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2010 Subaru CVT Winter Driving Questions and Concerns

Has anyone else experienced this?

Imagine driving on packed snow or ice--conditions in which only gentle changes in direction or momentum are safe. Imagine yourself approaching an iced bridge, or descending a hill and approaching a turn or slow traffic. Imagine yourself releasing your foot from the accelerator in order to coast or gently decelerate. Imagine your car appropriately coasting for 4 seconds, at which time the CVT uses engine compression to unexpectedly simulate a subtle downshift, at which time your tires break traction from the slick surface on which you are driving.

My 2010 Outback with the CVT transmission is my 4th Subaru, and until now I was a very happy Subaru owner. I am a very experienced winter driver--raised in Minnesota, have lived in many other snow states, and even in Greenland. I know how to drive on snow and ice, and this issue scared me (almost to death).

Subaru: Fix this critical safety issue!

Comments

  • wwestwwest Posts: 10,706
    You have just described, perfectly, VIRTUALLY SO, the horrible shortcoming of ANY vehicle that relies on the front tires' roadbed traction coefficient for both drive traction, leading or lagging, and directional control, simultaneously.

    At this moment it seems that only 2 automotive manufacturers have thought this dilema through, Acura (SH-AWD system) and VW.

    VW has just introduced a FWD vehicle equipped with manual transaxle that uses a
    new technique that somewhat addresses this very issue. In the VW should the driver inadvertently downshift to a level that results in wheelslip (FRONT WHEELSLIP) due to engine compression braking the new technique will automatically up-rev the engine to help regain traction and thereby potentially alleviate the follow-on possibility of loss of directional control.

    Perhaps that will be Subaru's solution via a "reflash".

    Subaru could even decide to reverse the downshift to an upshift in the case of front wheelslip developing.

    At this very moment many FWD and F/awd vehicle manufacturers are struggling with, over, this problem. Some are currently using the DBW control firmware to judge your "intent", thinking, as/when you lower your foot pressure on the gas pedal.

    A fast, rapid, foot pressure release quickly following a period of acceleration, even slight to moderate acceleration, will result in a downshift on the presumption that your action "signals" a wish to coastdown to a lower speed using the current gear ratio. Whereas a slow/easy release would indicate a wish to simply enter cruising mode and an upshift would be the most appropreate action.

    Oh, don't place the blame on the CVT, standard gearboxes are even worse.
  • wwestwwest Posts: 10,706
    "...Imagine driving.."

    And now imagine that same scenario going downhill with tire chains on the front ONLY as recommended by almost ALL FWD and F/awd manufacturers.

    Idiocy, SHEER IDIOCY...!!!!
  • mikey00mikey00 Posts: 462
    Not an issue with Outback. Owners manual says no chains anywhere.
  • wwestwwest Posts: 10,706
    Then I guess if I owned a Subaru it would just have to remain in its nice and warm, cozy, garage at those times of traction need. But what to do if "caught out"..??

    Rely on someone else for a ride home...??

    But thanks, now I know why Subarus are often part of the "collection" left helter/skelter around here on our freeways and inclined streets when we get the rather rare (thankfully) snow or ice storm.
  • fibber2fibber2 Mid Hudson Valley, NYPosts: 3,735
    I've had this same complaint about our FWD Honda Odyssey for years. The 'grade logic' built into TCU programming of many modern automatics uses a downshift & engine braking to reduce the reliance on the service brakes. Sometimes, as noted by the OP, this happens at the worst possible time - effectively unbalancing vehicle dynamics.

    I've had far fewer complaints about the transmission 'brain' on my Outback.

    Oh, and we do run dedicated winter tires on both vehicles to help buy an additional margin of safety on snow/ice. It helps, but nothing beats simply staying at home!
  • wwestwwest Posts: 10,706
    Assuming cruise control, most modern day FWD vehicles will NOT downshift to retard road speed unless the driver first uses braking. Retard the engine timing, yes, certainly, but NEVER downshift assynchronously except to maintain UPWARD roadspeed.

    Live long and prosper....

    NEVER drive a FWD or F/awd on adverse roadbed conditions.
  • fibber2fibber2 Mid Hudson Valley, NYPosts: 3,735
    Google "Transmission Grade Logic" and read up on the subject. The Honda corporate web site and several forums have postings as I described.

