CIH's Training Thread

[Tony]

DSP600

 

On the DSP600 you have to do a castor swing (20 degrees) this swing acquires the secondary angles but it's not displayed on the main screen unless prompted.

 

Ackerman and TOOT are the same thing just different terminology.... what understanding do you have of either?

[CIH]

DSP600

 

On the DSP600 you have to do a castor swing (20 degrees) this swing acquires the secondary angles but it's not displayed on the main screen unless prompted.

 

Ackerman and TOOT are the same thing just different terminology.... what understanding do you have of either?

 

I can't recall any options to view toot using the usual tabs ?

 

As for TOOT/Ackerman, I only understand so much as I understand it's a similar reason a car requires a diff. That is, the outer wheels travel a larger distance, and a different arc, when negotiating a given corner.

[Tony]

DSP600

 

On the DSP600 you have to do a castor swing (20 degrees) this swing acquires the secondary angles but it's not displayed on the main screen unless prompted.

 

Ackerman and TOOT are the same thing just different terminology.... what understanding do you have of either?

 

I can't recall any options to view toot using the usual tabs ?

 

As for TOOT/Ackerman, I only understand so much as I understand it's a similar reason a car requires a diff. That is, the outer wheels travel a larger distance, and a different arc, when negotiating a given corner.

 

Ok on your system it will be in "make additional measurements" then pull down the options and click "Toe-Out-On-Turns".

[Tony]

Before i can explain TOOT's dynamic influence i need to know if you read and understood this thread> http://www.wheels-inmotion.co.uk/forum/ind...t=0&start=0

[CIH]

Before i can explain TOOT's dynamic influence i need to know if you read and understood this thread> http://www.wheels-inmotion.co.uk/forum/ind...t=0&start=0

 

I think I can see where this is going but there's no point I'd like to clarify.

Am I correct in thinking that hard cornering, and the associated shifting of the vehicle's weight, will impact on camber ?

Ie; as the inner wheel moves to an unloaded state, as the weight of the car shifts against the direction of the turn, the inner wheel will move toward positive camber and the outer wheel, under load, shifts toward negative camber ?

I assume SAI won't change significally, save for any give in the rubber components ?

 

So, Scrub Radius (SR) is the actual point of contact between vehicle and tarmac. This is determined where Camber and SAI angles meet. When the wheels are at the straight ahead this should be at the centre of the tyre tread.

The SR will migrate across the tread during cornering, due to (or in part to) dynamic changes in camber.

 

Am I correct so far ?

[Tony]

Before i can explain TOOT's dynamic influence i need to know if you read and understood this thread> http://www.wheels-inmotion.co.uk/forum/ind...t=0&start=0

 

I think I can see where this is going but there's no point I'd like to clarify.

Am I correct in thinking that hard cornering, and the associated shifting of the vehicle's weight, will impact on camber ?

Ie; as the inner wheel moves to an unloaded state, as the weight of the car shifts against the direction of the turn, the inner wheel will move toward positive camber and the outer wheel, under load, shifts toward negative camber ?

I assume SAI won't change significally, save for any give in the rubber components ?

 

So, Scrub Radius (SR) is the actual point of contact between vehicle and tarmac. This is determined where Camber and SAI angles meet. When the wheels are at the straight ahead this should be at the centre of the tyre tread.

The SR will migrate across the tread during cornering, due to (or in part to) dynamic changes in camber.

 

Am I correct so far ?

 

Your on the right track although weight transfer is not the area i want to cover just yet, we'll do that when we move to the dynamics part of the training.

 

What we are going to do now is turn left in a modern car with negative camber/ positive castor/ mcpherson suspension.

 

With the steering dead ahead we have..for simplicity

Camber -30

Castor 4d

SAI 6d

TOOT 0

 

Our turn now has the outer wheel on a 20 degree lock, Geometrically we now have

NSF

Camber +30

Castor 7d

SAI 4d

TOOT 21.5d

 

OSF

Camber -1d

Castor 1d

SAI 8d

TOOT 20d

 

The NSF sprung corner has lowered and the OSF sprung corner has raised. The NSF SR has migrated inboard and the OSF SR has migrated outboard.

 

This entire series of transitions is determined by the castor position and the rotation of the TOOT initiator albeit the shape of the track-rod-end or the hub moving toward the centre of the inner wheels steer axis.

