premium. And, if it wasn't yet available in my size, I'd be happy to drive off with the Falken FK 452 and pocket the change. This pair were up the sharp end of the field so predictably often, they're an obvious choice if driving enjoyment really is your thing.

One obvious question: What if your car isn't running on 235/45R17s or 195/60R15s? Tyre-industry experts say a particular tyre - say the Goodyear Asymmetric that aced this year's test - is designed to deliver a particular level of performance across the range. After considering the loads likely to be imposed upon it by the car, it's built to provide that performance in each size. In other words, our winner is also an odds-on favourite in 16-, 18- and 19-inch sizes as well as the 17s we tested.

It's quite therapeutic to spend two days driving and measuring cars and tyres at the limit of adhesion. We come away with a bunch of numbers that quantify absolute performance limits. If you buy the Goodyear Asymmetric, or the Pirelli P6000 that won the 195/60 category, you're getting the highest level of performance potential. But you don't drive like that on the street ... usually. What that means is that when you buy the best tyres available, you've got the capacity for the highest level of fun factor on your favourite backroad. And for the other 95 percent of driving, you benefit from the biggest safety margin money can buy.

SETTLING THE SCORE
The winner in each test category was awarded 10 points, and the rest of the field was allocated points that were proportional to their proximity to the winning performance. This is fairer than giving, say, nine to second place, eight to third, etc, especially when ther's a photo-finish involved. In tests like these, second place really deserves 9.95 (or something) if it's really that close to first.

Final points across all the disciplines were totalled, and the total was adjusted to a percentage for the final score.

Read more on the Wheels tyre test here:

Intro:  Let's roll ...	Test 4: Wet slalom ...
Test 1: Dry cornering ...	Test 5: Dry braking ...
Test 2: Wet cornering ...	Test 6: Wet braking ...
Test 3: Dry slalom ...

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