CIH's Training Thread

[Tony]

Lets sat a car hit the nsf on a curb and the toe is 50' wrong, that's nearly 5mm, would you agree something is bent?, could you see a bend, probably not so most tech's would just correct the toe.

 

Since it's the DA your trying to maintain then by correcting the toe you have ignored the fact that the bend is in the steering mechanism, but where?

 

Even with a perfect DA the toot will prove the bend exists in the steering arm, track rod end or hub since it's one of those parts on all cars that activates toot.

 

An incorrect toot will wear the one tyre regardless of the toe position.

 

RR is the distance any given tyre makes per revolution, the tyres aspect ratio would change the radius..... The topic is more applicable to tyre fitment than chassis calibration.

 

In the absence of "live ride height targets" a tape measure is just fine.... It just means the trim position is only relevant to the unsprung chassis.

[CIH]

So correcting toe @ DA won't necessarily put the wheels in the correct position for TOOT ?

By extension, the only way to correct inconsitent TOOT would be part(s) replacement ie; steering arms, TREs, wheel hub etc ?

 

I was thinking about how to track down which part was bent but, if I understand correctly, an inconsistent Included Angle would indicate the Hub. Though, if IA were consistant across the axle, it would indicate not the hub assembly but TRE or Steering Arm.

So, in the case of the former, TOOT could also help confirm what IA indicates ie; wheel hub deformity.

 

Finally, let's say both camber, and by action IA, and toe @ DA were corrected but TOOT was still incosistent lock to lock. Then the customer should be advised of wheel hub deformity and if severe enough (say, > 1.5 ?) replacement advised ?

Otherwise tyre wear similar in appearance to Toe would result ?

 

Oh that reminds me, I would appreciate with some help with the math regarding lateral scrub but I think that's enough for today.

[Tony]

DA has nothing to do with toot..... Lets stay with this one for the moment.

 

We can use a simple axes X, Y, Z to formulate a position in space... left-right, up-down, fore-aft.

 

We could also use X,Y,Y or six combinations all describing a particular axes.

 

In the case of DA it's line of sight is Z,Z.. toot is X,Z..... both examples would use Y (SAI) in this case, but Y serves no interest to us.

 

TOOT is not adjustable, it's a fixed angle so if wrong conclusively proves a steering component that orbits X is damaged.

 

XYZ= line of sight.

[CIH]

Um, let me try to rephrase.

 

An incorrect toe angle has no bearing on TOOT ? But, if the angle of the wheels were incorrect @ DA would this not skew the TOOT result ?

 

Or, because of the shape of the TOOT initiator (either TRE or Hub) then any problems with toe @ DA are negated as soon as any steering lock is applied ?

 

I understand toe @ DA and TOOT are two different issues. I'm trying to understand if there is any interplay between the two.

[Tony]

Um, let me try to rephrase.

 

An incorrect toe angle has no bearing on TOOT ? But, if the angle of the wheels were incorrect @ DA would this not skew the TOOT result ?

 

Or, because of the shape of the TOOT initiator (either TRE or Hub) then any problems with toe @ DA are negated as soon as any steering lock is applied ?

 

I understand toe @ DA and TOOT are two different issues. I'm trying to understand if there is any interplay between the two.

 

Your getting there...

 

DA is the analysis of toe and the steering position, nothing more.

 

TOOT is an accentuated angle and cannot even be measured accurately until the wheels are turned 20 degrees, it's manufactured design is to allow the inner wheels steering mechanism to move toward that wheels centre and by doing so accentuate that wheels lock.

 

This image that i borrowed explains a little but it's actually flawed!!..... can you see why?

[CIH]

Looks like the steered wheels are turning through a parallel arc. In that picture, there is no TOOT as such.

 

Don't want to stray off track but can I have your advice on this Alignment I had in today please:

 

BMW E93 ('07) 325D CoupeCabriolet:

 

 

Came in for brake work but it was noted the front tyre outer tread area displayed heavier wear than the central tread. Feathered wear, nothing violent.

The SAI out of spec suggests to me the SR can't migrate across the tyre correctly but 2 problems. I didn't have an OEM spec castor figure from the database and, because I only had a number and a colour (red), I had no idea whether SAI was too far positive or negative. I thought I could move camber to compensate but didn't have enough info to make confident adjustments. In the end I adjusted the back end to be symmetrical and advised the rig indicated problems with the front suspension, possibily the suspension arms.

