Tires

There is nothing about a retread that would contribute to this condition. I would gusss that the wandering has more to do with the tread pattern and tread depth you have on your retreads than the fact that they are retreads. We often hear that drivers comment about wandering vehicles when they go from worn drive tires to new ones. The new tires squirm more and give the driver a wondering feeling. It will get better as the tires wear down but, if this is a big issue, you might want to consider switching to tires (or retreads) with less initial tread depth and/or a more rib-like tread pattern.

I don't think there is a good or bad time to do this. If the tires are the same brand and type and were installed at the same time, something is wrong for them to wear at such different rates. I would have an alignment specialist check to wear of steering and suspension components plus an alignment check if the components are OK.

We no longer make the G186 tire. I also do not find one 12.00R20 in our line up. This is a tube type tire. Tube type tires are slowly dying out of the marketplace. If you plan to keep the truck for a while, it may be worth the effort to convert it over to tubeless tires (new wheels and tires). We do make 11.00R20 (not sure if it has enough load carrying capasity) in the G287 MSA and the G288 MSA. You would need to know your maximum axle loads to determine if the smaller tire will meet your load carying needs.

I assume your are refering to the metric size designaton (such as 295/75R22.5) compared to the older size designations (like 11R22.5). New, is a relative term since the metric size designations have been around for over 25 years in North America.
For the metric size desigination, the first number (295) refers to the section width of the tire in millimeters. The second number (75) is the aspect ratio, the tires section height divided by its section width. In this case the tires is 75% as tall as it is wide. The R means that the tire is a radial. Finally, the last number (22.5) is the nominal diameter of the wheel (in inches) for this tire. The older size designations were somewhat more simple. The first number (11) is the section width in inches, the R again means radial and the 22.5 again refers to the nominal wheel diameter for the tire.

Suggest you call Customer Service for assistance (1-800-869-0435). The number he is providing is only the flex member part (just the rubber bag). In order to determine what specific air spring you need, you will need to provide some additional info.