I have used Nexen on my Santro (bought from Saif traders twice). They get hard after the initial 500-700 kms.
One of my tyre, rear left tyre, got deshaped (terha) after the tyres were driven around 10k kms. I changed the deshaped tyre with a new nexen one. Drove the car for like 10k kms more, I do tyre rotation every 7-8k kms.
Then after around a year I guess, the same rear left side tyre burst last year when I was on motorway and was at the speed of 120 kph. Tyre pressure was normal, and I couldn't find anything odd that could cause the burst. The tyres were around 20k driven then. I replaced all the tyres again with Nexen, and then sold my Santro six months after that.
Tyre experts told that it may be a problem with tyre, or cambering. Allignment and wheel balancing were alright.