 

An example of poor design where the TOOT and castor don't work in harmony is the Ford Galaxy, often you will see tyre wear in the sidewall of the NSF tyre, this is due to the TOOT/ Castor rolling the camber to far positive. The reason it's just the NSF is that to turn right you don't need so much lock, so there's less rollover.

[CIH]

I'm reduced to using Forza, and it's Replay Telemetry, while I'm at home but with steering on full lock, camber was diametricaly opposed.

 

Is that true of SAI and toot ? ie, the figures obseved with the steering in one direction should be consistant with the other direction ("mirrored"). Unless you were looking at a Galaxy, that is.

 

Is this a similar situation to Included Angle in that you're looking not for specific figures but for consistency acros the axle ?

[Tony]

I'm reduced to using Forza, and it's Replay Telemetry, while I'm at home but with steering on full lock, camber was diametricaly opposed.

 

Is that true of SAI and toot ? ie, the figures obseved with the steering in one direction should be consistant with the other direction ("mirrored"). Unless you were looking at a Galaxy, that is.

 

Is this a similar situation to Included Angle in that you're looking not for specific figures but for consistency acros the axle ?

 

Yes very much so....

 

Since Yaw is a collective state it's the migration that matters and uniformity of the values left and right, there will always be disparities on each lock due to the tolerances allowed, but how much?

 

So what do we know?.... well subject to a bend TOOT is a constant value with a globally recognised point for measurement at 10 or 20 degrees, SAI is just an angle with no globally recognized disparity and you cannot see it's migration, camber you can see migrate and it's initiation is castor/ toot.

 

Two points to absorb at this stage?

1: Once you deviate from DAH (Dead-A-Head) your on your own?.... All the data fields you see on the screen are up to you to analyze, no book, dvd, vid will answer your questions or tell you what your looking at or looking for..... It's at this point you answer your own questions by looking at the values and by observation imagine the forces consequence at that particular time in the chassis position.

 

2: We are not mechanical engineers?..... I wasted a lot of time trying to understand the design of the chassis and it's pii this and tan that.... it's not our field. Our field is to mop up after the designers have finished or to advance the chassis to compliment the design, but not the actual design.

 

Saying that though the forces within Geometry are a constant all that differs is how much, so writing a ground up calibration is something i do everyday, i hope that makes sense.

[CIH]

With the changes in castor the SR moves on the longitudinal axis travel too ?

 

I never would have guessed so much movement with a simple steering wheel input but it seeems obvious now.

[Tony]

With the changes in castor the SR moves on the longitudinal axis travel too ?

 

I never would have guessed so much movement with a simple steering wheel input but it seeems obvious now.

 

No the SR migrates (mid point) in-out depending on yaw, plus longitudinal mechanical trial, pneumatic trial is another topic.

 

What i want you to do when your back at work is measure the car as normal then turn the steering "about 20d" and observe what's going on lock-on-lock. Also with a PAS car (on solid ground) turn the steering left/ right and watch how the bonnet occilates up/ down?

 

What's happening and why?

[CIH]

No alignments done today but I did get to see some bonnet movement. Much more pronounced on German Cars, Mercedes Benz especially.

[Tony]

No alignments done today but I did get to see some bonnet movement. Much more pronounced on German Cars, Mercedes Benz especially.

 

Why do you think that is?

[CIH]

First I should probably clarify what I actually saw. With the car stationary, turing to the right, the bonnet would appear to drop to the left and rise to the right, before levelling out with the wheel at straight ahead. Turing to the left, the opposite would happen. As if the car were leaning against the "turn".

Cars I played with were: Renault Clio 2 (No movement to speak of), original & later Ford Focus' (subtle shifting), early Audi A3 & later A6 (pronounced shifting) & M/Benz C Class SportCoupe/Hatchback/Thing (sea sickness).

 

My impression is the bigger castor angles I'm use to seeing on Benz means a more pronounced impact on camber and the shifting of SR across the tyre.

The only reason for the bonnet to move is the spring being compressed which indicates camber "activity".

I figure they use a bigger castor and less camber to aid directional stability when doing high speeds down the autobahn, with the extra castor helping the SR shift and thus aid cornering.

 

Uh, how am I doing ?

 

On a similar issue, when I was playing Forza I tried -1.5 camber on the front which helped in the twistys but meant the car "felt" nervous doing high speed cornering and especially under braking.

[Tony]

Your doing just fine.

 

On the MB they have a very long castor, reasonable camber and a very declined SAI, normally around the 10d mark.

