Side wall cracks- when to replace?

How bad do sidewall cracks need to be to be unsafe to drive? I have some ms2's that are maybe 4 or 5 years old and have around maybe 40,000 miles on them, possibly more. There's still plenty of tread depth but I just rotated them and noticed the sidewalks of all 4 are starting to crack. In your opinions do you think I can get another year out of these? I'm not due for inspection until October next year (2 year schedule here in ma)

 

Those don't look bad at all. I had some bad cracking in a set of Coopers, they ended up getting warrantied. I'll find some pictures so you can see what they looked like but basically, you could fit a small flathead screwdriver head into the rubber a good ways. Yours looks purely superficial and I would not worry about it one bit. My current tires look a lot worse than that and I'm not concerned at all.

Edit: I don't have pictures of mine, but I could easily get my fingernail into the cracks, same with a small flathead screwdriver head.

 

I had a newish set of BFGs that blew the sidewalls out after 10k miles. Luckily I was only driving 10 mph at the time.

They were cracked down to the belts on inside side of tire.

 

I wouldnt worry too much, but interested to hear what the experts say, because my mom's car has tires that have same exact cracks as the above pics.

 

They may not be anything to worry about, but I put a lot of trust into my tires so I don't like taking the chance of a blow out especially at highway speeds.