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Dear Tire Doctor,

It’s been suggested to “break in” our steer tires on the drive axles for a short period of time because it creates a wear pattern the tire will retain for the better part of its life. Is this a viable practice or does it wear the tire just as quickly? view reply >>

What is the difference in construction of a 14-ply tire and
a 16-ply tire? And why is the air pressure so much different if
the tire is made stronger?
view reply >>

Can an 11.00R20 tire fit on a rim that generally carries a 10.00-20 tire?
Both are rear wheels.
view reply >>


Dear Tire Doctor,

It’s been suggested to “break in” our steer tires on the drive axles for a short period of time because it creates a wear pattern the tire will retain for the better part of its life. Is this a viable practice or does it wear the tire just as quickly?

Sincerely, Neil

 

Dear Neil,

Thank you for the opportunity to be of assistance.
The “breaking in” of steer tires on a drive axle wheel position has many advantages, and a couple of drawbacks. There are a couple of background items that need to be understood when considering this concept.

1.When a tire is first mounted, it will go through a period of casing growth.

2.Tires running on free rolling wheel positions (steer / trailer) are more prone to irregular wear.

3.The deeper the tread depth, the more susceptible a tire is to irregular wear

4.Tires run under torque on a powered (drive) axle wear very flat – with a very high crown radius.

Running new rib (steer) tires on the drive wheel position for 10,000 to 25,000 miles allows the tires to work through their growth period while in an ‘under torque’ application. This helps reduce the possibility of early life irregular wear and creates a tire that has a shallower tread depth with a very high (flat) crown radius.

Generally, tires rotated to the steer axle have a significant improvement in resistance to irregular wear. And with several 32nds of tread worn off, they typically run longer on the steer position than ‘brand new’ tires. Plus you get the added mileage of the miles run on the drive axle.

The drawback is the cost of additional labor to rotate the tires. Make sure any tires with repairs from road hazards are not rotated to the steer axle.

Generally speaking, this is a very efficient practice for an owner operator or a small fleet, but can be unwieldy to manage for a large fleet.

Hope this was helpful to you.

Best regards, Tire Doctor


Dear Tire Doctor,

What is the difference in construction of a 14-ply tire and a 16-ply tire? And why is the air pressure so much different if the tire is made stronger?

Thanks. David

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Dear David,

Let us address the second part of your question first.

We need to remember that it is the air contained within the tire that carries the load, not the tire components. If a 16-ply tire and a 14-ply tire of the same size are run at the same PSI, they have the same load capacity.

You can increase the load capacity of a tire in two ways: (1) Increase the volume of air in the tire (increase the tire’s size) for a given air pressure, or (2) increase the pressure of the air in the tire (increase PSI) for a given volume (size).

In the “old days,” tires were constructed using cotton cord material.  When designers needed to add air pressure capability to increase the load a specific size tire could carry, they would simply add more plies of cotton cord. Therefore, a 16-ply tire had 16 actual plies of cotton cord, while a 14-ply tire only had 12 plies of cord. This enabled the 16-ply tire to be run at a higher PSI and thus carry more weight.

Of course tires are no longer made with cotton cord. Modern truck tires only have one casing ply of steel. This is the reason the industry prefers to use “Load Range” rather than “Ply Rating.” But since old ideas die hard, ply rating is still with us today.

Now for the first part of your question regarding the differences between a 14- and 16-ply tire.  There is not a hard and fast answer to this question, since tires of different brands or pattern may use different means to enable the extra air pressure to be used, and thus gain extra load capacity.

While one tire pattern may use a cord body cable with a higher wire count in the 16-ply than in the 14-ply, another may have the same wire count but use a heavier wire. Some tires may use identical wire cables in the casing but use different rubber compounds in some components to help dissipate the increased heat generated by the higher loads of the 16-ply tire. And there are other possibilities as well. So, the only way to really answer the question is that the designers did whatever they thought was needed to a particular tire to allow it to function properly at the higher PSI and load capacity.

We hope this answers your question to your satisfaction.

Best regards, Tire Doctor


Dear Tire Doctor,

Can an 11.00R20 tire fit on a rim that generally carries a 10.00-20 tire? Both are rear wheels. 

Thanks, Mike

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Dear Mike,

Thank you for the opportunity to be of assistance.

The 10.00-20 tire is designed for use on a 7.5” rim.

It is, however, allowable to use the tire on a 7.0”, 7.5”, 7.5M, or 8.0” rim.

The 11.00R20 tire is designed for use on an 8.0” rim.

It is, however, permissible to use the tire on a 7.5”, 8.0”, 8.50VM, or 8.5” rim.

Therefore, if your vehicle currently operating 10.00-20 tires is equipped with either 7.5” or 8.0” rims, it is possible that it would be acceptable to run 11.00R20.

However, you stated these are rear wheels, and we are assuming they are dual assemblies, in which case there is a second consideration.

The 10.00-20 tire requires a “minimum dual spacing” of 12.5”.

The 11.00R20 tire requires a “minimum dual spacing” of 13.0”.

Therefore, while it is possible that this may work, we would highly recommend that you have the installing tire dealer confirm that the above requirements are met.

You should also consider that the 11.00R20 tire will have a substantial difference in overall diameter (about 1.3”) vs. the 10.00-20, which will affect vehicle clearance, actual final gear ratio, and speedometer/odometer accuracy.

Best regards,

Tire Doctor

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