In early autumn, NASA sent me a set of the new Hoosier RCES tires to evaluate them on a Spec Iron car, answer some questions the Spec Iron racers had about the new tire, and share this information with NASA racers who will be using the tire next year. I was not involved in the prior testing and selection of this tire, so I do not have as much time on them as some of the other racers who helped to test it, but I can bring a fresh set of eyes and an unbiased evaluation.
Size, Fit, and Weight
I weighed a new, unmounted 275-35-18 RCES at 21.9 pounds. I have not seen an official weight from Hoosier yet, but the R7/A7, which shares molds with the RCES, but not construction or compound, is listed as 23 pounds. I did not have any new Toyo RRs to weigh, but a well-used one was 24.6 pounds, with a published weight of 26 pounds. I would expect that comparing new tires, the RCES will be at least 3 pounds lighter per tire.
The Hoosier RCES looks wider, but it is only a quarter-inch wider than the Toyo RR at its widest point when mounted on the spec 18-inch x 9.5-inch wheel. The RCES is built with a bead protector, so the tire has a step right past the wheel flange that is the same width as the tire bulge, and that makes it look larger than it really is. It also appears that the shoulder has a more square profile that puts more rubber on the track, but without a new Toyo RR to compare to it’s hard to say that for sure. Diameter appears to be identical.
Measuring track width on the front of the car with approximately 3 degrees of negative camber, the difference was closer to an eighth-inch rather than the quarter-inch wider I would have expected. In theory, negative camber would decrease the difference in track width, but I think the difference has more to do with how toe plates sit on this tire. With the bead protector being as wide as the bulge, the toe plate has six points of contact instead of three. It sits slightly different on this profile, and it is a little tricky to ensure the plate is flat when taking measurements. Be careful when checking and setting toe with toe plates that you are getting a good reading.
With the new dimensions in mind, my recommendation was to increase the Spec Iron track width by 1 inch. My car did not have any clearance issues on the inside — I ran the same spacers as I do with the RR — but some other cars might, depending on how the slotted strut attachments on the spec struts are used. Adding a half-inch of track width would allow racers to put all of the extra width on the outside in case of clearance issues on the inside, and the additional half inch adds some room if additional camber is needed. There is plenty of clearance to the bodywork so the extra 1 inch of track width won’t cause any issues.
Driving Impressions
When NASA racers hear “Hoosier,” they tend to think of the R7/A7, sticky, fast, but tricky when they are cold and still a little tricky when warm. Those fast, big-power, big-tire cars in your run group tip-toe around for three laps getting in the way until they can get the tires up to temperature, then come blasting back by you. The RCES tires are anything but tricky to drive. I found them to have the qualities we all like in the Toyo RR, but more so.
The first session out, with the stickers still on the tires and much higher pressures than I would expect them to need, they felt solid and sticky from the moment I hit the track. I followed Hoosier’s recommendation for the first session to bring them up to temperature slowly and was careful about pushing too hard on a tire I had never driven. I was still expecting them to “bite” me in the first laps, but they never did.
As I continued to drive them — a total of four sessions and 90 minutes of track time — I found them to be incredibly good cold. On my last session, turning onto pit lane in first gear at 2,500 rpm, I stabbed the throttle to 100 percent and it just hooked up and went. No spinning, no drama, just a tire that was ready to go. As soon as you get to the first turn, you can push them hard with confidence. Race starts are going to be fun on these tires.
After I got past the first session break-in and into the second session where I could push them harder, my first thought was that it was a really good copy of a Toyo RR, and anyone accustomed to an RR would have no problem jumping right into these. As I got more time on them, I started to notice some of the subtle differences compared to the RR, and it made me like them even more.
On the more technical side, my feeling is that this tire has more cornering stiffness than the Toyo RR — it takes less slip angle to generate the same lateral grip — yet it has a more gradual curve near peak grip. The RR seems like once you begin to sense it is approaching the limit, it means you are pretty much at peak grip. Turning more won’t cause it to completely wash out at first, but it doesn’t make any more lateral grip, either.
On the RCES, the more gradual curve means that once you start to sense it approaching the limit, you can still add a little more steering angle and get some more lateral grip out of it before you reach the peak. So despite the higher cornering stiffness that would typically make it harder to drive at the limit, the limit is as easy to approach as the RR.
That translates to some qualities I think everyone will like. First, it makes the car feel more nimble — at least as much as you can call a 3,500-pound solid-axle Mustang nimble. It turns in a little quicker, reaches its peak quicker, and is more responsive to changing direction. It feels “racier,” like you hopped into a car that was just a little lighter and smaller. It is as easy to control as the RR, but it stays in a narrower range of slip angles. You can still drive it hard with confidence, but when you do reach the limit, the pushes and slides aren’t as exaggerated. You might need to fine-tune your senses to keep it at the very peak of the narrower range, but it’s not going to bite you. Your videos might not be as exciting to watch, but you will like driving it more.
