Data acquisition at work exploring a street tire question

Image by D.E. Baer
sharetweetemailBy: Philip Royle 9 hours ago
Comparing data from an early lap to a later lap shows little variance.
Diving into the specifics, we found our 2,750lb, front-wheel-drive T4 car on the Maxxis VR-1 street tires consistently attained 1.09g of lateral force and knocked out 1.08g of braking force from lap one to the end. There were g-force peaks from bumps on the track, but we stuck to the data that represented the car’s performance, not the track’s idiosyncrasies.




On its own, specific g-force data is interesting, but it doesn’t show a complete picture. This is where alternate comparative data comes in handy. As such, we accessed data from our Touring 4-class 2015 Honda Civic Si project race car that was also outfitted with an AiM data system, and discovered the 2,975lb Civic on 225/40-18 BFGoodrich R1 S R-compound tires could pull 1.3g of cornering force at the beginning of the 2016 SCCA National Championship Runoffs, although it struggled to hit 1.25g by the end of the race.




Surprisingly, we found the braking force was similar between the Civic on R-compounds and the Sentra on street tires, with the Civic pulling 1.07g on the same compound Hawk DTC-60 brake pads.

Analyzing lap consistency between the two cars, we found our race lap time variance was far greater in the Civic on R-compounds than in the Sentra on Maxxis street tires, as emphasized by the decrease in the Civic’s lateral g-force as the race progressed. This, however, could probably be attributed to the Civic’s 225lb bulkier weight and Mid-Ohio’s brutal circuit vs. Buttonwillow’s relatively mellow layout.

It was hard to reach a definitive conclusion on this one.
Overlaying tire temperature and braking force show’s the tire’s cooling rate between corners.
And what did the tire temperature data reveal? We found that as the race progressed, the tires would generally not cool as much on the straights, with tire temperatures sitting about 10-15 degrees F higher on the straights in the later laps of the enduro. The braking and mid-turn temperature peaks were roughly the same as early on, however, which further explains why the tires did not lose grip during the extended session.




Drawing Conclusions
Our data collection exercise showed multiple things. One is that 200 treadwear tires can take the abuse of racing. An analysis of the Maxxis VR-1 street tires after roughly 120 minutes of on-track racing showed that the lifespan of these street tires is comparable to that of the top-tier R-compounds we’re used to running. But the price is the kicker: a set of Hoosiers A7s or R7s for our test car would have cost $1,193 through Tire Rack, while four BFGoodrich R1-S or R1s would cost $1,095. Meanwhile, a set of Maxxis VR-1 street tires set us back just $511 from Maxxis.



Our test also showed that while our T4 car on street tires could brake just as effectively as our 2015 SCCA Runoffs-winning T4 Civic on R-compound rubber, the street tires just couldn’t sustain the lateral g-forces of R-compounds. What’s the ultimate lap time difference between the two types of tires? Obviously, we don’t know — we’d need to run R-compounds on the car at the same circuit on the same day as the street tires for that data, and we didn’t. But we do know that street tires are slower, and we know they’re slower because of decreased cornering force, not a lack of braking. In a big horsepower car, they probably would limit putting power down on corner exit, too, but with our test being on low-powered cars, that was not an issue.

Finally, data aside, here’s the ultimate question: Are 200 treadwear street tires a future that SCCA Road Racing should consider? That, my friends, is a question best answered by the SCCA through member input from you. But we will say that we had fun in our T4 car on street tires. So, come the next enduro, we’re going to order up another set of Maxxis tires and put the money we save into brats and beverages.

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AiM, Maxxis, SCCA / SportsCar Magazine