When I had bias ply tires, 8X19.5, on my 1 ton it would often take several miles for them to "round up" again. When it was cold out It was really bad even from just sitting overnight, would take 5 or 10 miles before they felt smooth again.

The 78 GMC dump truck I bought had bias ply tires on it. I paid the guy for it and proceeded to drive away, had to stop within a mile, as I was sure I had a flat tire or two. Got out and checked, all had air, then I remembered about bias ply tires and sitting for a while...
They were so out of round / bumpy it was almost unbelievable, and after 20 or 30 miles they were fine.

How long have your test rides been?

Grigg

•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-