senor honda

Data acquisition at work exploring a street tire question

Image by D.E. BaersharetweetemailBy: Philip Royle | 9 hours ago
The concept is nothing new, but we’d never done it before. So we loaded up a race car and headed to the track to compete on 200 treadwear street tires. The goal was to capture as much data as reasonably possible during a race weekend, and use it trying to figure out whether ultra-high-performance street tires could hold up to the punishment of SCCA road racing.

We also wanted to do this in a way that anyone with an affordable data acqusition system and a race car could mimic.

Our decision to race on street tires wasn’t out of the blue. Late in 2018, the SCCA queried its membership as to whether 200 treadwear tires should be introduced into club racing. The response was not overwhelmingly for the proposal, but the idea didn’t stop there. Soon thereafter, SCCA classed an optional configuration for the Scion FR-S and Subaru BRZ


in Touring 4, with these cars being given the choice to run at a reduced T4 weight if they met the bulk of the autocross Solo Spec Coupe rules — including the use of 200 treadwear tires (although they can run any brand, not just the spec Falkens required per the Solo Rules).

While SCCA’s street tire proposal for certain road racing classes didn’t pan out, it really made us wonder how our old Touring 4 Nissan Sentra would perform on them.

Our Testing Procedure
We wanted to gather data for this story via methods achievable by the average racer. We could have rented a track, brought in a professional driver, and sought out a professional data analyst to interpret the files, but none of that is easily reproducible by you. Instead, we entered an affordable SCCA Cal Club Region race at Buttonwillow Raceway Park that also featured a 90-minute enduro, and we brought along a reasonably priced, off-the-shelf data system to capture information about the 200 UTQG tires we’d be racing on.
For our street tire test, we purchased a set of Maxxis Victra VR-1s. Image by Phillip Royle
For tires, we ordered a set of affordable 225/45-17 Maxxis Victra VR-1 200 treadwear tires and installed them on our T4 Sentra. The VR-1 Maxxis tires may not be well known in SCCA circles, but they are used by several road racing and track day groups, and have a proven history of holding up to multiple hours of abuse at the track.

At less than $130 per tire, they’re also a bargain.

To capture data, we outfitted the car with an AiM MXm data acquisition system and AiM’s infrared tire temperature sensors. Admittedly, the AiM MXm data system was not our first choice — we originally planned to utilize an AiM Solo 2 DL to gather accelerator data. But a call to AiM turned us on to a different product: the MXm.
The AiM Sports MXm unit pulled and processed raw data from infrared tire temperature sensors.
Touted as a “compact data logger”, installation isn’t as straightforward as with the plug-and-play, battery-powered Solo 2 DL, but it’s nearly as easy. It requires some kind of mounting plate (we screwed it into a block-out plate on the dash) and must be connected to a 12v power source. The advantage to the MXm over the Solo 2 DL, however, is that it allows for the use of external sensors. Because of this, we ordered AiM’s tire temperature sensor kit to plug into the MXm. The bump in cost between the two is not outlandish: The MXm will run you about $1,099 vs. the Solo 2 DL’s $699.

AiM’s infrared tire sensors offer a 35-degree field of view, with the sensors measuring temperatures from -4 to 248 degrees F. The sensors cost about $100 each and plug straight into the MXm and AiM’s Race Studio software, making the setup so straightforward even we could do it.




We did discover that distance from the tire’s surface makes a difference in the temperature sensor’s readings, undoubtedly due to the amount of surface area the sensor can see. We mounted the passenger-side tire sensor nearly an inch farther from the tire’s surface than on the driver’s side to see what the difference would be, and we saw peak temperatures sometimes 40 degrees lower than the sensor placed closer to the tire. Does this matter? Not so much, as we were looking for general temperature fluctuation, not absolute readings in pinpoint tire locations.

Knee Deep in Data
Data is largely useless without something to compare it to, but that doesn’t mean you need reams of data from multiple cars and tracks to pull from. In our case, we were comparing data on the T4 car over the duration of a 25-minute race followed by a 90-minute enduro on the same day. Believe it or not, there’s plenty to learn from that scenario.




While there are many methods for analyzing data, for us, the lowest-hanging fruit in this test was lap consistency. We pulled up data from the enduro and discovered a lap time variation of no more than 0.776sec during the final 40-minute stint, with most laps falling within a half-second window. We also discovered that the driver turned his fastest time of the day on the penultimate lap of the 90-minute enduro, showing that the Maxxis Victra VR-1 tires were good to the end.
Lap time data from the final portion of the 90min enduro show tire consistency over the long haul.
Next, we pulled up lateral (cornering) and longitudinal (braking) g-force data. We initially compared our fastest lap to a lap earlier in the enduro and discovered the g-forces were nearly identical, so we decided to overlay a session from earlier in the day and found cornering and braking forces were all comparable. This showed that the tires ran hard for the duration of the day, taking more than 120 minutes of abuse without falling off.

senor honda

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