Winter Driving

[jaraczs]

I have to react to the negative user review as well and my take on it is very similar to that of MLucas.

The ASC is really great feature. I have tested it on a snowy residential road and was surprised how sophistically it helps to keep the car on track. And my impression is also that it disables regen when needed. When ASC is disabled, I was able to drift the car with joy at very low speeds but engaging in this activity at slightly higher speed was not so much fun.
I have had an occassion when making a left turn on snow covered road from my workplace (and I was purpusefully "less careful") and the vehicle ASC sensed some instability and applied brake on specific wheels to control the stability. I was really impressed.
Further regarding the review, I also noticed the poster describes shifting from B to D modes by making left-and-forward motions. Shouldn't it be right-and-forward? In addition, the description of the skid event is quite inconsistent? Was he spinning clockwise or counterclockwise? I cannot take this review seriously, sorry. If the event really occured, he must have been driving with ASC disabled or his ASC does not work properly.

 

[MLucas]

Well I finally got to drive my MiEV on unplowed/underplowed roads and it did just fine. I kept up with traffic, which on local roads was about 25-30 mph and on a brief stretch of highway it was about 45 mph. No problems. I kept it in E, used B mode to begin slowing when needed. I even got to test the abs brakes in my parking lot and it stayed straight as an arrow. The ride home may be more interesting as there might be some slippery stuff under any unplowed snow. This is with oem tires with over 7,000 miles on them. I'm happy!

Glad to hear you got a chance to try out your i-MiEVs snow going capabilities. The 'little car that can' really does well in the snow, which I am very pleased with.

I watched this video before I bought the car last year to see how the car does in the snow and I have to say this is the same experience that I had with the car this year: http://www.youtube.com/watch?v=Jh5zanLqXEQ

 

[Pier]

I was surprised this morning with the good traction of my I-MIEV.

Going up a long almost 1 km hill on hard snow- icy- wet 3°C road, I had to stop in the middle because 2 cars were stuck there ( front wheel drive toyotas). It is a forest road going to many maple sugarbushes. I had to go ask a friend uphill to tow theses two cars.

To my surprise, I could then go uphill alone with lots of TC grumblings. Very good traction in icy conditions, even better than my Smart car.

 

[tomrh]

2) I don't believe we have a limited-slip differential, so I assume when you disable ASC that one or both wheels are probably spinning as you work your way out(?)

Yesterday I switched off ASC and did some winter testing with one summer tire and and one spiked winter tire in our snowcovered yard. I pressed the throttle pedal firmly and both tires started spinning, then the spiked tire got grip while the summer tire continued spinning. But the car moved forward. With a regular open differential I would expect the car to stand still with one wheel spinning, but there were obviously some traction on both wheels simultaneously. What kind of differential does i-MiEV actually have? It cannot be a simple open differential.

 

[PV1]

Sounds like a limited slip, but it could also be that the summer tire had enough traction to push some power to the winter tire.

It would be nice to have a locking differential instead of relying on brake force distribution.

I found the other day that relatively fresh tires are a must if you run the stock tires. I know that's common sense, but I couldn't believe the difference of this year versus the previous two years, with nearly worn out tires this year. Overall, the i-MiEV does do pretty good with bad roads, but I tested the ASC yesterday by accident. I came around a corner that dipped down and had the back end come loose. A bit of counter steer and the ASC kept it in the lane, although I lost regen until I put the car in neutral then back into gear. I must have crossed a township boundary, because the road was wet until that point, then was practically untreated.

 

[Aerowhatt]

When I was researching the car I read on some official Mitsu literature that the car has "positraction" rear wheel drive.

Could be the differential design or the traction control system. If you apply braking to the spinning wheel with a conventional differential the other wheel will start receiving torque. We used to use the principle manually to get RWD vehicles unstuck frequently, using unbalanced emergency brake application.

Aerowhatt

 

[JoeS]

I changed the title of this thread to be all-encompassing. The huge East Coast snowstorm of the last few days should provide some stories...

 

[tigger19687]

I'm just north and west of Boston Near Burlington Mall MASS.
We got only 2-3 inches.

phew.... I had 9 feet last Winter so I am not complaining but was hoping for 6-7 inches

Broomed off the driveway and it is all melted and clear.

 

[PV1]

I got a story.

Starting around 2 PM on Friday, we got 6" south of Pittsburgh, PA. I left my work's logistics location around 3:30 (driving Koorz). There was plenty of salt on the road by the building, so it was just wet. I got onto the next road and started into a section of S curves. The second curve dips down. Right about there, the road becomes slush-covered ice. Between a combination of counter-steer and ASC, I managed to keep the drift within my lane. Beyond that, I slightly overshot the next road and my road on the way home. Koorz, however, easily climbed our driveway (which has been a problem this year with Bear).

Woke up Saturday morning to find Koorz buried under snow. The snow around the car was up to the side skirts. Digging out was quite easy as the snow is dry and light. Trying to navigate our road was interesting, but the roads beyond that were only wet.

Today, I finally had the opportunity to play around a bit in the snow. Quite fun indeed, almost as satisfying as playing around with a Tesla Roadster and a Model X (washing, checking out the Falcon doors, and moving the Roadster around in the garage)!

