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Car veering off line under heavy acceleration

20K views 37 replies 22 participants last post by  TinkerRS 
#1 ·
There have been a number of posts on this subject, many suggestions that various things like tyre pressures etc. are the cause, some suggestions that "pull drift compensation" may be able to be disabled to fix, a suggestion from one of our members that turning traction control OFF fixed his car. I have worked my way through all of these aspects carefully and methodically, my dealers techs could not access the pull drift compensation while they loaded the update to PCM about 3 weeks ago, and after driving car home could not detect any change in behaviour of car apart from a few gurgles and farts in normal mode which I don't think were there before, HOWEVER had the car 4 wheel aligned a couple of days ago, castor and camber were OK, toe in front and rear was uneven and toe in was slightly excessive. Working on the same theory as a FWD car I had once that had quite a bit of boost etc over stock and torque steered in a rather interesting fashion when booted, I had the alignment set at O/O F/R toe in. The reasoning here is that FWD cars "pull" the toe IN under power, by setting it "out" a little offsets this and car tracks better. In the case of my previous car we used to set a little "toe out", but with Michelins being the price they are I elected as a first try to use what we set O/O F/R............................................................ Now the good part, the tramlining has reduced considerably, and the crazy 3rd gear twitch has pretty much gone, in percentage terms probably about a 90% improvement. There may be further gains to be had, will monitor tyre wear patterns and see how it pans out. The interesting thing here is that various forums report differing results using combinations or applications of some or all of the above. What I can say is that it fixed mine, I was at the point of unloading the car because of this dangerous behaviour, worse than any car I have ever driven, including a variety of very High Performance race cars and road cars, one race car had a CIG locker in FWD and was quirky to say the least. Would be interested to see how others get on.
 
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#2 ·
I guess it couldn't hurt to get get an alignment on my car as its been a year on the crappy bumpy roads in Upstate New York
 
#16 ·
Just tried this - you're right, it makes for a significant improvement. I'd say the problem is tolerable in these settings, meaning it's about 50% better! Still plenty of room to improve, but that's a damn good start.
 
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#4 ·
Quite interesting findings actually. I've had a tramming effect on mine a couple of times under power changing lanes on a dual carriageway. Not so much directional pulling, but I likened it to probably too much toe-in on the front as when you changed across the camber on the peak of the road it wanted to dart off down to the side of the lane I was switching to.

I will get mine checked as well.
 
#6 ·
I don't have any answers either but I can definitely say this drives me nuts in the car, also to the point I'm considering moving it on. Accelerating hard, particularly on roads with uneven camber, and especially when in sport mode, is complete rubbish. I haven't bothered with the PCM update, as from most accounts, it doesn't resolve things. I'm going to try this as a last resort, though, but if it doesn't help, it's bye-bye RS.

Very strangely, I have driven a few different RSs and not all of them have this problem, which makes it all the more hard to diagnose. I have the Mountune springs and H&R swaybars in my car, and had an alignment done afterwards, but the problem is still largely the same.
 
#8 ·
Yup...tramlining. "Tramlining is the tendency of a vehicle's wheels to follow the contours in the surface upon which it runs."

We get at least two types on the roads of N.E. Washington State. There's the mild variety that occurs when you're hard on the throttle and pass over a crown in the center of the road. Then there's the vicious, "I wanna kill you" version that happens when you pass over the "ruts" that eighteen wheelers make over time. The latter being particularly breathtaking when the angle of attack relative to those depressions is large, and acceleration is high. There is unquestionably something that RDM (control module) is doing that exacerbates the effects. If you reduce the natural tendency to instantly try to compensate with steering inputs, it actually sorts itself pretty well. But under certain circumstances, it can be unnerving.
 
#9 ·
This is definitely not tramlining in the normal mechanical sense. It's far more severe than that, which is why there's so much conversation about it. It even occurs on a dead-set straightaway on a newly-surfaced race track, which is good sign there's a problem here.
 
#11 ·
My hunch is that it is definitely active torque braking on FWD axle as it occurs for me only when turning on steering wheel.

Since getting in and pressing the esc button once, no issues. I think this is somewhat similar to the track mode with dampers on normal.

You will find at lower speeds though <50km/h (30mph) that the tram-lining is notorious on the Cup 2's and this is separate to the issue being discussed and perfectly normal.
 
