Editorial Comment:

A photo and some additional information might have been useful to more accurately assess the situation but I will attempt to give you some ideas.

Tire cracking is usually associated with the effects of heat and sunlight, to a large degree.

For this reason I'd wonder if these tires are cracked only on the outside sidewalls and perhaps only those wheels which are habitually receiving direct sunlight if the car is parked in the same position all the time.

If all the tires are cracked and, also on both the inside and outside sidewalls, then the cause might not be sunlight and heat.

Strong detergents and certain chemicals can also adversely affect tires. You mention you wash the car. Is it washed frequently, and do you use some detergent or other chemical that might be affecting these tires?

Some people put something on their tires to make them look better. If this is not a product which is designed for use on rubber compounds, it could have a deteriorating effect.

You might try approaching a Michelin dealer and have them look at the situation, too, if these ideas don't give you any clue as to what's happened with these tires.

Tires these days are not usually experiencing this kind of deterioration under normal operating conditions, and when I see them there is most often some cause which stems from they way they are used or the conditions to which they are exposed which lies at the root of the problem.

I hope this helps you solve your problem.

TG