    If you touch the brake even ever so slightly to moderate the speed on a gentle downhill slope - as you likely would in slippery conditions - you risk a transmission downshift from 5th to 4th, or 4th to 3rd. My Honda does it, and the rental I had did it too. It is potentially very destabilizing, as only the front wheels experience the sudden advent of engine braking.

    I've never had this problem with the Subaru.
  • wwestwwest Posts: 10,706
    Yes, I believe the logic behind this to be, "if you touch the brakes even ever so lightly", then you are inadvertently acknowledging (unintentionally as that may be) that the roadbed surface will support downshifts that incur a substantial level of engine compression braking. Also remember, keep in mind, that as a matter of physics the clear majority, 70-80%, of actual braking will be at the front.

    This may well be "left over" logic from the days of RWD dominance. With RWD a substantial level of engine compression braking at the rear would more often be of help than not in the above stated circumstance. Whereas with FWD the logic undoubtedly will put, is putting, lives at risk.

    Speaking of which.

    Now that all four wheels, mostly, have an ABS/TC brake control manifold that will allow ECU braking application, release, or even "insolation", to any wheel(s) individually, why not disable driver initiated front braking altogether for light to moderate braking...REAR BRAKING ONLY.

    Even my '01 F/awd RX300 has this base capability, and also includes a brake fluid pressure sensor. So why not disable front braking until a defined (high) brake pressure level is sensed or rear ABS needs to activate...??

    Improved safety factor, braking safety factor, maybe even Much safer..!!
  • robm2robm2 Posts: 53
    Any time you're on a slippery road, and you down-shift to engine-break, this is always a possibility.

    If the road is *that* slippery, why not pop it in neutral?

    No different than any other auto-tranny that auto-downshifts at different speeds. When stopping in very slippery conditions, (when there is no need for evasive manouevers) it's always a good idea to go to neutral.
  • fibber2fibber2 Mid Hudson Valley, NYPosts: 3,735
    It's actually one of the reasons that I like hand operated parking brakes. In certain slippery conditions, I'll use a little drag on the rear wheels only to moderate speed, or to actually induce oversteear if the front end is plowing. I realize that this isn't good for the AWD system (sends the center diff into a tizzy), but it's better to sacrifice parts than to crash! The problem is how would the system know if rear-wheel-only braking is actually called for? There are still cases in which you and I can out-think the computer!

    In good traction downhill mode, you really do want mostly front braking, as this complements the natural weight transfer forward. I'm trying to 'retrain' myself to think this way even on my bicycle. We were all taught to use the rear first, when in reality we should be using the front more. Too hard on the rear, and you just skid. Too hard on the front, and you could go over the bars. More front than rear is the best balance, on the edge of rear lift. Anyhow, I think we've strayed off topic.

    But you are right in that staged/staggered braking until the computer can process what's happening will combine with other sensors and driver input to regulate braking in the future. Optical sensors to judge road surface conditions?
  • ateixeiraateixeira Posts: 72,587
    The Nissan Z has that new rev-match feature, which is new today, but I bet becomes widespread in the next decade or so, perhaps even on automatic transmissions.
  • wwestwwest Posts: 10,706
    Back in my days in MT, ~1960-65, I would often use, moderately/CAREFULLY use, the rear implemented handbrake to help maintain control, keep the behind "behind", on a slippery downhill roadbed.

    "..you really do want mostly front braking.."

    NOT...!

    If the roadbed is slippery.

    Methinks you're confusing dry, highly tractive, roadbed surfaces with what braking action would be most appropreate, desireable, on a slippery roadbed surface.

    "..in reality we should be using the front more.."

    Nowadays it doesn't matter, ABS prevents us from using the front "more".

    "...The problem is how would the system know if rear-wheel-only braking is actually called for..."

    No "system" decision required, ALWAYS use rear-wheel-only braking initially for light to moderate braking UNLESS/UNTIL rear wheel slip/skid is detected by the Anti-lock system or a pre-determined HIGH brake fluid pressure is attained. The level of brake fluid pressure could be used to determine when to switch the front brakes "ON".

