Real Time 4wd: How Does It Work With Vsa?

[weavie]

Ok, to me this is the most simple question, but I cannot seem to find a solid answer anywhere. I've called 3 Honda Dealers, speaking to someone in sales and service in each location. Got 3 different answers. I also called Honda Customer Service. I've read my manual. I've used Google. I still can't figure out my question. It's so simple. Here is my question: "Do I need to turn off VSA in the Snow, Ice and Heavy Rain in order for my Real Time 4wd to kick in"? . This is my thinking - The real time 4wd is automatic. It kicks in whenever it detects wheel slippage / loss of traction in the front wheels. I get that. BUT, when VSA is turned on, part of it's job is to "prevent" the front wheels from spinning. So technically, if VSA is on, and there is slippage in the front wheels, the system automatically reduces engine power to prevent the wheels from spinning anymore. Well if this is the case, and the front wheels are not allowed to spin, "when" does that ever give the chance for the real time 4wd to kick in? If VSA was turned off, then the front wheels would be allowed to spin in the snow and ice (ideally), which in turn, would require the rear wheels to kick in. I would WANT all 4 wheels to be working for me in the snow/ice in this situation, right? So I would say YES to turning off the VSA. I know the manual says VSA is primarily for oversteering, etc. But if you hit the gas too hard in the rain from a dead stand still, your front wheels will spin and then immediately after, the VSA light comes on and you can feel the engine power cut down and it stops the wheel spin. So I know VSA definitely affects the front wheels spinning. Does anyone else agree with my point? For the life of me, in this huge internet world, I can't find one solid instruction on how this works. I appreciate any feedback on this subject. Thank you so much!

[aslguy]

Well...give Honda some credit. They wouldn't engineer a system and put it in a 4WD car that would be self-defeating. So in most instances you won't ever have to worry about turning the VSA off.

The only instance that you MIGHT need to turn it off is if you NEED to spin your wheels. Meaning, your vehicle is stuck. Snow, mud, what have you, and you need to gain some momentum.

Another instance where you'll want to be careful, though not necessarily deactivate the VSA, is if you need to turn quickly into oncoming traffic. If your wheels spin due to snow, ice or debris during the turn, the VSA might cut your throttle to minimize wheel spin. This also minimizes your ability to get the hell out of the way of the oncoming traffic that you've just pulled out in front of. My suggestion would be to wait until a break in traffic rather than to pull out in front of someone whose stopping distance is also likely to be increased due to the same conditions that made your VSA activate in the first place.

[Honda Tech]

Here is my question: "Do I need to turn off VSA in the Snow, Ice and Heavy Rain in order for my Real Time 4wd to kick in"? .

Answer to your question. NO

The VSA system incorporates a number of different features. It is your ABS brakes, it takes the place of the mechanical rear brake pressure proportioning valve - brake hydraulic pressure is electronically controlled, it incorporates Traction Control, as well as Vehicle Stability Control during cornering.

The 'real-time' 4wd system operates on the premise of a differential in wheel speed between the front and rear wheels. If there is no difference between the front and rear wheel speeds, the rear wheels do not have drive torque applied - so "in order for my Real Time 4wd to kick in" is a bit of a misunderstood concept - the 4wd is only happening during the real moment in time when it is necessary. The fact is, the system will only apply driving torque to the rear wheels when it is physically forced to do so, based on mechanical principles - there is no decision process involved. If there is a very small difference between the front and rear, a mechanical cam actuates to reduce lag time of rear wheel torque apply, greater differences increase the pump pressures which apply the clutches to transmit the driving torque.

Traction Control will engage when conditions exist of extreme variances in driving wheel speeds and apply brake pressure to a slipping drive wheel and request a decrease in engine torque to the slipping wheel to enhance vehicle stability. Variances in wheel speeds are normal, during normal driving (when you are going around a corner, the outer wheels are traveling a greater distance than the inside wheels, so a difference in speed is both normal and expected, and obviously TCS/VSA should not and will not be engaged to counter-act this). It's when an abnormal variance occurs that TCS engages - if you are stopped, and suddenly the front wheels are spinning significantly faster than actual vehicle speed or if one wheel suddenly looses traction and begins to rapidly spin faster. If you accellerate on a slippery surface and spin the front wheels, RT4wd will engage (it has no choice, it's a purely mechanical action) but the traction control will kick in to stop the slippage. Without TCS, you'd just be slipping all four wheels until you backed off on the throttle and were no longer applying more torque to the wheels than the available co-efficient of friction between the tires and the road surface.

