Data acquisition at work exploring a street tire question

Image by D.E. Baer

Data acquisition at work exploring a street tire question

SCCA / SportsCar Magazine

Data acquisition at work exploring a street tire question

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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 ordered 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 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.

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