Death Valley Off-Road Adventures

I'm no expert but I think it cuts both ways.

Aired down can provide better traction on certain surfaces. I certainly feel this when I run the same road aired up or aired down. Aired up I get brief moments of drift on soft surfaces that aired down seems to prevent. I could certainly be fooling myself in regards to this though but I do feel like I have much better control on dirt roads when aired down.

I think the problem comes when you end up in a more extreme situation and are about to lose it. Aired down the sidewall can buckle with a large side load. This causes a "tripping event" in the parlance of solo rollovers. The vast majority of rollovers are caused by a "tripping event" such as a wheel hitting a curb or a tire leaving pavement and suddenly digging into a soft shoulder. A sidewall buckling or popping a bead would seem to be much of the same thing.

The classic "Moose Test" everybody references is for an untripped rollover. It turns out it is a semi-irrelevant measure of the probability of rollover for a vehicle because most rollovers are tripped and the moments required to cause a tripped rollover are much lower than for an untripped rollover. And because it is so easy to rollover in a tripped event that's also the reason why most all rollovers are of the tripped variety.

This also appears to be related to the reason why VSC systems are so insanely good at preventing rollovers. What they really do well in general is keep the vehicle on the road away from the edges of the road where a tripping event could occur. They aren't so much preventing rollovers inherently as they are just keeping the vehicle going in the direction it should so that it doesn't hit something that "trips" it.

So putting that all together I think aired down makes it more likely you stay on the road going the direction you intended because you have better traction. That means less likely to be "tripped" by the berm on the side of the road or a really soft shoulder. The flip side is if you start generating a severe side load the aired down tire can buckle and now it is actually creating its own "tripping event".

Again - I'm no expert and this all comes from having spent a few evenings reading endless NHTSA reports and presentations on rollovers, rollover ratings, rollover probabilities and the debate years ago on mandating VSC systems in all new vehicles. So I could be all wet on this!

 

That's generally how I concluded everything works, but I've never taken the time to seek out authoritative answers, just random people's opinions on the internet. (Which for all any one knows, their idea of off roading is 10mph on a fire road in their State Park)

As for VSC while cruising dirt, I have a suspicion that it played a part in the people who have stories that start with "I was cruising along and before I knew it I was flying off the road"

 

Great post. They had a flat on the front passenger, and the tire was off the bead on the rear passenger side. The passenger side was most caved in, we weren't even sure how he got out.

 

I haven't figured out VSC on dirt to be honest. If I'm likely to be driving at any sort of speed I have ABS disabled and near as I can tell that is also disabling VSC at the same time (based on the Christmas tree of indicators and the fact that VSC never starts clicking when I have my ABS kill switch active). I have had VSC kick in a bit on dirt when I have ABS enabled. In fact that's sometimes my reminder that I need to push the ABS kill switch!

In slower/sandier sections I'll often re-enable ABS specifically so I can then enable TRAC OFF to get some more traction control which does seem to help keep from bogging down. Ideally I really wish I could have ABS disabled while still having the increased traction of the horribly named "TRAC OFF" mode. In the big TRD OR ABS disable thread I posted a few years ago a possible way to do that involving a relay controlled by the brake pedal switch so that ABS disable only goes active when you actually apply the brakes. I've never taken the time to actually try doing it though.

 

They say there were record crowds out there this weekend.

 

For those dogging VSC, you should know, It will potentially save your rig just the same on the interstate, as it will hauling ass on a graded dirt road. It prevents vehicle from getting out of control and sliding. The technology is awesome. I've done lots of research in my rig and reading up on the tech. Invented by BOSCH.

 

My understanding as well though not enough direct experience personally. One of the reasons I wish VSC could be made to coexist with ABS disable.

 

Pretty sure your "ABS kill switch" disables VSC as well.....

 

The normal ABS sucks donkey balls in the dirt..

 

But if you are intending on going into a slide, having a computer attempting to correct it because it thinks you are in an emergency maneuver it could start to brake the wrong tire potentially taking an "under your control" situation out of your control.

I've watched the videos of how it works and other versions from other manufacturers. I can see situations where it may help and situations where I really think it would be a wild card I wouldn't trust. Having driven in a group and had my truck's rear end slide out for absolutely no reason where no one else's did, the only difference being that I neglected to turn off VSC when we started moving again, I'm not much of a fan of it offroad.

 

Me personally would rather not have any electronic assistance in the dirt what so ever. Also happy that my taco was the last year before it all came standard.

 

It's hard to argue modern ABS, in most situations, is a bad thing. Stability control depends on ABS to work.

Where the road surface is loose or slippery, ABS doesn't work so well because of the slippery surface. On loose surfaces, a locked tire digs into the surface if ABS is off and this leads to a faster stop. By design, ABS prevents or lessens wheel skid leading to longer stopping distances on a loose or slippery surface-this could lead you to run off the road surface.

I wouldn't say that ABS brakes the wrong wheel when you're trying to slide but more that VSC is trying to prevent the slide from happening. Most of us have modified suspension and tires but how many of us have taken the time to reset the VSC after finishing the work?

More modern ABS systems are definitely better than older systems, especially with stability control but off-road conditions are always a challenge. Motorcycles have begun using "riding modes" to define how much and when these safety systems activate (or don't) to mitigate the negative effects.

 

Hey, has anyone run Steel Pass recently? How does it look?

 

Did it a few weeks ago and it was in great condition. I would imagine not much has changed since there has not been any recents rain.

 

I'm never in enough hurry offroad to care if the ABS or trac is on.