(I'll post links to related threads once I post them).

 

[tomrh]

When I was researching the car I read on some official Mitsu literature that the car has "positraction" rear wheel drive.

Do you remember where you found this?

 

[Aerowhatt]

When I was researching the car I read on some official Mitsu literature that the car has "positraction" rear wheel drive.

Do you remember where you found this?

I don't, but I will attempt to ferret it out again and post it here if I am successful.

Aerowhatt

 

[Aerowhatt]

These specs under mechanical section of the document. So it's brake actuated limited slip. This was tipping point for me since I have driven just about every drive wheel combination up and down steep, curvy, mountain snow packed and icy roads. If it was a conventional differential I was going to pass on purchasing one. After some limited experience this first winter with some very slick conditions I'm completely satisfied with it's performance.


Motor: Electric AC SynchronousTransmission: Single Speed Fixed Reduction GearTransmission w/Driver Selectable ModeRear-Wheel Drive7.06 Axle Ratio80-Amp/Hr Maintenance-Free Battery w/Run Down Protection3329# GvwrGas-Pressurized Shock AbsorbersFront Anti-Roll BarElectric Power-Assist Speed-Sensing SteeringStrut Front Suspension w/Coil SpringsTorsion Beam Rear Suspension w/Coil SpringsRegenerative Front Disc/Rear Drum Brakes w/4-Wheel ABS, Front Vented Discs and Brake AssistBrake Actuated Limited Slip DifferentialLithium Ion Traction Battery w/22 Hrs Charge Time @ 110/120V and 6 Hrs Charge Time @ 220/240V

Aerowhatt

 

[tomrh]

So it's brake actuated limited slip.

That is strange since I had the ASC switched off. Or maybe the ASC button doesn't disable all of the electronic braking? The car has far better traction with ASC off than those other rwd cars with open diffs that I have driven.

 

[PV1]

I would have to say that the ASC off button doesn't completely disable the safety features. When trying to climb my driveway, the ABS was still making some noise even with ASC turned off. I believe this was mainly when holding the brake pedal while pushing on the accelerator. Also, with ASC off, my regen will still drop out if a rear tire slides.

 

[tomrh]

I had to get to the bottom of this diff thing so I dug a snow ramp and backed the right side of the car on top of it so that the right back wheel was almost hanging more or less in free air with only a little snow under. Now the car was stuck with one wheel spinning and the other not moving at all. The conclusion is that i-MiEV has an open differential.

And I also demonstrated how bad the traction control really is, because when I re-engaged ASP it should have braked the spinning wheel letting the other get some traction. It did not, but choked any forward movement completely. What I think happened is that it did try, but the other wheel started spinning a little too and then both wheels were braked.

 

[PV1]

The conclusion is that i-MiEV has an open differential.

Nice to know. Thanks for the investigative work.

And I also demonstrated how bad the traction control really is, because when I re-engaged ASP it should have braked the spinning wheel letting the other get some traction. It did not, but choked any forward movement completely.

So much for Brake Force Distribution :roll: .

 

[kiev]

The yaw and g sensors also contribute to the ASC, so having the side of the car jacked up on a snow ramp might throw a signal that causes it to cut off the wheel torque, especially if the switch was thrown while the wheel was spinning.

The front and rear wheel speeds are also used in both ABS and ASC, so non-spinning front wheels while the rear was spinning may not fake it out either.

 

[tomrh]

It is possible to draw some conclusions on when to engage or disengage ASC. When the wheels have different friction, i.e. there are melted patches of bare asphalt or the ice has been sanded, then ASC works best, giving traction to the wheel having the most friction. If both rear wheels have equally low friction the ASC should be switched off. Two spinning wheels + ASC will only choke our precious speed. With ASC off, if one wheel spins it will still transfer all of its friction through the open diff to the other wheel (cf. my summer+spiked tire experiment).

 

[Aerowhatt]

So it's brake actuated limited slip.

That is strange since I had the ASC switched off. Or maybe the ASC button doesn't disable all of the electronic braking? The car has far better traction with ASC off than those other rwd cars with open diffs that I have driven.

Spin differential is going to make a difference too. For instance you likely would have gotten better results if the "free" wheel spun slowly. ABS and traction control require wheels spinning within a range of the preferred spec to be effective. Remember we are talking about a computer software program which is making choices. A wheel (drive wheel) spinning outside of the parameters for brake action will get power reduction instead. So just like a non computerized drive system one must give it the right inputs to get the desired results. Unfortunately with a complex system it is harder to know just what those input are!

I know one thing for sure, it has far better traction on snow and ice (so far) than any open differential vehicle I have ever driven including my VW panel MicroBUS which had similar weight distribution. I believe it also has better traction than a positraction rear wheel drive Jeep pickup that I use to have. I'll need the rest of the winter to know how much better.

Interesting results in the wheel off the ground test. Raises more questions than providing answers (for me). I figured from the phrasing of the spec, that the differential itself was "open". Positraction provided by braking the wheel with less traction. Which from my experience with manually doing the same thing was preferable to a an actual limited slip differential both in possible available traction and free rolling resistance.

Aerowhatt