Handling Rough and Washboarded Roads at Speed

[carbon60]

My usual trips consist of 300-400 km of pavement, 200 km of quality dirt road, 100-200 km of terrible, washboarded, pot-holed dirt road and then a final 20-30 km of track with maybe a last KM of real off-road.

I've a 1996 Land Cruiser with a 2" OME lift already in place.

For the 100-200 km of badly washboarded roads, what can I do to improve control, comfort and my ability to maintain high speed (75 kph)? Ideas, so far, are to replace the shocks with new units (OME Nitrochargers), air down to 20 psi, etc.

Thoughts? Suggestions? Comments?

Thanks,

A.

 

[coax]

Not sure which OME shocks and springs you have, and how much weight you typically carry, but from my experience with the 850/863 combo and n73/74 shocks, when loaded w/ 2 people and lots of stuff (2 bikes, snow chains, arb/winch, food, gas, water, camping gear, etc) it still was VERY stiff and handled like junk on washboard. I ended up replacing the shocks with fox 2.0's and it handles much better.

 

[mattafact]

X2 on better shocks. 18-20PSI should be good as well as long as you're not too heavy. Bigger tires always help too.

 

[alia176]

Not sure which OME shocks and springs you have, and how much weight you typically carry, but from my experience with the 850/863 combo and n73/74 shocks, when loaded w/ 2 people and lots of stuff (2 bikes, snow chains, arb/winch, food, gas, water, camping gear, etc) it still was VERY stiff and handled like junk on washboard. I ended up replacing the shocks with fox 2.0's and it handles much better.

Can we get more info on your Fox shocks? Valving, length, remote res, etc.....

 

[LexusAllTerrain]

I have been using 18psi on my tires, and I have the OME shocks two people with plenty of items and 10 gallons of gas plus 5 gallons of water, 40 mph on the worst washboard roads in Baja no problems!

 

[Klierslc]

I had very good luck on washboarded roads with the OEM replacement Bilsteins and OME mediums--may not work as well with the heavy setup though.

 

[carbon60]

I have been using 18psi on my tires, and I have the OME shocks two people with plenty of items and 10 gallons of gas plus 5 gallons of water, 40 mph on the worst washboard roads in Baja no problems!

I'm wondering if I should try that before spending $500 on new shocks…

Thanks for the feedback, everyone!

A.

 

[spressomon]

^ What size tires do you have and is it a near or stock weight 80? The safe low pressure you can run is dependent upon your size tire and gross vehicle weight.

FWIW: Letting air out of the tires is important for smoothing washboard. Secondarily once I upgraded to mono-tube shocks with remote reservoirs (2.5" Radflo with huge remotes on the rear, can only fit 2.0" up front otherwise I'd have 2.5" there too...about 7,500-8,000lb GVW in full touring mode) I eliminated the fade from my then OME shocks. You'd be shocked how hot those shocks get while blasting across rough/washboard roads! Next time you're out on those types of roads for more than a few miles just stop and feel your shocks...they'll be darn hot! Although you don't want to oversize a shock for a given application generally more fluid capacity = mobetta damping and less fade.

 

[LandCruiserPhil]

Low tire pressure and high speed is not a good combination

 

[carbon60]

Low tire pressure and high speed is not a good combination

Can you define that more specifically?

 

[spressomon]

LandCruiserPhil makes a good point. Lower pressure = lower weight carrying capability (all things being equal). Lower tire pressures will generally run hotter. The tire size and your GVW come in to play with regard to how low and how fast you can safely roll...

Good info about it here: http://auto.howstuffworks.com/tire4.htm

 

[LandCruiserPhil]

Low tire pressure at speed creates heat

Excessive heat and causes the sidewalls to overflex. This diminishes the tires' integrity, making them vulnerable to premature failure.
Excessive heat leads to separation or cord failure
Excessive friction between wheel and tire beads can lead to bead failure


Below is a great article (not by me)about how to determine correct tire pressure this can also be applied to lower pressure at consistent speed. Using the system below you will find not all tire with the same specs are equal. I have used the below system and have been surprised on some vehicle how low you can safely go for highway speeds with E rated tires and get a much more comfortable ride.

I worked for Michelin Tire Corporation for 7 years and Yokohama Tire Corporation for 11 years. I have given numerous tire seminars on tire maintenance and especially how to determine the correct tire pressures. So here goes.
The pressure on the sidewall of the tire is the maximum pressure at the published load at approximately 55 mph. (The speed can vary somewhat but it is not important for our discussion).
The air pressure is required to support the load that the tire must carry in such a manner that the tire flexes at the designed place on the sidewall of the tire.
If the load on the tire changes then the air pressure should change accordingly to keep the tire flexing at the proper place.
The reason for correct air pressure is to prevent the tire from overheating. It was put together with heat and it will come apart the same way. An under inflated tire will eventually self destruct due to excessive heat build up. An over inflated tire will ride harshly and be more likely to burst upon impact. Sorry for the long explanation but here is the bottom line.
To determine the correct air pressure, check the pressure when the tire is cold. Run the tire for several miles at highway speed. Stop and immediately check the air pressue in the tire. It should be higher than we cold but no more than 10% higher.
Now here is the hard to believe part. If the pressure is more than 10% higher you must ADD AIR and test again. For example if you start with 50 psi cold. If the pressure is 60 when hot, you have exceeded the (10%) in this case, 55 psi maximum safe heat build up pressure. You must ADD AIR. In this case I would add 5 psi which would take the tire to 65 psi when hot. After you run the tire again you will find the pressure to actually drop because the tire will run cooler. The heat build up causes the tire pressure to increase when under inflated.
On the other hand, if the 50 psi cold pressure does not change when hot. You have more air than needed. You can remove 5 psi or so and test again when they return to cold. Like the next trip you take.
So a fully loaded rig will require more air in the tires than one with empty tanks and a light load on board. Always error on the side of over inflation. Thus the maximum sidewall pressure indicated on the tire is usually used. It usually is more than needed. Each axle has its own requirement based upon the load on that axle.



HTH

 

[carbon60]

Really interesting summary, thank you!

But we all run with less pressure, off-road, right? So, my question is how much less pressure can I run for, say, 100 km @ 75 kph? Not sure than article really answers my question.

 

[LandCruiserPhil]

Really interesting summary, thank you!

But we all run with less pressure, off-road, right? So, my question is how much less pressure can I run for, say, 100 km @ 75 kph? Not sure than article really answers my question.

Air down run at 75kph for several miles and re check your pressure. Full disclosure - I do not check but I rarely exceed 35MPH for any given amount of time off road...but sometime I'm bad:sombrero:

As for airing down I air down ANYTIME I hit dirt including my moto, MTB and trailer. I recently did an air down clinic for our club and figure I have air down over 500 times. A good air system will make it much easier.

 

[carbon60]

Air down run at 75kph for several miles and re check your pressure.

That makes a lot of sense, I'll try that.

Thanks!

A.