when did the "checks" show up??? recently? or have they been there and you just noticed??
If you are uncomfortable or have any doubts, by all means change them out, I have only run the GY's on my car so I dont know what to say about the Hoosiers without have them directly in front of me. but sidewall rubber compound is different then tread compound and it does "Check" where the 2 are vulcanized together. Cracking due to old age or letting the car sit on the tire while flat are issues, creases in the sidewall are never a good thing. Get new ones and use these for show or travling on and keep the new ones covered up with just enough air till needed.
Compounds--- I need tires and go to the truck or sales store, ask for my size and throw a compound number out there. they answer back with we only have this compound right now, I need tires so I buy them and never worried about it, Nascar,IRL,F1 or any other asphalt race tire that does not run on concreet and/or VHT is very compound sensitive and those cars go thru a boxcar full at a race for maximum performance. At our level and the types of tracks we run at, the tire gets old before we blow thru the tread, so compound is there for the first of many passes, and then goes away, but the VHT compinsates. Invest in a tire durometer and keep notes
Unfortunatly we dont have the time or money to do tire testing with differnt compounds and the tire reps are not interested in doing them because the sales volume is so low for them to do a comparisen, add to that, that they mostly deal with rear motor cars every week vs front motor cars 3-4 times a year
