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I can recall seeing one. I remember thinking I should create my own little profile when I get a motor.

 

To answer your question, no, I haven't.

 

The reason for the heads up was the 811 i use have two entrance fields 1: tyre preservation 2: performance, in the performance field you can input raw data which i do for known settings i have used in the past..... My point is if you choose the same model of car in the same field the machine automatically uses the inputted fields as oem. Well that's fine assuming you remember you modified the data for that particular model of car.

 

"Modify" data is in the DSP800 somewhere, if you have a non oem car and input modified data the screen colors will be correct.

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I think that'll be useful in the future, or the rare occasion when people ask for specific settings, but in the mean time I dount I'll use that feature.

 

Anytime soon you will need to evolve your understanding of Geometry and suggest how to advance the calibration.

 

Remember the OEM data is just a suggestion, any modified car needs unique settings and you need to listen to what the owner wants from the car.

 

Let's say "hypothetically" the car is an OEM MX5 but the owner wants progressive over-steer from the chassis..... what do you do?

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Um, give them WIM's phone number ? :) I don't know.

 

Would it depend on the exisiting postions ? I don't know what to expect to see on an OEM MX5.

 

Presumeably I'd be looking to reduce absolute grip at the rear so a reduction of Camber to a more neutral figure seems logical. But then adding a couple of psi to the rear tyre pressures could achieve that ?

 

Shall we start from the top ?

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Tyre pressure manipulates the pneumatic slip angle and only effected by significant pressure changes.

 

By design all cars under-steer when yaw is exceeded, that way hopefully you are going to hit whatever your going to hit head on.

 

Since we know this is the case for oem cars then studying the raw data speaks volumes, our hypothetical MX5 is fully X, Y, Z adjustable, and has a near perfect DI @ 1.0.

 

Study this image.... ok it's an aircraft but the laws are fundamentally the same

post-2-1223149702.png

 

Our X,Y,Z is tuned to the tyres contact patch and encompasses similar forces, although not many pilots would appreciate weight transfer :)

 

Back to work...... Our car is RWD and within our contact patch we have graduated camber distortion, lateral toe and longitudinal thrust bias on the tyres fore/aft.... this excludes and inertia/transfer forces.

 

Ummmmm you might think?.. well no actually because if you look at the Geometry and then the respective forces acting at the tyres contact patch it's a easy call to reduce or increase a calibration position, thus forcing a change in the tyres saturation limits.

 

An aggressive change from the oem "under-steer" desire to over-steer would start with an aggressive angle, namely camber but.... where would you change this, front or rear?

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Well first thoughts are the rear as it's that axle which will see the most pronounced behavourial change but I'm thinking it's not that straight forward ?

 

I'm gonna plump for front as the whole process would be initiated by driver input ?

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Well first thoughts are the rear as it's that axle which will see the most pronounced behavourial change but I'm thinking it's not that straight forward ?

 

I'm gonna plump for front as the whole process would be initiated by driver input ?

 

For oem (domestic) you should have stuck with your "very good" instincts, the rear.

 

Progressive over-steer needs to be almost passive for the domestic car so small changes in the contact patch is all that's required.....

 

I would look at the actual live image.... look at the suggested data... listen to what the owner wants then decide where to manipulate the chassis...

 

Think what's going on dynamically during yaw at the tyres contact patch. The car is in transition so how can we dissolve traction and with what plane?.... well if the contact patch is to busy the tyre will saturate without warning so a small reduction in the vertical plane (an aggressive angle) vastly opens the limits for less aggressive planes like toe and thrust.

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I decided to take a look at OEM settings to see what the baseline would be

img012.jpg

 

I know the 'C has some issues but it's the only one I could recall the ride-hieight values!

Well first thoughts are the rear as it's that axle which will see the most pronounced behavourial change but I'm thinking it's not that straight forward ?

 

I'm gonna plump for front as the whole process would be initiated by driver input ?

 

For oem (domestic) you should have stuck with your "very good" instincts, the rear.

 

Progressive over-steer needs to be almost passive for the domestic car so small changes in the contact patch is all that's required.....

