increasing rim/tire size to gain ground clearance - Fiberglass RV


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Old 12-09-2014, 07:18 PM   #1
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increasing rim/tire size to gain ground clearance

I'm sure this has been covered before, but this RV'ing is new to me. Just retired and bought a 1996 Casita Liberty 16'. Currently the tires are 175/80 R13's and I would like to gain some ground clearance by going to 15" rims and tires. It looks like there is adequate wheel well clearance all the way around so is should be as simple swapping rims/tires.

At some point the welded on axle will be removed and replaced and a lift kit added to give further ground clearance.

Any thoughts/help would be appreciated.
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Old 12-09-2014, 08:38 PM   #2
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Upsizing to 205/75-15 would increase ground clearance by a whole 1-1/2" which also means a 1-1/2" decrease in bump clearance.
Section width would increase by about 1-1/4".
It is important to remember when buying, that most trailer wheels are zero offset.
Another small advantage would be an increase in weight rating.
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Old 12-11-2014, 02:35 PM   #3
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With the Casita, you should be able to tell how much extra diameter tire it will take fairly easily due to the openness of the wheel well. I have a Scamp that came with 165/80-13s that I initially upgraded to 175/80-13 for the "D" rating and extra capacity, but those sizes are hard to find if you need one on a trip.
I eventually upgraded further to a 205/75-14 that is much more common on the shelf at tire shops and gave me about an inch rise in ride height compared to the 175/80-13s. I'm happy with those tires but keep in mind that 1 inch rise in the axle height will also require a 1 inch rise in your drawbar height to keep everything at the same level. I actually kept my old drawbar height, so I now tow slightly nose down which gives me almost a 2" rise in the rear bumper height, which can be a good thing when going through big dips in the road.
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Old 12-11-2014, 08:29 PM   #4
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15" wheels

I put 15" wheels and 205-75/15 tires on a 16' casita that had 13" wheels and it worked out well. I would suggest you think twice about your future plans to "jack it up". A new axle is a reasonable bit of maintenance but the further you put your trailer above the road, the more wind resistance and the more you will spend for gas or fuel. I never had any ground clearance issues with my 16' with new wheels. In my opinion, the high lift axle craze is just like the gluten free craze. Not necessary!!!
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Old 12-11-2014, 08:51 PM   #5
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Also, remember that after you put the new rim and tires on the trailer, the only other way you can increase ride height is to change the downward angle of the arms on the axle. Raising the trailer on the axle doesn't relate to increased ground clearance since your limiting factor, the axle, remains at the same height.

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Old 12-11-2014, 09:01 PM   #6
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Originally Posted by Spanke View Post
Also, remember that after you put the new rim and tires on the trailer, the only other way you can increase ride height is to change the downward angle of the arms on the axle. Raising the trailer on the axle doesn't relate to increased ground clearance since your limiting factor, the axle, remains at the same height.

Spanke

Thats only sorta-true. While the axle stays at the same height, the other low-hanging stuff moves up (sewer pipes, rear jacks etc..)
Some people only need extra height at the extremities for dip-clearance.

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Old 12-11-2014, 09:28 PM   #7
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Originally Posted by widgetwizard View Post
Thats only sorta-true. While the axle stays at the same height, the other low-hanging stuff moves up (sewer pipes, rear jacks etc..)
Some people only need extra height at the extremities for dip-clearance.

Jim
I feel it's more true than not. Most people do not need extreme clearance. Boondocking is a different story. I guess it all depends on the trails you take.

