Not to be funny...but....could you have possibly run over a small animal?....does your car "pull" hard any direction when you let go of the steering wheel?.....Do you have clay in your area? Being that it appears only on rim and side wall tire and not necessarily the treads....there could have been clay or dirt from a sludgy puddle "caked" inside the rim...Let me know if this helps...
If the tire looks fine, is holding air and the vehicle is not pulling to one side...you may have just had one of those days when the tire felt funny. I've had days like that too, only to check it out and find nothing is wrong.
Keep an eye on the tire and if it still doesn't feel right when you're driving, then take it to a shop and get it checked out.
As for the rusty colored dirt, that may just be brake dust. If you don't clean the wheels periodically this can build up. This is residue from the brake pad as it wears. It's nothing to worry about, but can be hard to clean off. They do make a spray that specifically cleans it though. You can find this at any automotive store. Hope this helps.
〉 Answered on Aug 2nd, 2007 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines