VSC, ABS, & Handling in General with P/T 4WD

[WCVanHorne]

Since I've acquired my 2012 SR5 I've been trying to research and acquire as much information as I can about how the vehicle and its advanced Vehicle Stability Control & ABS react while on road in P/T transfer case 4WD mode.

First I know I might have been better off with full time 4WD but the Limited was out of my budget and the 4Runner fit all of my other requirements where a Subaru, Nissan, Volvo, Explorer, other CUV/SUV didn't. That's why I'm here. Also I am pretty convinced at highway speed it is probably safest to leave it off due to even moderate understeer in curves (i.e. no "pull though", probably the opposite, with the potential for oversteer if the rear loses it). I'd love to test this but I'm not going to risk my life and vehicle is high speed experiments. If anyone has a link to some testing here it would be interesting as I've not run across it yet.

This sort of leads me to my main point, my own personal low/mid speed experiments. Due to some early snow and low temperatures we have some really nice low traction test conditions here now. Also for reasons I won't get into my Hakka SUV 7's are not going to get mounted till the weekend (OK shanked lugnuts for the winter rims if you must know ) so I have the relatively low traction OEM all-seasons on. Thus I've taken some time to spin around and get used to the RWD and P/T 4WD handling.

First observation is that in RWD the VSC seems to do a pretty decent job of applying the rear brakes to pull you straight once the back starts to swing out in a corner.

Second observation is that, obviously, in 4WD a rear lockup will cause a front lockup. However the ABS seems to take care of this, at least in a straight line stop; when cornering not so sure. More testing required.

Third observation is that, inspite of the understeer potential, one feels pretty good doing a tight circle in 4WD; better than in RWD with VSC. I suspect it's because the wheel slip is averaging out with the front actually keeping better grip some/much of the time and the rear spinning a bit faster and slipping. In other words I wonder if the oversteer is averaging out the understeer.

Fourth observation is not really an observation since I didn't manage to induce or test it to my satisfaction: I wonder if the VSC will apply the rear brakes in 4WD mode when it detects the back end getting loose. This is probably counter productive since this braking will translate to the front wheels where it is not helpful in straightening out the vehicle. More testing required here in a really large and empty parking lot.

Thoughts?

 

[BobsTrail]

Vsc

I think the VSC only works in 2WD and not in 4WD. I tried to find it in the book, but it was not clear.

I had mine in dirt and 4WD Sunday, but did not notice if the VSC indicator was showing. I'm curious, so I'll check next time and watch for other replies.

 

[WCVanHorne]

I think the VSC only works in 2WD and not in 4WD. I tried to find it in the book, but it was not clear.

I had mine in dirt and 4WD Sunday, but did not notice if the VSC indicator was showing. I'm curious, so I'll check next time and watch for other replies.

I'm 90% sure the VSC OFF light does not come on. But now you have me questioning my recollection so I will have to double check next time I have the unit out. It is certainly possible that the computer might disable certain aspects when the transfer case is engaged and front an back are coupled (ie. perhaps it would never apply both right and left brakes) but I'm pretty sure the VSC OFF light stays out....

Nuts to that, I'm driving around the block in 4WD right now. :driving:

 

[westwind77]

I wonder if the VSC will apply the rear brakes in 4WD mode when it detects the back end getting loose.

I believe VSC does not care what mode you are in (as long as it is active). It is a computer and it uses many different sensors to gain input about the 4R, from there it will decided what do to, when, and how. Every spin situation is going to be different so every result will differ (from the computers point).

I think the VSC only works in 2WD and not in 4WD.

VSC works in 2H and 4H, but deactivates in 4L (if i remember right the manual was very clear on that part)

 

[WCVanHorne]

OK here's the refresher:

_______Default_____________________Trac/VSC Button Pressed

2WD___VSC OFF indicator out_________VSC OFF indicator out
______TRAC CTRL OFF indicator out____TRAC CTRL OFF indicator *LIT*

4WD-H_VSC OFF indicator out_________VSC OFF indicator out
______TRAC CTRL OFF indicator out____TRAC CTRL OFF indicator *LIT*

4WD-L_VSC OFF indicator *LIT*_______VSC OFF indicator *LIT*
______TRAC CTRL OFF indicator *LIT*__TRAC CTRL OFF indicator *LIT*

Thus in 4WD-H there is basically no difference. I can also attest that at least the traction control seems to engage in 4WD-H when you break loose on a straight line acceleration; which is actually pretty tough even in slick conditions and all-seasons. Also as noted the effect of VSC in 4WD-H is harder to gauge since it is pretty difficult to break it loose in a turn with 4WD (at least without finding a really large, deserted, and uncleared parking lot). I'm going to have to wait till we get one of those 25 below, wind polished ice road situations later this winter (or get on a lake ) to test this properly I think.

