Hello, you guys were helpful with my last query, so I'm hoping you help me this time! I (finally) replaced the tires on my 74 Schwinn. However, when I ride a few feet, the rear tire shifts and rubs the frame, essentially stopping all motion. I took both tires/wheels into the bike shop and they confirmed there were on good and the right size and all that but maybe I hadn't set it in right and tighten the bolts. So I keep trying that but the tire/wheel keeps shifting, no matter how many times I put it back into "place"
It's not any issue with the tire. The problem is that one of the axle bolts slipping where you tighten the wheel into the frame. Most likely the drive side (right side) one is slipping forward. Either you just aren't tightening them enough or maybe a washer got lost or put back in the wrong place.
Assuming that your wheel is running true and the tyre is fitted correctly, this can only be due to movement of the wheel.
Check your axle, nuts and washers, and also check that the dropout slot where the axle fits hasn't opened up or is bent, if it has, you will think the wheel is tight, but when pressure is applied, the wheel moves forwards.
This is a fairly common problem on cheap bmx.
If it has, you may be able to get by using larger washers, if not , it will need resetting, which I suggest should be done by an experienced mechanic.