    This would/might also serve to even out the wear rate of the rear pads/rotors vs the fronts.
  • fibber2fibber2 Mid Hudson Valley, NYPosts: 3,735
    The physics of weight transfer on already front heavy vehicles doesn't support your argument of rear biased braking except under special circumstances that we have already covered. The horse is dead, let it rest....
  • wwestwwest Posts: 10,706
    Most Toyota and Lexus FWD vehicles wil actually UPSHIFT the transaxle as speed decays during coastdowns. I first noticed this within days of purchasing a new 2000 F/awd RX300. Coasting down to about 10MPH with the brake lightly applied it would feel as if the brakes releaseed slightly. Some have described it as feeling as if someone has bumped the RX slightly from behind. I assumed at teh time that this was the effect, feel, resulting from the RX upshifting to alleviate the dangers of engine compression braking should the roadbed happen to be slippery. I was later to learn that this upshifting technique was simply a matter of Lexus attempt at "covering up" a serious design flaw in the early RX300 transaxles.

    The RX upshifts below about 10MPH and then will NOT downshift into first until the vehicle comes to a full and complete stop..or the driver changes their mind and begins to accelerate.

    The same thing happens, but to a lessor degree, as you coast down below about 35MPH, the "slingshot effect" as some call it.
  • wwestwwest Posts: 10,706
    "..The horse is dead.."

    Must have missed that...

    Having rear-wheel-only braking for light to moderate braking would be very much like my judicious use of the e-brake back in my days in MT, no harm, no foul.

    The idea is much like the current BA (Brake Assist) technique wherein EXTREME braking effort ASSIST is made if the queing "signals" are detected. In the case of rear-wheel-only braking the same BA "signal" technique could also be used.
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,578
    I did not realize it at the time, but looks like I saved the best to the last today!

    Personally, I seek out slippery and adverse weather conditions simply for the joy or the experience. It is the one thing I truly relish about living in Fairbanks, Alaska.... I get up to six months of it! Drivetrains aside, the two most important factors when operating on ice are tires and competence (driver, not vehicle), and the OEM tires on a Subaru are simply awful on ice which automatically puts the driver in a tough place. ;)
    2010 Subaru Forester, 2011 Ford Fiesta, 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup, 1974 Ford Pinto Wagon
  • fibber2fibber2 Mid Hudson Valley, NYPosts: 3,735
    I did not realize it at the time, but looks like I saved the best to the last today!

    Are you picking on me, Wes?? :D

    Last week we got a note from management 'politely' asking us to not mess with the virgin sections of the parking lot. They plow roads and dedicated sections of the lot, and leave the rest alone. I got caught doing skid and spin testing. All in the name of science, I pleaded, but they have little sense of humor around here.
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,578
    Are you picking on me, Wes?

    Hahah, no, not really. The title to this thread offers exactly zero insight as to the liveliness of the conversation within. ;)

    I should take a trip down to the northeast to visit. I would be happy to take your management for a spin around their parking lot. I bet that by the time I dropped them off at the door, they would all be ready to be out there too! :shades:
    2010 Subaru Forester, 2011 Ford Fiesta, 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup, 1974 Ford Pinto Wagon
  • fibber2fibber2 Mid Hudson Valley, NYPosts: 3,735
    .... or maybe vomiting out the open passenger window?
  • wwestwwest Posts: 10,706
    "..I seek out.."

    It's been a goodly number years since my wintertime days in Anchorage or Fairbanks, or even Dead Horse and Barrow, but "seek out" was never an operative term with respect to slippery.....
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,578
    Sure, it can be. After a couple months of routine "slick" around here, I have been known to take the occasional run to Palmer to visit family during a warm spell just to have a bit of fun on the Parks (Hwy). :D

    It's all relative. We used to get freezing rain in eastern Oregon that would make the road so slick you could literally push a car sideways while standing off on the graveled shoulder with the car stopped on the asphalt. I have never seen it get that slick here - not once in fifteen years. Of course, down there, the stuff would be melted off by mid-morning the next day. So very few drivers were equipped to deal with it that, for the most part, the roads were abandoned... the holy grail of inclement-weather driving!
    2010 Subaru Forester, 2011 Ford Fiesta, 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup, 1974 Ford Pinto Wagon
  • wwestwwest Posts: 10,706
    Eastern Oregon...NYSSA..??
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,578
    Nyssa.... the town? Haha; not THAT far eastern! Helix.
    2010 Subaru Forester, 2011 Ford Fiesta, 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup, 1974 Ford Pinto Wagon
  • Hi fibber2 - Staying home is a problem for us skiers. In our quest for snow, we live for the "adverse driving condition" days.
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