 

At speed the MB depends on the castor trail rather than the SAI for directional stability, although this trail is being reduced with the advent of EPS.

 

On lock there's a "steady state" migration of the SR with a long very deep castor gain on the inner wheel (you should test that) but due to the camber migration (remember toot/ castor marriage) the inner positive camber gain is extorshinate hence the need for lock-stops.

 

Statically any move up/ down of the bonnet has nothing to do with the coils loading lock-on-lock, all they are doing is transmitting the castor sweep and KPI/SAI inclination/ declination, there's no actual change in the coils loading.

[CIH]

I bet Mercedes react especially badly to ill-considered modification.

[Tony]

I bet Mercedes react especially badly to ill-considered modification.

 

Leave it to AMG or spend you entire career studying Merc dynamics, they are a law unto themselves.

[CIH]

Okay, had a late model 525i on the rig today and had a play. I found SAI and IA though they weren't viewable as bar graphs, just in the initial readings screen (immediatly after compensation and castor sweep). They were displayed wiothin a green ("correct") or red ("incorrect") boxes. Can they not be viewed as a graph so I can see how far they are from spec ? If both were out of spec I'd have no idea how far.

 

Do you remember telling me I could shut down targets ? Where would this option be ? It was really annoying as I was trying to study Castor, SAI and Camber behaviour on turn I was loosing the screen as I would occasionally get in the way of the rear targets.

 

The other issue was I couldn't tell how much lock I was applying. I assume the best way is to view steer ahead so I know when I'm at 0, 10 and 20 degrees but then I can't see any of the seconday angles ie; SAI and IA.

 

This perticular car showed a 1 dgree disparity in Castor and SAI but included angle was just a few minutes out of sync. The tyres showed what I saw as camber wear on the outer edges. Straight ahead they were within spec so am I right in thinking it was during steering events when they were wearing ? Eitherway, I dialled in some more neg. camber to be bring it closer to spec.

 

On last thing. I wasn't really sure what we can extract from on-turn figures that we don't see from straight ahead.

Though, when I think about it, if I were looking to adjust how the car behaves I suppose on-turn figures are more important if anything. Try to remember I've always been taught to simply set to spec and not really think about what the car would actually do. Also remember you're average Fast-Fit customer isn't interested in over-under-steer but more if the car is "right" and, as is, I only have OEM to go off.

 

ps: Cookie beer FTW!

[Tony]

To view SAI IA you select bars then on the right hand side tools bar select "show all angles". Both angles are acquired at 10 or 20 degrees depending on your settings, unfortunately they cannot be view live.

 

Most time there won't be any EOM data for SAI IA since they are just angles, not neg or poss. Additionally these are used for diagnostics and the most common reason for the SAI to be wrong is coil sag.

 

The reason the IA was close must have been due the a camber disparity? and the fact you dialed more neg camber shows you are looking outside of the box.

 

TOOT is acquired from "make additional measurements", it's done on a full lock L+R and also gathers the lock angles, if the TOOT is not reasonably symmetrical then check if the castor position is off and them "symmetry and set-back" from make additional measurements then analise if the issue is the steering or a castor/set-back issue.

 

A simple live test is to have "steer ahead 0" then while on virtual view turn the steering wheel about 45d and compare the inners wheels camber/castor migration lock on lock.

 

While on virtual or bar view if you click the spanner icon that's next to each measurement you will see in the drop down menu "block one rear reflector"... problem is it's only one rear reflector.

[CIH]

Okay, thanks for that. I'll have another play around next time I get a car on the rig. A workbuddy keeps pecking to get his A6 in so that will be a good opportunity, presuming we get a quiet period. He complains of a very very slight pull but no unusual tyre wear. I'm thinking it's phumatic but I'm not going to throw away a chance to chuck a car on the Hunter.

 

Positions offered by the manufacturer are nothing more than suggestions!... excepting something is wrong then self-analyzing a solution is nothing more than healthy (good for you).... chassis dynamics even in the raw needs much dynamic thought.

 

An area i drum into students is do not look at the colors or the numbers displayed, look at the forces displayed?

 

Every position represents a static force, then a dynamic force... all angles swap their forces dynamically to induce some form of stability.... if you loss one force what! is the dynamic consequence? often the reply is .... so there is a real need to understand exactly what each angle represents before you can theorise dynamic Geometry with accuracy...

