Tuning for Oversteering and Understeering..

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Refering to this display/screenshot, has the writer got the corrections reversed/terbalik?

Yea, that's what I was thinking too along the lines of lower tyre pressure gives relatively higher grip than higher tyre pressure, everything else being equal.

Having said this, it bases purely on 'tyre engineering' or properties.

Could the writer approach this subject of over-steer/under-steer corrections from the perspective of vehicle suspension dynamics (which we ignore totally) during  turning/cornering, which may cancel, neutralise or over-run grip effects of lower/higher tyre pressure?

For all we know, the writer could be right ?

Btw, does higher tyre pressure results in higher spring rate of a car suspension spring system whilst lower tyre pressure results in lower spring rate of said suspension system?

Hi sifus. Please help me out here 😞.
I drive a perodua myvi 2nd gen which has torsion beam at rear. Went to do alignment today and mechanic told me my rear toe in totalling both side to 1 degree. He offered 2 solutions.

1. Change the whole rear axle / torsion beam costing around RM650 Inc installation.

2. (For my understanding) Add shims / washer at 1 of the wheel bearing/ nut hole. To compensate the degree.

Note:
Car has not been in an accident , only minor rear bang/light collision middle not side.

Can any sifu give me some opinions, since toe in will degrade tyre faster right.

If you look through the link I provided 2 posts above on shimming of Rear Torsion Beam/Hub, total shim thickness required by @nightlord in order to shrink its Rear Total Toes to factory specifications would be about 0.40 -0.60 mm on one and/or both sides combined.

Unfortunately the shims or washers thickness I found online is in 1 mm, 2 mm and 3 mm size.......
which imo is not quite suitable for such a typical Rear Torsion Beam shimming job.

Is there metal shims in 0.10 mm or 0.20 mm thickness available in the market, online store or retail shops? Mind intro one or two such outlets?

Replacing with a used rear torsion beam might end up with a rear camber/toe also out of factory specs. IDK.

Replacing with a brand new rear torsion beam would be very pricy. Even then the resulting rear camber and toe might look 'bad' or worse still, also out of specs. So it is a big risk too.

@Nightlord, as suggested above by @amduser do you experience 'understeer', excessive tyre wear?

Rear axle push to left and/or right sides when driving over bumps and potholes?

Car drifts or pulls to one side on straight ahead driving when both hands temporarily off the steering wheel?

With a centred steering wheel the car does not travel straight but move to one side?

Turning left steering effort or smoothness is different from turning right as your steer?

Update:

The 2 old tyres were never rotated but stay at the same rear corners throughout its life of 110-115K km.

Both exhibit even wear (between inside and outside edges) with (mild uneven) heel-toe wear around their circumferences, inside and outside.

Prior to free wheel alignment check, the alignment technician test drove the Avanza and found alignment ok. He too couldn't sense or detect the loosened RHS Front rack end assembly (which I didn't disclose to him).

I am wondering why the Front Left ride height is registered lower by 13 mm at 808 mm compared to Front Right of 821 mm?

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Why would current Front cambers (after about 15 months or 25K kms travel) of  Left -0°42' (Previous -0°15') and Right -0°49' (Previous -0°15') have such a huge difference by up to negative -61' combined?

The change in Front toes could probably be explained by change in Total Front Cambers during the 15 months, I supposed.

For the purpose of summary of alignment readings:
        Front Cambers are -0°42' (Left) and -0°49' (Right) with Front Total Cambers of -1°31';

        Front Toes are -0°01' toe-out (Left) and +0°03' toe-in (Right) with Front Total Toes of +0°02';

        Rear Cambers are -0°10' (Left) and -0°03' (Right) with Rear Total Cambers of -0°13'; and,

        Rear Toes are -0°09' toe-out (Left) and +0°03' toe-in (Right) with Rear Total Toes of -0°06' .

Previous rear alignment angle readings were unknown.

Thanks.

You have a valid point is suggesting there is no problem with my cambers, where being a live rear axle design the Rear cambers are non-adjustable without some kind of mods like shimming rear axle/hubs.

