The weeks between the U.S. Grand Prix at Mazda Raceway Laguna Seca (July 27-29) and Indianapolis Grand Prix at Indianapolis Motor Speedway (August 17-19) have nearly passed, and practice for the latter will start this Friday. MotoGP first came to this Hoosier city in 2008 on a composite track 2.620 miles long made up of the front straight of the famed oval, an infield Formula One section constructed in 1999 and a join section beginning with Turn 1. Each had its own pavement, and bumps were plentiful on this circuit’s 10 left-hand turns and six rights.
MotoGP runs counter-clockwise on this course, opposite to F-1. Race distance is 73.4 miles, and in the dry, the 28 laps take just under 47 minutes. The highest straightaway speed was achieved in 2009 at 204.99 mph, but the two first-gear and eight second-gear turns bring the race average speed down among the season’s slowest. Casey Stoner’s current lap record of 1:39.807 will surely be eclipsed.
Why is that? Because, in response to many crashes in 2010 that were attributed to the bumpy surface, 1.5 infield miles of the track were resurfaced shortly before the 2011 race. This left the surface so slick during Friday practice that Yamaha factory rider Jorge Lorenzo said, “To be honest, I have never raced on a track so slippery.” Another called it “green and gripless,” while a third said, “It’s as though it was wet!”
As bikes laid down rubber, the racing line improved, but off-line, the surface remained very tricky. Lorenzo said the track “is improving every session. Overtaking is a problem.”
Bridgestone tire engineer Hirohide Hamashima said, “The new surface started off slippery on Friday morning, and because of this, we experienced quite a bit of tire graining during the first free practice, particularly on the rear tires. The more laps were run on the circuit, however, across all classes, the more conditions improved.”
Tire “graining” is the formation of parallel “beach lines” on the tread surface, oriented at right angles to the thrust direction.
Hamashima continued, “The line became clearer and grippier as more rubber was laid down on the racing line, and this changed the challenge for the tire and also the focus of bike setup. As the general grip level improved, rear-tire graining was reduced a great deal, but as rear grip improved, many riders experienced the front tire pushing, and so front-tire graining and wear rate were higher. I can say that overall durability was good as many riders set their fastest laps toward the end of the MotoGP race, including Casey Stoner’s lap record on Lap 20.”
Many people commented on how unusual it was to find a track abrasive and slippery at the same time.
Now that a year has passed, all are hoping the binder oil in the new pavement has had time to evaporate in hot sun or be washed away by rain, leaving a mature and grippy surface. If this proves to be the case, faster lap times may result. On the other hand, this year’s new “fast warm-up” tires with their softer construction may respond to this track in some unforeseen way.
The higher the grip, the more likely it becomes that the factory Hondas of Stoner and Dani Pedrosa will encounter the chatter that has at some tracks reduced their corner speed. Because there is some hard braking at Indy, the problem of braking instability—brought on by the suppleness of the new front tires—may plague the Hondas, as well. The rapid sequences of turns may favor the agility of the Yamahas, but only race day can take the sum of all variables.
Hamashima’s description of the circuit is a good one. “Indianapolis is a relatively hard circuit for the left shoulders of our rear tires in particular because of the speed and long nature of left-handed corners, such as Turns 1 and 5. Being leaned over for a relatively long time at speed creates some of the highest rear tire temperatures of the year, and for this reason, Indianapolis is the only Grand Prix all year for which we have selected the extra-hard compound rubber in the left side of the rear slick tires.”
Both asymmetric rear tires offered by Bridgestone at Indianapolis in 2011 carried soft rubber on the less-used right side. Soft, medium and hard fronts were offered, the soft mainly for cool morning use in practice. Rears were offered with hard or extra-hard compounds on the left side.
In 2009, Bridgestone engineer Tohru Ubukata gave this useful description: “The infield offers a succession of slow corners followed by hard acceleration, and the circuit is also quite demanding on the front tire due to some very hard braking points. We have chosen our asymmetric rear tires for this race because the circuit uses the left side of the tires much harder than the right sides—there are more left-handers, and generally, the fastest corners are lefts.”
Here are the top-five finishers in each Indianapolis MotoGP, along with other useful information:
|Temps (F) air/track||70/68||68/81||95/133||81/135|
The American Midwest can be amazingly hot in August. My Indianapolis-born dad used to say that, “The daytime high of 94 degrees plummets to a nighttime low of 93.” Temperature is the variable that can make nonsense of rider tire choices. Watch it!
See the names at the top? Those are the “aliens”—the men who so often pull away from the pack as if propelled by a mysterious force not available to the others. Also notice the name “Dovizioso”; he’s always there. Much of the mystery, it turns out, is their wonderful ability to monitor tire condition on the fly and to manage it intelligently so they have grip at the end with which to fight off rivals. These riders also wisely set up their bikes to work through race distance, not for the fastest possible lap. Many more riders are fast than are fast at the end.