Photography by J.G. Pasterjak
Getting on track with a C5 Z06 is as simple as pulling up an event registration form online, entering a few credit card numbers, and packing a cooler. Few cars have ever been as ready for the track or autocross course as Chevy’s ultimate fifth-generation Corvette.
If you want to really compete, though, you’re going to need some good tires. Those few square inches of contact patch are the car’s only interface with that track surface, so you’ll need to make them count.
Fortunately, today’s world offers more than one kind of performance tire. We have street-legal race tires as well as race-ready street tires. Each tire category seems to have found its own motorsports home, but how do these categories actually compare? Time for a little intramural face-off.
What we’ve put together here is a little bit different type of tire test. Usually we’ll get together all of the hot brands in a single category, then pit them against one another in a winner-take-all showdown. This time, though, we’re comparing within a single brand (well, one parent company anyway, since Michelin owns BFGoodrich) to evaluate their tires from three different high-performance categories. We want to see how each type of tire goes about doing its thing.
This evaluation is less interested in determining the fastest tire. Instead, we want to show what each category brings to the table and how it gets the job done. So we mounted up our SoloStorm data recorder and set to testing.
The Contenders
As noted, we chose tires from three different categories for this autocross exercise. The max performance summer category was represented by the Michelin Pilot Super Sport. This is a tire that is used as an OEM fitment on some of the world’s finest sports and GT cars, meaning that it has to do everything well–and without sacrificing road manners.
That do-it-all nature plus the available sizes has made it a top choice for competitors in the Tire Rack One lap of America. “The One Lap crowd has a tough problem to solve,” explains Peter Calhoun, Motorsports Marketing Manager for BFGoodrich Tires and Michelin North America. “They have to use a single set of tires for the entire trip, and compete in vastly different venues, from track, to autocross, and even wet competitions. A tire like the PSS is kind of designed for that sort of situation. It tries to do everything well."
These Michelins carry a 300 treadwear rating and represent what we’ll call “typical OEM-style applications” for today’s high-performance machines. What’s that mean? Instead of a Miata-friendly 205/50R15 size, Michelin offers the Pilot Super Sport in lots of larger rim diameters, specifically 17 inches up through 22.
Carrying the flag for the Extreme Performance segment in our test was the BFGoodrich g-Force Rival S. It trades some road manners for even more performance, and that concession is a big reason why it’s sold as a BFGoodrich and not a Michelin.
This 200tw tire is one of the gold standards for autocross and road race competitors whose classing mandates this type of rubber–which covers a slew of hot categories, including all of the SCCA Street and Street Touring autocross classes, plus the Optima series and many of today’s lower-cost endurance racing programs. Accordingly, the BFG Rival line features sizes that are aimed more at autocross and road race competitors, so they range from 15-inch rim diameters–including the popular 245/40R15–up through 18-inch sizes.
Despite sacrificing some comfort, the Rival S is also fully street-legal, and that status is not just a formality. These tires work just fine on the street. We drove our newly purchased Corvette from Chicago to Florida through nearly every type of weather that late October had to offer and totally didn’t die. Despite their immense grip, the Rival S tires are completely functional on the street.
Did someone say immense grip? Well that would bring us to our dedicated race tire entry, the BFGoodrich g-Force R1 S. While still technically DOT approved and carrying a 40 treadwear rating, the R1 S is a dedicated race tire in every sense of the word: It’s molded with a slick tread that features just enough grooves to be considered street-legal. (And for those willing to sacrifice some grip for longer wear, BFGoodrich also offers the related g-Force R1.)
A look at our three subjects gives a hint as to their missions. From the top, the Michelin Pilot Super Sport, BFGoodrich g-Force Rival S and BFG g-Force R1 S apply an ever increasing amount of rubber on the road and, not surprisingly, an increasing amount of grip. All three tires were capable of pulling serious lateral g, but as figure 1 shows, the R1 S routinely got there first and stayed the longest.
The R1 S is aimed at road racers and time trialers who aren’t bound by that 200tw restriction–they just have to meet a DOT mandate. Like the Rival, the R1 line comes in more competition-friendly sizes: 15-to-18-inch rim diameters.
Now, here’s a little spoiler alert: We’re going to go ahead and tell you that based on fastest times, our test results followed the reverse order of the tire listings you just read. It’s no surprise that the R1 race tire set the fastest times while the Pilot Super Sport was slowest. The real story here goes beyond the fastest times and involves how each tire got there, as well as what our data revealed about driving them at their limits.
The Lineup Hits the Course
Let’s start this evaluation by talking about those lap times. We made our autocross runs on the World War II-era concrete found at Spence Field in Moultrie, Georgia. This concrete runway is an excellent analog to the grippy concrete found at the Solo Nationals in Lincoln, Nebraska, and provides excellent stick and great predictability without producing a lot of marbles.
