Used race tires, R-compound tires, slicks, etc are more often NOT worth the headache. There are too many variables to be concerned about....
Like:
A) Are you getting a matching set off of the same car, used in the same session?
B) How many heat cycles are on them? The more they are heated up and cooled down the harder they get.... Also remember some tires get hotter than others (its not likely they will be evenly heat cycled)
Be sure to try to pick out the tires yourself and use a durometer to measure a few different points on the tire, etc.

Generally its just not a great idea to get used slicks, unless either you just don't care, or you know VERY much what you want and what you are doing.... I have seen this practice of getting used tires go wrong more times than it has gone right... Just be conscientious.

I can understand that, however, I purchase the slicks that have over 3/4 of tread depth remaining. They are rarely used for more than a few sessions/heat cycles, so for 1/3 to 1/4 the price it's absolutely worth it. You can think whatever you want, but I can go through two or three pairs of the slicks and have a lot more fun than a street tire for the same price. The company who sells them hand selects them based on different parameters to make sure that the tires are in as good of shape as new, just with less tread.

I wouldn't be doing it unless the rears were in great shape, which they are. I have not experienced any issues with different heat up points or whatever. I'll keep an eye out for what you're warning me of, but chances are I'll pay $800 less per set of Hoosiers and deal with a little imperfection :tup:

:tup: Sounds good buddy ;) :tiphat: As long as it works for you, that's all that really counts then. :tup:

Not trying to ague with you... just here to help. :)

I buy used R comps myself since a new one is nearly $300. With the economy and tire prices, I plan to only buy one set of new tires a year (RE11). I will buy a set of used R comps later. I don't want to get Hoosiers just yet because I cant fit all four inside the car! I miss the RA1s, but I am not sure how much faster the RA1s are over the RE11, probably less than a second.

Umm, The Toyo RA1's are quite a bit faster than the RE11, easily about 2-4 seconds a lap depending on other variables (even the proposed used RA1's would be at least 1-3 seconds faster than a RE11 depending on how many heat cycles are on the used RA1) .
For one of the best R compounds try the Toyo R888 (replaced the RA1's)

I use Nitto NT01's (similar compound to R888's) and RE-11's and they are considerably faster on track, 2-3 seconds depending on the track layout.

I have used 245/40R18 on the front and 275/35R18 on the rear with excellent results on track days. The selection of tyres in 18" is MUCH better that 19" and the tyre sizes you are suggestion for 18x8 EOM front rim and 18x9" OEM rear rim are truly excessive.

In 18" you have the choice of Advan Neova AD08 as a semi-R spec, or Advan A048, Bridgestone RE55 series, Dunlop DZ series, Toyo R-specs etc. In 19", the choice is more limited.

Going with slight lower sidewall height will drop the CoG of the car, as well as the roll-centres and give you higher cornering limits.

With the standard spring/sway-bar setup of the Z34, I have no difficulty in running a smaller front than rear. If I was to move to bump/rebound adjustable dampers, adjustable sway-bars etc, then it is worth moving to same sized tyes front and rear, but that also implies new rims of identical width.

Maybe 2-3 sec, not sure about 4 sec. Of course it depends on the track. I can tell you my old car was 1-1.5 sec faster on RA1 than Azenis 615 (which had less grip than RE11) on a 1.5 miles course. Heck, A6 was only 1.5 sec faster than AD08 on the same course.

Unlike the R888, RA1 are a lot more consistent and heat cycles don't change it as much. I used to be able to run faster lap times near the end of the tire's life. Heck, I missed the days where I would buy $100 take off RA1s, drive them 600 miles to VIR and track them. I would usually get 3000-5000 miles of street/track/autox use out of them before I have to trash them. If they have it for cheap in the 275/35/18 size, I would probably drive them to VIR instead of the RE11s!

Don't get me started with the R888, they are probably one of the worst tires to buy. They might be faster than RA1 straight out of the box, but they slow down after a few short heat cycles. You could have tread on them, but they are no faster than RE11 by the end of its life. It's not worth the money, especially if you buy take offs. There is a reason why they are bringing back the RA1s.

I recently did a test of R888 vs RE11 at an autox in my car with the same driver. The R888 FELT a lot faster and stable, but the times were the same as the RE11s. They were take offs from race cars that had 3/32nd left on them.

Obviously, these tires are still slow compare to the Hoosiers.