Reflexion about PDAS (Traction Control)
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From: Paris
Reflexion about PDAS (Traction Control)
I recently re-read the Adrian Steatler description of PDAS (Traction Control) and I'm wondering if the understeer reputation for the C4 isn't due to a lack of understanding by drivers of how the traction control really works.
Basically, it says that :
- front and rear tire outside diameter MUST be as close as possible to each other, to avoid messing with the PDAS
- the PDAS works only when not braking (accelerating or not)
- the PDAS create understeer in the curviest part of the curve, because it locks at the beginning of the curve meaning the rear wheels are locked in a position where they push the car straight ("outside" the curve) and the front traction being 31% cannot help against this.
So the very simple action to avoid this understeer issue seems to keep the brake pedal slightly pushed until the middle of the curve, which is called "degressive braking" (french translation for Freinage Dégressif)
Meaning : never enter a heavy curve with the brake lifted !
It likely is a basic way of driving anyway, at least for track users, but I'm not sure the regular driver knew about this.
Last summer, as I just got the car, I frightened myself several times with this understeer, as I was going pretty fast on curvy roads in the mountains, until I started doing this "Freinage Dégressif" on each curve, even the small ones. Instantly the car behave better and I thought it was because the front wheels got more weight and then helped the car going along the curve.
But I wasn't really that sure, and now I'm pretty sure this theory about the PDAS "bad" influence in curves has something to do with my confidence ! I can't wait for next spring to try again !
What do you guys think ?
Basically, it says that :
- front and rear tire outside diameter MUST be as close as possible to each other, to avoid messing with the PDAS
- the PDAS works only when not braking (accelerating or not)
- the PDAS create understeer in the curviest part of the curve, because it locks at the beginning of the curve meaning the rear wheels are locked in a position where they push the car straight ("outside" the curve) and the front traction being 31% cannot help against this.
So the very simple action to avoid this understeer issue seems to keep the brake pedal slightly pushed until the middle of the curve, which is called "degressive braking" (french translation for Freinage Dégressif)
Meaning : never enter a heavy curve with the brake lifted !
It likely is a basic way of driving anyway, at least for track users, but I'm not sure the regular driver knew about this.
Last summer, as I just got the car, I frightened myself several times with this understeer, as I was going pretty fast on curvy roads in the mountains, until I started doing this "Freinage Dégressif" on each curve, even the small ones. Instantly the car behave better and I thought it was because the front wheels got more weight and then helped the car going along the curve.
But I wasn't really that sure, and now I'm pretty sure this theory about the PDAS "bad" influence in curves has something to do with my confidence ! I can't wait for next spring to try again !
What do you guys think ?
Last edited by ManuFromParis; Feb 14, 2015 at 10:39 AM.
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From: fairfield, CT
They go into this a bit in "wringing out the carrera 4"...
https://rennlist.com/forums/964-foru...-4-pt-1-a.html
Basically in the end if you can trail brake or left foot brake when necessary, you deactivate the locking of the diffs and the car acts well...
The other thing to try, and this hasn't been fully tested as to what it actually does or doesn't do, is to activate the diff locks with the switch and hold the switch for more than 10 seconds. There was a post a while back that said this also deactivates the diff locks. I tried it on a track, and it seemed to work, but then I was also trail braking and working on other stuff so can't really tell...so if anyone knows the truth behind this one, jury is still out whether I would break something driving it around with the switch off that way. I'm not convinced.
https://rennlist.com/forums/964-foru...-4-pt-1-a.html
Basically in the end if you can trail brake or left foot brake when necessary, you deactivate the locking of the diffs and the car acts well...
The other thing to try, and this hasn't been fully tested as to what it actually does or doesn't do, is to activate the diff locks with the switch and hold the switch for more than 10 seconds. There was a post a while back that said this also deactivates the diff locks. I tried it on a track, and it seemed to work, but then I was also trail braking and working on other stuff so can't really tell...so if anyone knows the truth behind this one, jury is still out whether I would break something driving it around with the switch off that way. I'm not convinced.
Burning Brakes
Joined: Nov 2013
Posts: 782
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From: Abbotsford, BC
In the summer I drive the Crowsnest Highway 3 in BC from Hope to Penticton in my C4 (lowered to RS ride height). Lots of tight corners with 30kph (18mph) warning signs that I can easily corner at over 100kph (62mph) and even push it further. I have not found understeer to be an issue, and am just really blown away at how tight and secure the car feels in high speed tight corners.
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From: Paris
Thanks for advises.
I would'nt go for a deactivation of PDAS since the traction control is so much fun and efficiency when bulleting out of a small corner, even on rough or graveled roads !
The more I remember about the corners where the car understeered, the more I'm convinced I wasn't braking on those occasions, or maybe went back to the brake pedal when it was already too late.
I have to mention that it was when I just got the car in early june and, just afterward, I did a training session on track, in one of those Formule Renault 2.0. With those cars you couldn't go out of a corner without entering it with a trail braking attitude !
So the following summer, I simply adapt my driving in the 964 with trail brake and have never been bothered with understeering afterwards.
The recent second reading of Steatler's documentation became suddenly so clear to me I wanted to share about this hypothesis.
Now the only mod that would make sense to me would be to limit activation of PDAS in accelerating mode only, especially since it looks like it can activate in a fraction of a second. I can't understand if it is already the case or if the LSD may be locked in decelerating mode...
I would'nt go for a deactivation of PDAS since the traction control is so much fun and efficiency when bulleting out of a small corner, even on rough or graveled roads !
The more I remember about the corners where the car understeered, the more I'm convinced I wasn't braking on those occasions, or maybe went back to the brake pedal when it was already too late.
I have to mention that it was when I just got the car in early june and, just afterward, I did a training session on track, in one of those Formule Renault 2.0. With those cars you couldn't go out of a corner without entering it with a trail braking attitude !
So the following summer, I simply adapt my driving in the 964 with trail brake and have never been bothered with understeering afterwards.
The recent second reading of Steatler's documentation became suddenly so clear to me I wanted to share about this hypothesis.
Now the only mod that would make sense to me would be to limit activation of PDAS in accelerating mode only, especially since it looks like it can activate in a fraction of a second. I can't understand if it is already the case or if the LSD may be locked in decelerating mode...
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From: fairfield, CT
By "deactivation" I meant to say to leave it such that the power to the front stays at 39% and 61% to the rear. That switch, holding it for more than ten seconds, was purportedly doing the same thing as happens when you trail brake..leaving the front rear power balance at 39/61. This would only mean one wouldn't have to trail brake, and therefore one could be off the brakes on "turn in", without incurring the pdas locking which creates the understeer. Locking the wheels together is nice in the snow for climbing hills...it's a disaster on a track...
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From: Paris
Yes, I think I got it but I would certainly not want to deactivate the whole system since I find the PDAS amazing and brilliant to get out of corners !
Anyway, I won't be using this C4 on tracks, except one half/day to setup the brand new Bilstein B16 I just purchased and that will be fitted soon !
Anyway, I won't be using this C4 on tracks, except one half/day to setup the brand new Bilstein B16 I just purchased and that will be fitted soon !
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