Michael Shank Racing Riley-Ford. (LAT photo)
The detailed analysis of what went wrong with Prototype tires during the first day of TUDOR United SportsCar Championship testing at Daytona International Speedway has only just begun, and certainly will occupy the coming days for IMSA, tire manufacturer Continental and Daytona Prototype chassis maker Coyote.
One concern for the TUDOR Championship’s November tests involved the move from last weekend’s outing on Sebring road course to the high banks at Daytona on Tuesday and Wednesday, where Prototype chassis and tire loadings would increase significantly on the oval portion of the circuit.
IMSA’s new, high-downforce DP package would ask more of the Continental tires on the Daytona banking than at Sebring’s fast Turn 1 section, and would also see the DPs sustain the loading for longer durations as cars exited the infield and made the run through NASCAR Turns 1 and 2, and again after leaving the Bus Stop complex to accelerate through NASCAR Turns 3 and 4. The right rear tire, wheel and suspension, specifically, would receive the highest forces. Whether all three items or individual components could stand up to the forces would have to be proven over a sustained period of running.
DP diffuser/lift generator (Marshall Pruett photo)
CHASSIS AND TIRE PREPARATION
Through a new dual element rear wing and an impressive tunnel/diffuser package for the DPs, IMSA increased the overall downforce figures from 2013 by 60 percent, leading chassis manufacturers Coyote, Dallara and Riley to conduct reviews of the design tolerances throughout their respective prototypes. Those efforts were done to ensure the extra downforce and cornering speeds would not exceed the limits on mounting points, suspensions and all of the other components a massive spike in downforce would impact.
?We didn’t have anything to change because we have so much history with the DP cars, we know the loadings and what they can withstand,? Bill Riley told RACER. ?The DPs are already heavily overbuilt; we normally put 20,000 miles on the suspension and 10,000 miles on the hubs between changeouts, so the extra downforce was something we were comfortable with.?
Leading up to the Daytona test, the series and Continental had also established two separate data points regarding high-downforce prototypes and high speeds at Daytona. Conquest Racing took part in a test with its P2 chassis on Continentals in November of 2012 where no issues were reported, but runs were kept to 10 laps or less. Two other items of note came from the test, where the team reported differences in the lateral loading capabilities of the Continentals compared to the Dunlops it used in the ALMS. Softer sidewalls were also noted on the Continentals, requiring the team to stiffen its springing package to compensate for the differences.
(It’s worth stating that the Conquest test was done to gather information on how the Continental tire worked on a P2 car, making differences in grip, lateral loading characteristics and any other takeaways an expected part of the exercise rather than a declaration of any deficiencies.)
Continental’s 2013 Daytona 24 Hour tires were used during Tuesday’s test, and as one DP engineer told RACER, other than a slight change in spring rates, minimal setup changes were required between the 2012 and 2013 DP tires.
Although some private concerns about how the DPs would fare with the extra downforce and tire loads at Daytona were expressed leading up to the test, it’s accurate to say the chassis manufacturers and Continental felt confident about their products taking to the track for testing.
Between the SDR and AXR accidents, Westbrook’s was far worse, taking place at the highest speed portion of the track entering the braking zone into Turn 1.
The failure on Westbrook’s car involved a few different dynamics coming into play, starting with the location. The Briton had exited the steepest portion of the banking in Turn 4 and was accelerating toward a top speed in the 190mph range as the banking decreased prior to his planned braking and turning left at the first corner.
Westbrook’s right-rear tire then failed without warning, causing the car to rotate 180 degrees. With the bigger rear wing and sizeable diffuser facing the oncoming air at such a high velocity, both items instantly transformed from generating downforce to producing lift, which elevated the back of the No. 90 off the ground and launched it into the air, where it did numerous pirouettes before crashing down to the tarmac, executed a few flips and skidded on its roof before rolling over and coming to a stop on its tires.
The right-rear tire issue was the second of the day for SDR. The first, which has not had a cause assigned, was caught prematurely and did not incur any damage to the car.
