rear wheels are probably toed out and need an alignment
205/75/15
The correct tire is 215/75R/15 and the correct tire pressure is 35Psi
Drivers door sticker shows it is 205/75 R15
215/75/15 ifits a 15"
Front end is out of alignment. Take it to a trusted alignment shop and have an alignment performed.
You can access the mechanism to lower the spare tire from under the van.
Remove the tire and wheel from your 1998 Chevy Astro Van. Remove the brake spring and caliper. The brake pads will come off. Reverse the process to install the new front brakes.
LOOK ON THE inside of the door!!!!!!!!! OR READ THE TIRE
Inside the trunk near the spare tire.
There is a table of Astro Tire Sizes at http://astrosafari.proboards.com
tires steel inner belt has shifted or separated
Check on the inside of your drivers side door. It will tell you Chevy's Factory recommendation. The tire will also have a max PSI rating on the sidewall somewhere. I ALWAYS go with the PSI rating on the TIRE