Big ugly tires!!! The tires I selected for the rough roads look like they came off a WWII troop carrier. HA! The tire choice probably wont make sense unless you read about the terrain we have out here in southern Utah and the off-roading I do. Also see "references" at the bottom of this page. These tires are only for the long dirt road trips I make frequently. I still have the 14" Marathons mounted and stored out of the sun so if I want to go highway traveling I put them on.

The rough tires are 700-15 bias ply from China costing $70 each. They are eight ply with six ply sidewalls... 30.5" diameter. You can see how they fit in the nest egg below. It is pretty close particularly on the forward side since if they will hit the fiberglass it will be forward, not aft (the tire rotates a bit forward due to the torsion axle arc).

These tire/wheels are mounted on the Casita high lift axle and gives the egg more clearance. The best way to find the lift advantage is to measure from the hub center to the ground. By going to these tires I got close to two inchs more lift (clearance) than the original 14" Goodyear Marathons. The majority of that lift comes from tire diameter not wheel diameter. However there exists no 14" road/trailer tire that has a 30.5" diameter and there are many 15" tires that do. By the way a good combination tire would be the MAXXIS M8008 225/75R15 8ply radial. It is 28-1/2 inch diameter and has a load rating of 2150lbs. This is what I use most often now as I have two sets of 15s and will be selling the 14" marathons and rims.

As already mentioned in the My Terrain page, I think the best way to avoid punctures out here is to look real close at the road ahead and drive slow and purposeful. Another way is to have as much rubber on the tires as possible simply to have the thickness to withstand a rock cut . I found the graphic on the left on the Mechelen web page. Although they are trying to educate us on the benefits of radials over bias it does point out the one unique factor bias has over radial. Namely lots and lots of rubber in the right places with bias belts (at least when compared to radial trailer tires).

Also to consider is tread groove width. Wider grooves pick up and lodge larger rocks which get pounded deeper into the tire with each rotation¹. Big knobby off-road tires may look tougher but they pick up bigger rocks and if that rock is sharp and doesn't puncture the tire the first time around it might after a hundred revolutions or so. Of course the narrow grooves on my tires have much less grip than a knobby or the like that but as long as you don't lean the egg too far one way or the other sliding should not be a problem (speaking of 20 mph max on dirt roads only).

Sidewall punctures account for more than half of the tourist flats on our roads². Even road graders can get flats from a side piercing piece of shale². Not that my tires wont get flats this way. Indeed, if I travel these roads enough I will get flats I am trying just to increase my odds against that.

I chose the cheapest 8 ply narrow grooved tire I could find that also had real thick sidewalls. I think of the tires as disposable at $70 each. The ranchers tell me they get about 20,000 miles on theirs³. They have to drive the highways more often to get to the meat houses and places so maybe they wear them out on the asphalt. Not sure. I may drive an asphalt highway 80 miles once in awhile to get to the rough road turn off but that is the only time the bias ply tires hit the smooth pavement.

If you want to compare the advantage and disadvantages of radial vs bias ply you will see why bias ply are the best choice when:

You never go over 25 mph.

You don't care about cornering and traction

You don't drive much distance on hot pavement

You don't care about sidewall flexure

You don't care about fuel economy

What you “do” care about is resistance to puncture and vibrations. The bias ply will take longer sharp rocks than the radials can handle The part that is not taken care of is vibration⁴. The bias ply are rock hard! They transmit a ton of jolt to the axle. I am going to have to experiment with tire pressure to see if I can smooth that out some. The good thing is that I can expose a lot of sidewall to the rocks when I deflate the tire but I still have a six ply sidewalls further from the ground than the radials..

References

¹ Larry Unser, NORRA crew chief

² Jim Boner, Kanab tire

³ Tim Johnson, Farley Hatch, and Bowman Smith, AZ strip ranchers

⁴ Martyn Davies chief engineer Adventure Trailers LLC

Links for offroad trailering (not for eggs I can assure you)

http://www.youtube.com/watch?v=Rt9Jsb2Hu7g (what a video)!!!!

http://www.tentrax.com/gallery/gallery.html

http://www.brakhah.co.za/camper/camper_main.htm

http://www.bushtracker.com/Brochure.htm

http://www.desert-wolf.com/

http://www.kimberleykampers.com/default.php

Addendum 03-03-07 I just got back from a washboard road trip. 15-20 mph over 50 miles of tire bouncing ruts. The 30-1/2" dia. tires did not touch the Casita body as evidenced by the lack of rubbing marks.

KW says, "Most 15"wheel/ tires combinations are the SAME overall diameter as 14" tires (unless you intentionally go oversize), and are smaller than the Load D 14" tires many of us are using ... The wheel size has little to do with the diameter of your combination, or the wheel well opening needed to accommodate the tires."

It doesn't matter how many times you point out how illogical the above statement is this keyboard weasle will keep coming back with more of the same.

1- Intentionally go oversise? Well of course! Why not? What makes you want to change to a 15" rim and then mount a tire that is the same diameter as the ones you took off? Read putting on a tire with 1/2" less section height just so the 14 and 15 inch tires come out to the same diameter (see graphic below). As shown in the photo on the right I went to a 30.5 inch diameter tire on 15" rims from a 26-27 inch tire on 14" rims. Jeezuz even!

2- The rim diameter has little to do with the tire diameter? What has he been smoking? Given the same section height the 15 inch rim will raise the trailer 1/2" higher! Additionally there are dozens more tires to pick from on a 15" rim!!! All the way to 32 inch dia which lifts you MUCH higher. Duh!

3-FAR more 15" wheel tire combinations are LARGER than the 14" Kumho. Where does he GET this stuff?

4- This KW wants (and argues about) everyone putting Kumho light truck tires on their Casita and no one should even breath the words "fifteen inch". As pointed out in these pages I wanted 15" so that I could get max diameter in the wheel well and more lift so that I could take my egg over rugged rock roads with ease. Not to mention the load carrying increase. Also not to mention that when flattened these tires present a much larger footprint to sand and remove a substantial amount of psi on sharp rocks.

label: kumho, trailer, 14", 15", keyboard weasle, idiot, off road, casita, high lift axle, maxxis