Tire max load rating

[OilUzer]

My trailer tire sidewall says:

• Max Load 1820 lbs 50 PSI
• Max Load Dual 1610 lbs 50 PSI

My trailer has one axle and a single tire on each side.

Curious why "Dual" rating is less than single tire rating?

My thoughts and you can ignore as I just made it up:
On the surface, the only thing I can think of is you could for example have a max load of 3220 (1610 x 2) on 2 tires (Dual configuration) and each tire is getting ~1610 lbs (within spec) but since your total weight is 3220 lbs and if you go over a bump or if tires are not evenly on the ground (for whatever the reason), one tire could momentarily get more load than 1610 lbs on that side of the axle. that's why they left some room for safety and specified rating of 1610 which is below the 1820 lbs of a single tire spec. Not sure!

 

[fsdork]

Results of a quick Google search suggests that one of the main factors is road crown, which makes sense. The inboard tire would tend to take more of the load in a dual application due to the pavement under the outboard tires being at a slightly lower elevation.

 

[fsdork]

Or I suppose the opposite could be true for the driver's side of the vehicle. All dependent upon road construction and vehicle position on the roadway, of course.

 

[ollie]

Reason dual rating is less is simple friction. Overload a dual set of tires and the sidewalls can touch. Not good.

 

[CR94]

What if one tire gets punctured, throwing nearly all the load on the surviving one on that side?

 

[CapriRacer]

There is also the issue of production variation in tire diameter.

Also, the inner dual gets hotter than the outer dual, so the diameter of the inner tire increases more than the outer.

 

[CR94]

... Also, the inner dual gets hotter than the outer dual, so the diameter of the inner tire increases more than the outer.

Because of road crowning, difference in air flow across it, both, or some other cause?

 

[CapriRacer]

CapriRacer said:
... Also, the inner dual gets hotter than the outer dual, so the diameter of the inner tire increases more than the outer.

Because of road crowning, difference in air flow across it, both, or some other cause?

Difference in air flow. Crowning would affected the outer dual towards the center of the road.

 

[meep]

Yeah, I always thought it was reduced cooling/airflow. Road crown is interesting too.

 

[JohnnyG]

Or that COULD be the load rating PER TIRE. So, 3220 in dual use?

 

[OilUzer]

Good info everyone!

Based on what you are saying, the lower load rating for dual tire has to do with:

a)
Road crown.

b)
Air flow and the extra heat that is retained due to tires being adjacent to each other.

c)
remote possibility of tires rubbing against each other or puncture.

d)
with dual, you could theoretically carry twice as much load since there are 2 tires on each side and there is a possibility of load shift from one tire to another ...

Aren't the road conditions (road crown, ambient/road temperature ,etc.) the same either way (Dual or Single)?

Still trying to digest this but isn't road crown (a) same for a Dual vs. single tire? Why not list the single rating as 1610 lbs?
I guess I can see (a) causing issues due to (d) if we are not on a flat road.

Basically I'm trying to figure out which is a more contributing factor? a,b,c or d.

Also any other contributing factors besides a-d?

 

[CR94]

... Aren't the road conditions (road crown, ambient/road temperature ,etc.) the same either way (Dual or Single)?

...

If the pavement is convex (in the lateral dimension) and if both tires are equal diameter and pressure, the inner tires would carry slightly greater load, just from the geometry. Whether that effect is significant is another question.

 

[CapriRacer]

....... Basically I'm trying to figure out which is a more contributing factor? a,b,c or d.

Also any other contributing factors besides a-d?

Basically it's about tire diameter. The tire with the larger diameter will carry more load than the smaller tire - hence when tires are dualled up, to prevent overloading one tire, the max load is reduced.

In the case of the crown in the road, that one tire is deflected more than the other.

 

[Heywood_6078]

What if one tire gets punctured, throwing nearly all the load on the surviving one on that side?

Then you slow down, take it easy and avoid anything if possible that might puncture or ruin the remaining tire and drive to the nearest location to get the tire repaired or replaced. Assuming of course, you aren't carrying a spare an a jack.