I have owned many sets of R888 tires and have driven them a bit on the street, for the ultimate summer tire they might be the one if I went to 100 wear rating but the RA1 in full depth would be far better, as mentioned, in the rain so overall a bit better choice. Since I happened to run shaved and heat cycled ones for track tires on this car I considered running new full depth on the street then using them up on track once well worn.
When I picked the 225 Rival S it was well proven to need a 9" wide wheel to be at its best and it was the only 225 15 I could get that was street legal(RA1 and R888 are not technically legal if I recall correctly) , nothing else available in the US. I wanted 225 and I want the challenge of making them fit under the car on 9" wide wheels. Having put quite a few miles on them including standing water in a monsoon rain storm where they were a bit tricky even at full depth. I would gladly give the new 1.5 version a try on 8" wide wheels though would not run them since my car is already running 9's which I still have 10 wheels in that size.
In the end, any really good setup can include 205 or 225 wide tires(actual specs and use absolutely needs to taken into consideration) on a 15x8 will be damn fast and responsive, the gain in adding an inch to the width is not going to make a real difference unless going all out which means faster than one should drive a well sorted out quick car on public roads.
RA1, R888, sure they would be faster than what I now run as I know from using them but on the street the Rival S is already faster than I can safely use so a stickier tire is mostly pointless.
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I much prefer the style of the bit heavier Helix wheels I run in 15x9 over the lower weight 6UL in 15x8 or even their 9" wheel. If I went nuts and all the way to the 6ul 15x11 that might be a different story
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With the advent of low cost high strength flow formed wheels available(sadly most if not all in 4x100) and the number of race cars running such type of wheels very successfully I not even look into far more costly custom wheels.
I like to have at least one spare wheel per size, preferably 2 and like running the same wheels on the street and track when I can thus I end up "needing" at least 10 wheels but normally have 14 to 18 wheels in the same size. In order to limit the space and weight I ended up with 10 wheels with 4 summer tires and 6 track tires(need to rotate them often and not loose expensive track time so much have at least 2 spares) and then a set of wheels for the AS tires which were not wide enough for 9's so had to go to 8's and the 6UL was absolutely the best wheel in that size for the money and 11.4 lbs! The Helix is in the 12.5 lb range and would of been used but not made in the proper offset, I had to rebuild my front BBK mounts at considerable effort and cost to fit the 6ul as well.
I have ran VERY expensive custom wheels on numerous vehicles and simply can no longer recommend them for any application that one can find flow formed wheels there are better ways to spend the money on making the car faster so unless those are already done, in the budget, etc....build from a whole car concept, that is what I always do.