CapnCrunch

I am trying to understand the load ratings for certain tires. It seems to me that there are a few different classifications or rating systems out there, or maybe I'm just confused...

For example the Toyo Open Country AT 285/70R17, on their site it says load/speed 121S. Nitto Terra Grappler 295/70R17, says 121R.
What does the 121 mean?

How do I find out the if they are a 8 or 10 ply tire?

And lastly how do these numbers fit into the lettered load range system ( D or E range)?

Jay

bmoeller

http://www.tirerack.com/tires/tirete....jsp?techid=35


http://www.rma.org/tire_safety/tire_...wall_story.cfm

1sttruck

From what I've figured out;

8 ply or 10 ply is an old description that should be ignored, but 8 ply is in general load range D and 10 ply is load range E.

Load index, like 121 or 113 or whatever, indicates the maximum load OVER the tire, where we we need about around 120 or so, which is around 3000 lbs. Look at the published tables for specifics.

Load range is more confusing as it's similar to load index but includes more attributes like lateral stability due to sidewall flex and such, and is the rating that we need for our trucks. Dodge states that we need load range E, which is usually indicated by about a 3000 lb maximum load and an 80 psi maximum tire pressure in the tire sizes for our trucks. Most people running running big tires don't understand or ignore the load range requirements, and not surprisingly more than a few end up 'death wobble'.

SuperGewl

In the glove box of the truck you should have received a Tire information bulletin that will explain somewhat the tire myth tho you. THat bulletin is a very good source for the proper air pressure that you should be running in your tires depending upon what you are doing. If you run the tires to the proper pressure as stated in the bulletin then your tires should last about 50k miles with proper rotation and balanceing. By adusting the tire pressures as per the bulletin will also improve ride quality alot.

CapnCrunch

Thanks for the input guys.

I have looked for tables online to explain the "121" etc... ratings, no luck so far. I have learned a little but nothing all that clear.

My stock tires are nearing the end of their lifespan and its time to switch them up. To make a long story short; I put 315's on a few weeks ago, death wobble like mad. I should mention that I also had mild DW with stock set up since 20,000 KM. Back to stock tires and a new steering stabilizer from dealer, no more DW for the time being. This post isn't really about DW though.

So what tires? I have seen lots of people reccomending the Toyo Open Country AT. Load carrying is comparable to stock but it is an 8 ply. What do you guys think? Same goes for the Nitto Terra Grapplers.

I believe Greg Boardman(?) was strongly reccomending the Toyo's, stating that the BFG's were a major contributor to other problems (DW).

Need to buy tires soon, please help.

Thanks

Beavermike

The 121 "s" is the Speed rating for the tire. Usually people with sports cars look for a tire with a high speed rating. The S rating is 112 MPH.

Q 99 mph 160 kph
R 106 mph 170 kph
S 112 mph 180 kph
T 118 mph 190 kph
U 124 mph 200 kph


I'll see if I can find the load part of this index (121).

Beavermike

The Load Index for trucks is kinda hard to find, but here is a link:
http://www.roadwaywholesaletire.com/LOAD-RATING.htm

The number 121 is 3197 lbs (1450 kg).

"It is not recommended to install tires with a lower load index than what came on your car from the factory."