Greater On-(Dirt) Road Capability

[bajajoaquin]

Most people here are searching for greater off road capability, but I need better on-road capabilities. My 4x4 Class C has all the capabilities my family will let me use with them in it. And it does great at most things. I’ve gone places that people are surprised to see a rig that big in.

But long dirt roads suuuuuck. I can go for miles and not get above 5 or 7 miles per hour. The interior of the camper just shakes itself crazy. I don’t want to destroy the not-tough RV interior and I dont want us to have than unpleasant an environment. Some places I go have a 25 mile dirt road at the end of the trip and that turns into a really long slog.

I have 265/75-16 tires which were the biggest I could fit without tires rubbing on the duals. I can’t air down much because I’m at 15k lbs. First time I aired down to 55 I ran on the sidewall and got a rock puncture in the sidewall. And I couldn’t go really any faster anyway.

I can’t lift or body trim my way to 20s and MPTs.

Does anyone have any experience with this weight and tire restriction? Am I close, and if I went to 285s or 315s would that provide meaningfully more cushion? I’m thinking that going to any larger rim size would decrease the air volume and be counter productive but I’m willing to listen to opinions.

is there another reasonable solution? Even moving up to 2-3 mph in some sections would me a meaningful improvement.

 

[Peter_n_Margaret]

You don't tell us much about the vehicle?
This is a tyre AND suspension challenge.

Cheers,
Peter
OKA196 motorhome

 

[DiploStrat]

The usual rules for washboard/tole ondulee/corrugations are:

-- Soft tires with tall sidewalls (low pressure)

-- Soft, long travel suspension

-- Big, big shocks with closer to 50/50 valving.

The first production vehicle that I know that incorporated most of these elements was the early 1970's Range Rover.

 

[alanymarce]

-- Soft tires with tall sidewalls (low pressure)

-- Soft, long travel suspension

-- Big, big shocks with closer to 50/50 valving.

My reaction is essentially that you have some combination of the opposite of these:

Not much you can do, apparently, with the tyres.

Not much you can do with the suspension travel either, although if you have put in stiffer springs maybe these are too rigid for the sprung mass.

How many miles/km do you have on the dampers? If you are not damping the spring movement then you will get "bounce",

For what it's worth, we run the same pressures on corrugations as on tarmac, and air down only for sand or extreme (for us) rock. I believe that a lot of people run higher pressures on tarmac than we do, in which case airing down is probably a good idea.

 

[bajajoaquin]

The usual rules for washboard/tole ondulee/corrugations are:

-- Soft tires with tall sidewalls (low pressure)

-- Soft, long travel suspension

-- Big, big shocks with closer to 50/50 valving.

The first production vehicle that I know that incorporated most of these elements was the early 1970's Range Rover.

Thanks. Your comments are essentially going back to basics, and that's helpful. My first reaction was that a RR is way lighter than my rig, so there's not much there. And there's not. But "not much" is not "nothing." I don't think I can do much to soften my suspension and control the weight very well, but that doesnt mean I can't do anything.

Bigger tires with bigger sidewalls may not get me all the way there, but maybe with a bit more travel, especially in rebound, and softer shocks, it will get me a couple more mph. Right now, I'm averaging about 7 mph on the dirt roads I'm traveling even when they're pretty good. So 2 mph is 45 minutes saved on a 25 mile dirt road. That's a big deal.

My reaction is essentially that you have some combination of the opposite of these:

Not much you can do, apparently, with the tyres.

Not much you can do with the suspension travel either, although if you have put in stiffer springs maybe these are too rigid for the sprung mass.

How many miles/km do you have on the dampers? If you are not damping the spring movement then you will get "bounce",

For what it's worth, we run the same pressures on corrugations as on tarmac, and air down only for sand or extreme (for us) rock. I believe that a lot of people run higher pressures on tarmac than we do, in which case airing down is probably a good idea.

Your reaction was mine as I mentioned above. And that was the frustration. I wasn't going back and looking at parts, I was just getting frustrated at the whole.

Shocks are an area I can improve on, for sure. Budget kinda ran low when I bought the camper, as I bought it at the height of the RV price surge and it needed 7 tires, shocks, suspension bushings, all new belts and hoses, and other things from being undriven (but low miles) for years plus solar. Two things I considered were buying new wheels to go with the tires so I could go larger, and a shock upgrade.

I'd guess I can fit 285s with another inch of ride height and some light trimming at the front. Maybe one of the van companies makes flares that would help me fit 315s. Since the rears don't steer, I think there's room back there. Wheel offset is going to be an issue, though.

Regarding shocks, any recommendations?

 

[Peter_n_Margaret]

Parabolic springs?
Not as good as much longer standard leaves, but a much easier conversion.
Cheers,
Peter
OKA196 motorhome

 

[DiploStrat]

I used Fox shocks with external reservoirs, but, in reality, for a loaded camper, that is probably overkill - you simply ain't gonna go that fast that long.

You could do worse than to consult with U-Joint. Chris and his crew have lots of experience with Ford vans and camper conversions.

E Series 4×4 Conversion | Ujoint Offroad

www.ujointoffroad.com

 

[bajajoaquin]

I used Fox shocks with external reservoirs, but, in reality, for a loaded camper, that is probably overkill - you simply ain't gonna go that fast that long.

You could do worse than to consult with U-Joint. Chris and his crew have lots of experience with Ford vans and camper conversions.

