GatorGreg

Hey all, I was looking at the old Truck Trend's Ultimate 4x4 Challenge ( http://www.trucktrend.com/roadtests/...nge/index.html ) where the GX finished in 4th place out of 7 "hardcore 'wheelers". Not a bad overall finiish IMO given the competition it was up against - and the GX did get the top honors for on the road performance over the winning Range Rover.

If you look on page 5 I think it shows the results for the so-called "Sand Drag" and for the GX it says "DNF". Anyone know WHY it did not finish? The article fails to explain what happened exactly. My THEORY is that they failed to remember to lock the center diff, which therefore meant VSC would still have been active, and therefore the throttle was probably cut by the computer, thereby leaving them stranded in the sand. I'm assuming that had they simply locked the center diff, they could have used heavy throttle to overcome the ATRAC braking action and easily have finished the Sand Drag. Probably would have bumped the GX's overall score into 3rd place I'm guessing.

I noticed that in the following year's test ( http://www.trucktrend.com/roadtests/...nge/index.html ) they explained on page 7 that the Grand Cherokee got a DNF in the hill climb test cuz it's CV joints blew. So I don't understand why they didn't feel the need to explain the DNF for the GX in the prior year's test???

begone

The article said - "In other cases like the Lexus and Range Rover, there is no way to fully defeat the electronics that pull out engine speed or wheelslip when on sand. "

Ouch...

GatorGreg

Since you CAN fully defeat the electronics that pull out engine speed by locking the center diff, this makes me think they did NOT lock the center diff. Therefore VSC would have been active and would have been cutting the throttle making it impossible to get through the sand. With the center diff locked ATRAC would still be on but that does not cut the throttle, it only applies the brakes. With heavy throttle it will overcome the braking action of ATRAC and would have given them plenty of traction to get through the sand.

bgsntth

We had this discussion on here in prior year's past, so there was a healthy discussion.

I think the problem is that even with the GX in 4Lo, first or second gear, center diff locked, the traction control is still on. Hence, if all tires have no and each are spinning, the system will brake each tire and not send power to any of them; hence let you spin the tires to power out of a bad situation. I did an experiment on the same loose dirt, grassy hill-side with my GX and Outback XT.

GX: Starting at the base of the hill from a dead stop the GX would get about 3/4 of the way up, all the tires would lose traction, forward momentum ceases, all whole lot of knocking and clicking from the ABS/traction control can be heard, the engine is reving; but it will not spin the tires, and you have to back down the hill.

OBXT: Let out clutch in first gear, all 4 tires are spinning with power going to which ever one has more traction, power up the hill, which is now devoid of grass. Smell the burning clutch. But it made it up the hill.

I tried the same hill with our LR3. The difference between the LR3 and the GX is that the Terrain-Response Mud & Ruts program will let the tires spin freely when it recognizes you need to spin the tires to free yourself; which is a good thing, because the OE GY tires provide almost no traction off-road.

No flames please. I do not process do know everything about each vehicles systems, and am only relaying my experiences. For the record, I have sat for a good 15-30 seconds with the RPMs at plus 4K waiting for some computer to get with the program and spin the tires; but all I have noticed is a lot clicking/knocking.

That said, my GX with Revo's can get up the same hills as the LR3 with much less drama; but I'm much more confident in the LR3, as I know the "system" will not let me down. I have had situations where I was by myself, miles from anywhere, and the GX's traction control was adding a lot more drama to my adventure than I would have preferred.

GatorGreg

Thanks BG, it's always good to read real life feedback. I did do a search on this forum for old threads about this article but didn't have any luck - if you happen to find any please post a link I'd love to read them.

There are some good threads/discussions about A-TRAC and VSC on the 4Runner (same as GX AFAIK) at T4R.ORG here: http://www.toyota-4runner.org/showth...hp?threadid=12

I posted some quotes from some of the posters over there below. I've yet to take my GX off-road but I plan to take it on some light trails with lots of sugar sand within the next month or two. Based on the info I've seen, my plan for when I hit the sugar sand trail is to lock the center diff and thereby disable the throttle-cutting VSC system. Then I will apply a heavy lead foot on the gas when necessary to overcome the braking action of the A-TRAC system. Seems like the key is to not let all the noises of A-TRAC dissuade me from applying heavy throttle. I'll report my findings after I get it in some sand

By Bulldogyota:
"I haven't driven my Runner on ice yet, but in snow, mud and soft sand. My experience have been that even when driving in a straight line, VSC dethrottles when you loose traction and it does so pretty quickly. It also modulates the brakes. This has been a source of frustration for me and lots of other people trying to get up a hill as it seems the 4Runner almost dies on you as it basically stops building momentum. This was until I figured out ATRAC still works but VSC turns of when you lock the center diff. Makes a big difference!"

