4 ply vs. 6 ply bias ply tires

[Den41Buick]

Can someone tell me the difference of a 4 vs 6 ply bias ply tire? Do they ride the same? Is one better for heavier cars? I am looking for new tires for my 41 Buick and I did not know I had options. Don't want to get the wrong ones. Thanks.

[Rusty_OToole]

The old bias ply tires had a carcase that was built up out of layers of fabric. The most common for many years was 4 ply or 4 layers of fabric. In the sixties, new stronger fabrics meant most car tires went to 2 ply construction at least all the OEM tires I know of.

Six ply tires were available for heavy cars, such as limousines and hearses.Eight ply, even ten ply tires were made for heavy trucks.

The fewer plies, the more flexible and smoother riding the tire. The more plies, the stronger and more weight it would carry although, the thicker carcass meant more heat buildup at speed.

The best plan is to use the least plies that will hold the weight of the car. You will have to consult the weight rating of the tires then calculate the max weight of the vehicle given its shipping weight plus gas, oil, passengers and luggage. Or find out what kind of tires the manufacturer put on and buy the same kind.

My guess is your car originally came with 4 ply tires but modern 2 ply tires would be just as strong and less prone to blowouts at high speed.

[Guest Bob Call]

Early bias ply tires were made with cotton cord which isn't very strong. Thus the need for 4, 6, 8 and 10 plies for various weight ratings. In the 30's came rayon cord, a little stronger. So they were able to make 4 ply 6 ply rated tires which rode a little softer than actual 6 ply. After WWII the manufacturers switched to nylon cord that was super strong. By the 50's 2 ply tires became the standard for passenger cars. In the 60's manufacturers added a steel belt over the 2 nylon cord plies to reduce tread squirm. Then we (US companies) "discovered" steel radial ply tires that Michelin and other European companies had been making for over 60 years.

[Guest noncompos]

While you didn't say if you had a Special or a Roadmonster/Limited, a point to consider is what kind of surfaces you'll be on...I assume you'll keep it on the pavement, but with the condition of some of the pavements these days (and likely to get worse as States cut back on maintenance and/or tear up the pavement to return roads to gravel) you might want to consider 6 plys for increased impact (potholes, stones, etc causing X-breaks, which pinch the tubes) resistance.

If it's strictly on good pavement 4 should be plenty, ride better as already stated. I wouldn't always rely on what the mfr put on, unless you want originality; I can't comment re' Buick, but I've known new car buyers who negotiated better tires or drove off the dealers lot and down to the tire shop to have better tires put on.

[Rusty_OToole]

I wouldn't use 6 ply, too stiff. My preference would be 2 ply but if you plan on carrying heavy loads and don't plan on going over 60, 4 ply might last longer.

Have you considered radials?

[Restorer32]

When 2 ply tires first came out (mid '60s as I remember) folks were very suspicious of them, including my Dad who operated a tire and recap shop. As a comparison he hung a cut open 2 ply tire next to a similarly cut open piece of radiator hose. The hose had more plies than the tire.