Doing tire research, I looked back through the google archives. There is a lot of talk about Thornbirds being 2-ply, some tires being bias-ply, others being other kinds of "ply." I am not familiar with this term... could someone tell me briefly what it means?
layer of material
The 'plies' are the layers or belts that are inside the tires.
A heavy duty truck tire can be 8 'ply' which means there are 8 different layers of belts in the sidewalls.
A Thornbird you say only has 2 plies.
The cheap BFG second line of mud tires, the Mud King's, only have 2 sidewall plies, real BFG muds have 3 sidewall plies.
This makes the sidewall much stronger and much more resistant to pinches or perforations. It also makes it less flexible under full air pressure.
So a 2 ply tire will lean into turns and dive the front end down way more than a 3 ply sidewall or 8 ply one will do on the street.
Some tires will also list X number of plies for the tread and X # of plies for the sidewall.
Bias ply means the belts go sideways at something like 20-45 deg across the tire alternating zig zag front to back where radial plies go straight across in a 90 deg to the rim or in line with the tire 'radius'.
Radial tires flex way more and couldn't work until technology improved back in the 70's I think it was.
That is why bias ply tires should be rotated in a cross pattern, because the belts go both ways, so the best wear is had my making them turn the opposite way by flipping them side to side.
A steel belted radial will 'break in' the belts in the rotation they were installed in and can and 'will' blow a belt if crossed in a rotation so they spin the opposite direction.
'Modern' radials are 'supposed' to be able to be cross rotated according to the tire makers, the same folks that want to sell you new ones remember, eh....
Meanwhile, 'both' of my original Jeep owners manuals state point blank to only rotate the tires front to back with radials, if you want to rotate the spare in, it goes on the right rear, because the right rear is the highest wear tire. It is the default power wheel for a stock open diff. Dump the clutch and the right rear is always the one to spin. The right front goes to the spare, then back to the right rear on the next rotation. The left side only ever rotates front to back.
That is the main reason I only have a used BFG AT as a spare for my BFG mud tires. As a spare, I am only going to use it to get to a place to fix my 'expensive' tire so I don't give a shit what side it has to go on if I get a flat and it blows a belt as a spare. I can get another for the cost of mounting it.
I just tossed 10 tires out of my garage, all with good tread and belts that had let go. I bought the tires used from the scrap yard cheap with the 50/50 factor if I could guess which way they were previously installed.
I bought my Cherokee in 99 with 'modern' radial tires on it that were cross rotated, and one blew a belt out. They were Hercules 'Terra Trac' tires.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT'sJoshua Nels>
Ply means layers.
Plywood is wood that is layered. Plys on tires are similar. The plies can run around the circumference tire, and they are called bias plys when they do this. Radial plies run across the tire.
2 ply tires have 2 plies, 3 ply tires have three plies. The higher number of plies is presumably stronger, or stiffer, but if the plies are thinner, they might not be stronger.
Joshua Nelson did pass the time by typing:
A fly with a speach impediment.
:)
Number of layers in the sidewall. The more plies the stiffer the tire.
and for the sake of completeness only, older tyres which have layers going round the circumference were called crossplies.
Dave Milne, Scotland '99 TJ 4.0 Sahara
: > Doing tire research, I looked back through the google archives. There : > is a lot of talk about Thornbirds being 2-ply, some tires being : > bias-ply, others being other kinds of "ply." I am not familiar with : > this term... could someone tell me briefly what it means?
Dave Milne did pass the time by typing:
I want a five ply chocolate cake please.
Mmmmmmmm.....
Mike
Also most new tires are *ply rated, which means they can be a 2 ply tire but the composition of the plys allow them to be rated as a 4 ply tire, and so on.... New compositions have allowed this, which in turn has produced a lighter tire with the same ratings as an older and heavier tire. gordon old cj-7
But beware salesmen who ply their trade by adding the side ply to the tread ply to make a 3-ply tire a 4-ply.
It's what Japanese folks do when they are taking off their hubcaps!
From:
Main Entry: 3ply Function: transitive verb Inflected Form(s): plied; ply·ing Etymology: Middle English plien to fold, from Middle French plier, from Latin plicare; akin to Old High German flehtan to braid, Latin plectere, Greek plekein Date: circa 1909 : to twist together
Main Entry: 2ply Function: noun Inflected Form(s): plural plies Etymology: 3ply Date: 1532
1 a : one of several layers (as of cloth) usually sewn or laminated together b : one of the strands in a yarn c : one of the veneer sheets forming plywood d : a layer of a paper or paperboard 2 : INCLINATION, BIASMain Entry: bi·as-ply tire Pronunciation: 'bI-&s-"plI- Function: noun Date: 1968 : a pneumatic tire having crossed plies of cords set diagonally to the center line of the tread
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