 

No. It doesn't work that way (explained below). Leave the feature turned on and try and drive aggressively Try it and you'll see. If you wanted to slide, you would have to turn it off. I used to slide my truck when it was close to stock.Was fun!

I would have been one of the morons who rolled their trucks in Death Valley if it wasn't for VSC; it's a life saver operating at speed, that's its sole purpose, to keep the vehicle from going sideways. It samples numerous metrics 30-times a second, such as:

• Steering wheel angle--to sense drivers intention,
• Yaw angle--the direction the vehicle is actually traveling,
• The rate at which all four wheels are turning,
• Force of brake pedal.

If it senses the vehicle is about to go into a slide, in a f'ing instant the system can brake 1,2,3, or all 4 wheels at varying force to self-correct and keep the truck going sideways. A human being is incapable of doing what the computer can do with the sensors and hydraulic brake booster.

So many people misunderstand this concept. Remember it this way: Speed = VSC Safety feature. I would leave VSC on when pushing the truck and going fast in wide open areas where there are turns.

The downside to going fast, as @DVexile hinted at, is you'll have to contend with ABS when stopping which can be a real f'ing problem as it greatly increases the distance necessary to stop on loose or soft surfaces like gravel, sand or snow.

I am with you. Slower is better, and safer seven days a week, 365 days a year. I will tell you this one short story though. I almost died going off a cliff in Anza-Borrego because ABS activated on a downhill section, I was in 4HI, and I could not stop the f'ing truck when fast approaching a ledge / drop off. I think I shit my pants. That experience caused me to research and author the ABS disable switch mod: ABS Kill Switch mod for 05+ Offroad EASY WAY! (PICS).

As a matter of practice. I generally kill ABS when airing down my tires. And don't drive fast anymore.



Now to put my post on topic. I wish so very much I could be in DV right now. Ugh...

 

Nick, thanks for your write-up on the VSC re-calibration. I had put on new shocks and lifted the front end up some (about a year ago) and I was on the 190 heading downhill in a turn towards Panamint and the truck went weird with vibration and noise and I thought it was the ABS going haywire. Not so sure it wasn't the VSC just doing it's thing instead. Anyway, went outside and just did your trick to re-calibrate the VSC and next time out that way will see how it handles those turns. Great info as I'm pretty sure no one where I had it done(shocks & tires) bothered at all about the VSC after having the alignment done twice!

 

To add to @Crom's excellent post remember there are three systems at play each with its own vagaries and trade-offs:

• ABS primarily interrupts braking on a wheel that is about to lock (i.e. lose traction on account of too much braking force). On certain surfaces this also happens to somewhat shorten the stopping distance because static friction is higher than dynamic friction but that's not actually the point of it. By preventing wheel lock ABS allows the wheel/tire to also still provide side forces so that the vehicle can still be steered. That's the real point to ABS, to still be able to steer during an emergency braking maneuver, and that is considered more important than stopping distance so in fact in many conditions ABS can actually result in a longer stopping distance but at least you can still steer which is usually a good trade off. On soft and loose surfaces like sand and certain kinds of snow the stopping distance penalty can be extremely severe though and the driver might prefer a dramatically shorter stopping distance even with the loss of steering. That's largely the point of disabling ABS when off road - being able to steer but take 500 ft to stop is not a good trade off compared to stopping in less than 50ft in a straight line. In theory a human can somewhat emulate ABS with appropriate braking technique though naturally a computer with individual wheel sensors and actuators is likely to do a better job.
  
• VSC primarily applies braking to the appropriate wheel to counter act understeer or oversteer. The idea being that if the steering input and vehicle yaw do not match the vehicle is either understeering or oversteering and the way to correct this is to "drag" a wheel by applying braking to an individual wheel. Sort of like turning a boat by dragging an anchor on one side. VSC can also interrupt the throttle to reduce power to the drive wheels to help correct a slide. It is impossible for a driver to emulate this as we don't have four brake pedals even if we could decide quickly enough which wheel to brake to correct the steering error.
• Traction Control primarily applies braking to a wheel that is spinning so that an open diff will transfer some power to the opposite non-spinning wheel. It also can interrupt the throttle to try to maintain traction though this is typical never desirable off-road and can be disabled (this is TRAC OFF mode which you get by a quick press of the VSC button resulting in traction control only via brake control without any throttle interruption - the default TRAC ON mode uses both brake and throttle control). Things like lockers or limited slip diffs can achieve similar results to traction control - especially TRAC OFF where throttle control is not applied.

All three systems require using the individual brake actuators and sensors. VSC also requires a yaw sensor and steering input sensor.

So we can see the "ideal" off road setup would be ABS disabled, VSC enabled (at least at higher speeds) and TRAC OFF (meaning despite the stupid name that Traction Control is actually on but only does so by applying brakes and not by interrupting the throttle).

As it stands if you have an ABS disable switch you can only choose between no ABS, VSC or TRAC of any kind or dealing with ABS but getting the benefits of VSC and traction control.

I tend to use ABS disable when going down a bog standard washboard road where I might need to stop in a hurry but naturally I need to be careful about speed and cornering as there is no VSC. I also am not a fan of ABS being enabled on downhill sections for the reason Crom described.

When going through sand I prefer to leave ABS enabled so that I can get the benefits of TRAC OFF which actually performs quite well in my experience.

And wrenching back to Crom's original topic - I was just in Death Valley last week and already miss it and want to go back!

 

After spending last weekend in the Sedona area I'm ready for some solitude. I think I'll plan a trip to DV for Feb 2-4th.