rks

iTrader: (6)

I haven't seen any other flamefest but I understand. Sorry.

AnalogWorld

VDC was certainly in the "on" mode, but don't know if the skid warning light was on at the time. The condition of the roadway was perfectly dry (not that much rain in Cali), and it happens on both slanted and non-slanted surface of the exit ramp.

Also, I thought that the ABS was supposed to help the wheels from locking up when slammed on the brake, but why the tires screeched? I like how the tranny down shifts to put you in the right gear for the right speed, but it's hard to convince me that this problem is normal.

I personally tried this experiment couple times, the same thing happened every time, and the screeching gets louder as you step harder on the brake. I even tried this in the manual DS mode, which could show what gear you were in. You can do the up and down shifting manually but it will still down shift for you automatically (which doesn't make any sense in this manual mode). However, I didn't see the problem appear in this mode.

So if you get the chance, try it out and see if you think this is normal to you!

______________________
'10 G37S sedan, 7AT, MW/graphite

colburs

Was this straight off-ramp or more like a clover leaf?

If you were turning while braking then the combination of the rev match (engine braking), foot braking, and turning over powered the amount of grip available. Some tires are more audible than others. If you're pressures are off even a moderate amount of braking can get the treadblocks to squirm and set up an audible noise.

No traction control system on the planet can overcome the laws of physics. Go too fast and the car falls of the road.

KLB

When did rev-matching and engine braking become issues?

zmzmzm

If the tires are screeching and the steering becomes light then it just means you are at the limit of traction. VDC/ABS/etc do not change the laws of physics. One of the things with a sport sedan like the G is that you don't always feel like to are going super fast because it feels so stable. Road conditions, weight shift during braking, etc can all get you into trouble.

I have not done much track driving but did do BMW level 1 and 2 driver training (which you don't have to own a BMW to take). That kind of defensive driving course is lots of fun and helps you keep out of trouble.

I seriously doubt that what you describe is a product issue... except that stickier tires might move up the limit of traction for you.

MOB

Since you can reproduce this.....go do it again, have someone standing on the side of the offramp with a vid cam, and post up the results for everyone to see.

15951

Does VDC allow more "play" in DS mode before stepping in? That could explain this. Some systems allow a bit of traction loss in performance modes for track use, etc.

RISKY GUY

iTrader: (9)

Stickshift is childsplay, I drovd my 1st stick at 14.

Back then they were always better & especially in a sports car.

I learned to drive on a stick & passed my road test with one.

Not that I can't drive one, why bother.? I live in massive traffic & have a neck & back problem, so don't want a stick.

Everyone with a stick I know has messed up & either put into the wrong gear or mis shifted & grinded at some point, don't lie.

Not to mention when you are on a hill & someone is on top of your bumper, me not rolling back isn't the problem. It's the genius who has nver drove srtick in their life can't understand that you are rolling because you are not at the proper friction point for the clutch.

I could drive stick with no tach,(car I learned on had not tach.)

Auto is the deal why do you think the manual is on its way out?

Because dual clutch auto will outshift you all day without a mis.

rks

iTrader: (6)

Is this you? I'm your biggest fan.

Warp37

Rev matching? I though rev matching only happens when you *manually* downshift in DS mode in the automatic when *not* braking so that the engine *already* is at the appropriate RPM for the gear into which you will be shifting and there is no huge engine braking.

When driving a stick and you want to downshift, but are not braking / slowing significantly (such as when passing some jerk who's trying to deny you), you gun it some while the clutch is in just before grabbing a lower gear and fully mashing the throttle so that the synchros allow the shift and / or so the shift is smooth and the car *does not* engine brake. (Heck, sometimes the sequence is mash, clutch in, grab the gear, clutch out, flip off jerk who tried to deny the pass.)

Here, I don't think rev matching should be confused with downshifting itself. What I think is happening is that you brake, fairly aggressively, in DS mode and the car downshifts -- sometimes more than one gear -- because, after all, you are in DS mode and the car expects you will be flooring the throttle very shortly thereafter.

That said, there is no way the car should break traction. I did brake fairly late, and therefore aggressively, for a stop sign in DS mode and the car sure did downshift mightily. I'm not real comfortable with that response, yet. But as someone else said, this just needs some getting used to.

As my brother says, there are two pedals in the car, and one should be to the floor at all times.

voltic

iTrader: (5)

I thought we were like... not turning this into an AT vs MT ******* waggling contest?

Anyway, if you're in the SD area let me watch you do it and I'll let you know if you're doing it wrong or not.

Also, VDC can almost definitely change the laws of physics.

twin_snails

iTrader: (2)

I know exactly what he means. He mentioned that it was raining. Was the road surface asphalt? I suspect it may have been.

I could easily duplicate this situation in my 2004 G35 Coupe, albeit in a manual trans. I would brake for a light sometimes and downshift to second gear and let the clutch out at around 30mph. The downshifting without rev-matching causes a phenomenon where the rear wheels are not spinning fast enough to keep up with the vehicle speed. The result is almost always a feeling of "loss of control", even with VDC turned on because it takes the VDC system around a half second or two to dispatch the electronic nanny which applies the brakes lightly to wheels it detects as "in a skid".

Granted, this issue should be far less of an issue in a vehicle with rev-matching, however, it can still occur because the effect of engine braking slows the wheel speed to a point where the wheel is spinning slower than the car is traveling, causing the tire to lose contact with the road, which results in a skid. I've even experienced it in my 2010 Sedan (7AT). I usually stay out of DS mode most of the time but I always stay out of it in the rain as it can cause such situations to occur.

I don't know if that makes any sense but it's especially duplicatable in manual trans cars. Very easy to kick the tail out in the rain by down shifting on a well-worn asphalt road surface.

Mike

iTrader: (1)

If you knew the car, you'd know what gear its in without looking at a display that tells you.

cbach1997

I've been in DS down some sharp grades through S-curves and the engine braking has been strong enough to begin to lock the rear wheels, which could result in the said scenario. VDC was on, and as the rear continued to lose grip the car eventually decided to apply a small amount of acceleration to even things out, which caught me by surprise.

Fortunately there was no one around and I'd planned on working the car out so the whole cherade was planned and I didn't lose enough control to chicken out and brake.

TinsleyC

This happened to me - in DS mode, no manual shifting. Accelerate quickly from a stop (but not full throttle) let it hit 2nd gear, and then brake firmly. At least for me, the sudden downshift to 1st gear revved the engine so much I could feel the car accelerate briefly, even though I am braking.

Sort of freaks me out.