More durable/affordable tire option?

[39PitCrew]

Handling: I think this is one of the most fascinating aspects of this tire. I have heard so many times that popping on a fresh set of RR’s will cure all of the car’s handling issues. People love how these tires handle when they are new and hate how they handle when they are all used up. Changing the overall amount of grip can have a small effect on handling balance but it shouldn’t dramatically change the handling.

I believe what is changing is the effective shape of the slip angle graph. The slip angle graph for this tire seems to have a pretty flat and wide peak on fresh RR’s. This wide peak allows good grip over a variety of slip angles and masks subtle balance issues and handling deficiencies. As more time/abuse is put into the tire, not only does the peak grip level dip down a bit, but the peak becomes sharper. This sharp fall off of grip past the peak quits masking issues and requires the driver to sense much more subtle inputs to keep the car near the peak grip level. The car is just flat harder to drive. The drop in performance depends not only on the condition of the tire but also the base handling of the car and the ability of the driver to deal with the sharper peak. If anyone has any further insights to expand or contradict this thought, I’d love to dig into it deeper.


On a practical application of this knowledge, we’ve found driving through a handling imbalance is a bad idea with these tires. One event at Cresson had Dan with a bit of understeer early in the weekend. He thought it was tolerable and didn’t want me to change anything. A couple of sessions later, he had abused the front tires enough that the front tires were signing off and the understeer was now magnified to intolerable levels. We made changes every session that should have made the car an oversteering pig with no success. I didn’t catch a clue to what was happening until we got back to the shop and looked at the differential tire wear front to rear. Now I hammer on balance with Dan early in the weekend and we often end up changing rear springs or sway bars during the event to keep on top of it. When the engine runs, anyway…


Richard P.

Richard, I'm not any sort of expert on any of this but the mechanic in me thinks what you say makes a lot of sense.
As I've read a couple of the tire threads here, I'm left to wonder about some things.

If I understand the issue: consistent performance over many driving cycles; where "many" is some arbitrary number, say 20.
The secondary issue: amortizing $$$$ spent across the # of driving cycles before the tire tread thickness reaches gone/cords
or the tire becomes substantially uncompetitive or dangerously unpredictable for door-to-door competition.

It seems to me that some of the discussion is adding in a performance component, that is, how "sticky" the tire is during it's usable life.
I think the primary goal of the discussion is two-fold - keep performance fair and keep the consumables budget reasonable.
So the dilemma is: the softer (stickier?) the tire, the faster it wears ($$$) but you get better (lower) lap times. But, a
soft tire also has a much smaller sweet spot related to it's maximum performance over a certain number of driving cycles.
A tire that has a harder compound will wear longer. But the trade off is that maximum acceleration, braking and cornering forces
are reduced by some amount. (And I get it, we're talking about race cars so it's hard to say higher performance is a bad thing.)

So, if the choice is made to use a harder compound tire, does it follow that the car's set up and the driver's racecraft must be better
to achieve the same performance (ie. lower lap times) that comes with a softer compound tire?
And a possible corollary: the more grip a tire has, the more wear/abuse the car's mechanical parts take.
So, more heat/wear in the brakes, diff and trans loads are higher, more heat and higher loads on wheel bearings, more chassis torsional forces, etc., etc. - right?
And based on threads here on the forum and many random discussions at the track over the years - car set up is hard. Well, mechanically
it's easy, dialing it it for optimal track performance is hard. Even NASCAR and F1 teams who have really smart people and spend millions of dollars
to figure that stuff out don't get it right every time.

Thoughts anyone?
Scott

[mach1]

I didn’t even consider the lower wear and tear with a 200tw tire, longer hub and brake life, #winning!

[drecords]

I didn’t even consider the lower wear and tear with a 200tw tire, longer hub and brake life, #winning!

Truth! We'll see how different the laptimes really are

[RichardP]

Tire test setup:

It’s important that if we do a tire test, we pay special attention to a wide variety of parameters to make sure the full package is suitable. We don’t need a different tire, we need a better tire. We also need to agree on the definition of “better” in this context.

First, per the rules, if a race car isn’t on Toyo tires, it isn’t “racing” in CMC (or AI). Without Toyo’s, no CMC season points are accrued, no Toyo bucks are earned. Also, if a legal CMC car is fighting for position with a non-legal CMC car, technically that could be considered out of class racing.

There are a couple of different ways to run this. If you have a non-legal car, you can “fun run” in your normal class. I think a better option is for the tire test folks to run AIX. That keeps things a bit separate and the “winner” of the tire test potentially gets a plastic trophy, some winner stickers, and a season championship! I’m happy to supply AIX stickers to any tire testers for this test. When we had both CMC and CMC2 racing together, I pushed for decals on the windshield and back glass so competitors could easily tell who they were racing for position with and who they weren’t. I think something like that would be good for this.

As I posted earlier, there are a number of relevant parameters we would be testing for. How does the tire feel, how well does it stand to abuse, if you overheat it does it come back after easing up for a lap or is it dead for the rest of the session, etc.??? These are pretty easy to test for in just a few sessions. In my opinion, we can only really tell what we want to about the tire under full race conditions with cars fighting for position.

