1-26 Inner Tube Mayhem

Our beloved 1-26 (the Karmann Ghia of sailplanes) keeps busting inner
tubes. Like every other flight! NOTE that there is nothing rough on
the inside of the tire or rim.

My thinking is that we have a mismatch between the tube and the tire.
The are in fact of different sizes. I should have written the sizes
down and should have reported it here. I will do that soonest.

So, riddle me this - If the tube is too large then it will become
pinched which is bad. Right? If too small, won't it just inflate to
the correct size/shape, within reason that is? We are using talcum
powder - is this good or bad? Or should the tire and tube be of
identical size?

Thanks for any suggestions.

- John