[bbradley406]

Tires have been around for a while, but the average weight of a personal car greatly increased after the 80's. Sure there were some heavy land-boats in the 50's and 60's, but it seems now everyone is driving something 3.5k lbs or higher.

Also consider the expansion of the US highway system (starting in '56), increased freight trucking, popularity of tuning / high performance cars etc. I'd imagine more tires are getting shredded into the environment than at any point before the 80's, even with improvements in tire compounds.

[chrisco255]

Cars were even heavier in the 30s, 40s, 50s, and 60s. They had steel bodies, chrome bumpers, massive trunks, V8 engines too. It wasn't until the oil crisis in the late 70s and the introduction of Japanese brands that cars got small.

Take a look at a 1950s Coup de Ville, Buick Roadmaster or any other famous models from that era. All pushing 4K, sometimes 5K pounds.