 

 

I noticed this when searching for DI threads. Perhaps, given all of my preconceptions have been shot-down, you could elaberate (once we're done with the current discussion) ?

[Tony]

Okay, thanks for that. I'll have another play around next time I get a car on the rig. A workbuddy keeps pecking to get his A6 in so that will be a good opportunity, presuming we get a quiet period. He complains of a very very slight pull but no unusual tyre wear. I'm thinking it's phumatic but I'm not going to throw away a chance to chuck a car on the Hunter.

 

Positions offered by the manufacturer are nothing more than suggestions!... excepting something is wrong then self-analyzing a solution is nothing more than healthy (good for you).... chassis dynamics even in the raw needs much dynamic thought.

 

An area i drum into students is do not look at the colors or the numbers displayed, look at the forces displayed?

 

Every position represents a static force, then a dynamic force... all angles swap their forces dynamically to induce some form of stability.... if you loss one force what! is the dynamic consequence? often the reply is .... so there is a real need to understand exactly what each angle represents before you can theorise dynamic Geometry with accuracy...

 

 

I noticed this when searching for DI threads. Perhaps, given all of my preconceptions have been shot-down, you could elaberate (once we're done with the current discussion) ?

 

What area of your preconceptions did that post shoot?

[CIH]

Okay, thanks for that. I'll have another play around next time I get a car on the rig. A workbuddy keeps pecking to get his A6 in so that will be a good opportunity, presuming we get a quiet period. He complains of a very very slight pull but no unusual tyre wear. I'm thinking it's phumatic but I'm not going to throw away a chance to chuck a car on the Hunter.

 

Positions offered by the manufacturer are nothing more than suggestions!... excepting something is wrong then self-analyzing a solution is nothing more than healthy (good for you).... chassis dynamics even in the raw needs much dynamic thought.

 

An area i drum into students is do not look at the colors or the numbers displayed, look at the forces displayed?

 

Every position represents a static force, then a dynamic force... all angles swap their forces dynamically to induce some form of stability.... if you loss one force what! is the dynamic consequence? often the reply is .... so there is a real need to understand exactly what each angle represents before you can theorise dynamic Geometry with accuracy...

 

 

I noticed this when searching for DI threads. Perhaps, given all of my preconceptions have been shot-down, you could elaberate (once we're done with the current discussion) ?

 

What area of your preconceptions did that post shoot?

 

Not that post specifically, just well, pretty much everything since I joined WIM really....

[Tony]

@CamInHead

 

Try not to be disheartened, i did warn you the field of chassis calibration is much wider then the furrow KF lead their staff to believe.

 

The fact you have absorbed and questioned various topics already is a credit to yourself, not just in understanding the topic but the fact you question the topic at all and that shows you have the drive to learn.

 

Chassis calibration is all i have ever done, sometimes i forget to slow down and really answer a question efficiently, if i don't "say so!"

 

I do think we are going to fast and to deep with your training.... Getting an overview of the overall picture is hardly the full package.

 

Let's perfect your current situation.... Your in FF, you certainly have a desire to perfect your position so in your current position what grey areas would be best filled?

[CIH]

Hmm, perhaps I should have put a smiley in that last post...

Please, don't take my words the wrong way. I'm not dishartened at all have thoroughly enjoyed what we're doing here.

Also, don't worry. I'm not afraid to chirp-up if I'm getting stuck and I certainly don't mind having preconceptions corrected.

I want to keep going.

 

Besides, I (quietly) harbour some serious disdain for the way FF works nowadays. Breaks the heart to see a tracking sold on the basis of what could only ever be excessive-camber wear, or sending out a car uncorrected because there's no factory adjustment and FF aren't interested in aftermarket corrective parts.

 

I'd love to get into the aftermarket trade and do this full-time.

[Tony]

I'm sure you will because you enjoy something most in FF avoid.

 

The mention of "Geometry" leaves most in FF reeling like a worm in bleach and that includes the manager but the few that excel in this field are prized possessions, more so for the independent trader to be honest.

[CIH]

Something I don't quite understand is what do we see in TOOT that we can't see with steering at dead-ahead (DA) ?

Presumeably any bends or play would be evedent at DA ?

 

Also, back to the original questions I put up, can we cover rolling-radius ?

 

 

oh I nearly forgot! Any advice as to how to accurately measure ride-height without the Hunter power tools kit ?

So far I've just offered up a tape measure and done it by eye.