Fish Tailing on Washboard Roads

[Dan Higgins]

Yes, I know that washboarded roads can be dicey. We have a lot of them here in Colorado. But I was somewhat concerned when climbing a narrow, winding, shelf, 12% grade, washboarded road the past weekend at about 10-15 mph and the back end of the LC was moving around quite a bit. Definitely more than I felt in the LR4 or my prior vehicles. Somewhat contributing may be the LT tires (BFG KO2 285/65R18 E load) set at 41 PSI (cold). Maybe I'm just not used to the stiffer suspension. Just wanted to make sure this was "normal".

 

[LandCruiserPhil]

Try it next time @ 14PSI

 

[kreiten]

Yes, I know that washboarded roads can be dicey. We have a lot of them here in Colorado. But I was somewhat concerned when climbing a narrow, winding, shelf, 12% grade, washboarded road the past weekend at about 10-15 mph and the back end of the LC was moving around quite a bit. Definitely more than I felt in the LR4 or my prior vehicles. Somewhat contributing may be the LT tires (BFG KO2 285/65R18 E load) set at 41 PSI (cold). Maybe I'm just not used to the stiffer suspension. Just wanted to make sure this was "normal".

There have been a ton of threads on this over the years, mine was really bad when I had stock suspension. It gave me a "floating" feeling while on washboard roads, and I felt I had very little control at times due to that. After replacing my suspension this problem has gone away almost entirely! Letting some air out of the tires will help also, but IMO the suspension is also a big part of what you're feeling.

 

[Dan Higgins]

OK. Thanks. At least I know I'm not imagining things. Airing down is an option if I am off road. But in this case this past weekend it was night and the steep, narrow washboarded section was only about a quarter mile. Knowing that this is something to be expected I'll be more careful with washboarded roads. Not sure I want to change the suspension at this point. And if/when I do I need to make sure I don't lose anything with respect to towing my 6K# travel trailer. Or anything that would effect my extended warranty.

 

[mcgaskins]

E rated tires inflated over 40psi will make just about anything behave that way on washboard.

 

[crikeymike]

That is strange, especially at that slow speed. Keep off the brakes and on the gas, and if it's safe, drive on the opposite side of the washboards, as going in the other direction they're normally not as bad.

Tire pressure was the first thing I thought.

 

[Romer]

Try it next time @ 14PSI

Thats too low. These vehicles are heavy. I was running at 18PSI and the tread was pouching out and I sliced a tire. Cdan and i dug into this and based on the weight of the vehicle I air down to 22 psi and havent had an issue

That is why we air down. Did you have it in 4LO with the center diff locked? The center diff doesn't lock automatically like on many vehicles

 

[LandCruiserPhil]

Thats too low. These vehicles are heavy. I was running at 18PSI and the tread was pouching out and I sliced a tire. Cdan and i dug into this and based on the weight of the vehicle I air down to 22 psi and havent had an issue

That is why we air down. Did you have it in 4LO with the center diff locked? The center diff doesn't lock automatically like on many vehicles

Heavy
UNLADEN WEIGHT 5798 lbs

My guess it wasnt the PSI it was the tire choice for your failure or driver error

Wash board is very popular in AZ and south of the border and 90% of the people I wheel with regularly run 14psi for years without any issues at much higher GVW

 

[Dan Higgins]

Just to be clear, I wasn't driving a true off road trail. Just a steep, narrow shelf road for about a half mile. But there are lots of other forest and mountain roads out here that are washboarded. 20 mph posted. So, no, I don't drive those roads in 4L. You can easily drive these roads in a Corolla.

 

[Romer]

Heavy
UNLADEN WEIGHT 5798 lbs

My guess it wasnt the PSI it was the tire choice for your failure or driver error

Wash board is very popular in AZ and south of the border and 90% of the people I wheel with regularly run 14psi for years without any issues at much higher GVW

Well phil then we agree to disagree

My tires are Toyo's with the stronger sidewalls. I am probably 1000 lbs heavier than that with all my options. Dan and I were running a trail going up a ledge and the tire pinched and sidewall cut. We stopped and looked the situation over to fully understand what happened

After that I changed it to 22 it still ran fine and gripped fine and less sidewall was pooched and exposed (vulnerable). This was primarily going through Moab trails with lots of rocks at the sidewall level. On other trails riding lower psi wouldnt be an issue. I would have no concern with 14psi on just washboard roads. Since I have the ride and grip I want I set my stauns at 22 and that is what I run .