Barbosa’s crash bore many similarities to what Westbrook experienced, taking place at a high rate of speed, but slightly slower, closer to the 170mph range.
Coming off of the Turn 2 banking, the Portuguese driver had the right-rear tire fail without warning and had his AXR car go airborne, albeit to a much lesser degree, once the tunnels and wing were fed air from the wrong direction. Barbosa did not tumble through the air, thankfully, as his car lifted up, rotated and eventually set back down on all four tires.
?We didn’t see anything before the crash,? Barbosa told RACER. ?We saw the inside shoulder was getting a little hot, but there were no blisters or anything like that. There was no vibration; the rear tire blew out just as the track started to flatten out. I went around about three-quarters backwards and then it took off.?
SDR and AXR had put approximately 20 laps on new sets of Continentals when their crashes occurred. Westbrook’s happened at the close of a morning session than ran until Noon, and Barbosa crashed as the test drew to a close at 5 p.m., making it hard to pinpoint similarities in track or ambient temperatures as a contributor to the failures.
?In our situation, we were within one stint (on the tires),? Barbosa continued. ?We didn’t do a full stint on full tanks, but we were within a regular stint like we’d do (in 2013). We definitely weren’t trying to double-stint our tires or anything like that. We had done the same number of laps on the first set in the morning and there were no issues, so (the crash) was a surprise to us. The temperature was a little bit warmer in the afternoon, but there was no big change.?
Infrared tire sensors (Marshall Pruett photo)
Following Barbosa’s note regarding higher-than-expected inner shoulder temperatures on the right-rear tire, many DP teams reported the same issue during Tuesday’s test. An overall increase in tire temperatures were seen, and the biggest change came with the temperature differentials across the tire carcass.
Teams and tire engineers use temperature probes to document the heat just below the surface of the tire after most runs, and usually do so with a three-point data capturing process. The temperature close to the outer edge is recorded, then the center of the tire, and finally, the inner edge is documented, giving engineers valuable information on overall temperatures, plus feedback on how camber and toe settings are affecting the tire at each corner.
Tire pressure data is also recorded during the process. In general terms, and provided the camber, toe and tire pressures are close to optimal settings, it’s normal for the inner portion of the tire to be the hottest value of the three recordings, followed by a modest drop in temperature in the middle of the carcass and another drop on the outer edge.
The differential from the temperature at the inside shoulder to the outside shoulder is commonly referred to as the ?split,? and with Continental’s DP tires, something in the 30-degree Fahrenheit range is common. Some teams reported the split being more than double that value on Tuesday, if not higher.
?We had no issues at all,? Michael Shank told RACER. We ran 155 miles on one set (43 laps). The tire degradation was normal, tread depth degradation was normal, and the temps were high, but they weren’t something that we’d never seen before. The temps we saw on the inside were temps we’ve seen before. The splits here high, but it wasn’t anything that alarmed us. We didn’t have any tire issues whatsoever, but I get why IMSA stopped the test and support their call. It was a tough one, but the right one to make.?
Shank, who uses a Riley DP chassis, was on the same 2014-spec high-downforce package on Tuesday as the Coyote DPs, and questions whether the extra downforce set the failures in motion.
?It’s hard to put it all on the loading we’re seeing,? he continued. ?We’re about 1000 pounds of downforce more, overall, than last year,? he explained. ?That part’s really good, but there were a bunch of cars in the new (high-downforce) configuration and not everybody had tire issues.?
Another variable to come from Tuesday involves the Highway To Help DP team.
The Riley users went to Daytona in 2013 DP specification, opting to run without the high-downforce package, yet experienced similar tire issues (without having a blowout).
DP team owner Kevin Doran, who assisted the Highway To Help program on Tuesday, reported an inner shoulder issue on the right rear tire that took place sans the extra 1000 pounds of downforce.
?It was a very unique manifestation on our car,? he told RACER. ?It wasn’t blistering or delamination; our car saw the inner edge wear through and break down the tire structure. I’d never seen it before. It wasn’t a downforce or camber issue. It was odd because we’ve put a lot of miles on these tires and they’ve always been very strong.?