I also did a few really hard hits on the brakes — 2,000 psi from 130 mph — and the ABS worked quite well with the RCES. My guess is that the more gradual grip peak is easier for the ABS to control. I’m sure this will vary depending on what pads you use, but I think it will be easier to get the car to turn while you are still hard on the brakes, instead of it wanting to go straight with the ABS cycling like mad. Having more confidence and control when you are deep into the ABS will make the racing that much better. You might be able to make that optimistic move work after all, but please try it on someone else!
My sessions weren’t long enough to get a great read on it, but I found the RCES was consistent throughout the duration, even during the last session where I purposely over-drove it to try to get it to fall off. It never did. Certainly the peak grip changed as the tires got hotter and the pressures changed, but it never felt like it was falling off or getting sloppy.
Performance and Wear
I did the track testing at NJMP Thunderbolt on a sunny day with highs in the 60s. I know the track, but I had never had my Spec Iron car there. In fact, there isn’t even a Spec Iron track record because there has never been one raced there. Despite that, I was able to compare notes with friends who race in NASA and other organization’s other classes there, and compare times for my Spec Iron car at other tracks where we both race. I’m confident that these tires are going to be at least 1-2 seconds a lap faster on a 1-minute, 30-second track.
NJMP Thunderbolt was repaved this year, and it is similar asphalt to what was used at Mid-Ohio, which we have found to be grippy, but not abrasive. I didn’t put enough time on the tires to make a good evaluation of wear — 90 minutes over four sessions — but by the end, three of the four tires still had the mold line in the center visible and none of the tires looked like they had any significant wear.
Pressure and Setup
Four sessions isn’t much time to work on tire pressures, but my car has tire pressure monitoring, so I can correlate how the car performed at different times during a session with the actual pressures. I still have some work to do, but I am expecting that the ideal hot pressures for Spec Iron will be in the 32-35 range, which matches the Hoosier recommendation.
The setup on the car was unchanged from my last race at National Corvette Museum on Toyo RRs. At no point did I feel that it needed any balance adjustment from the sway bars or springs. Considering that I usually have to make slight adjustments as we go from track to track throughout the season, I am confident that switching from Toyo RR to Hoosier RCES won’t require anything more than small adjustments, if any. There are probably some performance gains to be made from optimizing the camber, but you can swap to the RCES without concern that your car will need a lot of work to get it balanced again.
Mounting and Balancing
According to my tire guy, it was a little more difficult to get the tire on the wheel compared to the Toyo RRs. The sidewall seemed stiffer, but once it was on the bead, they seated quite easily. On the RR, he has to remove the valve stem core to get air in fast enough to seat the bead, but on the RCES he didn’t have to. That points to a slightly larger inner diameter, which is notable because the RCES slipped on the wheels quite a bit on the track. Balancing didn’t require excessive weight, which points to good tire uniformity.
With the RR it wasn’t unusual for the tire to slip on the wheel initially, but it tended to be a small angle — less than 30 degrees — and once it slipped the first time it stayed where it was. The RCES slipped on the wheel every session. On three of them, the slip was modest — the worst one was about 75 degrees off after four sessions, and by the fourth session they only moved 5-10 degrees — but the left rear slipped significantly more. By the fourth session it had gone past 360 degrees, and moved as much or more in the fourth session than the previous sessions.
My tire guy knows to use as little tire lube as possible, and uses one that is not supposed to be slippery after it dries. These tires were mounted less than 36 hours before they were used, so they may have slipped less if they had more time to dry.
There is only one second-gear turn on Thunderbolt, and it is a tight left, so I would have expected that the right rear would be most likely to spin. It is possible that the left rear wheel, while the “same” wheel as the others, had more paint on the inside of the rim or for some reason was more slippery than the other three.
The R7/A7 can slip on the wheels as well, and Hoosier is going to provide some suggestions on how to minimize it. If the uniformity of the tires is good, it might be best just to have the wheels balanced once with no tires on them, and then mount tires without balancing. As long as the new tires have less imbalance than what is typically seen in use from wear and rubber pickup, it won’t make a difference.
Dyno
A few days after testing on the track, I tested the Toyo RR and Hoosier RCES back to back on a chassis dyno. Each tire had three simulated compliance sessions of three consecutive pulls, nine total. The Toyo RR was run first and all nine pulls were within 2.5 horsepower and 3.5 pound-feet of one another. The Hoosier RCES was run second, and all nine pulls were within 2.7 horsepower and 2.4 pound-feet of one another. The RCES was an average of 3.8 horsepower and 4.2 pound-feet lower than the Toyo RR. The dyno difference equates to approximately 45 pounds, which will more than offset the weight loss from the tires of approximately 12 pounds.
Overall, I am very impressed with the new RCES, and I am looking forward to racing on it next year. If the durability and consistency match the Toyo RR — and everything I know so far says that they will — this new tire should be a positive change for Spec Iron.
