15" wheels on a older Casita?

[saucesquatch]

We needed to upgrade our axle, it had not been updated since 1997 and was not looking too great. Since we were upgrading/updating I opted to get the axle with the 10 degree option so it would be sitting two inches higher. I figured that would give me my clearance needed for larger 15" wheels (as it has 13") wheels right now.

So ordered up wheels (axle has not shown up yet) and these things are MONSTERS lol
I guess I didn't realize how much larger a 15" is over a 13", I thought it would be two inches and it's more like 4"

It will fit in the wheel well, but will I need an additional lift to get these on?

Also, the spare is going to look ridiculous on the back of the camper being so big, it will sit higher than the belly lip.

I'm afraid I went too big, perhaps I should have gone for the 14" instead...

[thrifty bill]

It’s the tire not the wheel. My F150 can be had with a 17 inch, 18 inch or 20 inch wheel. With a tire mounted to them, they are all the same height.

[Nor Cal Mike]

Here is my mid 80's Casita with 15 inch Ford Ranger wheels. I am running the stock axle but dropped the axle mounting position 3 inches during a chassis repair which effectively raise the trailer by the same amount.

[saucesquatch]

Thanks Mike and Bill, definitely making me feel like I made the right decision.

From everything I read it sounded like the right upgrade, but like I said I was a little shocked how much larger they are.

I will roll this thing out to the camper in the morning and snap a pic.

[starbrightsteve]

I used to have a 1999 16’ Casita that came with 13” wheels. I installed new 15” rims and Carlisle tires and had no wheel rubbing problems. But.. Larry at Little House Customs has said that sometimes the axle is located slightly too far fore or aft in the wheel opening and then the tire may rub. My 16 had the standard axle configuration. (It was not high lift)

[Wayne Collins]

Wheel size, 13", 14" 15" etc is a measure of the rim diameter at the bead seat.
So, going from 13" to 15" is an increase of only 1" radius … the amount it will raise the axle. BUT Tire size is a factor too. The ASPECT RATIO determines the overall diameter and rolling radius.

[Jack L]

Originally Posted by Wayne Collins

Wheel size, 13", 14" 15" etc is a measure of the rim diameter at the bead seat.
So, going from 13" to 15" is an increase of only 1" radius … the amount it will raise the axle. BUT Tire size is a factor too. The ASPECT RATIO determines the overall diameter and rolling radius.

OK, let me expand on Wayne's statement about tire size. A tire size is usually stated as 3 numbers, but its somewhat confusing at to what they all mean. The first number is the width of the tire in millimeters , at the tires widest point on the tire when it is mounted on the rim and inflated. Some people think incorrectly that the first number is tread width. The second number, the aspect ratio is the distance from the bottom. (or top) of the tread, to the rim edge, as a percentage of the width. The third number is the easiest. It is the outside diameter of the wheel in good old inches.

My trailer has 225-75-15 tires, so the diameter is figured by multiplying the width of the tire by .75 , 225 X .75 = 168.75 MM from the bottom of the tread to the rim. Now, lets convert this height in MM to good old inches. 1 inch equals 25.4 MM so 168.75 translates to 6.64 inches. This makes the tire 28.28 inches in diameter. 6.64 from the pavement to the rim plus the rim plus the distance from the rim to the top of the tire.

If you had a narrower 15 inch tire with an aspect ratio of 75, it would no be as tall as the wider tire.

Don't forget, as the tire tread wears down, the tire diameter is reduced.

[ehoepner]

My 17 ft Casita SD had 14 inch tires and I went to 225 R75 15 inch tires. I had to raise the axle to do that. You can buy a new Dexter axle that can be installed with more angle which gives you more Hight which allows for 15 inch wheals.

[Jack L]

Aspect ratio is also some times called the "series" or "profile"

[Wayne Collins]

[QUOTE=Jack L;737956]OK, let me expand on Wayne's statement about tire size. A tire size is usually stated as 3 numbers, but its somewhat confusing at to what they all mean. The first number is the width of the tire in millimeters , at the tires widest point on the tire when it is mounted on the rim and inflated. Some people think incorrectly that the first number is tread width. The second number, the aspect ratio is the distance from the bottom. (or top) of the tread, to the rim edge, as a percentage of the width. The third number is the easiest. It is the outside diameter of the wheel in good old inches….. QUOTE ]

To be precise, the third number is the same as the rim diameter measured at the bead seat, not the outside diameter, a difference of maybe 1.5 "

[Joe Romas]

When I updated to 205 15 R75 in my 1999 17' SD I had rubbing on one side only. Turned out the egg is on the frame slightly off. So I made a 1.5" lift and all was well. That was about 7 years ago and this past year I replaced the axle. this time it was much easier because I used Dexter's weld on brackets previously.

I'm perfectly happy with my small lift and standard, 10 degree up, axle. My knees notice the 1.5" lift everytime I step in and with a new axle it's even more.

[John in Santa Cruz]

note your original torsion axles on a 97 are probably shot, and need new rubber elastomer spring elements anyways. when you do this, you can raise the trailer for larger wheels.

re all that talk about tire aspect ratios and stuff, trailer tires don't come in all the same sorts of low profile sizes as car/truck tires. some folks do run LT truck tires on their trailer instead of ST trailer tires.

[saucesquatch]

Thanks all. Lots of knowledge in this forum...

The tire we ended up with is a ST225/75D15
28.1" outer diameter

sounds like what Wayne is running... So I'm feeling good about these beefcakes. Except for the spare... Do I need to reinforce that back wall at all for this big old wheel go in the spare spot?

And John the axle is most definitely shot; new one should be delivered this week... and on that note here is a link to my axle dilemma thread I just started.
http://www.fiberglassrv.com/forums/f...tml#post738047