16 inch to 19.5 wheel conversion

[eastfizz]

Our RV is a 1997 Rexhall Aerbus XL3250 (32 ft length, single slide), with 21,000 miles on it, based on a Ford F53 chassis with a GVWR of 17,000 lbs (11,000 lbs rear / 6,000 lbs front). The tires are 235/85/R16 E load rating. The tire load ratings at 80 psi(max for the rims) provide very little extra load margin for these tires at the GVWR. Additionally, the availability of commercial grade tires with steel belted sidewalls in this size seems to be more limited than a 19.5 inch tire/wheel combination. Rickson Wheel makes a 19.5 X 6 inch replacement wheel for this chassis that would enable a 225/70/19.5 tire to be used, thus providing a significant improvement in tire load margin for the GVWR. Tire diameter between a 235/85/16 and 225/70/19.5 is almost identical. Does anyone have any experience / opinions with this conversion? Since I need to replace the four original rear tires anyway due to age, I am contemplating upgrading to the larger wheel/tire combination. Don't need any negative comments about the "older F53 chassis"� and all of its ills - just interested in results of anyone that has done the aforementioned conversion. Thanks in advance for any help / information provided.

[MCPO Ret]

I'd be interested in seeing comments also. I have a 1996 Thor Residency with 16 inch wheels - it would be interesting to see if the switch is possible - should increase stability.

[Map40]

My MH had the same rims, but smaller tires (215/85/16). I ended upgrading the tires to 235/85/16, but in the process I found a company that would sell me the tires and rims for my coach (and they should fits yours). Here is the website:
http://www.ricksontruck.com/
Hope it helps.

[George Miklas]

Welcome to iRV2 eastfizz,

I understand what you want to do, but have to ask you a question. You said that you want to put on heavier tires to provide a significant improvement in the tire load margin. Are you looking to increase your GVWR/GAWR? If so, will the chassis support a higher GVWR/GAWR?

George

[eastfizz]

Thanks to all that responded. I should have mentioned a couple of things in my original post. First, I have no intention of overloading this motorhome. It is not safe, not to mention being illegal. Just won't do it!

That said, we are the second owners of our motorhome, having purchased it in June of 2006, shortly after my retirement, and put about 3000 miles on it since on a few short trips. Over the next 5 years, we do plan several long trips in it and I anticipate loading it very close to the rated GVWR of 17,000 lbs. at various times. We will be towing a light, 2700 lb. RAV4 Toad, so we are well within the 25,000 lb. GCWR weight of 25,000 lbs. The safety margin, running almost at the tire limits with the 235/85/R16 inch tires, is my largest concern – poorly stated previously as "load margin"� (note the 2006 F-53 15,700 through the 22,000 lb. chassis spec tire / wheel combinations of considerable greater capacity than the axle limits). There are probably many pre-1999 F-53 chassis motorhomes running the 16 inch tires close to these limits with success. Perhaps I am overly concerned from a tire safety standpoint. Additional advantages I see over and above the tire safety margin are that the 19.5 inch wheels should also improve brake cooling. Stability may also be better due to the shorter sidewall, possibly at the expense of a slightly rougher ride (TBD - loading and tire pressures also being a factor). Larger tires for the 16 inch wheels are a good consideration, however I have not found any that will fit on the 6 inch wheel width, with the correct dual spacing, etc., thus I would have to find wider 16 inch wheels.

The 19.5 inch Rickson's are not cheap at $174.64 per wheel plus shipping (~$200 to Colorado). Other than the Rickson's, there are other 19.5 options available, including using GM 10-lug,7.25 inch bolt-circle, 19.5 x 6 inch heavy duty, 3500 / "P-series"� wheels and having a machine shop enlarge the hub center circle from 5.25 to 5.46 inches. This is basically what Rickson does. Haven't made a decision yet, but will follow-up in the future and let the forum know how things worked out.

