Tuesday, Jun 05, 2012 at 12:01
Angie - It's easy to get lost when examining tyre brands, sizes, tread patterns, ratings, etc, etc. They're multitudinous and confusing.
In essence, the tyre load rating system between heavy-duty car tyres and light truck tyres overlaps. The load rating system for passenger vehicles has the load rating "index", denominated in numbers - the last numbers in the sidewall code.
Passenger car tyres have "P" as the first letter in the tyre sidewall code.
Light truck tyres generally have "LT" as the first letters, if they're American.
In the tyre example you put up above, the load rating index is "111", and the speed rating is "T". This indicates a load capacity of 1090kg per tyre, and a speed limit rating of 190kmh.
http://www.bobjane.com.au/load-speed-ratings.html
Light truck tyres use an alphabetical code that is American in origin, whereas most other tyre codes are European (metric) in origin.
The Americans call this alphabetical code, the "load range".
The alphabetical load range code starts from A and goes through B, C, D, E & F. As the letters go further along the alphabet, so does the load capacity of the tyre increase.
This alphabetical code rating replaced the tyre "ply rating" that was initially used with crossply (or bias ply) tyres to indicate tyre capacity for loading.
A period ensued where radial tyres were rated with "ply ratings", when they did not actually have the number of wall plies indicated - but this "ply rating" indicated a comparison with the load ability of a crossply (or bias ply) tyre with that number of plies in the wall.
As crossply (or bias ply) tyres are nearly extinct now, the later rating systems with "load index" and "load range" now rule.
Load range/ply rating codes -
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=55
How to read tyre speed rating, load index and service descriptions in tyre codes -
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=35
Other tyre codes used by American manufacturers are:
"LT" = Light Truck
"AT" = All Terrain
"MT" = Mud Terrain
"HT" = Highway Terrain
The type of tyre tread you choose is important. All tyres are a compromise. Big heavy-lugged tyres are great for off road muddy conditions, but at the expense of harsh ride and lots of road noise. Heavy load rated tyres have thick, stiff walls, and give a harsh ride.
At the other end of the scale, a tyre with small lugs and lots of concentric grooves and lots of small grooves is a highway tyre that gives smooth riding, low noise and good traction on sealed roads. These tyres are pretty useless off-road.
Therefore, you must envisage what you require most in a tyre, as determined by the amount of off-roading and the amount of sealed road travel that you do.
Most people go for a tyre that gives fairly good highway ride and modest noise levels, with reasonably good off-road capabilities.
It always amuses me to see
young blokes roaring around town with horribly-noisy, huge lugged tyres, when they hardly ever go off-road!
There's some good tyre testing reports on this following South African 4WD
forum - but the testing was actually an Australian
test of different makes and specifications available here.
Unfortunately, despite the tyre
test being very comprehensive, it could not properly measure one important tyre factor - durability. This only shows up after extended use over a serious length of time.
http://www.4x4community.co.za/forum/showthread.php?t=23570
Cheers - Ron.
AnswerID:
487695