Originally Posted by
Katiesmalls
I think, I have done, you could put your shoe against one side of the rear triangle,both paws opposite and stretch your foot enough to make those bomb proof Continentals, varsity's collegiate's, any size, including 250 MOTORCYCLE TIRE. They are strong flexible, and adopt to anything. With those bicycles, "frame dimension is adjustable"
You don't want to ever spread the stays by pulling one side against the other. Each side must be moved outward in a measured way, one side at a time, else the yielding will always concentrate on one side, putting the frame out of alignment and with the original center reference lost.
You can use a length of 2x4 as leverage bending one side at a time, or you can lay the bike on it's side and push the lower chainstay down with your foot, using the pedal, saddle and handlebar to "tripod" the bike in a fixed position while bending and measuring. Then you can flip the bike over and bend the other side, measuring again to bend another 3mm for a total width increase of 6mm.
But these 1970's Schwinns were set at about 126mm at the factory, as per metacortex and my own recollection.