Rear tires "cupping"

My 2013 Mazda5 has 19,000 miles on it, recently I was hearing a rhythmic "thrumming" sound at 20mph and above. The car was tracking fine and I wasn't getting any noticeable shake indicating an alignment was due. Wife never noticed anything. I decided to bring it in for a wheel balancing. The tech saw the "cupping" right away (inside rear tires) and told me it was due to not rotating the tires.

After doing some reading on tire wear it seems this problem is due generally to strut/shock issues rather than rotating tires and alignment issues. Would this be a warranty issue? Has anyone had this problem with the 5 (I know I never had with the last 5 cars I have owned and I put very high mileage on every car I own)?

Thanks

Welcome to ownership of a Mazda 5. These cars are famous for eating rear tires, a problem that has existed throughout the cars history. The problems have been lessened somewhat in the later generations by changes in bushings and factory alignment settings. Rotating the tires will do ABSOLUTELY NOTHING to cure the problem, only wear out four tires instead of two. Replacing the shocks will help, but can also hide larger issues like trailing arm bushing failure and lateral link wear. SPC sells a rear camber arm that is adjustable and is probably the best cure out there. HTH

Rotating tires just spreads the wear issue to all 4 tires instead of just two. This is an issue on a lot of (not all) Mazda 5 (3 as well according to my dealer). Ours got loud almost the same time yours did, and was unbearable after 30k miles. Some tires are better than others at suppressing this. A lot of posts on here about it.

I don't suppose any of this is covered under warranty?

Look into a set of rear camber arms, it will help eliminate the issue.

Not much hope of warranty coverage directly as shocks and tires are "wear items" if you have a good dealership/service manager they may "fix" it for you once for free as a goodwill gesture.

I know the OP says cupping but, is it cupping or feathering? Feathering occurs normally with the lack of cross forward rotations. Some tires are more prone to it than others. It can be accelerated with incorrect toe settings. Just because the car tracks straight doesn't mean the alignment is good. Especially if its the front toe that's out. Both wheels will always want to center. On the rack it may say L=0.06 and R=0.00 but on the road its correcting to L=0.03 and R=0.03.

Cupping occurs just as your research says, usually from worn suspension components. The fact that the car has only ~19k makes me think it's feathering rather than cupping.

The camber in the rear by it's self is not going to cause the feathering. But, add to that incorrect toe and and you'll not only get the feathering but accelerated tire wear. Adding camber arms will correct the narrow wear pattern but unless the toe is corrected it will still feather and wear faster. Also, be careful when dialing out the camber in the rear. It was put there for a reason. Most likely the engineers wanted to dial in some understeer with out having to increase the front swaybar size and sacrifice ride quality.

I tossed my stock Toyos at 11k. Got some Bridgestones RE760s and an alignment. Couldnt have been happier. The REs were quite to the end.

One last thing... The alignment from the factory is junk. It's set with everything new. Once everythings had a chance to settle it's all off. If you haven't had an alignment done since driving it off the lot, it's due.