 

[Markuson]

Well phil then we agree to disagree

My tires are Toyo's with the stronger sidewalls. I am probably 1000 lbs heavier than that with all my options. Dan and I were running a trail going up a ledge and the tire pinched and sidewall cut. We stopped and looked the situation over to fully understand what happened

After that I changed it to 22 it still ran fine and gripped fine and less sidewall was pooched and exposed (vulnerable). This was primarily going through Moab trails with lots of rocks at the sidewall level. On other trails riding lower psi wouldnt be an issue. I would have no concern with 14psi on just washboard roads. Since I have the ride and grip I want I set my stauns at 22 and that is what I run .

Wouldn't psi bead tolerances vary dramatically based on tire design, stiffness, sidewall, etc.?

 

[Romer]

Wouldn't psi bead tolerances vary dramatically based on tire design, stiffness, sidewall, etc.?

I don't know. It would seem to me as long as the pressure difference inside the tire is significantly greater than outside the tire the bead will hold until a force great enough to move the tire seperates the bead. Last year at Cruise Moab two trucks lost their bead and we got them both back on with just jacking te tire up. One was on Hells Gate the other was coming down a ledge that you wouldnt have thought twice about

 

[LandCruiserPhil]

@Romer the thread is about psi for washboard

@Markuson I agree the psi would react differently on a load range C than a load range E for the reason you posted

Hells gate @ ~14psi - seemed to work pretty good unlocked btw

 

[NLScooby]

I just went camping this past weekend with a group of fathers/sons and encountered miles of washboard in addition to smooth dirt roads and slow, more challenging trails. I'm on stock suspension but on Rock Warriors with Terra Grappler's. At 30-31 psi she handled quite well.

 

[Dan Higgins]

Are the Terra Grapplers LT (E rated) tires? If so, do you always run them at that pressure or did you lower them for the weekend?

BTW, sounds like a great time!

 

[gaijin]

Are the Terra Grapplers LT (E rated) tires? If so, do you always run them at that pressure or did you lower them for the weekend?

BTW, sounds like a great time!

Either way, the cited pressures are suspect.

If P285/70-17, then the correct pressure should be 27psi F/R

If LT285/70-17, then the correct pressure should be 40psi F/R

Just sayin'

HTH

 

[LandCruiserPhil]

Either way, the cited pressures are suspect.

If P285/70-17, then the correct pressure should be 27psi F/R

If LT285/70-17, then the correct pressure should be 40psi F/R

Just sayin'

HTH

How do you arrive at these numbers?

 

[gaijin]

How do you arrive at these numbers?

Are you really going to make me go through all the math again?

In summary, based on the Toyota recommended pressure for the OEM P-Rated 285/60-18 tires (2,512 pounds Load Limit @ 33psi F/R), and published info in the 2014 Yearbook of the Tire and Rim Association, the pressures I cited are the correct pressures for those tire sizes.

I hate to pull the "do a search" line on you, but please search in this forum for my many posts clearly explaining how these pressures are calculated.

HTH

 

[LandCruiserPhil]

Are you really going to make me go through all the math again?

In summary, based on the Toyota recommended pressure for the OEM P-Rated 285/60-18 tires (2,512 pounds Load Limit @ 33psi F/R), and published info in the 2014 Yearbook of the Tire and Rim Association, the pressures I cited are the correct pressures for those tire sizes.

I hate to pull the "do a search" line on you, but please search in this forum for my many posts clearly explaining how these pressures are calculated.

HTH

I did thing anyone would off road P rated tire

This system works as a street pressure no matter what tire you are running- But then again the thread was about pressure on washboard roads not street pressure.

I'm not the author -


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.

 

[gaijin]

I did thing anyone would off road P rated tire

This system works as a street pressure no matter what tire you are running- But then again the thread was about pressure on washboard roads not street pressure.

I'm not the author -


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.

You may want to review this thread for my thoughts on tire pressure for the LT285/70-17 E-Rated tires in particular: Tire Pressure for Rock Warriors with LT285/70/17, Load range Es?

And, yes, the poster of the 30-31psi numbers did not clarify whether that was an "aired-down" pressure just for the conditions, or whether it was the pressure they normally ran.

And, like it or not, Nitto does manufacture the Terra Grappler in BOTH P-Rated P285/70-17 and LT-Rated LT285/70-17 - again, the poster did not clarify which he was talking about.

And, I put about as much faith in the "10% method" you cited as I do in the infamous "chalk test." Instead of sound engineering science, those methods simply disregard too many variables, the most notable of which is ambient air temp. So, rather than simply "getting in the ballpark" with some half-baked test, why not determine the correct pressure?

HTH