011 1200c with 5500 miles. Just noticed severe cracks in the sidewalls of the rear tire. Plenty of tread and the front tire is a Michelin Scorcher as well and has no cracks. Overfill?

 

6 yr old tire!!!!!

 

Run, don't walk, and get new shoes for that bike!

 

Tires don't just wear out, they can also age out.
Rule of thumb for tires and age is ~6 years, so that would make your 2011 due for new rubber. There's a manufacture date code on the tire and depending on how long it sat in stock before being used, it might be older than 2011.

 

Overfill? nope... old and deadly

https://www.jakewilson.com/

 

I hear ya, just wonder why the front one is the same age and has no cracks. I'll replace it.

 

The Scorcher tires are manufactured in Spain and Thailand. Like many other tire companies, the fronts may come from one country and the rears from the other.

 

That would explain that. And the tires on my Fat-Bob are older than these tires and have no cracks. They're Dunlops.

 

Replace them too. That's insane your riding on them.

 

Oddly enough we had our campervan serviced last week, 2011 model, and discussed tyre age and replacement. I also found a website that gave advice for recreation vehicles, which often do low mileages. The advice from both is to replace at around 7 years - or when cracks appear!

So you have cracks? - Replace! You have tyres 7 years old or more (insert date of choice!)? - Replace! I'll replace our van tyres next year as they look fine and dandy at 6 years old, as do our 2011 SuperLow tyres, although I'll probably replace them at the end of this riding season, ready for next Spring.