The N/S/F (left) ride-height was a few mm or so away from O/S/F (about 6/7 IIRC). No clear signs of anything bent, broken, impacted etc.

[Tony]

Good to see you are using the secondary angles.....

 

A few points..... Did you add weight to the car?

 

The SAI is just an angle and never positive or negative but it's involvement with the IA will determine a + - position depending if the lines interact above or below the tyres contact patch.

 

You are correct to assume the camber needed adjustment but the weights if needed are vital!!.

 

Off topic slightly your Hunter is it the DSP600?

 

And did you think about the question i asked you about this>

 

What's wrong about this example?

[CIH]

Good to see you are using the secondary angles.....

 

A few points..... Did you add weight to the car?

 

The SAI is just an angle and never positive or negative but it's involvement with the IA will determine a + - position depending if the lines interact above or below the tyres contact patch.

 

You are correct to assume the camber needed adjustment but the weights if needed are vital!!.

 

Off topic slightly your Hunter is it the DSP600?

 

And did you think about the question i asked you about this>

 

What's wrong about this example?

 

In your picture, looks like the steered wheels are turning through a parallel arc. In that picture, there is no TOOT as such.

 

Yes DSP600.

So that's why I can't find an SAI bargraph huh ?

The BMW had the weights in. Is the specific positioning important ? In the nearside, I had two on passenger seat and two in the foot well. Offside, one in foot well and 3 on the seat so as not to block brake pedal depresser and steering-wheel clamp.

[Tony]

I didn't expect you to answer the question correctly but i did want you to think about it and you have.

 

The toot is an accentuated angle that we capture as a measurement at 10 or 20 degrees, well great but there is a law attached to toot.

 

You know the radius of each wheel on a turn is different, for the toot to work correctly the angle (lock) of the inner front wheel (with toot) will by steering in degrees project the same radii arc to the absolute rear thrust.

 

Or in other words... If the inner wheel is turned 10 degrees then a 10 degree arc must intersect a zero thrust. So in essence you have one actual pivotal point (the front) and one imaginary pivotal point (the thrust)

 

If the toot is correct all four wheels will assume the correct radii on that given turn at that given lock (accentuated)

 

So in that image the toot missed the thrust so as an example it's wrong

[CIH]

So once TOOT is initiated, the arc of the inner wheel needs to intersect with our imaginary rear thrust pivot point ?

So how should that image be adjusted to be correct ?

I understand the concept but I'm struggling to visualise it.

[Tony]

TOOT begins as soon as you deviate from DA but it's not discernible to us until around 10 degrees.

 

For correct handling the inner wheels deviation from DA, lets say 10 degrees will extend a 10 degree curve to the expected zero thrust angle. This makes the thrust angle an imaginary pivotal point allowing the car to corner correctly.

 

It's for this reason the machine prompts you to correct the thrust before you attempt any corrections at the front. it's also for this reason the image i displayed is wrong or the TOOT is wrong

[CIH]

TOOT begins as soon as you deviate from DA but it's not discernible to us until around 10 degrees.

 

For correct handling the inner wheels deviation from DA, lets say 10 degrees will extend a 10 degree curve to the expected zero thrust angle. This makes the thrust angle an imaginary pivotal point allowing the car to corner correctly.

 

It's for this reason the machine prompts you to correct the thrust before you attempt any corrections at the front. it's also for this reason the image i displayed is wrong or the TOOT is wrong

 

 

If everything is correct, once TOOT is effective the angle of the inner steered wheel actually defines the thrust angle heading ?

[Tony]

Yes.... If the inner wheels toot does correlate then the other three wheels turning radius is correct.

[CIH]

I had never even thought about Thrust Angle in that context.

So is that why TOOT is required ? To ensure correct Thrust Angle deviation ? Or are there other benefits too ?

Also, does the outer (steered) wheel display any special infulence/behviour ? Or is it simply passive ?

[Tony]

Toot is to ensure each wheel can turn without dragging or pulling the front tyres at that particular lock angle... On measuring the outer wheel is used for reference on driving it is a passenger as are the other wheels on their radii.

 

Performance on a lock = toot value + it's location at thrust, if the car is expected to corner well then the toot angle by degrees needs to meet a 0 thrust.

 

Lets assume we have a perfect front calibration but the thrust is 30' +-..... How would you expect the car to turn left or right?

[CIH]

Well I'd expect the car to feel "lazy" turning against the thrust ie; to the right but I read in the technical theory areas that the car would only be sensertive to the thrust factor beyond 30'. Or is that just @ DA ?