 

I would look at the actual live image.... look at the suggested data... listen to what the owner wants then decide where to manipulate the chassis...

 

 

Meh. If pushed I would have guessed camber but couldn't have told you why. :rolleyes:

 

..Think what's going on dynamically during yaw at the tyres contact patch. The car is in transition so how can we dissolve traction and with what plane?.... well if the contact patch is to busy the tyre will saturate without warning so a small reduction in the vertical plane (an aggressive angle) vastly opens the limits for less aggressive planes like toe and thrust.

 

Don't quite follow you here. By transition do you mean from understeer to oversteer ? What's actually happening to the tyre during transition ? I assume the tyre has to saturate in order for oversteer to occur ?

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"Transition" is an area you really need to work on in your evolution to fully understand what chassis dynamics means.

 

Transition is the pinnacle moment Geometry transits the suspensions articulation during yaw, allowing X,Y,Z to orbit fluidly... meaning during the articulation there is specific changes in the values maintaining the tyres contact patch.

 

We have already explored how the camber/ castor migrates, well in this example we also have weight transfer acting on that migration.

 

Let's assume our imaginary car has -30' camber on each front wheel, what happens to that on a turn?.... we are turning "left".

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Slightly off-topic but I discovered Hunter's VideoTech movies and spent most of sunday and monday morning going through them. Some cool stuff in there, including toot and tips on how to interept the angles to find bent/damaged components. ;)

 

"Transition" is an area you really need to work on in your evolution to fully understand what chassis dynamics means.

 

Transition is the pinnacle moment Geometry transits the suspensions articulation during yaw, allowing X,Y,Z to orbit fluidly... meaning during the articulation there is specific changes in the values maintaining the tyres contact patch.

 

I can't quite follow you here. Could you rephrase "..Geometry transits the suspensions articulation during yaw.." please ? :rolleyes:

 

We have already explored how the camber/ castor migrates, well in this example we also have weight transfer acting on that migration.

 

Let's assume our imaginary car has -30' camber on each front wheel, what happens to that on a turn?.... we are turning "left".

 

Well we've established the inner wheel moves toward positive camber and reduced castor, while the outer wheel sees additional castor and moves toward increased negative camber. I'd expect the weight transfer to emphasize the geometry movements.

 

:D

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You have a fair understanding what each angle does but you need to learn how to customise a cars set-up..

 

The quote "..Geometry transits the suspensions articulation during yaw.." means your understanding needs to visualise how the Geometry changes during steering/ bump and transfer.

 

Example

Setting a 5 for track days i would set the rear cambers deep, plenty of toe in, the front cambers 2/3 of the rear, the castors long with minimal toe in.

 

Then test the positions static?

 

With the front data visible on the screen i would pull the rear down to simulate "squat" and watch the castor gains, then i would pull the front down to simulate "submarining" and watch the camber/toe migrations.

 

Finally i would turn the steering and watch how fluid the camber/ castor swaps values, this exchange should be surgical.

 

On a turn the inner wheel gains castor and the outer loses it by the way.

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Would a lot of castor produce some under-steer ? edit:- actually, probably not a bad thing for driving at 10/10ths ?

 

I have a fair idea how camber and castor can impact upon a car's behaviour but, beyound thrust angle, how does toe work ? For a quick experiment I used the factory NC numbers on an NB MX5 in Forxa but accidentally set toe to +6.0, as apposed to .6, and it was super-oversteery. Fun, but impossible to put down a fast time.

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Most times more castor will generate over-steer with rapid steering actions....

 

Toe owns a static position that suggests once the car in in motion the play/ compliance in the bushings will allow a zero toe.

 

If you aggressively move the static toe to retain a positive dynamic position then (for the front) the road is approaching the tyre laterally from the outside in.... this suggests a "ready in" turn position for the tyre.

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Well done for the castor check.... what adjustments did you make at the rear?

See for yourself ;)

 

R32Golf.jpg

-Owner stated no mods (well, save for a Turbo) but seems odd Castor would be beyond OEM but also identical ?