Besides, I had a known (to me) loosened free play at my Right front rack end assembly reported earlier on and I won't get to enjoy this free alignment checking but to pay up RM30 for alignment adjustment if I wish front suspension angles adjusted or altered at the time
..... which doesn't make sense for the loosened suspension parts at the moment.

However, since 15 months ago (of about 25K-27K kms) my Avanza has been drifting/veering slightly to the Left whilst driving straight ahead on straight roads/hiways and it has been capable of occupying the whole of left hand side lane in about 7-9 seconds with both hands temporarily off the steering wheel.
I'm bearing with this slight irritants/nuisance for now.

This irritant is, imho partly caused by the front and rear cambers namely:
Front Cambers -0°42'(Left) and -0°49'(Right); and
Rear  Cambers -0°10'(Left) and -0°03'(Right).

Note:The front and rear toes seem to incline to pull the vehicle towards the Right imo but it is somehow being neutralized and overcome by the Left leaning cambers.

Correcting/adjusting the front cambers may give me a chance of getting the vehicle tracking straighter, if not rock solid straight, I believe.

Yes, cambers and toes in wheel alignment speak are normally look at or assessed on the per side (Left or Right) basis. Imho, this approach is premised upon and based on the ideal conditions that Left/Right cambers or toes on the same (Front or Rear) axle are always exactly equal at the same value whereby the Cross cambers and Cross toes (i.e left camber/toe Minus right camber/toe) are always Zero in an ideal world.

But alas, the real world is always not ideal  whereby Left side cambers and toes are NOT exactly equal and same as the Right side cambers or toes on the same axle, all the more so with non-adjustable Rear Torsion Beam and current Rear solid live axles.

In the super majority of Asian cars and some Continental cars (including that of segments C and D cars) the stock original front strut system does not have provision for camber adjustment too, i.e not ideal.

Hence I prefer to read suspension alignment angles in the perspective of Front/Rear Total cambers/toes.

Equally important is Cross cambers and Cross toes which is typically not exactly Zero in real world, but that is another different topic for another day.

For example referring to my Avanza's current suspension angles I intend to increase my Front Total Toes of +0°02' to say a range from +0°04' to +0°08' to overcome current driving experience of wobbling/loose/unsteady steering wheel movement on tekan-minyak acceleration in a curve or corner.
Exactly what Front camber/toe angles to adopt shall be influenced by the prevailing Rear cambers/toes angles at point of alignment adjustment.

Similarly one way to counter the Avanza propensity to oversteer on cornering experienced currently is to make/adjust my Rear Total cambers of -0°13' to be more negative like -0°30' or -1°00'.
Meanwhile, current Rear Total Toes of -0°06' is real real bad for oversteer phenomenon.

I found the road to modding Avanza  rear live axle in Klang Valley for improved Rear suspension angles is slow, difficult and rather frustrating. Having said that , there is a far away (300+ km) JB alignment shop recommended above by @nightlordccc79 keeps the weak flame and hope alive.

Hi all Sifu , mind share what is the best toe setting for cruising highway ?

I should have clarified earlier on that the sets of Lower Control Arm, outer tie-rod ends, shock absorbers, absorber links and sway bar bushes for the Front axle and Rear shock absorber sets were all replaced some 25k kms ago in December 2020 at a cost of some RM1750 .

However, all 4 absorber top mounts and front steering rack end assemblies were not replaced then, from which Front right rack end is currently found loosened (some 2 weeks ago) and yet to be replaced. 

I'm from the camp of non-adjustable front/rear cambers and rear toes  (commonly found in Front MacPherson and Rear Torsion Beam or solid fixed axle) is a bad thing in the context of flexibility in making adjustments to suspension alignment angles in individual tyre, hence leading to generally much lousier and less enjoyable driving experience  or pleasure but hey..... it is cheaper to purchase and maintain compared to a complex independent rear and front suspensions normally found in very pricy segment D continental cars.

Interesting that you have front (total?) toe of -0.2 (degree or is it mm?) and cambers at -3° and -2°. Mind sharing what car this belongs to and how is highway high speed straight ahead driving experience, wobbly or steady?
Not sure whether the 0.5 refers to unit in mm or decimal degree or degree/minute?