After lengthy discussion about longest lasting tires, I mentioned cupping on the inner part of my front tires. It has been recently aligned and Mazda said my shocks are good. However I just noticed the rear driver's side is about 1 1/2" lower than the passenger side. I'm going to have it looked at but just wondering if it would most likely be a shock or spring? There is no apparent signs of an issue when driving like clunking or bottoming out. Also could this cause the cupping on the front I am experiencing. Car has 37k miles on it.

 

It might be the bumpstops. They're an active part of holding up the car. If one has disintegrated, it might explain your issues. Would be surprised at 37k but you never know.

 

It actually helps hold up the car? Wow. I would think it would act more like a door stop over bumps.

 

The Miata NC/RX8 chassis uses the speedbumps to create progressive spring rate. It has a soft section followed by a hard section which is the actual door stop.

So it could be that, it could be the shock losing pressure (which would match the tire wear you're seeing), since the shocks also support the car. The least likely culprit is springs, at that age.

 

The gas charge would not be 1/2” height change, but maybe 1/8”. Also the suspension is not necessarily equal on every corner because if you put it on a set of four corner scales they would indicate that the weight is not equally distributed on every corner. The suspension also doesn’t sit on the bump stops in the static position, but only engages them on heavy bumps, heavy body roll, or in the extreme case of heavy weight loading.

what model year is your RX8?

.

 

It's a 2005. I took for a run and did some sharp left turns to see if I could distribute more weight on the higher side and checked the height difference. It went from 1 1/2" to barely 1/2 ". So I did some sharp right turns to see if it would go back but it remained at barely a half inch difference. As I drove on various roads I looked out my rear view mirror at the spoiler and the car was pretty much level across the rear of the car taking into account for the road pitch. I'm guessing it may be slightly lower on the driver's side due to the fact I am the only one who is ever in the car.