wheel size-might be the dumb question of the year

Golden_HVAC has it right!!! It is all about axle and tire weight ratings, not length or ride.

22.5 tire /wheel combinations probably cost less because they are used by the millions in the heavy truck industry ?

Hi,

Most 16" rims are limited to only 3,050 pounds, except a few trailer rims at 3,500 pounds.

19.5" rims are typically rated between 3,000 and 6,500 pounds.

22.5" rims are rated between 4,500 and 7,500 pounds.

So the larger rims will carry more weight, and manufactures of tires also make the larger tires carry more weight. Over the road trucks typically will have 24" rims with ratings up to 12,000 pounds per tire.

There are exceptions to these rules, such as the special tires run on low boy trailers, such as ones to carry large equipment to a worksite. They might have 14.5" rims rated at 5,000 pounds each, and then have 4 to 8 tires per axle! Many low boy trailers have 19.5" rims with a 6,500 pound rating.

The larger rims are there to accommodate larger brakes under those rims.

Tiffan might be using 22.5" rims because they get a great deal when buying many at once. And they can use the same 10,000 pound front axles on all their models, along with 20,000 to 24,000 pound rear axles, and this will keep them from having to buy separate sizes for each chassis length. Installing something rated a lot higher than the GVWR will cost the manufacture a little extra, but it is OK and will save them in liability later. The brakes will work better because they are larger than required for the load inside the RV.

Fred.

I have 19.5" on my 93 Airstream I have put 80,000 on the coach myself with 2 sets of tires 1 set still in use I have air/hydraulic braking and disk brakes all around the back brakes changed this winter at the 98,000 mile mark. My ride is good and I have changed the shocks to Bilstien about 30,000 miles ago. My coach weighs in at 21,000 loaded checked on the scales. So if I had 22.5's on her how much further would I go ? I know the weight might affect the MPG and I do not think it would roll out any better. This is a Spartan Chassis so I think they probably spec'd out the tires. I have to agree that sometimes the body looks a little big for the feet. All those miles and places and good brake and tire results I think I have truly saved a good deal of money over the last 21 years.

I saw the Winnebago Vista 30T sitting next to a Sightseer 30A. The 19 inch wheels on Vista and larger on Sightseer. The Vista looked like body was too big for the feet.

Before you write off 19.5 tires you need to look at 265 and 285/70 19.5 tires that have load ratings of 6000 lbs. There is no reason to go with a 22.5 tires for more load carrying. Look at the spec for this 19.5.

With the older Workhorse chassis, the W20 and W22 came with 19.5 wheels as standard. The W24 came with 22.5 wheels as standard. Now if you wanted to pay extra, you could get 22.5 wheels on your W20-22 from some coach manufacturers. Basically the same frame, but with larger wheels.

Corkey05 has it right. The shorter lighter coaches can do just fine on smaller wheels and tires. It wasn't too many years ago that all gas coaches were using 16" wheels. As they grew in size and weight they also got bigger wheels. Diesel coaches have always been considerably heavier and have used truck/bus sized wheels. The air pressure, required to carry the total loaded coach weight, has more effect on ride than wheel size. (hitting potholes excepted)

My old coach uses 16" wheels (the actual diameter of tire and wheel is only about 1-3/4" less than the 19.5" combo), so the ride is not much different.

The coach builder has to decide what length/weight coach he is going to put on a given chassis. It's part economy, and part matching the chassis to the coach, that determines the chassis configuration and required wheel size.

Personally, if I wanted a small coach I would certainly NOT rule out one with 19.5 wheels if that was all that was required to handle that weight. I might even prefer it for tire replacement cost considerations.

My point is, that 22.5" wheels (while maybe makes you feel more like one of the BIG Boys) does not guarantee a better ride. In fact, on a small coach, it may well be the opposite.

I see the larger tires on most 32 foot. So what are shocks for?

Don't forget, from an engineering point of view the design has to call for managing unsprung weight of the tires and wheels. Larger tires and wheels on a light chassis ups the percentage of bouncing weight that chassis has to manage. It's way more than a cost issue.

Put your motorhome tires/wheels on you car and you can see what I mean. The tire bounce would take the car with it.

Usually the 22.5 wheels don't show up until the motorhomes cassis reach the 34-36 ft length, with a 18k+ chassis.