I recently removed some very heavy 9-22.5 tires that were new in 1965 and had less than 10,000 miles on them. Those things were so stiff and crispy I had to use a jigsaw and cut around the sidewalls same as you did to get them off. The tires were no less than 3/4" thick at any one place, no fun at all.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-