 

[WCVanHorne]

So just to add some more discussion points, this is a site frequently referenced (here and elsewhere):

http://www.4x4abc.com/4WD101/def_turnpart.html

Now while it is a great overview I find a few items questionable, overstated, and perhaps even conjecture.

For example:

Here is another important fact: Since front and rear axles are not able to rotate independently ABS will not work properly.

Well the ABS is certainly active in P/T 4WD-H on the 4runner and IMHO it is working properly. Actually I think it is even more neccessary with P/T 4WD-H since if you lock up both rears it means your front will lock up. Actually I suspect the coupling of the front to rear means in P/T 4WD-H it is harder to lock up the back since they are forced to turn by the front (or in rare instances vice-versa). Basically how can ABS be less effective since it releases one or more of the brakes and lets more wheels turn?

I also haven't really noticed massive understeer and he seems to assume it is always the front which will be forced to slow down and slip rather than the rear which will speed up and slip (oversteer). Contrary to finding that the "handling of the vehicle is unsafe" I've so far felt somewhat more surefooted with the P/T 4WD-H engaged; even in corners.

Finally with a tire always flexing and the tread crawling even on dry pavement I don't know if wind up, when basically going straight, is as drastic as implied. If it were that serious I'm sure there would be exploding transfer cases everywhere from all the kids who seem to own pickups with P/T 4WD.

 

[1engineer]

So just to add some more discussion points, this is a site frequently referenced (here and elsewhere):

http://www.4x4abc.com/4WD101/def_turnpart.html

Now while it is a great overview I find a few items questionable, overstated, and perhaps even conjecture.

For example:



Well the ABS is certainly active in P/T 4WD-H on the 4runner and IMHO it is working properly. Actually I think it is even more neccessary with P/T 4WD-H since if you lock up both rears it means your front will lock up. Actually I suspect the coupling of the front to rear means in P/T 4WD-H it is harder to lock up the back since they are forced to turn by the front (or in rare instances vice-versa). Basically how can ABS be less effective since it releases one or more of the brakes and lets more wheels turn?

I also haven't really noticed massive understeer and he seems to assume it is always the front which will be forced to slow down and slip rather than the rear which will speed up and slip (oversteer). Contrary to finding that the "handling of the vehicle is unsafe" I've so far felt much more surefooted with the P/T 4WD-H engaged; even in corners.

Finally with a tire always flexing and the tread crawling even on dry pavement I don't know if wind up, when basically going straight, is as drastic as implied. If it were that serious I'm sure there would be exploding transfer cases everywhere from all the kids who seem to own pickups with P/T 4WD.

You have made a lot of correct observations. Do you have a specific question(s)? I think I did a winter driving write up for this system I will try to find it.

 

[WCVanHorne]

I don't know if I've run across your writeup. A reminder link would be great if you have a moment, but I can always search.

As to specific questions I don't know how concise I can be. Basically my thoughts, study, and experiment revolves around when to go into P/T 4WD-H for my on road situations:

Snow/Icy Around Town Paved (0-70 km/h) => I think ON
Snow/Icy Freeway/Highway Paved (80-120 km/h) => I think OFF
Snow/Icy Uphill to Ski Hill Paved (0-100 km/h) => I think ON
Snow/Icy Downhill from Ski Hill Paved (0-80 km/h) => I think OFF
Snow/Icy Level or Uphill Gravel/Logging Road (0-100 km/h) => I think ON
Snow/Icy Downhill Gravel/Logging Road (0-100 km/h) => I think OFF

And in the non-winter theme:

Level or Uphill Gravel/Logging Road (0-100 km/h) => I think ON
Downhill Gravel/Logging Road (0-100 km/h) => I think OFF

After writing all those permutations I think it largely boils down to Low Traction Level or Uphill turn it on, Downhill or Highway/Freeway turn it off. Not really different from the prevailing advice.

