What does PR stand for in tire size?

[Slippy]

Anyone know what the PR stands for in a tire size of 13.6-24-8PR R1?

 

[ArTrvlr]

PR= Ply Rating. In this case, 8PR means the tire has the strength equal to a tire with 8 ply's of cord in the body of the tire. The newer term for the same thing is load range. The PR is a hold over from the early days of pneumatic tires, when the only way to make one stronger, or support more weight was to add another layer of cord. Not sure what they used in those days, but let's just say it was cotton. When stronger cords (nylon, rayon, whatever) were developed, they could make a tire with, say 4 layers of cord that would be equal to 8 layers of the older cord material. So that tire would have a 8PR although it only had 4 ply's. Most car and light truck tires now use the load range system to indicate the strength of the tire. Not sure, but I think that all on-highway tires use load range letters to comply with a DOT standard. Ag tires are probably not subject to the same standard, so can use ply ratings or load range.
PS: I am not a tire expert, I do not play one on TV, and I did NOT stay at a Holiday Inn Express last night, so anyone who knows more or different, please correct me!

The short answer is, it is a measure of the strength, or load carrying capacity of the tire.
jp

 

[Gary Fowler]

The 8 PR mean 8 ply rated. It may have only 6 actually plys of cord in the construction that are larger than standard cord or mybe just stronger.

 

[Slippy]

Which is better, the 8pl or the radial tires?

 

[john_bud]

Which is better, the 8pl or the radial tires?

Uh, you do know that both have plys and are both ply-rated, right?

Radial is just the direction that the ply is wrapped in the construction process. Radials have more sidewall flex and can transmit more tractive force because that lets them put more treads on the trail (without airing down).

 

[Slippy]

Right, but they make both. Which is preferred, if there is a preference?

 

[schmism]

Right, but they make both. Which is preferred, if there is a preference?

usually there is a preference based on use.

trailer tires vs driven tires vs LT tires vs heavy truck tires.

whats the use?

 

[RickB]

Right, but they make both. Which is preferred, if there is a preference?

In most applications where the hours/miles of use are fairly high per unit of time, radials offer performance advantages that pay for their extra cost. In most applications where the tires will dry rot and otherwise deteriorate rather than wearing out, bias ply tires can be more economical.

Radials typically run cooler at high loads and speeds, and offer better traction and less ground pressure (soil compaction) than similarly sized bias tires.

 

[Slippy]

I'm so sorry. I should have explained it is for a tractor. The rear tire size is 16.9-34-8PR R1. I have looked at tractor tire sizes and they generally say R, not PR. Does that mean ply radial. I understand a radial tractor tire will put more tread on the ground, but I have also been told you should not load radials. I just was not sure how PR is classified.

 

[RickB]

I'm so sorry. I should have explained it is for a tractor. The rear tire size is 16.9-34-8PR R1. I have looked at tractor tire sizes and they generally say R, not PR. Does that mean ply radial. I understand a radial tractor tire will put more tread on the ground, but I have also been told you should not load radials. I just was not sure how PR is classified.

My post was general enough to apply to highway and off-road tires. The tire size information you have listed is for a bias ply agricultural tread (R-1) tire of 8 ply rating. Radial tractor tires are not "ply rated", but use a "star" rating system to to identify the load rating they are constructed to carry. They have star figures molded into the sidewall in an area apart from the tire size. Two star radials are roughly equivalent to 8 ply bias tires. A radial tractor tire also has an 'R' included in the tire size immediately before the rim diameter. The radial equivalent of the bias size you listed would be 16.9-R34. Somewhere else would be ** load rating.

Whether or not to load radial tires can be debated, but liquid ballast is the cheapest ballast available for most applications, and many, many radial tires carry it.