I'm not an old timer just yet...I haven't hit 40 yet but I'm getting closer every day...As a "tweener" which guys in their mid 50's call guys my age I remember old & new. FWIW I worked in the tire & auto business from 1989 - 1998. Yes there were cars out their with bias ply tires back in like 1990 & 1991.
Do not mix radial with bias ply tires. Back in the day auto manufacturers said bias can be in front & on the rear but never on the rear & in the front and a double no no if they were on the same axle (Example: L/R bias, R/R radial).
Funny thing is I remember E 78x14, F78x14 which then went to what? P195/75/R14 or P205/75/R14 on 2 door coupe Ventura's, Nova's, Regal's, Cutlass and even non Z28, non SS Camaro's. I even remember the bias ply snow tires back then.
Heck back in like 1991 a buddy of mine who worships the ground Mustang's drive on sand blasted my 14x6 Rally's and gave me his JC Penny Scat trac 60's (They were L60x14 in size) for the back of his Camaro....LOL!!! JC Penney Scat Trac 60 white letter tires!! I think those things were made in the early to mid 80's or something before I got my drivers license!!
Bias Ply tires are also called diagonal belted tires for the way their belts run. Radial's are much different and their belt runs perpendicular to the sidewall. Thus both tires result in different handling.
As far as flat spots on bias ply tires, you got that right. Hey I just checked here ya go.........http://www.wisegeek.com/what-are-radial-tires.htm
*******While tires may look simple they are actually made up of a series of layers of different materials. If we peeled back the tread in bias-ply tire one would see a nylon
weave (these are the plies
) beneath, running in a diagonal pattern meeting in the centerline of the face of the tire. The weave runs at an angle down the sidewalls to the bead — the part of the tire that fits on the wheel's rim
. Nylon ply is stronger than polyester
but compresses and sets when under load especially when left for periods of time, resulting in "flat areas" on the tire. Due to the direction the ply runs on these tires, the sidewalls don't bulge even if the tire is low. This design allows tread to wrap down over the sidewall because there is no transition point from the circumferential face to the sidewall.
A radial tire is constructed differently. Rather than diagonal nylon plies that meet in the centerline it's made with polyester cords that run perpendicular from bead to bead, up over the face of the tire and down each sidewall. In other words it's "wrapped" at a right-angle to the direction of the tread. On the face of the tire over this polyester wrap, is a belt that runs below the tread. The belt is nearly the width of the tire and runs the circumference. This gives the tire a "squared" look. Though belts used to be made of rubber-coated fibers nearly all belts today are made from steel fibers. Hence the steel-belted radial. This belt helps stabilize the tread, reducing wear. Because of the construction of a radial tire, the sidewall will always have a bulge at the point of contact. Because of this bulge, when radial tires were still fairly new to the market many people assumed they were under inflated.***********
Bottom Line: I ran those L60x14 JC penny Scat Trac 60's with P245/60R14 radial's up front. That 1969 Camaro back then was squirm as all hell. Not good! I would not recommend doing that unless it's a race car. Most slicks I think are still bias ply but I'm not sure on that as I am not a hard core "race only" guy. Just my 2 cents!!