joepa

Been thinking about this for a few days and wanted to get some input from other G owners. I've had my G37x for almost 5 years now, but this was probably the worst winter we've seen here in NJ during that time. My previous 2 cars were FWD manuals, and I tend to drive my G in manual mode most of the time. I noticed this winter that it's surprisingly easy to make the rear end fishtail when downshifting in the snow...quite an unsettling feeling when you're not expecting it. Was curious to see if others have experienced this.

I've seen a lot of websites that encourage downshifting and engine braking in slick conditions, with no mention of the type of drive system in play. I think this has the potential to be a dangerous recipe in a RWD automatic (despite the AWD capability of the G).

I'm also curious if anyone understands why the downshift causes the rear end to break loose. I've found a few explanations around the web but none that really satisfy my engineer side. Everything from increased torque at the wheels, to weight transfer, to wheelspin, even something called trailing throttle oversteer...was wondering if someone can make sense of all this? Thanks!

Serpens

Trailing throttle oversteer is a little different.

When I think of your situation, I would tend to say the increased torque at the wheels and the weight transfer (since your effectively slowing the car down) cause this sensation. You could evoke a similar situation if you approach a turn in a FWD manual car in the snow, select a low gear (say 4th to second, causing a large RPM change), and then let the clutch out mid-turn. This will upset the car, although it will just cause understeer.

ANMVQ

iTrader: (13)

I tend not to do that in the snow as the few times I did it , the car slipped the drag cause the wheels to slow or stop will cause slipping. at least that's what I've encountered on mine, I use the paddles in my car all day everyday I just change the way I shift or downshift in the snow

dkmura

As a road racing driver, I experience some lateral movement when I don't properly revmatch when downshifting for a turn. It's a combination of the factors you listed above: engine torque when going to a lower ratio, weight transfer (weight shifts under braking, making tail lighter) and some wheelspin (engine braking may cause limited traction loss). On snow, this occurs because the coefficient of friction between the tires and roadway drops due to temperature and moisture- similar to what happens when speed increases and the contact patch of the tires shifts rapidly.

Trailing throttle oversteer is what happens when corner entry speed is too high, and the driver craps his/her pants. At the cornering limit, snapping the throttle closed will naturally shift weight forward and the yaw will take the tail of the car out- sometimes completely off the road.

joepa

Great info guys, thank you.

At lower speeds on flat surfaces, this is probably a non-issue. But I could see getting into trouble if you downshifted on a decline or curve in the snow, especially if your speed was in excess of 30 mph or so.

guyinswmo

I had an '06 galant gts (fwd) a few years back and managed to put it in the ditch one day because of this. I crested a hill with a slight decline and was slowing down to make a turn. The car had the manual mode so I was utilizing it to slow the car down instead of braking in hopes I had better control on the snow/ice covered roads. Well the car only had a 4 speed transmission so when I went from 4th to 2nd fairly quickly it caused a surge in the rpm's and before I knew it I lost control and slid into the ditch.