A couple of comments on the 1997 F-53, and some earlier year's F-53 chassis; it uses a Dana 80 rear axle as does the 2006 F-53 18,000 lb. GVWR chassis and, from the rear transmission mount aft, has the same frame rail dimensions and steel strength rating (ref: 2006 Motorhome F-53 Body Builder's Layout Book). From what is shown in the layout book (and actual F-53 chassis measurements), the major changes Ford made with the 1999 and up chassis are in the forward portion; in adding the V-10, and increasing the frame width for the wider, heavier duty front axle, along with increased brake and wheel/tire sizes all around. ABS was added as were heavier duty Dana rear axles for the 20,500 and 22,000 lb. chassis. Appropriate spring/shock changes were made based on the chassis GVWR.

[eastfizz]

Note, the ~$200 shipping from Rickson to Colorado is for 7 wheels.

[TomBr]

I suspect the manufacturer of the tires buils a substantial safety margin into the tire ratings.

[jupoa]

We just bought a 97 XL3250 ourselves a few months ago. We have the stock rims and shocks with Michelin LT235/85R16 tires which so far I have been running at 85psi with ~70psi in the rear air bags. After about 6K miles I haven't noticed the tires running hot and the handling is pretty good even in a nasty crosswind. The ride in front is lousy though. I have been considering a conversion to 19.5" aluminum rims and 235/85R19.5 tires as part of a solution to the ride problem. There seems to be enough clearance in the front wheel wells for the larger tires with the exception of triming back the reverse fender flares.
One step at a time though. I just received new Koni FSD shocks to install on the front. I'll let you know how that works out.

[billyb]

i had the 19.5 on my last mh, and all i know is that the 19.5 were way heaftyer then the 16.

[Hikerdogs]

While the new 19.5" wheels may physically fit your coach I'd do a little more research before I made the purchase. For one thing the difference in the size of the wheels will affect the accuracy of the speedometer. It could also have an impact on some of the engine management systems.

It may be as simple as reprograming the engine management computer to correct the speedometer. To be sure I would contact Ford customer service before spending $900.00 on wheels and shipping and another $1,900.00 (the price of 6 Goodyear G670 245/70R19.5 tires in 2006) on new tires.

[TomBr]

According to the Michelin website, the original 235/85R16 tires turn 655 revolutions per mile. My speedometer reads fast, and it appears that 245/70R19.5 tires, at 625 revolutions per mile, would almost exactly correct that. I am also interested in the greater margins in weight capacity. The extra centimeter of width also seems an advantage. However, the minimum dual spacing for the 245/70R19.5 requires 10.7 inches, while IIRC the 16 inchers require 10.6 inches. Do you know the dual spacing on the Rickson rims?

[jupoa]

You are right about there not being much extra load margin for these tires. The Michelin site lists a max load rating for LT235/85R16s (my tires) of 3042 single and 5556 dual. On the scales with the RV loaded for a trip, 1/2 tank of gas and no water, we were already 5980 front and 11,360 rear. That's within a 100lbs of the max on the front and more than 200lbs over on the rear with no water! Hard to know if the load was even balanced side to side.

Like you, I have been considering upgrading to 19.5" wheels when I'm ready for new tires. I wanted to go to aluminum rims to help improve the ride. Unfortunately, 10 bolt Alcoa rims that will fit if you bore the center hole to 5.46" are only good for a little over 2700lbs each. I'm thinking about scouting the local RV junk yard for a complete F53 front axle with the 8 bolt 19.5" rims.

I just installed Koni FSD shocks on the front and took it for a short trip. The ride over moderately rough pavement was definitely better although I thought on the really big hits it was about the same. Overall, I thought the improvement was worth the expense.

[John90XJ]

Has anyone done this wheel swap yet? I've been thinking about it as well.

[Panbob]

Don't forget bigger rims=more weight. The lighter you keep your unsprung weight the better handling and ride you'll get. I'd look into a higher load rated tire (a co-worker runs 10 ply 16" tires on his F-350 for this reason). Just my two cents!