Tyre test 2008: Test 6 - Wet braking

WHAT WE MEASURED & HOW
Pretend for a moment that there exists in society a class of people who drive cars only because they must. For these people, driving is an inconvenience that must be suffered in order for the modern world to function. Uninterested drivers generally aren't very good at driving, and the thing that they really aren't very good at, at all, is stopping in the wet. People like that find stopping in the wet absolutely terrifying.

At the coal face of tyre retail, the two most common questions posed by punters are - in order - demands for cheap tyres, and for ones that stop well in the wet.

The wet brake test is a carbon copy of its dry counterpart, right down to the speeds, testing procedure, track section used and Vbox operation - only with the irrigation system running. As with the wet cornering tests, the water acts as a lubricant - it reduces grip and extends stopping distance.

TESTING TO BRAKING POINT
Brake testing is a balancing act. On one hand, it would be great to do brake tests from 120km/h since the higher energy levels at that speed (2.25 times the energy of an 80km/h stop) would exaggerate the differences in stopping distances. Two problems with that: firstly, the rather abrupt stop into concrete when you run out of skidpan at Eastern Creek, and secondly, you'd end up killing the brakes before you'd finish the testing. When you're testing tyres, it's not ideal if the brakes change at all - the only variable should be the tyres. So from that point of view, the brakes should be tested from as low a speed as possible so as not to degrade the brake system.

The balancing act lies in selecting the point of reasonable compromise. Our past testing (brake parts littering the pits at Calder's Thunderdome during the first Wheels tyre test...) clearly demonstrated that brakes cannot be punished all day from 100km/h+ to zero without throwing in the Sheridan. But 80km/h isn't a problem as long as there's a reasonable spell between sets (as there is when you're also cornering, slaloming and making a pit stop for fresh rubber).

NITROGEN: A LOAD OF COLD AIR
Tyre retailers eager to separate the 'fully sick' from their paychecks commonly offer to fill their new tyres with nitrogen. It's done in racing because the nitrogen expands slightly less than plain old air as the tyre heats up, meaning the operating pressure stays a little more constant across a range of tyre temperatures.

For the street it's a waste of money for a bunch of reasons. Firstly, air is 80 percent nitrogen anyway, so when you fill up at the servo you're getting most of the benefit for free. Secondly, driving on the street just doesn't generate much heat, so the benefits are negligible anyway. Thirdly, while it might deliver a few hundredths of a second per lap in racing, on the street, the benefits are immeasurable. But you do get red valve caps and bragging rights...

POWER GAMES
Brakes are easily the most powerful component in a car. By a country mile. Look at the stopping distances - the worst stop on record here was 33.24 metres. Do you suppose the Calais could match that stop under acceleration? Could it accelerate from rest to 80km/h in the same distance? Not a chance. (If it could, it'd be capable of 0-100km/h in 3.7 seconds. That's supercar territory.)

The worst average deceleration measured here was 0.76G. Hitting the brakes at 80km/h and delivering 0.76G worth of braking means the brakes are generating 295kW - seriously more than the engine. And that's the worst stop.

The best stop, by the Goodyears in the dry, at 0.94G, equates to 366kW. And if the Calais could accelerate like that, it would be a 0-100km/h proposition in three seconds flat.

So, if you think you've never driven a 300kW car, you're probably wrong.

? WINNER: 235/45R17 - Bridgestone Turanza ER300
This is the Bridgestone Turanza ER300's moment in the sun - a fleeting but significant one. Not to rain on its parade, but the result seems anomalous. It's significantly better than the tyre's dry brake result, but the records of the test show not one but two blinders in the wet - with 27.88 backed up by a credible 28.1-metre stop ensuring mutual consistency well ahead of any other in-category result. If there is one test to ace in the minds of mainstream tyre buyers, this is it. And by a significant margin, too - with more than 1.5 metres (or five percent) the gap back to - you guessed it - the Goodyear Eagle F1 Asymmetric. This was also the only test in which the Falken didn't rate.

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