There are those who'll tell you the most important thing about your car is its tires -- and they're not far from the truth. They're the only contact between you and the road, and their ability to remain in contact can have far-reaching consequences.
Of course, we all know this, which is why we undergo a careful selection process when buying new tires based on perfor-mance, cost, reputation, marketing, and even appearance. The problem is, a wrong decision could be catastrophic. So how can we be better informed? Well, one of the best places to start is www.tirerack.com because the retailer has its own test facilities and the team rigorously tests every new product. The results are posted on the site, and customers are invited to add their own opinions.
So, no need for a test then, we'll just refer to the Web site? Not quite. We wanted to gather our own information, and Tire Rack kindly allowed us to use its excellent facilities at the company's head-quarters in South Bend, Indiana (see side panel). In addition to an intelligently designed track with a sprinkler system for wet testing, the company also has a fleet of four stock BMW 330Ci test cars and a sophisticated timing system. So all we needed to bring was a sample of perfor-mance tires and some drivers.
Most of the tires were removed from The Tire Track's huge stores when the employees' backs were turned, so that only left the pilots, and since we were using the 330Ci, who better to do the driving than Turner Motorsport's Will Turner and Don Salama (see side panel)? Besides being good friends of ours, they share a TMS 330i in the Grand-Am Cup racing series (www.turnermotorsport.com) and flew to our test directly from taking second place at Mid-Ohio. Having tuned, tested, and won in these cars, there are few people more qualified to drive the 330Ci.
Before owners of VWs, Audis, 5-Series, and so on turn the page, please under-stand the results you see here apply equally to your car. We simply used BMWs because The Tire Track decided the cars are sufficiently rugged to tolerate the constant abuse and the rear-drive chassis is nimble enough to provide excellent feedback without introducing understeer, as front-wheel drive is prone to do. All the 330s have the Steptronic transmission for reliability and consistency, and the traction control was obviously switched off.
The Test
When our drivers first arrived, they were put behind the wheel of a 330Ci on control tires. These were OE-specification 205/50-17 Goodyear Eagle RS-As on factory 17x7-inch wheels. The drivers were invited to complete a series of three-lap familiarization sessions to learn both the track and the car. Times were then recorded before swapping to our test sample.
For the test, we used a common upgrade size -- 17x8-inch wheels (in this case, Shuk WR1 with ET40 weighing 18.5 pounds) with 225/45-17 tires. Obviously, we were tempted to go for 18- or 19-inch wheels, but it was agreed that these could introduce factors that may distract from gathering raw data about the tires' performance.
The test tires were fitted to one of six sets of identical wheels The Tire Track keeps for such occasions. They were tested at 35-psi pressure and were then fitted to a second, identical 330Ci -- leaving the control tires on the first car to allow the drivers to refer back if necessary.
Each driver completed three timed laps on each set of tires in both the wet and dry. The fuel tanks were topped up before each session to ensure greater consistency. Wet-weather testing took place on the first day, dry on the second. All three laps were timed, with the driver taking a running start from the "pitlane" to get up to speed quickly -- in fact, the first lap was sometimes the fastest.
To ensure consistency, our drivers tested the first sets of tires for a second time at the end of the day. If there were large discrepancies, we could assume the drivers had "learned" the track during the day. Yet the drivers were within tenths of a second of their original times, despite the laps being separated by about seven hours and maybe 12 different sets of tires.
What was amazing to us was the consistency and analytical powers of both drivers. Despite driving 13 different tires (including the control) over each day's seven-hour period, they were able to estimate their lap times to within a couple of tenths of a second and rank the tire correctly against its peers. They also completed the three laps within a few tenths of a second of each other, and on occasion, just hundredths of a second separated their lap times. To say the event was competitive would be an understatement.
While proving what great drivers they are, it also proved both were getting the maximum performance from each tire. We then asked for their comments on each tire as they stepped from the car, and as you can see, both agreed almost exactly on all but a few. To us, this confirmed we'd chosen the right people and were getting the right information. The fact they agreed with The Tire Track's research was an added bonus.
If you turn to the results page, you'll see wet and dry figures for the overall lap time. This represents the fastest recorded lap by either driver, to show the full potential of the tire. Then there are wet and dry g-force numbers, which show the ultimate grip the tire's able to generate. You'll also find wet and dry slalom times, which record the time through the lane-change section and illustrate the tire's ability to change direc-tion. The ambient temperature during our tests varied just 3 or 4 degrees all day, which is not enough to affect the results. We also have wet and dry braking mea-surements. The Tire Track's test engineers recorded these using our sample batch of tires on a different day. Brake testing is a very demanding exercise that requires the exact same amount of pedal force to be applied at the same point and speed with mechanical consistency. Given Will and Don's lack of experience in this area, and having only two days available to us, we decided to leave it to the technicians.
The brake testing was performed using a Vericom VC2000 Performance Computer that captures entry speed, time to stop, distance to stop, and peak and average g-force. Entry speed is 50 mph and the driver makes 10 stops. The average stop-ping distance is then calculated from this information. Because of some delivery problems, several tires had to be tested after the majority, but some of the first batch were retested to ensure consistency in the results.
The Tire Rack Track
The track has several combinations, but we used a figure eight layout for its combination of 90-degree bends leading to a 200-foot skidpan circle. Cones were used to provide a lane-change exercise, in addition to tightening some corners. This combination provided a variety of handling situations, as well as braking tests and g-force assessment. The track is ringed with laser beams that time the overall lap, the time through the lane change, as well as a section of the skidpan (from which a g-force measurement could be extrapolated).
The surface is smooth and unpatched. A series of sprinklers around the side allows the track to be doused with water, simulating typical rainfall. The surface is cambered 1 degree to the inside, as are most public roads. The idea is to recreate the sort of driving conditions you might encounter every day.
The track is a relatively simple layout to help drivers familiarize themselves quickly. There are no complex corners to learn, so drivers can concentrate on consistency. Certainly, Will and Don were able to repeat times recorded at 9 a.m. by getting to within tenths of a second some seven hours later on the same set of tires. This proved to us they hadn't "learned" the track but were driving flat-out all day.