On my last return, I was noticing a slight vibration from the rear of the Breakaway. Wasn't bad but annoying.I knew I had to change the left rear brake rotor so I would address this issue later.

Getting to the brake rotor I found another Alcoa wheel damaged by the previous tire installers use of impact wrenches. I elected to replace the inner wheels with steel wheels and rebalanced all, even thou I had dynamic balancers. I noticed a slight tire hop on the two wheels but the balancing was double checked and all was well-----I thought!

Everything was smooth until about 50 miles and the vibration returned. Vibration would come and go and for no reason.I would hit a bump on the road and it would smooth out, later vibration would return. Fought this the entire trip until I stopped at the NM/AZ border. Looked at the rear tires and the outside passenger side tire was starting to cup on the outside edge. GRRRR I had this problem with a front tire (same make) and was told it was alignment, this time it was the rear.

Did a hillbilly balance and continued home, arrived safe but very tired! Cord is starting to show on the passenger side and cupping is showing now on the drivers side. Checking, this seems to be an issue with the R250 tires.

As I have had so much trouble with Alcoa wheels cracking (not due to Alcoa but to incompetent tire centers using impact wrenches)and I have wanted to get larger tires I am having 4 steel wheels 6 3/4" wide made. Unsprung weight increase will not be an issue with the weight of the rear. I will be able to use 245R70/19.5 tires now. I will go with the Goodyear G670s. I will get back a reduction of 70 RPM at cruise that I had with the original 8R19.5 tires.

If you are getting custom wheels have you considered 22.5" as an upgrade?

Yes I did, not enough clearance in the wheel wells. The other issue is the gearing, I would not be able to use 6th gear and it would be a dog off the line.

Example:

Currently my rear diff ratio IS 4.1:1, going to one of the smaller 22.5 tires 245/70R22.5 changes the effective gear ratio to 3.54:1, Would have to change the rear end ratio to 4.75:1 to have the same performance/engine RPM per mile. Going to the effective 3.54:1 ratio would have a significant impact on acceleration.

This is why some of the longer Breakaways with 22.5 tires have the Allison MD3060 transmission with it being limited to 5 speed operation. Very early longer Breakaways had 22.5 tires and a MD3060 6 speed transmissions could not be programed to 5 speed operation. They would shift into 6th but not until 74 MPH or so.