 

[1engineer]

Here ya go:
http://www.toyota-4runner.org/5th-gen-t4rs/101977-winter-driving-electronic-aids.html
http://www.toyota-4runner.org/5th-gen-t4rs/109496-toyota-4runner-te-vs-fjc-ttse.html

Just remember with the 4Runner you need to know what is going on, meaning "do I have it in 4wd" or "Is the VSA on" and things like that. For example, I was driving around in 20" of wet snow picking up my wife yesterday from work. As I live in the mountains I go up and down hills constantly. I was in 4WD Hi and stopped going up a hill because a vehicle was stuck in front of me. I went to pull forward and started to spin and then felt the engine cut off and brakes chatter as the electronic aids were trying to reduce wheelspin and give me traction. Well, this is fine if you are moving but when you are trying to get started sometimes you have to spin a little to get moving. I just reached up and pressed the button and I could spin all I want. I got started and after a short time turned the nannies back on again. So, there is places they are good and places they are not. Have fun up there!

 

[scanny]

I don't know if I've run across your writeup. A reminder link would be great if you have a moment, but I can always search.

As to specific questions I don't know how concise I can be. Basically my thoughts, study, and experiment revolves around when to go into P/T 4WD-H for my on road situations:

Snow/Icy Around Town Paved (0-70 km/h) => I think ON
Snow/Icy Freeway/Highway Paved (80-120 km/h) => I think OFF
Snow/Icy Uphill to Ski Hill Paved (0-100 km/h) => I think ON
Snow/Icy Downhill from Ski Hill Paved (0-80 km/h) => I think OFF
Snow/Icy Level or Uphill Gravel/Logging Road (0-100 km/h) => I think ON
Snow/Icy Downhill Gravel/Logging Road (0-100 km/h) => I think OFF

And in the non-winter theme:

Level or Uphill Gravel/Logging Road (0-100 km/h) => I think ON
Downhill Gravel/Logging Road (0-100 km/h) => I think OFF

After writing all those permutations I think it largely boils down to Low Traction Level or Uphill turn it on, Downhill or Highway/Freeway turn it off. Not really different from the prevailing advice.

I normally put truck in 4hi when I feel that I might need additional traction and steering stability. In other words in winter when I see patches of snow/slush on a higway or I'm off the pavement I engage 4hi and keep it on until I hit dry pavement. If VSC is beeping when you're in 4hi - your speed is way too high. VSC is basically tries to make sure that you're going in the direction your steering wheel supposed to take you. It's better to be on when you are driving in slippery contitions, I would turn it off only when I'm certain I need all the wheel spin I can get. That's why you need to keep "TRAC/VSC OFF" button for 3 sec to rurn it off. TRAC is just to reduce wheel spin, sort of softer version of LSD or A-TRAC - it's easy to turn off and it turns on back again when you reach 50 km/h.
City driving in winter is different - you get more sharp turns and dry pavement , speed are low so 4hi for me is mostly when road is covered by show or there is a lot of slush. And I'm more likely to turn on 4hi in a city when I didn't have a chance to make my mandatory 16 km in 4x4 this month : )

 

[Intruder]

I'm going to have to wait till we get one of those 25 below, wind polished ice road situations later this winter (or get on a lake ) to test this properly I think.

Last winter I did a driving course on Ghost Reservoir and it was definitely worthwhile. Tires at street pressure and VSC/TRC off. We did things like straight line braking where you let ABS do everything and also threshold braking, brake and avoid, inducing under/over steer and recovering, and of course some drifting. It was tons of fun and really helped you learn how your truck handles and reacts under adverse conditions without fear of hitting anything.

 

[WCVanHorne]

Last winter I did a driving course on Ghost Reservoir and it was definitely worthwhile. Tires at street pressure and VSC/TRC off. We did things like straight line braking where you let ABS do everything and also threshold braking, brake and avoid, inducing under/over steer and recovering, and of course some drifting. It was tons of fun and really helped you learn how your truck handles and reacts under adverse conditions without fear of hitting anything.

When did they do that and how much $$? I'm down pretty often with a sister in Springbank and a condo in Canmore so sounds like fun & good experience. Although they probably do something up here on one of the lakes too.

 

[WCVanHorne]

I normally put truck in 4hi when I feel that I might need additional traction and steering stability.

The latter, steering stability, is what I've been trying to understand and experiment with. The site I previously referenced:

http://www.4x4abc.com/4WD101/def_turnpart.html

Basically has dire warnings that the use of P/T-4WD will hurl you off into space, with your transfer case & drive train disintegrating around you, if used anytime other than on a gravel or sand straight away.

Now I completely understand the geometry, physics, and mechanics of the situation but so far I've *NOT* experienced this kind of handling degradation at lower speeds. Quite the contrary.

