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Rear wheel steer effect


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2006 1.9PD estate with 225/45/17s on sports option suspension.

Tyres, alignment, shocks, springs, bushes(?) are good however when cornering, especially on undulating/bumpy roads the rear end feels like it has a mind of its own.

I am unable to identity the suspension component(s) responsible for this unwanted characteristic, has anyone any idea which part would most likely cause this behaviour?

I would tend towards the trailing arm bushes but cannot see/feel any play.

I even figured the grip afforded by the fattish tyres exceeded the suspension design's ability to maintain proper geometry... it looks like a weak design where on skinnier tyres the grip would go before the suspension was torqued sufficiently to be noticed as the rear steer effect.

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I recognise those symptoms. I hated my car when I first got it after the Octavia 1. Lurchingly squirrely.

Did what you have done, checked all bushes and alignment (which in my case was miles out) much better fuel consumption and steering feel, still lurched like a greased pig on the undulating French back roads.

Fitted Superpro eccentric wishbone bushes, slight improvement. I liked the slightly heavier steering feel and more positive self centring. Still wallowed though.

When I uprated the Rear Anti Roll Bar the symptoms went away.

Not too expensive <£200 for the popular Whiteline Adjustable. (you are changing the balance, so a front ARB is not needed).

Easy to fit.

Transforms the feel of the car, both for the driver and passengers, because of the reduced rear roll.

The car goes where it is pointed and stays on that line.

You can tighten the line by applying throttle.

No degradation of ride comfort, no additional harshness.

Why didn't skoda do this????

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Hmmm... interesting.

I will be looking at it again but I'm fairly certain I was able to flex the trailing arms during a recent shock replacement, one of the bolts I worked on caused a noticeable bend which would cause a couple of degrees of steer.

Like I said I will be investigating again at some point, if the arms are flexing as I recall I may try welding a length of angle iron along them to add stiffness.

Please keep the comments/questions coming.

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My vrs has been nicknamed 'the boat' by the family. The rear end seems to be totally disconnected from the front end, under steer is chronically bad, and passengers feel like they are sliding out of the car on bends.

I don't understand how skoda managed to get the handling so wrong, especially on a 200bhp car...

So much so that next week, I am having a h&r cup kit fitted, along with a white line rarb. Which hopefully should get the handling somewhere closer to where it should be...

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I assume you gents are all running around 34-38psi in your tyres?

 

Also, this may help those of you that have some DIY skills & don't want to spend money.  I did a 20mm shorten but I think you could stretch it a few mm further.  I'd also recomend you grind of the 90 degree corners to make it look nice.

 

http://www.briskoda.net/forums/topic/309101-diy-a-tiny-bit-more-stiffness-from-the-stock-rear-arb/#entry3695817

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If you have the plate style trailing arm (I presume this is what you meant) the one which is parallel to the longitudinal axis, then the fact you can bend across its thickness is of no consequence. Can you imagine bending it across its depth?

The hub is constrained by other transverse struts, so it only has to resist forces for and aft, not side to side.

Adding stiffness is unlikely to make any positive contribution, and may even make things worse.

Skoda, like the vast majority of car makers, engineer their cars to be "safe", ie to go into terminal understeer, to scrub off speed if overcooked into a corner. It not nice, but its what the insurance world deems "right".

If it was common for cars to spin out every time a corner was misjudged, then perhaps we would not be able to afford the insurance.

However sporty even a vRS is perceived, it is still a family car.

We are lucky to be able to change it so easily.

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I fully understand the need for a tendency to understeer (almost all FWD cars I have driven are setup like this - with the noticeable exception of my Hyundai F2 coupe).

But, many other 'family' cars manage to have slightly more neutral handling, and certainly less body roll.

 

Maybe it is because my last car was an Alfa 156 (which cornered brilliantly as standard, and was fairly refined), and my wife's car is a Hyundai Coupe (which handles well, but has harsh ride comfort), but I find the vRS just does not inspire confidence on bends.

 

As you say, it is a good thing that we can change it so easily (I'll find out next week!), but a shame that we have to make changes...

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I think the ARB will help in terms of wallow but the skittishness you seem to describe is exactly what I had, particularly on adverse camber rough surfaces, and fixed it with stiffer lower control arm bushes (on the front). I remember nursing the damn thing around corners while other cars shot off into the distance - just embarrassing.

Edited by TsvRS
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Hunter alignment is all good, tyre inflation to spec.

re plate style trailing arm, I will check my theory by raising the car and loading the rear wheel aft and checking the trailing arm with a straight edge.

I'm pretty sure the wheel hub assembly can be twisted a degree or two, something I've never seen before and can't imagine is good for handling, the rears seem to flex outwards when loaded in a turn or when knocked by a bump which makes the car want to oversteer.

ie right hand curves, the steering is to the right, with provocation the rear left feels like it steers left.

I should point out that this isn't a constant feeling, it needs a bump or undulating surface at speed to appear.

It could well be worn bushes but as I said, I can't see/feel/hear anything untoward.

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Hunter alignment is all good, tyre inflation to spec.

 

Skoda spec for tyre pressures is something ridiculously low like 32F / 29R on 225/45r17.  That will make the car feel like a floaty boat.

 

I'm actually asking what specs your alignment guy set the car to so I can see what the angles might be influencing.  I was an alignment specialist for a long time.  Factory settings aren't necessarily good settings.