 

Did a latemodel Subaru today

 

SubaruLegacyOutback.jpg

-Wasn't sure what to make of that SAI ?

Really nice car. That Subaru 3.0 flat-6 is a gem.

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On the Golf did the program ask for fuel or added weight and did you respect that if it did?

 

As for the Scoob the IA suggests a bend or past adjustment around the strut area.... In truth the difference between the ns&os is to small to worry about.

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On the Golf did the program ask for fuel or added weight and did you respect that if it did?

 

As for the Scoob the IA suggests a bend or past adjustment around the strut area.... In truth the difference between the ns&os is to small to worry about.

 

I can't remember now TBH but I do respect such things nowadays.

 

Th scooby seemed odd as no other angles displayed any major issues, though IA is nearly a full degree different. Maybe a minor strut top mount issue ?

I was going to check my notes (most of the techie stuff from the home page) but they were at home! IIRC an inconsisent IA points toward a bend somewhere in the sprung chassis doesn't it ?

Not an issue I know, I was just curious.

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Latest:-

 

Polo14-10-08.jpg

 

Came in after kerbing the N/S/F. A bent stering arm was replaced but the O/S/F displayed some serious geo issues. The O/S/F lowerlink (wishbone) bushes were found to be knackered.

I've been trying to figure out where the issue is. The bushes were clearly responsable for atleast some of the deviance as a few minutes castor movement was observed on-screen (in real time).

What would account for such a large IA and castor deviance though ? Could the wishbone be bent too ?

 

I've managed to have two definitions of IA in my notes. From WIMs front page:

 

Example

Specified Values Observed Values

Wheel camber +2 deg +1 deg (less than spec,)

Kingpin inclination 6 deg 7 deg (more than spec,)

Included angle ( +2 deg 6 deg ) = 8 deg 8 deg = constant

In this case, the likely deformation, or irregular positioning of the parts, will be related to either the suspension arms or the suspension arm mounts, in this case the kingpin and the wheel hub positioning has not changed,

If, on the other hand, the following measurements are observed,

Wheel camber +1 deg

Kingpin inclination 6 deg

Included angle 7 deg = inconstant

Then there is a deformation in the kingpin-hub assembly

 

and the other, I think from the forum:

 

The IA is used as a diagnostic tool to determine if there's a bend in the chassis or suspensions sub components. As you should know the IA is the SAI + or - the cambers + or - position.

 

For Example:

NSF

Camber -30

SAI 11d

IA 10d 30'

 

OSF

Camber -1d

SAI 10d 30'

IA 9d 30'

 

And the data said the osf camber was out of tolerance then it's a fair bet the bend is within the un-sprung chassis namely the wishbone. If the IA was even but the camber still outside of OEM positions then the bend would be in the sprung chassis.

 

The two appear to contradict. Presumeably, if the wishbone was bent the Camber and KPI would be evenly affected and IA would be consistant ?

We've got the car untill sometime tomorrow and I'd like to advise the customer where in the suspension the rig indicates damage.

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The confusion between the two examples is due to the cambers starting position (positive-negative) in the case of your example it's best we stick with the latter.

 

I don't think you've been given the full picture regarding this cars impact!..... So before any conclusion can be assessed you need to adjust the OSF camber, replace the steering arm/worn bushings and measure again.

 

Also measure "symmetry and set back" from the "make additional measurements" prompt.

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The confusion between the two examples is due to the cambers starting position (positive-negative) in the case of your example it's best we stick with the latter.

 

I don't think you've been given the full picture regarding this cars impact!..... So before any conclusion can be assessed you need to adjust the OSF camber, replace the steering arm/worn bushings and measure again.

 

Also measure "symmetry and set back" from the "make additional measurements" prompt.

 

Ah, I hadn't noticed the positive-negative. So, looks like the wishbone/mounts may be to blame.

 

It doesn't have dedicated camber adjusters, just some movement in the upper wishbone-to-strut link. I'm not expecting much movement (~4/5') and when I tired to free-off the bolts prior they were hella stiff. Either way, seems mute untill the bushes are replaced.

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