Let's talk traction on these bastardized 86s!

[TRS]

Originally Posted by ZDan

A given tire's load capability absolutely does correlate with pressure. That's why sidewall markings always list the max load at a specified pressure, e.g. Max load 1609 lb. *at 50psi* on my new 245/40-17 Yok A052s. At 30psi, max load is much less. But of course for my application the max pressure on the sidewall is irrelevant as static load per tire is way less than 1609 lb. Max sidewall pressure again has zero to do with optimizing pressures for performance. I aim for 34-36psi hot (~26-28 cold)

Sorry, I again have to contradict. Keeping with the example of a constant tire size, the behavior of the tire is a function of its construction and the actual pressure inflated. In reality it is wrong that the pressure is the only variable of relevance. And it is wrong that any tire of the same dimension will work on the same car (same load, samoe model, etc) with the same pressure at optimal Performance. Many track racer will confirm this. If you change the tire for your track tool, and again Im talking about keeping the dimension but changing the brand, you will have to check and realign the pressure. The pressure used before is in any case a good starting point and in some cases you will keep it, but not in every case. If the tire you changed in has a equal design concept, neccesary changes will be minor. If it has a different construction pressure changes might be more drastic.

What is true is that, when you are looking for the pure weight you can carry, you can look at a table and find which pressure is needed for which tire dimensions at a given wheel load. But those are tables for the standard road use. Of course, you can ride on a semi with stiff construction and a UHP which still is more comfort oriented, with the same pressure found on the table without any issue. But pretty likely for both of the two and definately at least for one of them this pressure will not be the optimal performance setting to track race.

And once more: Everything said can NEVER be a generalized rule. It is always necessary to test for the perfect tire pressure for optimal performance. Dont trust any generalized statememts about tire pressure. If one says "thats the always and ONLY good pressure" , this Person dont know the details behind. There is simply no "one and only good pressure".

What can be said is a pressure one uses on a specific tire on a specific model of car. The tire brand/type and size is the minimum of data to make this staetemant at least suitable as a starting point. Wheel alignment, weight distribution, stabilizer settings, suspension specs and road drive one would be only a Hand full of the variables needed to make it a "hard value". Since this is far behind of what can be discused on a plattform like this, the given numbers stay what they are, a starting point.

[ZDan]

Originally Posted by TRS

Sorry, I again have to contradict. Keeping with the example of a constant tire size, the behavior of the tire is a function of its construction and the actual pressure inflated. In reality it is wrong that the pressure is the only variable of relevance.

I never said or even implied that pressure is the only variable.
I clearly stated that for a *given tire*, load is correlated with pressure. Internal construction is a factor as well of course, hence LL, SL, and XL ratings.

And it is wrong that any tire of the same dimension will work on the same car (same load, samoe model, etc) with the same pressure at optimal Performance.

I never said or implied that either. I will say that most 200tw tires will have a quite broad rage of pressures you can run and not impact lap times all that much.

If you change the tire for your track tool, and again Im talking about keeping the dimension but changing the brand, you will have to check and realign the pressure. The pressure used before is in any case a good starting point and in some cases you will keep it, but not in every case. If the tire you changed in has a equal design concept, neccesary changes will be minor. If it has a different construction pressure changes might be more drastic.

And a tire's "max pressure" rating is not *any* kind of indicator of what the optimal pressure for max performance will be. That was your point that I took issue with.

As far as finding absolute optimal pressure, for most of us with limited track time, you're just not going to be able to home in on it exactly, because within a fairly broad range of pressures the lap time difference is going to be less than track variability between run sessions.

For me, 34-36 hot works for just about any 200TW tire (RE71R, A052, CR-1, etc). 36 may be a bit on the conservatively high side, but better to err on the high side than the low side. Also some of these tires start to fall off with temperature, and running higher pressures will stave off overheating a bit.

And once more: Everything said can NEVER be a generalized rule. It is always necessary to test for the perfect tire pressure for optimal performance. Dont trust any generalized statememts about tire pressure. If one says "thats the always and ONLY good pressure" , this Person dont know the details behind. There is simply no "one and only good pressure".

Like I said, for most 200TW tires, on most FT86s that go to the track, there's going to be a quite broad range of pressures that will work fine. If you're talking about a lightweight formula car with downforce, it's going to be very much more pressure specific, and one psi can make a big difference. For 99% of us who track FT86s, that's not the case.

As stated before, for the vast majority of us who track these cars, we just don't get enough clear track time to establish "optimal" pressures within, say, 2psi. The lap times just aren't that sensitive to tire pressures within a reasonable range. You'd have to be a *very* consistent driver, have a track pretty much to yourself, and have a bud in the pit lane to adjust pressures. Even then I doubt that most of us would be able to get it down to within a couple of psi.

[TRS]

Maybe thats the point. I didnt say that the Max pressure rating gives any sign for a specific pressure. What I said is, that a different max pressure (and therefore different max load rating) is an indicator that it is likely that the optimal pressure will be different. An indicator, no hard rule. And maybe the same pressure will work out.

Im with you that you will be able to achieve comparable track times over a broad range iof pressures with many of those tires in question. But my expierience is that, even if the times are still good over a wider range, the band to achieve those times while keeping the tire in an optimal temperature distribution and not overheating them weather on the middle nor towards the sides is far more narrow. The time you can achieve during a two or three lap session will not change much. But over a 10 or 15 lap session there will be an effect. As well this will wear and/or cycle out the tire much quicker then necessary.

One last thing I can say, try to run a RS-R in the 245/35/18 range at 2.4 or even 2.6bar and if it is not instandly obvious to you that the tire doesnt like such a high pressure, hmm, what can I say. The RS-R might be a little special in that point, but it also the proof that same tire dimensions can realy reqire far different settings depending on their construction. And to be honest, I was surprised about the amoint of the necessary change myself. I was close to throw that brand new set into the trash bin since they behaved very wired and poorly, but then I started to vary the pressure settings very widely and I found the RS-R beeing a very good bang for the buck if you just run it with the pressure it likes.

What maybe also is worth mentioning: The RS-R can live with this low pressure pretty well without jumping of the rim. This, at least in my understanding, has the same reason which makes it a PITA to mount this tire. It have been very few times that we had to push our mounting machine with two person to get a tire installed. As well I didnt see that many tires in that range of side wall height passing the hump at 4bar. Most other tires are passing at 1.5 to 2.5 bar latest.

[brzlegend]

One last thing when you get traction your more than likely going to have a new problem of going lean caused by the fuel pumps located in the front of the tank.