WHAT HAPPENS NEXT?
Tire issues, big and small, took place on high- and low-downforce DPs at Daytona, and across two different chassis. When turned mostly backwards at a significant rate of speed, the next-generation DPs also went airborne, and with time constraints to deal with, fixes are needed with the opening race of the season, held at Daytona, just 67 days away.
All three items will force IMSA, Continental and Coyote to act quickly as they complete their investigations and come up with answers to verify in pre-event testing. The next official test ” the only official test, at the moment ” will take place at Daytona on January 3-5, but DP teams will want to sample whatever updates can be offered ahead of the Roar Before The 24.
Both Chevy and Ford have mid-December tests scheduled at Daytona, and with the lessons gained from Tuesday, Continental says it will soon embark on building its 2014 Prototype tires. The timing for the release of those tires for testing is currently unknown.
?It’s a test, so we’re here testing and we’re going to take what we’ve learned from data, take the tires back and formulate something that will address these issues that we’ve seen,? Continental Tire director of marketing Travis Roffler told RACER. ?It’s a process, it takes some time, it began last night, and we’ll address the issues seen here and move forward.
?The tires that were run yesterday were a design that’s been run here previously. They were used in last year’s 24-hour event, they were also tested on the Conquest race team’s P2 car here at Daytona. This was the first opportunity to put that tire configuration on the new (DP) car design and we’ll take what learn from this test and once our analysis is done, our 2014 spec will be made and released.?
IMSA monitored the tire situation as it developed on Tuesday, and made the necessary choice to halt Prototype testing (along with the Continental-shod PC cars), and began amassing data from the teams in attendance to conduct an investigation.
?It was more of a slow creep,? said IMSA VP of competition and technical regulations Scot Elkins of how the issues came to light. ?We saw a couple of instances early in the day and then it kind of came along (in the afternoon). The reason we did what we did is because we’re not completely sure what’s causing this. We can’t say it’s just loads. It’s happening at a variable amount. We’re just not there yet.?
Elkins told RACER he’s hoping to have some solutions in place for teams to use during private, pre-Roar testing at Daytona.
?We have some other testing that’s already scheduled; it’s not IMSA testing, but we’ll use those tests to define what we need to do before we get to the Roar,? he said. ?It’s a group effort.?
The series has conducted a number of wind tunnel tests at the Windshear facility of late, including one on Monday where Elkins says they ran a DP in yaw ” at three percent” to gather data. Turning a 2014-spec DP close to backward ” somewhere in the 120 to 180 degree range” in the wind tunnel would serve little purpose as the results would be predictable, but looking at ways to limit airflow into the diffuser and tunnels when a prototype is turned around, either by contact, driver error or mechanical/tire failure seems like a worthy project.
DeltaWing hinged tunnel blocker (Marshall Pruett photo)
For all of the negative comments the DeltaWing has received about its styling or visual appeal, designer Ben Bowlby incorporated an incredibly smart and relatively unknown item into the vehicle. With almost all of the original DeltaWing’s downforce being generated from beneath the car, and with the use of venturi tunnels, Bowlby added what’s most easily described as ?NASCAR roof flaps? to the tunnel exits.
With the DeltaWing headed backward while at speed, the flaps would pop open, pointing down in this case, to block air from flowing into the tunnels and creating lift. The devices cannot guarantee liftoff will be prevented; a hit from the side or chassis tilt in general can feed the tunnels, but it’s a rather simple concept to explore on the 2014 DPs.
Another item worth consideration is the allowance of infrared temperature sensors in testing, and possibly during the Daytona race. The rules currently prohibit IR sensors being used to log and transmit real-time tire surface temperatures over telemetry to pit lane, requiring teams to rely on tire pressure sensors and the general temperature data they capture from inside each tire to look for warning signs.
Cost control has been cited for prohibiting IR tire temp sensors, but with the need to capture real-time data and a genuine safety concern having emerged from Tuesday’s test at Daytona, arming teams and drivers with said information would be a worthy change of policy.