Dixie Region SCCA, who usually runs at this site, provided logistical support for our test. Based in North Florida and South Georgia, Dixie Region also hosts one of the big kickoff events of the SCCA’s autocross season every year, the Tire Rack Dixie Champ Tour at South Georgia Motorsports Park.
We designed our test course to maximize the opportunity for tire evaluation and minimize driver variables, so the layout was fairly simple. It featured a blend of medium- to higher-speed, second-gear sweepers and transitions, plus a couple of discreet braking areas–both straights and turns that required some trail-braking.
We mounted the Michelin Pilot Super Sports in a combination of 275/40R18 front and 295/35R18 rear sizes, as close to OEM as we could get in a modern max performance tire. Our Corvette needed 29.931 seconds to complete our course on the Michelins.
BFG’s Rival S and R1 S were both mounted in a popular square setup featuring a 315/30R18 tire at all four corners. The Rival S lapped our test course a full 1.8 seconds faster than Michelin’s true street tires, setting a best lap of 28.114 seconds, while the R1 S led the pack with the best time of the day: 27.703 seconds. Those times placed the Rival closer to the R1 S than the Pilot Super Sport–something that rather surprised us, to be honest.
Side to Side
The rest of the story lies beyond those raw times. Let’s take a look at dynamic performance characteristics, specifically lateral grip. Our SoloStorm data recorder gave us the ability to view and log lateral g-force readings, as well as view them over time. Surprisingly, all three tires were capable of producing very high–and very similar–peak numbers. The differences became clear, however, when we looked at the graphs over time.
For example, take a look at figure 1, which shows the g-force readings plotted over time through a right-hand corner. All three tires peak impressively high–1.18g for the Pilot Super Sport and 1.23g for the Rival S and R1 S–but the data curve for the R1 S sits outside the other two curves. What does this mean? While the maximum g-forces generated on each tire through the corner were similar, the average g-force through the corner was clearly biased toward the more aggressive tires, and the R1 S in particular.
This particular corner was a bit of an outlier, too. Most corners looked more like figure 2, with the R1 S clearly having the edge in g-force load while the other tires plateaued at lower levels and fell off accordingly.
Figure 2 shows how the BFGoodrich g-Force R1 S (red trace) simply offers higher limits–more g-forces–through a turn. And as figure 3 shows, that R1 S (red trace) also offers superior transient response over the Rival (green trace). The race tire goes from max g in a left turn to max g in a right turn while the Rival is still building force.
The data in figure 3 makes clear the race tire’s ability to handle hard transitions. The steep climb of the g graph of the R1 S shows how quickly it transitions from its maximum left-hand g to its maximum right-hand g. The race tire is hitting those higher g-force readings while the Michelin is still in the process of transitioning.
Get on the Gas
The next chart we’ll look at is throttle position. SoloStorm can log throttle position in real time, allowing us to see just how aggressively we could apply power at any given point.
The throttle traces looked fairly similar for the most part, but there were a few interesting highlights. For example, figure 4 analyzes a section of course that followed a fairly tight left-hand corner. The Pilot Super Sport was able to hold 47 percent throttle, while the Rival S allowed us to apply 55 percent throttle. The R1 S, however, allowed us to reach 87 percent throttle, which had us going 4.4 mph faster at the end of that short acceleration zone.
More grip means more throttle, just as figure 4 demonstrates. When we tried getting that deep into the throttle with the Pilot Super Sport (figure 5), the loss of traction forced us to take a big lift. Figure 6 shows the R1 S maintaining excellent speed through a corner, while the Rival and Pilot Super Sport had slower cornering speeds. The Rival’s excellent forward bite allowed a strong exit, though, and speed rose quickly to match the R1.
Even when we did manage to get into the throttle with the street tires, it wasn’t always a good thing. Figure 5 shows a situation where we juiced it pretty hard on the Pilot Super Sports–all the way to 87 percent. We paid dearly for our mistake, having to get way off the power; we didn’t recover until we dropped to 24 percent throttle. The Rival and R1 S, by comparison, were able to maintain well above 40 percent throttle through the same maneuver.
When we look at our Corvette’s highest levels of throttle opening–the range above 90 percent–over the entire length of the run, we see our most dramatic difference. The R1 S spent nearly 9 percent of the entire run above 90 percent throttle. The Rival S finished just a tick behind–about a percentage point. In fact, the traces of the Rival S and R1 S were, for the most part, eerily similar, with the R1 S just trending a bit higher on a very similar graph.
The Pilot Super Sport lagged more than 2 full percentage points behind the Rival S. It spent just 6 percent of the run above 90 percent throttle, and the data traces show a lot of throttle actuation was necessary to balance the car.
Speed Trap
The final data point we’ll look at is speed. Not surprisingly, this one follows a trend very similar to throttle opening. The R1 S, aided by its higher grip through the corners, was typically the fastest tire after the corner, but the Rival S showed an excellent ability to make up some ground in spots. While the latter might have been slower at corner exit, it quickly matched the R1 S’s speed down the next straight.