By Thai:
"When off-roading in rough terrain or mud, you need to LOCK the center diff because it turns OFF VSC. Because, if you are stuck in mud, VSC may interpret your attempts to get out as oversteer/understeer (especially if you are sliding back and forth). Therefore, it WILL cut power (dethrottle). With VSC off, ATRAC can function with full engine power to get you out. Thus, you can spin all four wheels! I have seen this on my brother's Lexus LX470 and Discovery. THAT IS WHY YOU LOCK THE CENTER DIFF, among other reasons!"

"Don't forget, when you're stuck in mud/snow, VSC will activate because you're sliding around, which will be interpreted by the computer as oversteer/understeer. Also, the effects of ATRAC can be interpreted by some as cutting engine power (even though it doesn't when center diff is locked). If you're gentle on the gas pedal, it will feel like you're not getting power to the ground. That's why you need to really press on the gas pedal to overcome ATRAC when going up a sandy hill (or getting out of a mud hole). Like posted above, when the rpms go past about 3000 rpms, ATRAC intervention decreases."

bgsntth

Yep the trick is to keep forward momentum and look for areas where at least one wheel will have traction. I do not like this, as when crossing a rocky, muddy stream with steep decomposed granite banks on our property, I go through much quicker than I would normally feel comfortable because I'm so paranoid about getting stuck.

The LR3 is almost comical, as it controls wheelspin and finesses its way through things like the stream, much as the GX; but when it does get stuck, there is about 2-3 seconds of nothingness and then all hell breaks loose and the tires just start spinning an clawing its way out.

tigmd99

bgsntth, looks like you need a vehicle with locker(s).

tyoung88

I recently got my GX and am new to some of the terms that Toyota uses for Traction Control. Are ATRAC and VDC both forms of tractioncontrol based on either application of brakes or cutting of throttle?

Is the general consensus that if I lock the center differential and go to 4Lo that the GX can get out of sand and mud in the event that all 4 wheels have no initial traction by applying throttle until one of the wheels catches or do the various computer systems ultimately keep the GX from gaining traction?

Based on bgsntth's feedback it seems that there are some situations where the GX computer systems will keep the vehicle from gaining traction. Some of the quotes gathered by GatorGreg may contradict this as it seems that locking the differential should turn off some of these prohibiting systems.

GatorGreg

Tyoung, in a nutshell the VSC computer (Vehicle Skid Control) will apply the brakes AND cut the throttle, designed to keep you from skidding out of control off a road and down a cliff. Problem is VSC kicks in even when you don't want it, cutting your throttle when you are in sand for example. Locking the center diff disables the VSC computer, therefore your throttle will no longer be cut by the computer.

In contrast, ATRAC is always on even if the center diff is locked and while it does apply brakes it does NOT cut throttle. It's a pseudo limited slip system. But when you're in sand (based on what I've read) the braking action can be overcome by using HEAVY throttle, this will provide the beneifits of a llimited slip front and rear axle and should allow you to spin all 4 wheels to get through the sand. If you don't apply heavy throttle the action of ATRAC applying the brakes might be perceived as the computer cutting the throttle even though it's not.

This assumes of course that your tires can get some traction in sand. Even if you had a Mercedes G Wagon like tigmd has with locking front, center, and rear diffs, you might get stuck in sand with crappy tires.

tyoung88

Thanks for the clarification GatorGreg. I have yet to take my GX offroad but am excited to do so soon. For the average trail I'm thinking it will do fine. I'll just avoid any hills with course sand/pebbles.

tigmd99

Be careful with your running boards which hang quite low.

tigmd99

That is true...from personal experience....

bgsntth

Yes, a locker would be good. I'm using 4Lo about 15-20 times a year, and have thought seriously about getting something like a Unlimited Rubicon; but then I would have to drive it on the street for the other 345 days. Plus, I am always taking surveyors, lawyers and such around the property, so the GX is nearly ideal for pampered off-roading.

Pertaining to ATRAC. As I've said, I have tried applying judicious amounts of throttle when all 4 tires cannot find traction, and all that happens is the engine revs, the ATRAC knocks around lot, but no tires spin, and the GX refuses to try and extricate itself. You are forced to put it in reverse. I've tried this using a small 8 foot grassy hill, to understand the system better. So how much throttle/RPMs do you have to apply to get the ATRAC to back-off?

tigmd99

You can overcome ATRAC above 3K rpms...that was how it was with my 2002 4runner with ATRAC.

Cabinetman

You DON'T want to daily drive a Wrangler. I have a 2005 Unlimited Rubicon that is a trail rig and I hate driving it more than a few hundred miles on the street. The ride is not terrible with my long arm suspension, but the tire and wind noise is enough to drive you nuts after a few hours. I would only own a Wrangler as my primary vehicle if I spent 80% of my time off-road.

With all that said it is hard to beat 35" tires and front and rear lockers when on the trail. Another plus is you can armor the hell out of a Wrangler so you are willing to try a lot more things than you would in a GX for fear of body damage.