E Series 4×4 Conversion | Ujoint Offroad

www.ujointoffroad.com

I'm not sure that those shocks are overkill. I'm talking about trying to stabilize a heavy load with high frequency vibration for 3+ hours straight. It's not high shaft speed or long travel, but that's a pretty significant load for a damper. I think you were exactly right to point out that damping is likely one of the parts of the issue. The question for me is going to be how to find a product that is optimized to my situation, and not to long-travel, high (piston) speed applications. I reached out to King yesterday because they came to mind, and I'll see what they have to say. But I get the impression they're focused on race or looks ("lifestyle") and not essentially commercial severe duty applications.

I remember reaching out to him about wheel offset and tire size when I got the camper, and he was super nice and helpful. It was my first thought, but I recognize that he runs a business, and I'm not buying from it. (As an aside, I was looking for a Class C with the mind to sending it to him for conversion later, but found one already converted.) But it's a good idea. I can reach out and see if he's got some ideas. Thanks again.

 

[bajajoaquin]

You don't tell us much about the vehicle?
This is a tyre AND suspension challenge.


Cheers,
Peter
OKA196 motorhome

Sorry, for a US audience, a lot of that stuff will be understood by some of the other things. But here it is:

1998 Jamboree 24' Class C (cutaway van chassis with cabover RV box)
"Factory" 4x4 conversion (done after the factory, but offered from new) by Salem-somethingorother out of Tacoma. No longer in business
15,500lbs fully loaded
Probably 4"-6" of lift over stock 2wd
158" Wheelbase
Dana 60 high pinion front, Dana 80 Rear
Borg-Warner 1356 Transfer case (2.:1, I think)
4.63 gears
Air Locker rear
Gabriel gas shocks
Stock 6.5" steel wheels
I said I had 265-75/16 tires, but I'm not sure now. Looking at specs, that requires a wider rim than I have. Probably 235-85s, now that I look at it again.

Parabolic springs?
Not as good as much longer standard leaves, but a much easier conversion.
Cheers,
Peter
OKA196 motorhome

Can you tell me more about parabolic springs?

 

[Peter_n_Margaret]

The best way to get a better ride from conventional leaf springs is to make them longer. That is generally a difficult thing to achieve. Parabolic springs are a good compromise. They are not a consistent thickness like standard leaf springs, and are thicker in the centre than at the ends. Usually just 2 or 3 leaves instead of larger numbers. All Terrain Warrior in Oz fit them to Canters and other Japanese light trucks. The 4WD Iveco has them as standard ex factory.
The down side is they do not have the inter leaf friction to provide damping that conventional leaves provide, so they need better dampers and may wear them out faster.
Parabolic Suspension Isuzu — All Terrain Warriors
Cheers,
Peter
OKA196 motorhome

 

[DiploStrat]

As noted, I was happy with Fox w/reservoirs. Don't think that they are valved any differently, my only comment on the reservoir was to debate whether you really need the extra fluid capacity. But it never hurts and doesn't cost much more.

 

[bajajoaquin]

The best way to get a better ride from conventional leaf springs is to make them longer. That is generally a difficult thing to achieve. Parabolic springs are a good compromise. They are not a consistent thickness like standard leaf springs, and are thicker in the centre than at the ends. Usually just 2 or 3 leaves instead of larger numbers. All Terrain Warrior in Oz fit them to Canters and other Japanese light trucks. The 4WD Iveco has them as standard ex factory.
The down side is they do not have the inter leaf friction to provide damping that conventional leaves provide, so they need better dampers and may wear them out faster.
Parabolic Suspension Isuzu — All Terrain Warriors
Cheers,
Peter
OKA196 motorhome

Got it.

I found your old thread on the OKA forum with some details on your camper. You're about the same weight as I am, but you have considerably more tire. I think that allows for the lower pressures you run. Do you have any other threads or posts where I can see more of your camper?

I think I'll start investigating how much tire I can get in there for the next time I buy tires. I've got a lot in these and only 10k on the so far, so I've got another year or two before I can justify replacing them. But better shocks are something I can look at sooner, as I don't have much invested in them. Probaby springs when I do tires.

 

[gatorgrizz27]

Reservoirs on shocks are only there to deal with heat. You likely aren’t overheating your shocks at 5 mph. “Better” shocks are also likely to be stiffer, which handle larger hits better but usually not washboards at 5 mph.

Your issues are tires and springs. You likely need the stiff springs you have due to the weight, unless you go to a lighter weight rear pack and then add airbags to handle the weight on the road.

If you can find tire that will handle your weight at 35-40 psi you will be amazed at the difference. It’s going to be the cheapest, easiest option, if your current tires are nearly new, you can sell them. You might have to run wheel spacers in the back to air down with duals. It’s only 2,500 lbs per tire, assuming you’re near 5k front/10k rear. You’re going to need something with a real sidewall, not a highway tire.

A BFG KO2 would be a good choice IMO.

 

[rruff]

If you can find tire that will handle your weight at 35-40 psi you will be amazed at the difference.

^^^This. For low speed on washboard you can go a lot lower than the rated psi for high speed pavement. Check temps.

I have 265/75-16 tires which were the biggest I could fit without tires rubbing on the duals. I can’t air down much because I’m at 15k lbs. First time I aired down to 55 I ran on the sidewall and got a rock puncture in the sidewall. And I couldn’t go really any faster anyway.

I can’t lift or body trim my way to 20s and MPTs.

Durable tires with durable sidewalls are what you need, and air down. Tallest and fattest tires you can fit. Suspension has a hard time dealing with washboard no matter how much you spend.

What tires do you have? I've heard Cooper STMaxx are quite stout, but you pay an mpg penalty for tough sidewalls.

 

[LeftCoastKiteboarding]

We run about 12-13k loaded. I’m running the Nitto Ridge Grappler in an F rating. Great tire and I can air ‘down’ to 30 without issues. Handles Baja washboard at 25mph with ease.


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