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Old 12-12-2014, 07:22 AM   #8
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I was not going to post as during my axle swap I decided NOT to go with a larger tire/rim but stuck with 13" (on new 5 hole rims). The advantage quoted above for going to a taller tire (ground clearance) was the deciding disadvantage why I did not change. I did not want to step up (or down) any higher each time I entered and exited the Scamp. I am satisfied with my decision, the new, properly down angled axle gives me all the clearance I need. And it is bolted on so if I do decide to go "off-road" at some point I can easily lift the axle and install way taller rims/tires as needed. The biggest advantage to a taller rim/tire as I see it is circumference and not diameter (although they come together of course). The larger circumference will turn a lot fewer times as the miles rack up reducing heat and wear.
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Old 12-12-2014, 07:58 AM   #9
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Quote:
Originally Posted by Radar1 View Post
With the Casita, you should be able to tell how much extra diameter tire it will take fairly easily due to the openness of the wheel well. I have a Scamp that came with 165/80-13s that I initially upgraded to 175/80-13 for the "D" rating and extra capacity, but those sizes are hard to find if you need one on a trip.
I eventually upgraded further to a 205/75-14 that is much more common on the shelf at tire shops and gave me about an inch rise in ride height compared to the 175/80-13s. I'm happy with those tires but keep in mind that 1 inch rise in the axle height will also require a 1 inch rise in your drawbar height to keep everything at the same level. I actually kept my old drawbar height, so I now tow slightly nose down which gives me almost a 2" rise in the rear bumper height, which can be a good thing when going through big dips in the road.
John, maybe I misunderstood you, did you raise the trailer from the axle as well for the larger tire to clear the wheel well ?? I'm also looking to get an inch or so more height and nose slightly down to limit fishtail. This will also allow me to mount bikes on the rear of the trailer without worrying about rear weight. Thanks Jeff.
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Old 12-12-2014, 11:12 AM   #10
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Quote:
Originally Posted by jgraps1958 View Post
John, maybe I misunderstood you, did you raise the trailer from the axle as well for the larger tire to clear the wheel well ?? I'm also looking to get an inch or so more height and nose slightly down to limit fishtail. This will also allow me to mount bikes on the rear of the trailer without worrying about rear weight. Thanks Jeff.
Jeff, I simply added the 14" tire and wheel assemblies and did not touch the axle. I was prepared to have to trim some of the fiberglass to allow the tires to fit without hitting the fiberglass, but was pleasantly surprised to find out they fit without any trimming. I have over 22,000 miles on the 14" tires now over some really rough roads and there have been no clearance problems at all. I like the resulting rise in the rear bumper height especially when pulling into steep driveways from highly crowned streets, less chance of the rear bumper dragging.
While the nose down attitude will shift the center of gravity slightly forward and raise the hitch weight a little bit, if you are having sway problems then this would not be the cure, and adding bikes to the back would make any sway issues worse.
I've added some images, one with the 13" tire, and the other 2 with the 14" tire.
Hope this answers your question. Although it appears it's very close, our tires actually swing on an arc rather than going straight up and down like they would with leaf springs. The arc provides additional clearance from the front.
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Old 12-12-2014, 03:22 PM   #11
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Quote:
Originally Posted by jgraps1958 View Post
John, maybe I misunderstood you, did you raise the trailer from the axle as well for the larger tire to clear the wheel well ?? I'm also looking to get an inch or so more height and nose slightly down to limit fishtail. This will also allow me to mount bikes on the rear of the trailer without worrying about rear weight. Thanks Jeff.
Perhaps its the angle of the photo but it appears that your trailer is already slightly down on the nose. If you put it down to low you may not be all that happy with that result either.
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Old 12-13-2014, 01:04 PM   #12
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Get rid of those 13 inch tires if they are Goodyear. Blowouts are common so the factory in Rice TX started putting 15" tires on the Casita and this solved the problem I think. The Casita needs to be lifted for Boondocking even with 15 inch tires. The black & grey water pipes can be ripped out easily as they sit too low. Now the Oliver which is like the Casita in many ways has the pipes up high in the body so boondocking is no problem. I think this is the Sportsman model.
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Old 12-13-2014, 05:20 PM   #13
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My local trailer shop is where I have it inspected annually so I'll talk to them about sway bars. I get a little sway at 60-65 mph and out on the interstate I don't want to do 55 just for this reason, those trucks will run me over and barley even feel it. I try to stay safe and limit it to 65. Thanks for the help John.
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