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All suspension requires a degree of compliance or very short travel.

The rubber/poly bushes allow the different elements - transverse, longitudinal and anywhere in between to describe their arcs as they pivot though suspension articulation. Otherwise they would just bind and lock the suspension.

Levering the hub, or any other part will always produce some movement as you compress or stretch the compliant bushes. The basic suspension design is pretty good, and can be made to be very good.

If your handling - how the car feels and roadholding - how it sticks to the road is as bad as you say, then maybe you should get it checked out properly.

It sounds as if either the settings are out or something else is amiss. Did you say what tyres you have? Other alterations from spec?

Find a proper suspension specialist who can look at what's there and see how or where it is wrong.

A guy with an expensive rig is not necessarily a suspension specialist.

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Skoda spec for tyre pressures is something ridiculously low like 32F / 29R on 225/45r17.  That will make the car feel like a floaty boat.

 

I'm actually asking what specs your alignment guy set the car to so I can see what the angles might be influencing.  I was an alignment specialist for a long time.  Factory settings aren't necessarily good settings.

 

Thank you. At last. Incredible how many believe that the Skoda spec is some sort of holy scripture.

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Thank you. At last. Incredible how many believe that the Skoda spec is some sort of holy scripture.

It's not just Skoda that stuff it up.  When I was on the tools (years back) I had my own settings for various Mercedes, Toyotas, Fords, etc and some were nothing like factory.  Mercedes used to be sent to Australia set up for Euro roads & would drift to the left down the road camber like a mofo - not sure if the UK got treated like that.

 

The biggest issue (IMO) is that the alignment settings are produced when the car is new.  When they get a bit of mileage, eveything settles a bit & gets a bit soft (springs, dampers, bushes, even the level of slop of bolts in a fitting) so you have to account for that.  A good aligner will look at how the tyres are wearing before doing anything else & adjust the geometry to suit.

 

edit:  It sounds to me like the vehicle in question might be running a bit too much toe-out at the rear but without all the settings I really can't say

Edited by brad1.8T
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  • 4 weeks later...

As the suspension bushes degrade over time - as they will - the suspension geometry will no longer be held in the correct relationship. 

The vehicle can be set up perfectly on a jig, but as soon as it moves the relationship between components can/may change if the bushes are unable to constrain the various forces.*

 

The rubber element of bushes is quite complex.  The properties will be degraded by oil/fuel spills, ozone and sunlight.  Not to mention wear from normal use.

Its a built in entropy. 

Replacing the most squidged, most heavily loaded bushes should help.

 

*My personal experience is extremely positive,  and not to devalue the use of a jig. 

In this case, the results could be considered of diagnostic value.   As ever, the experience of the operator is of greatest value.

They may be able to advise if you ask.

.

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My hope was to hear some advice on which particular component(s) caused this degradation of road handling without throwing cash I don't have at it, buying new bushes etc like they were going out of production.

As I said initially, there is no apparent excessive movement in the bushes but I am still thinking the hub is able to twist with provocation as can be seen by the plate style trailing arms bending when I exert force on the wheel with it on axle stands.

This has to affect things and give a rear wheel steering effect.

I am talking about twist at the hub which isn't able to be controlled by the various links and not general sloppiness of the suspension as a whole.

I will be looking deeper into this in due course.

@brad1.8T

I haven't uploaded a photo of my alignment specs due to tech issues but they are all within tolerance.

re tyre pressure

It's not a pressure issue I can assure you, I'm experienced enough to be able to tell when a tyre is wallowing from under inflation or overly sensitive to surfaces from being over inflated.

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The alignment maybe within tolerance of the settings stored on the machine, the other members would like to see the settings printout to establish what the machine vs. actual settings are. If the hunter rig has not been updated recently it could have old out of spec settings stored which although your now within tolerance are wrong. Skoda changed the rear alignment specification on the MK2 Octy following issues with sawtoothing rear tyres.

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As I mentioned before, the trailing arm does not see and is not designed to resist twisting forces at the hub.  It controls the longtitudinal location only.

In order for the suspension to work at all, there must be compliance, ie the bushes must allow a certain amount of movement.

So far you have failed to grasp how suspsion works and get narky when told otherwise.

If there is excess movement, then either something is broken or worn.  That will likely mean replacement of some parts. 

From this distance and with only a vague description of what is happ ening this is the best I can offer.

Ta Ta.

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M

@brad1.8T

I haven't uploaded a photo of my alignment specs due to tech issues but they are all within tolerance.

re tyre pressure

It's not a pressure issue I can assure you, I'm experienced enough to be able to tell when a tyre is wallowing from under inflation or overly sensitive to surfaces from being over inflated.

 

 

If you don't wish to listen I can't help you.  I've only done about 9000 alignments so I haven't a clue but a little hint: The specifications aren't always right and only sheep follow the book all the time. :notme:

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Where does it say I don't listen, don't grasp concepts and get narky? I'd say the opposite where preconceived ideas and experience blinker some to the possibilities of 'I've never seen that before'.

I am aware something needs replaced, just wanted to narrow the list down to the most likely candidate.

This is an open forum where we are free to express our views... Anyone would think I had demanded certain members for input.

As far as I'm concerned this thread is closed as it clearly isn't going well.

Thanks to all for reading and taking the time to offer input.

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