More durable/affordable tire option?

[liquidroam]

With a thought of changing from the spec tire, I thought I would put down some of my thoughts on the current RR’s. First, some relevant tire parameters:

Life – I’ve found the current RR’s have a pretty long life. I regularly run tires that are on their fourth event (‘cause I get them for free). Josh has run sets well into their fifth event multiple times before they completely give up or cord out. In order to get them to last that long, you can’t flat spot them when they are fresh and you have to have reasonably good camber and balance. You also need to flip them on the rim, preferably after every event. Still, that’s a lot of laps for a race tire.

Durability: Dan got a puncture at the last event but I think that’s the only time I remember having an issue. Also, there is a potential issue with the tread seam coming apart. We run the tires in the recommended direction at the first event and then ignore the direction for the rest of the tire’s life. Our team has only had an issue with the seam on one tire when it was new and that came with a serious vibration. Seems to be a pretty tough tire to me.

Endurance: How hard can you push the tire in a session before the grip goes off? The biggest complaint about the 888 was that if you pushed it at all, it would get greasy and grip would vaporize. It was no fun to drive and almost prohibited on track battles. It was horrible for racing. In this respect, I think the RR’s are pretty amazing. You can abuse and over drive these tires and, for the most part, they seem to keep holding their grip. I think abusing these tires hurts their effective life but they hang in there. I think this is a critical parameter to an exciting race tire.

Looking at that stuff, it seems like a great tire. I actually think it is. If someone was handing out fresh tires every race day, I think this would be a spectacular spec race tire. But, tires aren’t being given out and there are a couple of other critical parameters that make these tires not so good for a class that needs to run a set of tires in multiple events to make the budget work. In a class that is supposed to give each competitor equal grip from a spec tire, this tire has more variability than any other performance parameter.


Heat cycling: This is a common term for the performance of the tire falling off after a certain number of track sessions. I see numbers all over the map of how many heat cycles people think these tires are good for. I’ve come to the conclusion that the term “heat cycles” probably isn’t the best terminology for these tires. It’s not that heat cycles don’t apply to these tires, it’s just that heat cycles aren’t all created equal. I think it’s more that the tire is capable of a certain amount of time at temperature. The higher the temperature, the less time you have. The number of effective heat cycles you get depends on how much abuse the tire sees. These tires tolerate over driving pretty well but it comes at the expense of reduced effective performance life.

So why does the performance of the tire drop after use? Tire construction, materials, chemistry, and processing is very complicated and generally considered complete voodoo even by tire engineers. In the past, it’s been said that race tires effectively come as partially cured rubber. Further heating and distortion of the tire finishes up the curing process and the tire becomes harder. There is some thought that Toyo could process the tires differently and deliver them fully cured. In theory, this would lower their initial performance but make them more stable over their life. I’m not sure if that’s true but I sure would like to see it. I believe Toyo’s incentive to do that is low…

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.

Sooooooooo that is a yes, you are volunteering Dan to run the 615s? but seriously..... Dan?

[liquidroam]

Nvm... that was a waist of my post, just saw the list on the roll call thread