The much bigger question is how much do the tires degrade with heat cycles? If all of the tire testers start and run the whole weekend on fresh tires, we learn exactly zero on this aspect. Ideally, this test needs to span multiple weekends and possibly multiple sets of tires. In order to figure anything out, we need to have a guy on stickers battling a guy who has at least one full weekend of abuse on his tires. We could have some testers start the weekend on fresh tires and have others wait until Sunday to put the stickers on. Josh is running a Houston DE the first weekend in March and could do his best to wear the test tires out before our race weekend. The more testers the better if we hope to get any real findings.

Getting useful data from a test like this is pretty tough. Initially, we have to figure out what these tires want and get them to work with our cars. What tire pressures do they want? Do they do better or worse with our camber settings? Do they work better with stiffer or softer sprung cars? Slapping on a different style of tire and judging them after a session or two without tuning is very useful. Also, some drivers adapt to changes quicker than others.

The other question is what specific data are we going to be looking at? Certainly lap times are key. Comparison of test tire lap times to Toyo tire lap times is certainly interesting but not really relevant to our test. We need to be looking to differences between tire test competitors. We need to pay special attention to lap time degradation between test subjects, especially those that are on tires with differing heat cycles.

One of the hardest parts of these types of tests is the other variables that are hard to control. Weather, traffic, car setups, etc. are all a big deal but not as significant as the difference between drivers. One example of things we can try to mitigate would be to have competitors swap tires between sessions. Have Josh start the race weekend on heat cycled tires while someone else starts on stickers. After a couple of sessions to set a baseline, have the two swap tires and see the relative change. This could help answer if the difference between cars is the driver or tire wear.

One other thing that would help with testing. The test drivers actually need to race each other. Starting on pole for the invert because you had a problem in the first race and trying to run away with it is something that I might want to do (OK, have done) but it isn’t helpful for our testing. Traffic, cautions, or other situations might lead to some of the test drivers having to wait up for the other testers.

On a personal preference note, I would prefer to suspend any tire testing for the Hallett event. The racing there is too much fun (sacred even) to split up the group. I’d love to see everyone on a fresh set of Toyo’s for this spectacular, multi-region event.

Richard P.

[Al Fernandez]

A couple of additional variables:

What is the tread depth of the test tire as it sits on the shelf and would they be faster if shaved? If indeed there is a compound/design that eliminates drop off due to heat cycles (or Richard's time at heat) then would the tire actually get faster and faster as the weight is shaved off and ultimately being fastest right before it cords? Is it possible we flip to a "thin to win" world where you're buying new tires every weekend, shaving them to 1/32" and hoping to not cord them before the checker?

Why the Azenis? There are at least 10 200utqg rated tires in 255 (which we ran for years) and some are a lot cheaper than the 615+. The Kumho V720 is 140!

[Al Fernandez]

So ok, taking my competitor hat off and putting on my series official hat...
Cars that are not cmc legal can’t score cmc points, so classing cars in six would appear logical. What Will does with such a run group would be his call. I have told Shawn Meze (nasa national competition director) about this discussion so hopefully atwe will get some input from nasa on the situation.

[64GunPilot]

People talk about the R888 debacle. What went wrong there? 615's vs R888 vs R888r? Prices are about the same on Tirerack. Curious to know why everyone dislikes the R888?

[Sook]

A couple of additional variables:

What is the tread depth of the test tire as it sits on the shelf and would they be faster if shaved? If indeed there is a compound/design that eliminates drop off due to heat cycles (or Richard's time at heat) then would the tire actually get faster and faster as the weight is shaved off and ultimately being fastest right before it cords? Is it possible we flip to a "thin to win" world where you're buying new tires every weekend, shaving them to 1/32" and hoping to not cord them before the checker?

Why the Azenis? There are at least 10 200utqg rated tires in 255 (which we ran for years) and some are a lot cheaper than the 615+. The Kumho V720 is 140!

The azenis have at least some pedigree in other race/track classes. See TT street tire class, and spec Corvette, without shaving (so far).

- Josh

[Supercharged111]

Because this is a science experiment at this point, have you guys considered super sizing and running the 615 in TT or PTX/STX and Toyos in CMC in the same weekend to preserve car counts?

On a side note, will 225 tires fit my Z06 wheels? The desired end state here is reduction in costs, sure would suck if I had to run out and find new wheels.

[RichardP]

What is the tread depth of the test tire as it sits on the shelf and would they be faster if shaved?

Definitely one of the advantages of the current RR is no shaving. Shaving adds cost and significantly reduces the places available to purchase. I think a rule that tire shaving isn't allowed would be fine. We already have rules that are hard to police (including using tire treatment on the current tires). In order to cheat the no shaving rule, you would have to buy shaved tires and then run them hard for a while at an event where there aren't any other competitors to see what you are doing. If the tire grip doesn't degrade with use, this would likely be a big hassle and a waste of time.

Of course, the big disadvantage of the current RRs is that they don't work as rain tires. You need an extra set of wheels with a special set of tires (that are probably going to dry rot before you get to use them) to be competitive when the skies open up. The difference between the haves and have-nots is huge in a downpour. You also have the game of guessing what the best tire is when conditions are changing.

I was looking at 255s, the price difference to the 275 is substantial. I think for the first test we should all be on the same size tire.

https://www.tirerack.com/tires/tires...15KP&tab=Sizes

- Josh

255s sound good to me. $600 every two events vs. $1100 every event would be a serious game changer in overall racing costs. Also, your rain tires would just be the next set of fresh tires that you were going to buy and use anyway.


Richard P.