 

Slightly off-topic but I had a tough day today. Had an E46 come-in. As usual the customer had left the car and the damn supervisor hadn't asked any meaningful questions ("just wants it doing, oh it pulls to the left"). It had been to a garage earlier that day and had bushes, ball joints etc checked. Anyway, lined her up and spent ages fighting the camber as it just wouldn't stay-put. Car comes back about 10 minutes later apparantly just the same. Got to speak to the fella and had a test drive. Car was pulling and you could feel the car shift when applying any steering action to the left. Turned out bottom ball joints had play and the wishbone compliance bush on the N/S/F was shagged. So, lessons learned:

1) Don't take anyone's word for anything and do the checks yourself

2) If the tyres look fine then it probably isn't geometry (that is right, isn't it ?)

3) Don't let idiots make you rush

 

One other thing too. Had a late model Astra SRi in. Tried to do front camber with the axle lifted and only managed about 0.20 improvement. Locked it in place, lowered the jack (following the on-screen prompts) and the camber had shifted to spec (about 0.60 total movement). This isn't the first time camber has shifted like that. Any ideas where I may be going wrong as it totally undermines any confidence I have in the adjustments ?

[Tony]

Your correct, on one lock the car will over-steer and the other lock it will under-steer. Our realm regarding thrust limits is 12' max, recently this has been moved to 30' but we desire 0.

 

The "jack and adjust" problem is tricky.... i suggest you check the positions then check if they have changed after the lift? i find sometimes the cameras miss part of the lift between the infrareds flickering.

 

Get yourself into a routine regarding the inspection, it only takes a minute or two ands pretty much the same on all cars.

 

Never trust the tyre to talk to you.... you have no idea of it's history, anything could have happened to it in the past? so unless the owner can convince you it was ok before and now it's worn ignore it.

 

When i was working fast-fit i would ask the manager "what's the complaint" and he would say "your the expert you tell me?"

 

Well that's not right.... Even the best Harley street doctors need to now the complaint!!... the chassis is to complex so we work best if given a clue.... spend loads of time with the chassis we would identify the complaint but isn't the manager keen to be rid of the car asap ready for the next?

 

Another area that goes against the grain.... i rarely drive the car in advance of a calibration?..... i don't know the car, so i could read all manner of things about it..... additionally i don't drive any of the track cars for two reasons

 

1: I don't race

2: I could set my own standards

[CIH]

Had a better day today. This time, I set toe before the camber lift, then readjusted toe. Seemed to go much smoother. Wouldn't have been do-able without the lift so I'm glad we perservered with it.

 

 

Put a workbuddy's A6 on the rig too. Beam suspension on the rear. :angry:

 

Told him it was just like a big Fiesta ha ha

[Tony]

Good work :angry: ..... As a heads up regarding "I beam's" most times there is thrust adjustment if you release all the mount points.

[CIH]

Good work :angry: ..... As a heads up regarding "I beam's" most times there is thrust adjustment if you release all the mount points.

 

Yeah that was in the Illustrate Adjustments tab but we only had about 20 minutes. I haven't tried it before and didn't fancy experimenting so late in the day.

Is that true of most beams ? Never seen the option except in the case of this A6.

[Tony]

Good work :angry: ..... As a heads up regarding "I beam's" most times there is thrust adjustment if you release all the mount points.

 

Yeah that was in the Illustrate Adjustments tab but we only had about 20 minutes. I haven't tried it before and didn't fancy experimenting so late in the day.

Is that true of most beams ? Never seen the option except in the case of this A6.

 

Yep most beams..... If you release the ramp bed so the rear is floating then undo the chassis bolts each side you can shunt the beam.

[CIH]

I'm wondering what implications there are regarding Thrust Angle using such adjustment.

 

If there is no individual toe adjustment then how can TA be corrected ?

 

oh and thanks for the praise btw.

 

edit: I also spotted how to switch between Thrust Angle ALignment, Total 4 wheel Alignment etc. I had always assumed Hunter defaulted to whatever applied to the specific car/set-up.

[Tony]

Improve the TA with the shunt.... if your / / and shunt \ \ with a loose beam you may end up with | |.

 

Thrust and FW needs manually setting, it's a pain in the arse really.... Another heads up, do you input modified car data?

[CIH]

How do you mean ?

[Tony]

How do you mean ?

 

Undo the bolts that hold the beam to the body and "push/ pull" the beam in whatever direction will help the TA... if it only moves 5' then it's an adjustment for the better.