I'm getting old.

[smlobx]

Did somebody say dunes?

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[ACAD_Cowboy]

You sir can take your Namib and enjoy it.

 

[SleepyJeep]

Give me some 15x10 D Windows and 37's. Takes me back to the early 2000's NEUROC competitions. Those were the days...

Holy Crap man!! You own 23 Jeeps??!! There has to be a great story behind it, pray tell.

 

[Ole Cowboy]

So in keeping with the rules of protocol, I do whole heartedly concede that this bit from Boeing is a bit specific to their chose tire and their methods are tuned to their work however the methodology is sound as a tool for tire selection.

Were you armed with corner scales on a built rig you could Devine the patch size for nearly any psi down to ambient air pressure.

To me the real takeaway from it is the realization that the size of the tire carcass doesn’t drive but is driven by patch as a function of inflation pressure and that ground contact pressure == inflation pressure.

In my typical trails I have glacial moraine and screw mixed with loamy soil that may or may not be mud. Rock features tend to be large and relatively smooth. Inflation pressures for my stock MT with a reasonable amount of gear and people (and food because what better to do watching other people than eat a sandwich or two?)
Is around 12-15psi which results in a compliant sidewall that’s not too sloppy and a compliant tread face that can still hog down. The fee OTR portions are fuuuun as it rises like a caddy from the 70’s, just smooving.

When out in deep snow I will on occasion drop to 20-25psi, closer to 20 if the plow is on to soak up ice clots stuck to the road. Again you gain some flotation but don’t lose your dive and dig.

Sand driving is very limited for me, when last on the outer banks I think I went right to 20 and left it alone as we were drive right after the tide went out. My state will hang you, shoot you, crucify you then take you down to draw and quarter you then burn the whole mess should you even steer a wheel towards the dunes on the little beach you can ride, god help you if you go near beach nests. As such dry dune driving isn’t something I’ve gotten in to.

For the record I’ve never lost a bead and never lost forward momentum due to lack of tractive effort. I have been unable to climb up the scree gravel filled muddy creek with the 60* incline, made it about 2 lengths up until it bent left and just could t make it happen. Front was just kissing and the back was just digging deeper and deeper.

You bring up a lot of points that must be considered: Street, highway, mud, snow, rain, rocks, Moab Rocks which is a whole nother ballgame, shale that slices tires, sand from compact to soft. Then, of course, lateral loading. If you don't the psi right you get optimal performance.

Let's talk X Y: X being the size of the contact patch and Y being the PSI and I am NOT talking air pressure, but Pounds per Square inch as in the load from the weight. The BIGGER the contact patch the LESS distributed weight you have across the CP and conversely the smaller the CP the more weight per sq in. Too big of a CP and you end up with 'floater' for tires, which is may NOT be all bad if you do a lot of mud and swampland.

US Army M1A2 Tank tips the scales at 69.5 Tons, but has a ground pressure of only 15.4 pounds per square in, which allows that 70 tons to traverse almost any terrain and not sink down to its belly.

The goal then is to find where the X Y cross based upon the terrain you are traveling in and your key is the air pressure you run which determines the size of the CP.

TIP: For you extreme or hope to be extreme off-road folks, get access to some patch scales and weigh your rig and if you are a rock hound then what you want to do is to get the weight of your rig +/- 25 lbs on each corner. Do that and you will get some incredible stability and some L/R leaning angles that will ensure NO ONE will ride with you at all...

 

[ACAD_Cowboy]

Ground pressure and contact area! An Abrams can haul ass where I can’t even walk because it has half or less of my ground pressure because of a HUGE contact area.

Big’ol super swampers work the same way, like an agricultural flotation tire, by maximizing the contact patch and gaining traction from big gnarly lugs, look at a Michelin XM47, the crown king of off road tires for soft conditions. But you have down sides, while the big lugs act as paddles you also have very small contact area for on road driving. Combined with stiff sidewalks and it makes for a scary looking curve when you plot lateral loading against adhesion to the surface, there will come a very sharp and sudden vertical line which is you bum rushing the other lane if not the guide rail. Combined with the known behavior of solid axles over irregular surfaces (death wobble) and you can be skittering about.

As noted the Boeing data is not designed for our tires, aircraft generally have ballon tires that are not driven however it gives us a frame work for constructing our thinking. Conceptually the short axis cannot exceed the rim bead width because the ox bow of the side wall would pull the bead away. Likewise the king axis can’t exceed the length of a chord line drawn through the tangent point of the rim parallel to the ground as the OD can’t change but the effective radius can. Effective radius is the distance from center line of hub to ground and changes with inflation and load. This also means you can use this to your advantage as phantom gearing.

 

[Capt.Grumps1075]

On a jeep yes smaller wheel bigger tire. Depending on the vehicle other than jeeps 20/ 22s can make it look sharp, if they are the right wheel. But tn beauty is in the eye of the beholder lol

 

[DirtySaylor]

It's funny that years ago, I thought 20s looked silly on anything. Over the years, more and more factory trucks and SUVs came with them as standard equipment.

Fast forward to now and I think most trucks look ok with them due to proportions. I wouldn't have less or more than a 20 on any of my SRT Jeeps or trackhawk. When it comes to offroad Jeeps, more tire, less wheel is still the way to go. 17s max for me.

Yep. The bigger rims/tires look great on the JT. Anything smaller looks like a skinny guy in a tank top trying to look buff

 

[Hurley82]

Seems like this has less to do with age and more to do with purpose. Off-road more tire less rim. But look at the new Audi RS6 wagon, the thing looks mean as hell.

 

[Bbannongmu]

Curved brim and smaller rim preference here. Old too ! OlllllllO.

 

[LANGeek]

Me too!! 17 maybe 18 with lots of rubber wrapped arounded 'em.

 

[EXTORTION]

I'm old too I guess. I prefer the 17-18 inch wheels with more rubber on the tires, especially if off roading.

 

[Skull]

Hey @ACAD_Cowboy love to know who makes these step bars. Thanks

Maybe Orange County choppers?

 

[livewire_3020]

i agree, i went with 37s on 17s. love the look of the big sidewalls

 

[Renegade]

It so entertaining when a long-dead thread comes back to life...

 

[Lynn_F]

22" w/ 37's. This thing will never see a rock trail. I had 17" w/ 37's on my wrangler but this is a truck that I use for mostly truck things. To each their own. Same type of setup on my SxS 20" w/ 33's - it only sees mud and light trails.

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