justkickin

So last year I ran the RS3's for autox on my C5Z. This year, was thinking the new Dunlop Direzza Z2 which is getting decent reviews so far. The Z2 will likely be the better tire for my climate as we do not have that many really hot race days where the RS3 works best.

However, the RS3 is a 285/35/18 compared to the 285/30/18 Z2. Since I only use these for autox and turn off all traction aids, I am not too concerned about the stagger etc problems this size may introduce.

As the Z2 will effect gearing, does anybody have a spreadsheet or formula that would show me the math on where shift points would move to by speed based on tire sizes for a C5Z?

Anybody else thinking of using the Z2 for autox?

wtb-z

Could try the 275/35/18, then it won't be so crazy short.

Supercharged111

I can't find the damn spreadsheet I made. You plug in a tire diameter, rear end ratio, trans ratios, and it spits out shift speeds at desired RPM. The formula to determine shift speed is:

(tire diameter/2)(3.14)(shift RPM)/(trans ratio * diff ratio)(3,801,600)

talon95

I pre-ordered the 255/275 ZII's for my C5Z. I'll report back when I get them. I also had the 255/285 RS3's last year. It is too bad they don't make a wider/taller 18, but I wanted something better in the cool/wet.

reece146

In our local club (Ottawa area) the RS3 and *Spec are both popular but like you said the RS3 needs heat to work well. Some of the more hardcore guys had both on hand depending on the day's conditions. Basically used the *Spec as their "rain tire".

We ran *Specs on my wife's auto-x car (non-Vette) and they worked well in all conditions but she had a noticeably harder time getting on the podium when the pavement was really hot against the other cars running RS3's. I don't have personal experience with them as I've been running R888s on my car the last number of seasons.

HTH

talon95

BTW, TireRack has a review up on them comparing to the Z1SS.

http://www.tirerack.com/tires/tests/...y.jsp?ttid=168

I'm likely going to run A6's at National events, but will use these for everything else and as a pseudo rain tire (dedicated r-comp rains would likely be better, but I refuse to waste money on them)

Alludc

im still waiting on my backordered Kumhos. I LOVED my rs3s...loved loved loved. But im just not gonna buy another set of tires that I feel are too small for the c5. I can deal with 255 fronts, they were fine. but 275 or 285 out back simply doesnt cut it IMO.

Really wish we could get some real life reviews from the 'new' Falken rt615-k. The "k" is supposed to be a significant improvement, but I wont shell out 800+ for rears until i see em in action

talon95

Do they have an estimate for the Kumhos? I've been wondering if they are going to get more of them, or just switch to the new tire that is supposed to be coming sometime this year.

wtb-z

The 315/30/18 Kumho?

When I bought some for the 2011 season the 18s were already 2008 build dates, and they seem to have been out of stock since then. I am starting to think we will never get more.

I had a hard time noticing any difference between a 285 RS3 and the 315 XS in the back of the car. But it is too bad they are unobtainable now because the 275/315 combo worked pretty well.

Alludc

I just checked with my contact ( VP of Discount Tire ), and while the 315 Kumhos are not yet discontinued, they are still not in production, and they have no current ETA of going back into production. So Im assuming that means these tires will be no more. How unfortunate. I wish we could get a larger offering from hankook or Dunlop

talon95

I bet they are just working toward the new tire (V720):

http://www.s2ki.com/s2000/topic/9821...ho-ecsta-v720/

I agree about needing more sizes and it's even worse for the C6Z.

talon95

You could try the 255/295 Yoks. Pricey again though and the 295 is short (25.0").

Alludc

ya the yoko price is annoying...

wtb-z

Is the 615K competitive at all in AX? For road course duty it doesn't seem like it has the heat capacity, but that shouldn't be as much of an issue at least in some AX venues.

Alludc

I dont know of anyone, at least anyone competitive that im watching running them yet. i think the non K version of the 415s have people wary of them. That and the $400+ per price tag of the rears

Supercharged111

Non K is a death wish. I had them on another car and they were so bad when they got hot that I won't even try the Ks which everyone says is better. Better than death is still marginal at best, so I'll spend my money elsewhere.

So I found my spreadsheet with T56 info in there. The parameters outlined in red can all be changed and the shift speeds will reflect, so you can experiment with different tire diameters, differential ratios, individual trans gear ratios, shift RPM, and see how it affects your shift speeds.



Only problem is I don't see a way to attach it. . .

justkickin

Thanks for the feedback folks.

I have driven the Z1's on STR prepped Solstice's and S2K's. The feedback was much better than the RS3. This is why with the new Z2 getting favorable reviews already I am interested in switching.

There is no point to buying R's for our lot up here and not sure yet if I will make Nats. If I go to Nats I would go for RTR as I am not buying R's for 6 runs.

I didn't want to go to the 275 Z2, because as alludc puts it, the 285 is under tired. Going to use that formula above to see how the shift points change and decide from there. May end up with the 255/275 though. Seems like a better option than another set of RS3's given our weather. The Z2's would essentially be my R's. I just change them in the garage and don't need a trailer.

Alludc, I wouldn't bother with the XS's, even though they are wider. I have 295 XS's I use as my fronts on the street. At the last weekend (last year) my rear RS3's were corded so I put the XS's on the back of the car. Me and my codriver (both regular top 5's here raw and he has trophied at SCCA Nats and Tours) thought the XS's were just plain numb. Absolutely no feedback. The RS3's definitely talk more than the XS, which isn't saying much for the RS3. After that event there was no way I was buying XS's, no matter what size I could get them in.

As for the 615K, Andy Hollis included them in a GRM review last year and they were slower than the XS, RS3 or *Spec IIRC.

Like you alludc, I loved the RS3, especially on hot days. On cool days, I was dreaming of *Specs, and we get more cool race days than hot ones up here.

justkickin

Thanks, PM sent with email address and I can host and post download link for it.

justkickin

Here is the file to download. You will need Excel or a compatible program to open/view the file.

Thanks Supercharged111

BTW, just found this as well and thought I would share.

http://xse.com/leres/z06/calculator.html

Supercharged111

The top transmissions are various combos for my Corolla, I added the MN6 and M12 T56s to the bottom values for the Corvettes today. The top ones can be manipulated the same way the T56s can.