This shows how well the Rival can put down power–and how it’s strong enough to close the gap gained by superior corner speed. In fact, there were a few instances where we saw the Rival S equaling the R1 S in ground speed. Just as we saw when measuring lateral g, however, the full-race tire would hit those top limits sooner and sustain them longer than the more street-oriented rubber.
One particular sequence showed how quickly the R1 S can make up time: We overdrove this tire through a tight left-hand corner, so the Rival S was almost 4 mph faster through the same maneuver. However, within a couple of turns, the R1’s superior grip had erased the speed differential and put almost 2 mph on the Rival.
Analyzing Our Data
There were no surprises in our empirical results. Going in, we knew that the race tire would set the fastest times, and it didn’t disappoint. What we really wanted to show was how each tire best works in a certain situation, clearly demonstrating how each one needs its own driving style.
Even the most street-focused of these tires–the Pilot Super Sport–is a very capable track tire. It’s only when compared to its more extreme counterparts that it exhibited what could be described as weakness.
The Pilot Super Sport has high limits and great transitional abilities, but it required some attention to keep it in line. This true street tire needed the most and coarsest inputs when driven on track. When pushed beyond its limits, it broke away predictably, but frequently required a lot of throttle correction, which limited speed. Still, a novice driver could comfortably drive the Pilot Super Sport on track.
The Pilot Super Sport was also, hands-down, the most forgiving and civilized tire off the track, delivering a noticeably quieter and more comfortable ride than the BFGs. Remember, as a Michelin, this tire has to do everything really well. And if we had to pick one tire to do everything–and we do mean everything–this would be a top selection. It’s a tire that you could easily drive to a track day, run hard, and then drive back home. This one does present some performance compromises, though, and we’ll get to them in a second.
The R1 S dominated the other end of the spectrum–no surprise. Although it carries a DOT approval, it’s a true race tire, featuring stiff, responsive sidewalls. Its grippy tread flings every pebble against the bodywork, and park the R1 S in the paddock after a hard session, and it’ll bark loudly next time it’s asked to move.
The R1 S also faces some limitations. It requires some warmth for optimum grip, beginning to do its best work above about 120 degrees and really coming into its own once it passes around 135 degrees. Those same tire temperatures will cause a noticeable drop-off in the Pilot Super Sport’s performance. That tire’s ample void area delivers excellent wet weather performance, but those same tall tread blocks also lead to a lot of tread squirm–something that’s much less of an issue with the R1 S. More tread squirm means more heat buildup, and too much heat pushes a tire out of its comfort zone, degrading performance. This means that the R1 S can be pushed hard in its intended environment: the race track and autocross course. Just hope that it doesn’t rain.
Which bring us to the Rival S, which delivered perhaps the biggest surprise of our test. We knew the Rival S was fast, and we expected it to outperform the true street tire. We just thought that the three tires would land equidistant from each other in our results.
The data, plus our own experience, shows that the Rival is essentially a race tire dressed up as a street tire. Its limits are slightly lower than the full-on R1 S, but the required driving styles and overall approaches to speed are remarkably similar.
While he was bound by corporate confidentiality and couldn’t reveal too much about the chemical or architectural nature of these tires, Peter Calhoun did provide some good insight into what makes the various performance rubber work. “People get too hung up on ‘compound’ and the actual nature of the rubber when it comes to tires,” he explains. “And, sure, there are differences in the rubber compounds, but the differences aren’t as extreme as you might think.
“Just as important–maybe more important even–is the construction of the tire itself, and how the tread face relates to the sidewall, how the sidewall is supported and, in turn, how that sidewall supports the tread face. That’s really going to be what makes some of the more dramatic differences. And, as your results showed, the Rival is way more similar in construction to the R1 than it is to the Pilot.”
Indeed, our testing bore this out. The Rival and R1 S both can be driven similarly–the Rival just delivers slightly lower limits. Driving the Pilot Super Sport hard takes a lot more control inputs and more managing of its limits, while both the R1 and the Rival seem to reward the exploitation of their limits.
After studying our data, it’s a bit of a revelation that the Rival is even barely suitable for street use–let alone perfectly capable of cross-country travel. That performance comes with a cost, though, and when we say that the Rival behaves more like a true race tire than a true street tire, we mean that in regard to comfort as well. While it doesn’t have the harsh, unforgiving ride of the R1 S, the price for the Rival’s superior response and grip over the Pilot Super Sport is a decidedly less civilized ride. And while all three of our tires lost a similar amount of tread–about a millimeter to a millimeter and a half–the Rival S offers less tread depth to spare than the Pilot Super Sports. And if you’re worried about treadwear on the R1, then you’re looking at the wrong type of tire to begin with.
If we were to offer any kind of conclusion here, it would be just how extreme today’s crop of extreme performance tires has become. They’re basically race tires with the added bonus of some streetability. Unless you happen to run in a class or venue that requires true race tires, the complete track tire experience is available in a more civilized option.
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