http://knowledge.wharton.upenn.edu/index.cfm?fa=viewfeature&id=232
There was a worse, much worse FIRESTONE tire than the 721. The FIRESTONE 500 was unbelevably bad. There was a set, new, on one of our family cars and at least seven replacements were made until the dealer put a set of MICHELIN X on the car. (The "X" designation was used on many successive designs, from the 1960's forward).
GM had their own tread/build design for tires in the mid-late 1970's, made by numerous American manufacturers. A "GM tread-spec" was common parlance as a tire description. Not hardy, nor particularly roadworthy by todays standards, they were at least consistent.
The 500, however would blow out on you anytime. Many of the stories I have heard about the 721 are really about the 500. They'd blow out hot, cold, sitting still (we --Dad and I -- went armed one night to the garage after hearing a gunshot from there. And another just before opening the door . . . just a pair of 500's blowing out).
Let's remember though, that the bias and belted bias tires being replaced were truly horrible in all respects save soft ride. They lasted, if lucky, about 15-25m miles (7-9m on an Eldorado or Toronado), had no grip in the rain, terrible propensity to flattening (just show 'em a picture of broken glass), and gave one a healthy respect for "polar moment of inertia" in emergency handling.
Engines were big, brakes were drums, and real men . . . .
Radials, even the 500 (or other baddies), were still a step ahead. If you were willing to flip for them (and had a buddy in the biz) you could get "police-spec" radials good to 130-mph (no steel belts) that were assembled with extraordinary care. We just didn't have many choices.
A set of LR-15 Michelin X, four, ran to a little over $1000.00 in todays money. A cheaper alternative was welcomed. It just took awhile longer than it should have, and too many people were killed or seriously injured in bringing the American car market to radial tires.
I ran retreads while in college (couldn't afford "real tires" on my little FORD), and I was suitably limited to 55-60 mph on cool days. I also carried two spares. More than once had to change two tires on a 300-mile trip to home or back. I still got a few thousand miles out of them -- hard, howling, no hydroplane resistance -- as I had to constantly inspect them for incipient tread separation.
But compared to, say, my father-in-law, where a trip from Victoria to Austin (Texas)all day and 2-6 flat tires to be expected, it wasn't seen by me as much of a hardship compared to those Model T and Model A days.
I'd have gladly run 500's if I could have afforded them, as they were night & day better than what I was forced to use.
Tires today are wonderful, dirt cheap, and last an amazingly long time with proper care and driving aimed at low overall vehicle wear. I'm real glad to be able to put tireson my vehicles today that are so much better. And I don't have to give up handling for ride comfort, or noise, in any proportion to what once was.