#23 · (Edited)
Is there any easy to understand way how the effect in question is different from torque steer?
Torque steer, as the name implies, is the unequal transmission of torque to (usually) the drive wheels that are being steered. This is a problem with FWD and AWD vehicles....particularly those with transversely mounted engines with unequal (length, torsional rigidity, angle, etc.) drive shafts. Tram-lining is a separate effect caused by the tendency of a vehicle's wheels to follow the contours in the surface upon which it runs. (Keep in mind that this is an extremely over-simplified description...particularly as to torque steer.)

The topic here is trying to get at how our unique drive configuration may be interacting with one or both of these two effects, and how it may be causing the concerns some here are having.
 
#17 ·
I can't say I have experienced any of those issues but I came from an awd turbo car with wide low profile rubber and coil overs so maybe it just feels normal to me. I have the cup 2s and can't imagine getting a different tyre for the car.
Sure, I can feel some torque steer in the front on hard acceleration but my last awd car did it as well and doesn't bother me at all. Certainly not enough to change lanes.
 
#18 ·
I've tried alignment (helped some), lower tire pressure (43/40), have a Tune+ (helped a little) but the most significant improvement came from using track mode in normal suspension setting (ESC set to sport). I believe that the combination of the ESC and the altered vectoring setup in Track mode plays the single largest role in this issue. It is now substancially improved and much less severe.
 
#19 ·
Has anyone skilled in turning off the RDU and interested in torque steer - drive the car with it off and comment?

My theory is the torque vectoring is turning the car from straight when large throttle and some steering is sensed???
Turn off the RDU and I suspect the behaviour will diminish to familiar FWD levels.
 
#20 ·
I've also noticed a significant improvement when in Track mode vs Sport. I'm sure this problem has something to do with the ESC rather than anything mechanical. OP should try track mode with soft suspension and see the difference, preferably on the same stretch of road.


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#21 ·
I am told that alligning thse isnt as simple as something from days gone by. Something to do with the electronic steering and so e sensor or whatnot needing recalibration... have booked mine in for an alignment in a few weeks due to the unpleasant tramlining that im experiencing....
 
#22 ·
It can be a little unsettling, but I have come to kind of like it. It forces me to be aware of how much steering input I'm giving it under various road and throttle conditions. It reminds me of the pronounced torque steer on the ST that seemed like it was trying to kill me at points. :)
 
#27 · (Edited)
As others have said, change to track mode, put the suspension back to normal mode, and enable traction control.
Car stays much straighter with heavy acceleration.
I just tried it today, and it's ~80% better.

In sport mode, the RS would pull significantly left and right (felt like torque steer) under heavy acceleration.
(Used the same roads and distance with WOT acceleration for comparison between sport and track mode.)
 
#28 · (Edited)
The term "torque steer" may not correctly describe the issue or at least may be a part of the issue. Torque steer is fairly obvious.....on a flat road accelerate with your hands off of the wheel.....if it pulls either direction then torque steer is present. In my case my car does not exhibit this characteristic, but it did pull when passing on a 2 lane road.

So what's different when passing with the RS? First of all if you are not on the accelerator the car is in fwd no matter what drive mode you've selected. So if you pull out to pass, 99% of the time you are tipping into the accelerator and thus the awd system/RDU is activated. Since the RDU is designed to sense front wheels steering angle it will induce some amount of vectoring. In addition there is a slight delay in switching from fwd to awd, which combined with the uneven surface and timing for throttle application can create front tires/wheels following the road crowns (tramlining). The drive mode/ESC setting is also a contributing factor, IMO. For example, in Track mode the car car has less aggressive ESC intervention (sport ESC) and allows for more steering angle input before intervening. Since the RS uses a combination of electonic wheel braking to aid rotation, this mode minimizes braking to correct/offset steering angle.

Putting these together would suggest that torque steer is really not the cause, but a combination of ESC intervention, switching from fwd to awd and RDU vectoring maybe the primary causes. Yes tire pressure, alignment and tune power delivery are factors but I suspect second order contributors vs the ESC and drive mode settings (vectoring)......at least in my case this seems to be true.
 
#29 ·
Are you using your indicator when passing? If not the chassis and RDU modules will think you are just going around a regular corner and do as the car was designed and will induce the beautiful rotation of the chassis.
 
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#31 ·
Here is an interesting experiment to try. Next time you go to pass pull out in the other lane and straighten out the steering wheel before accelerating. Then try passing by getting close to the car you're passing and floor the throttle then pull out around them, and compare the amount of "pulling".
 
#32 ·
I've already done a similar experiment. I back off and start to accelerate while driving straight. Then change lanes (while still accelerating) and go around them. When I do it that way, I don't get torque steer. It only happens when I start accelerating and turning at the same time. That's why I thought your previous post made so much sense.
 
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