My take is that he only focuses on the understeer assuming that the fronts will always slip (and both). I believe that usually you get a combination of the fronts and rears slipping a bit and the understeer and oversteer average out to decent handling. The other subtlety in the dynamics, which I think he glosses over, is which wheels will tend to slip. I think, on average, it would tend to be the inner ones, both front and rear, due to weight transfer in the turn. Factor in acceleration and deceleration weight transfers and you probably only end up with one wheel (least traction one) taking up most of the slip. This seems to have minimal effect on handling in mixed driving as something is always slipping a bit and if the least traction one is spinning, so what. The question is if this scales to highway speeds and handling.

City driving in winter is different - you get more sharp turns and dry pavement

:lmao:

Not here!

Busroutes, arterials, and freeways are sometimes dry (if frozen solid with frequently low ambient temperatures such that even winter rubber starts to lose some of its gripping ability) but between November and March there is usually permanent residential/industrial/commercial district snow pack. If skidoos were legal on the roads you could probably cross large sections of town with only a few bare crossings.

 

[Intruder]

When did they do that and how much $$? I'm down pretty often with a sister in Springbank and a condo in Canmore so sounds like fun & good experience. Although they probably do something up here on one of the lakes too.

It's through CT4WD. There's one day in classroom then a couple weeks later on the ice. Last year it was late Feb and early March, but it's also dependent on the thickness of the ice.

 

[Zeder]

The latter, steering stability, is what I've been trying to understand and experiment with. The site I previously referenced:

http://www.4x4abc.com/4WD101/def_turnpart.html

Basically has dire warnings that the use of P/T-4WD will hurl you off into space, with your transfer case & drive train disintegrating around you, if used anytime other than on a gravel or sand straight away.

Now I completely understand the geometry, physics, and mechanics of the situation but so far I've *NOT* experienced this kind of handling degradation at lower speeds. Quite the contrary.

My take is that he only focuses on the understeer assuming that the fronts will always slip (and both). I believe that usually you get a combination of the fronts and rears slipping a bit and the understeer and oversteer average out to decent handling. The other subtlety in the dynamics, which I think he glosses over, is which wheels will tend to slip. I think, on average, it would tend to be the inner ones, both front and rear, due to weight transfer in the turn. Factor in acceleration and deceleration weight transfers and you probably only end up with one wheel (least traction one) taking up most of the slip. This seems to have minimal effect on handling in mixed driving as something is always slipping a bit and if the least traction one is spinning, so what. The question is if this scales to highway speeds and handling.

:lmao:

Not here!

Busroutes, arterials, and freeways are sometimes dry (if frozen solid with frequently low ambient temperatures such that even winter rubber starts to lose some of its gripping ability) but between November and March there is usually permanent residential/industrial/commercial district snow pack. If skidoos were legal on the roads you could probably cross large sections of town with only a few bare crossings.

Don't forget 3 hours of freezing rain followed by a predicted 10-15cm of snow, like this moring!
Remember the "Oh What a feeling" Toyota commercials from a way back? That was me this morning driving to work! Weeeeeeeeeeeeeeeeee, TC locked in 4H and the DuraTracs sticking to the ground. It was fantastic VSC works great in 4H by the way. I really had fun on my committee! Cant wait to drive home after it snows all day!

 

[scanny]

Now I completely understand the geometry, physics, and mechanics of the situation but so far I've *NOT* experienced this kind of handling degradation at lower speeds. Quite the contrary.

My take is that he only focuses on the understeer assuming that the fronts will always slip (and both). I believe that usually you get a combination of the fronts and rears slipping a bit and the understeer and oversteer average out to decent handling. The other subtlety in the dynamics, which I think he glosses over, is which wheels will tend to slip. I think, on average, it would tend to be the inner ones, both front and rear, due to weight transfer in the turn. Factor in acceleration and deceleration weight transfers and you probably only end up with one wheel (least traction one) taking up most of the slip. This seems to have minimal effect on handling in mixed driving as something is always slipping a bit and if the least traction one is spinning, so what. The question is if this scales to highway speeds and handling.

I tried to drive fast (when it was safe to do so) on snow, gravel and heavy rain in 2WD and 4HI and my truck seems to be more stable in 4HI. On dirt roads and trails I didn't drive fast enough to feel the difference in stability : )
When you turn on slippery surface in 2WD you have to do it slowly and VSC/TRAC might still engage with stock tires, in 4HI you drive like it's solid pavement. Highways don't have sharp turns, so I think it's not a big deal if you happen to go into turn in 4hi when pavement gets dry all of a sudden. I usually turn on 4hi when traffic slows down to 80 km/h because of snow/rain and turn it back off when travel a few kilometers on grey dry asphalt. Changing lanes especially over a small heap of snow between them seems to be better in 4hi.

