I have S-drives (215/40R 18) on my JCW Conv which are 4yrs - 4 mos old with 16,700 miles on them. I already have dry rot issues. Yes, car is parked outside and I live on the east coast, but still? Has anyone experienced same problems? Any adjustments, confirmation, help from tire dealer or Yoko? Need to replace but if new set is going to be the same then I need to look at another brand. Thoughts/comments appreciated.

 

Any car left outdoors in the Sun exposed to the elements can develop dry rot in as little as about 3 years, typically with low mileage.

The tire sidewall is aging and drying out. Tire dressings often make the problem worse.
Tire dealers won't likely offer assistance but you can ask a Yokohama dealer to have prorated credit for treadlife remaining to get your business on replacements.

see warranty info-
http://www.tirerack.com/images/pdf/warranty/YOKO2.pdf
Limited to 60 months from date of purchase or 72 months from manufacture date on tire.

This happens to many makes of tires, it is seen throughout the country. Avoid using any tire dressing. Garaging out of sunlight helps. Keep tire inflation pressure up.