Under certain circumstances, like being stuck in snow or starting from a stop on glare ice, wheel slippage may be a desirable operating condition, which is why Honda provides a VSA switch to manually defeat the system.

So, bottom line (and I hope the answer to your question) is that VSA does not defeat the real-time 4wd, but is an enhancement to safe operation of the vehicle. If you drive in a manner that is constantly engaging the TCS feature, you would be better advised to alter your driving habits than worry about trying to spin all four tires at the same time.

[Dahmer]

not to seem nasty here, but I personally believe that spinning your wheels to get through mud or deep snow or if you're stuck in a rut is the kiss of death.

the best way to get out of any bad road conditions is to use traction control to stop your wheels from spinning out. otherwise your tires just rip up more mud or snow and dig your V further in. and especially in snow, spinning wheels will actually compact and melt the snow into ice and then you're in real trouble.

I personally would only turn the VSA off if I wanted to feel out of control. I do this every so often at work, which is always covered in snow, and I play around doing donuts and whatnot.

and secondly, if you were to have to speed around someone in snow and veer into oncoming traffic out of control, would you really be thinking of pressing a button that removes your traction CONTROL?

[Honda Tech]

not to seem nasty here, but I personally believe that spinning your wheels to get through mud or deep snow or if you're stuck in a rut is the kiss of death.

Dahmer, you haven't done any real off-road four-wheeling, have you? :D

Spinning tires and slinging mud is what it's all about - keeps the treads cleaner and actually prevents sinking if you can keep the vehicle speed up.

But that's not what this discussion is about, since that type of heavy-duty mud bogging is not what any CR-V was designed for.

The big issue with TCS is that the reduction in engine torque is so extreme that the vehicle has trouble getting out of it's own way, and the operator (who probably shouldn't have attempted to pull out in front of on-coming traffic under the conditions in the first place) tends to panic and keep the throttle matted instead of letting the spinning stop and then proceeding at a more sedate manner - mostly because they are staring down approaching traffic and running out of time (and cursing Honda for adding VSA)

If you look at your owner's manual, Honda specifically outlines why there is a VSA 'OFF' switch provided. It is there in the event that the vehicle becomes stuck and the reduction in engine output torque becomes more of a hindrance than an advantage.


The main point that I hope the OP understands is that the instant the front wheel speeds exceed rear wheel speed, the 4wd is engaged, so VSA/TCS does not prevent 4wd, it just kicks in to stop the wheels from spinning. I think the OP is under the impression that 4wd would keep the front wheels from spinning - it won't, and without TCS you'd end up spinning the rear tires as well. (as I do frequently in my non-VSA Element)

[tsmithvt]

I have always thought of the VSA as a valuable driving aid and I leave it on almost all the time. I do, however, think of VSA and the TCS as different systems even though they are the same. To me VSA is directed at correcting excessive oversteer/understeer and the TCS is directed at helping the open differentials in the CR-V or Element. VSA applies the brakes on one side of the vehicle or the other to correct oversteer/understeer. The TCS does the same thing combined with throttle control to "push" torque from a drive wheel (2WD or 4WD) with little or no traction (spinning) to a wheel with traction. It is applying an old technique called "left foot braking". In the days before LSDs, fancy electronics and wheel speed sensors, left foot braking was used to control open differentials ("push torque").

The RT4WD System, in effect, looks at the average wheel speed of the front axle as opposed to the average wheel speed of the rear axle. This is because the front pump is turned by the propeller shaft which is, in turn, turned by the transfer case which pulls torque off the back side of the front differential ring gear. The rear pump is turned by the rear axle pinion. Therefore RT4WD is reacting to AVERAGE axle wheel speed or the undifferentiated wheel speed. The TCS helps augment the RT4WD System by controlling situations where there is a large difference between wheel speeds on an axle (primarily front).

As for spinning wheels in low traction situations, I agree that it is sometimes the only option and completely unavoidable UNTIL FORWARD MOTION STOPS. When you stop moving, better get out of the throttle. When I see a snow drift or have to punch through a plowed up bank, that's when I turn the VSA off. It's these low traction situations when progress is marginal and spinning wheels are unavoidable that I don't want the VSA/TCS to surprise me with throttle intervention.