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2010 Subaru CVT Winter Driving Questions and Concerns
canoetripper
Member Posts: 2
in Subaru
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!
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!
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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.
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...!!!!
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.
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!
Live long and prosper....
NEVER drive a FWD or F/awd on adverse roadbed conditions.
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.
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..!!
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.
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?
"..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.
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.
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.
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.
Are you picking on me, Wes??
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.
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:
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.....
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!