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Bigger Tires


Krashking

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I think they are a nice improvement but I'm no fan of 19 inchers if there is any possibility of 22s.

 

One thing I really noticed was a difference in ground clearance for the differential when I was shopping for an MDT, the 19 inch truck had about 2 inches less clearance than the 22 inch version.

 

What type of truck or RV are you looking at?

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They have a much larger footprint each time you go up in diameter. That means a more stable ride, better traction, more load capacity, and usually better wear characteristics. Of course it also means a higher price as well. While I do agree that 22" would be preferred over 19.5" tires, I'd certainly not pass on a used RV for that reason alone. We had a class A with 19.5" tires for 14 years and were quite happy with them, especially when compared to the 16" tires on our previous motorhome.

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One thing to look for is availability of replacement tires. I was talking to someone just a few days ago that had a small Isuzu motorcycle tow truck with 19 inch wheels and tires. He has been looking for 2 years for new tires and cannot find them anywhere. He is also having an issue finding wheels to replace as the truck has a unique lug bolt pattern.

 

With the multitude of current wheel and tire combinations and some really strange OEM offerings, It gets sometimes very hard to locate certain tire sizes. 13 and 14 inch tires that used to be popular for all the compact cars have been replaced by 16 and 18's. Other than the popular 15 inch mud tires on a lot of the 4 wheel drive vehicles you cannot find many places that have any 15 inch tires.

 

All of this I have heard and experienced owning a Jeep with 15 inch wheels. Converted it to 16's so I could have a choice of a less aggressive (noisy) tire.

 

Rod

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They have a much larger footprint each time you go up in diameter. That means a more stable ride, better traction, more load capacity, and usually better wear characteristics. Of course it also means a higher price as well. While I do agree that 22" would be preferred over 19.5" tires, I'd certainly not pass on a used RV for that reason alone. We had a class A with 19.5" tires for 14 years and were quite happy with them, especially when compared to the 16" tires on our previous motorhome.

Actually, if the weight of the vehicle stays the same and the tire pressure stays the same the footprint stays the same regardless of the width or diameter of the tire. 80 psi in a tire means that each square inch of footprint supports 80 lbs.

 

Rich

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Actually, if the weight of the vehicle stays the same and the tire pressure stays the same the footprint stays the same regardless of the width or diameter of the tire. 80 psi in a tire means that each square inch of footprint supports 80 lbs.

That is only true if the tire inflation point is 80#. When you put larger tires on an existing RV, the weight of the RV has not changed and if you use the tire properly, you look at the tire manufacturer's inflation tables and adjust the inflation pressure to what that tire should have for the RV's load on each tire, thus giving the larger footprint which it was designed to have. That is the reason for inflation tables. With the larger footprint you have less weight per square inch if comparing to the same weight on a smaller tire and you will have a lower inflation pressure. That lower inflation pressure allows the tire to flex and absorb more of the road changes and thus a better ride for the occupants. That larger footprint also means better tire contact with the road and thus better control of the vehicle. When used properly, tires are not inflated to the maximum pressure unless they are carrying the maximum load.

 

In addition, the carrying capacity of any tire is determined by the design or that tire. When you install the tire on a vehicle, you are determining what weight the tire will be carrying, but that has no impact upon the tire capacity which is a design limit. The weight carrying capacity of a tire is the maximum that it is designed to carry and can not be changed by where it is used.

 

If you look at the inflation tables for any RV tire, you will see that lower weights on each tire call for lower inflation pressures in that tire. The reason is to get the proper amount of footprint each the tire was designed to have.

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That is only true if the tire inflation point is 80#. When you put larger tires on an existing RV, the weight of the RV has not changed and if you use the tire properly, you look at the tire manufacturer's inflation tables and adjust the inflation pressure to what that tire should have for the RV's load on each tire, thus giving the larger footprint which it was designed to have. That is the reason for inflation tables. With the larger footprint you have less weight per square inch if comparing to the same weight on a smaller tire and you will have a lower inflation pressure. That lower inflation pressure allows the tire to flex and absorb more of the road changes and thus a better ride for the occupants. That larger footprint also means better tire contact with the road and thus better control of the vehicle. When used properly, tires are not inflated to the maximum pressure unless they are carrying the maximum load.

 

In addition, the carrying capacity of any tire is determined by the design or that tire. When you install the tire on a vehicle, you are determining what weight the tire will be carrying, but that has no impact upon the tire capacity which is a design limit. The weight carrying capacity of a tire is the maximum that it is designed to carry and can not be changed by where it is used.

 

If you look at the inflation tables for any RV tire, you will see that lower weights on each tire call for lower inflation pressures in that tire. The reason is to get the proper amount of footprint each the tire was designed to have.

My only point was, and still is, that the tire diameter does not dictate footprint area as you intimated. Footprint area is solely determined by the vehicles weight and the tires inflation pressure.

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