 

[WCVanHorne]

Don't forget 3 hours of freezing rain followed by a predicted 10-15cm of snow, like this moring!
Remember the "Oh What a feeling" Toyota commercials from a way back? That was me this morning driving to work! Weeeeeeeeeeeeeeeeee, TC locked in 4H and the DuraTracs sticking to the ground. It was fantastic VSC works great in 4H by the way. I really had fun on my committee! Cant wait to drive home after it snows all day!

Yeah another great day of winter testing up here eh? :lookout:

Nothing like ice covered in snow! Although I have to say the 30 below polished ice is worse.

Anyhow I didn't take it out of 4WD-HI until I parked it in the garage today. I did try and see if I could induce some rear end fishtailing but it's actually pretty hard without a lot of space. I.E. you have to be going pretty fast around a turn in 4HI to induce it and that's pretty scary without tons of room for the potential spinout. Anyhow I think the VSC still pulses the rear(s) in 4WD-HI. I'm not actually sure if this is "a good thing" since if it is both sides this will definitely transfer to some braking force on the front, as opposed to a center diff which would transfer torque to the front. The former will make things worse in an incipient spin while the latter would help.

After thinking, and driving under some decent test conditions, that scenario is probably my main fear: How naive is the VSC when you are in 4WD-HI? Will it inadvertently slow the front (due to transfer case coupling) while trying to slow the rear, thus worsening an incipient spin situation?

 

[WCVanHorne]

It's through CT4WD. There's one day in classroom then a couple weeks later on the ice. Last year it was late Feb and early March, but it's also dependent on the thickness of the ice.

Found it:

Winter Driving Course - CT4WD.com

With the CT4WDA membership it's $300. Hmm not cheap but it looks like that's for two. I'd definitely pay it if I could get VSC algorithm questions answered by a Toyota engineer (submitted in advance of course). :

 

[Intruder]

After thinking, and driving under some decent test conditions, that scenario is probably my main fear: How naive is the VSC when you are in 4WD-HI? Will it inadvertently slow the front (due to transfer case coupling) while trying to slow the rear, thus worsening an incipient spin situation?

On the weekend we were driving on an icy gravel road on the way to a trailhead and having a little fun. I was in 4Hi and forgot to turn off VSC and it really wouldn't let me break into a skid of any kind. Unless you're trying to do some drifting I'd say as long as you drive to the conditions and having the nannies only kick in for the odd surprise instead of pushing as hard as you can and relying on the nannies to bail you out, you'll be fine.

Found it:

Winter Driving Course - CT4WD.com

With the CT4WDA membership it's $300. Hmm not cheap but it looks like that's for two. I'd definitely pay it if I could get VSC algorithm questions answered by a Toyota engineer (submitted in advance of course). :

We don't have access to any Toyota engineers (maybe a tech) but we've got people with tons of experience driving Toyota 4WDs in all types of conditions and situations. Pretty sure you could get your questions answered.

 

[WCVanHorne]

So those of you up here in Edmonton know it's been a real urban winter driving clinic the last couple weeks. Freezing rain, 10-15cm snow, thaw, ice, 25-35cm wet snow, freeze, more snow, 20 below, thaw, etc. Right now it's that great oatmeal, with ice and ice ruts under on quite a few arterial routes. Anyhow it has certainly been a great time to test the 4WD and my studded Hakka 7 SUVs.

So far I'm pretty impressed. Some times I have to give it a bit of gas in a tight reverse to get at least one wheel to break loose. That or drop it to 2WD but then it's hard to turn too. Have found the VSC helps more than hinders in 4WD in terms of straightening the beast out.

Only other situation I've been in where I'm not quite sure of the best strategy is the complete curling stone scenario. Traction, even with studs, is a dream and you canna break the laws of physics. Sailing along at 20 degrees to my vector for a second or to I didn't have enough time to see if no gas, light gas, or hard gas was the best extrication strategy. Luckily the tires bit reasonably far from the curb and I got back on track. The VSC didn't kick in since it probably didn't have enough inputs to figure out the situation. Have to get out to lake soon.

Of course I was just out today in my Yaris, also with studded snows, and practically running circles around white knucklers sporting bloody no-seasons doing 30 (with one lane missing due to windrows) so really it's about the tires and skill.

If this last couple weeks doesn't get most people here finally over to winter tires on their own then we should really pass a law like Quebec. They are bloody road hazards.