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Old 04-26-2018, 07:22 AM   #1
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Tire size impact on ride

OK, thought I had decided the important things in my next purchase of a class A gas motorhome. My list originally included the following "requirements" in a new(er) coach, primarily at least 3 years newer than mine, full paint, larger refrig (her "need"), gas/elect water heat, basement air, fiberglass roof, at least 5 seat belted positions.

Found one that meets these needs, Winnebago Voyage, but this model (32H) has the same 19.5" tires that are on my coach, and I had assumed most of what I would look at would have 22" tires. Like all other aspects of the coach, but was looking to get a ride improvement by going to something with 22's and am now hesitant on this coach.

Am I correct in my assumption that ride would be better with 22's?

All other aspects of this are great.

Thoughts....
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Old 04-26-2018, 07:39 AM   #2
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I think tires are matched up with necessary weight rating requirements per the vehicle. The suspension is more what makes the ride...not so much the tires.
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Old 04-26-2018, 07:59 AM   #3
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The Ford F53 22k/26k is available on either 19" or 22.5" wheels, while the 24k/30k and 26k/30k come only on 22.5" wheels.

All else being equal, a larger diameter tire is going to provide some level of a smoother ride than a smaller diameter. How much smoother and under what conditions is of course variable.

A smaller tire is also going to require a higher pressure to carry the same load, but I'm not sure how that impacts the effective spring rate of the different size tires vs. the load.

The other thing to keep in mind, is that in some / many cases, given how the house structure sits on a gas F53 RV on 22.5" wheels, you will (probably) get larger / taller storage bays, and the engine hump will not intrude as much into the cockpit allowing for more insulation / isolation from heat and noise.

I think you'll also find that the higher end gassers on 22k chassis will have the 22.5" wheels, and my bet is that they will also have a better wheelbase to overall length ratio (longer wheelbase for a given overall length) which is proably even more important to handling and load distribution......

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Old 04-26-2018, 05:10 PM   #4
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Take the exact two different tire sizes and plug them into a tire comparison web site. I doubt you will find much difference in the diameter or revs/mile. There are some very heavy duty 19.5 tires.
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Old 04-26-2018, 07:10 PM   #5
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My old coach had 19.5 tires. They were difficult to find in some locations. Carry a spare. The 22.5 are a more common size, and generally a lot easier to find. Not many ford trucks have 19.5 tires.
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Old 04-26-2018, 08:09 PM   #6
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The larger wheel and tire will always ride better because the overall diameter is greater. Consider this: if you hit an 8" diameter pot hole which tire will drop further into that hole. Obviously the smaller diameter tire will drop further into the road imperfections causing a greater shock to the suspension.
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Old 04-27-2018, 12:46 AM   #7
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I have 19.5's and my ride is good. I also carry a spare. 22.5's bolt torque is 450 ft lbs on the bolts. 19.5 is 160 ft lbs. It's the difference of being able to do it yourself if that matters. 22.5 will marginally have a slight edge on comfort but its close. Brand of tire will have the biggest impact on ride quality.If you don't carry a spare, and rely on roadside assistance then this response doesn't matter.
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Old 04-27-2018, 04:24 AM   #8
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Originally Posted by Ivylog View Post
Take the exact two different tire sizes and plug them into a tire comparison web site. I doubt you will find much difference in the diameter or revs/mile. There are some very heavy duty 19.5 tires.
I don't understand that post. A 19" and 22.5" are not the same size, period. 22.5 is taller, much larger circumference and will have significantly fewer revolutions per mile.
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Old 04-27-2018, 06:18 AM   #9
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Simply out of curiosity.....

For the 22k F53, which comes on either the 19" wheel or 22.5", here is some comparison data from Ford and Michelin

The 22k chassis has an 8k front axle rating, and a 15k rear.

The 22.5" tire size is 235/80 (XRV)
37.1" diameter
556 rev. / mile
90 psi yields 4,140#s load per side on the front
90 psi / 7,530s per side dual rear

The 19" tire size is 245/70 (XZE)
33.6" diameter
619 rev. / mile
95 psi / 4,100#s per side front
95 psi / 7,760 per side dual rear

So tire pressure difference is only 5#s on the front and rear to support the rated axle loads, while the diameter and correlating revolutions per mile differ by ~10%.

I still question how the tire pressures relate to actual effective spring rate of the tires given the size differences, but not going to dig into that......
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Old 04-27-2018, 06:28 AM   #10
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Another big factor, revs per mile will be less with larger diameter tires but it will lower your RPM at a given speed, thus changing your torque. You will have to run a little faster to keep the same "power to the ground". Stay with the original size spec'd for the gearing of the coach unless you're willing to change out the rear gear.
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Old 04-27-2018, 06:37 AM   #11
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Another big factor, revs per mile will be less with larger diameter tires but it will lower your RPM at a given speed, thus changing your torque. You will have to run a little faster to keep the same "power to the ground". Stay with the original size spec'd for the gearing of the coach unless you're willing to change out the rear gear.
One thing I find ingesting looking at the F53 specs, is that the 22k chassis is the only one with the 19" or 22.5" wheel / tire option, while it uses the same rear axle for both, there is nothing at all noted that the rear end gearing is any different......
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Old 04-27-2018, 04:14 PM   #12
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Originally Posted by MoCoTom View Post
The larger wheel and tire will always ride better because the overall diameter is greater. Consider this: if you hit an 8" diameter pot hole which tire will drop further into that hole. Obviously the smaller diameter tire will drop further into the road imperfections causing a greater shock to the suspension.
I had to play with this one a bit

Using the 33.6" and 37.1" diameters as listed above for 19" and 22.5" tires respectively, I drew them out in my graphics program, and set both tires in an 8" wide "hole"...

Based purely on the diameters (not factoring air pressure and flex, which should be pretty equal anyway)-

the 19" tire protruded into the 8" hole exactly .48",
the 22.5 tire protruded .433" --

that's a difference of only.047", just a hair more than 1mm and less than 1/16"... and IMHO, this would present a totally insignificant difference in the ride quality of an 11 ton vehicle...
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Old 04-27-2018, 09:05 PM   #13
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I put the sizes from post #9 into a calculator and came up with:




It seems like the only parameter that would really affect perceived ride quality directly would be sidewall height. Since that's only slightly over 1/2 inch, under 10%, I just don't know that it would really matter all that much.

Overall circumference and revolutions per mile don't have a real impact on perceived ride quality.

So what if you replaced the 19.5" tires with 245/75? The sidewall height difference becomes insignificant.

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Old 04-27-2018, 10:05 PM   #14
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Donít overthink this. If the floor plan and power plant check off most of your wants or needs, then go for it.
The difference in the two tires is negligible. Other than one cost more than the other.
Good luck with your decision.
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