For debate#2

[Tony]

This time a bit different and a bit harder but 'hay' this is a Geometry forum..... From this report can you extrapolate what is the owners complaint?

 

 

[discount tyres dan]

before or after the geom?

[Tony]

before or after the geom?

Assume this is the final report, so the complaint remains.

[discount tyres dan]

pulling to the let and maybe a bit of inner edge tyre wear, particuly on the drivers side

[Tony]

pulling to the let and maybe a bit of inner edge tyre wear, particuly on the drivers side

I assume you meant 'pulling to the left'... if yes can you explain why?

[discount tyres dan]

yes i meant pulling to the left,

 

looking at the front camber, both wheels are leaning towards the kerb, n/s/f has +ve camber and o/s/f has

-ve camber.

[Tony]

yes i meant pulling to the left,

 

looking at the front camber, both wheels are leaning towards the kerb, n/s/f has +ve camber and o/s/f has

-ve camber.

Spot on dan well done... The conical positions are indeed in conflict, nsf outside of the car, osf inside of the car, so there is a camber 'push/steer'. One interesting area on the final report is the Castor position?... i wonder how both the nsf and osf obtained 7 degrees 42' since there was no interior adjustment made

[Tony]

Try this one...

Front

ns:camber -1d 15'

os:camber -1d 35'

Total toe:0

Castor:ns +6 deg

:.os +6deg 10'

Rear

Camber:ns -35'

:.os -45'

Toe:ns -20'

:.os +20'

Total toe: 0

Thrust: +30'

 

From this what is the customers complaint?

[discount tyres dan]

i think i know but i'll let someone else have a try

[Tony]

i think i know but i'll let someone else have a try

Go for it!!!! others can read between the solutions.

[discount tyres dan]

ok i think the car would be wearing front tyres on the inside, the steering wheel may not be straight (slighty left) and the car pulling to the right. mostly all down to the rear toe being at -20' and +20'

[Tony]

ok i think the car would be wearing front tyres on the inside, the steering wheel may not be straight (slighty left) and the car pulling to the right. mostly all down to the rear toe being at -20' and +20'

Correct... well done... the -20' and +20' rear toe displaces the cars centre line (Thrust angle) so the driver needs to compensate through the steering position to manufacturer a new thrust position.

 

 

One more example then we will move on to modifications....

 

Example: This car is camber/castor/toe adjustable

Front

Camber nsf -45'........ osf -40'

Castor nsf +5d 59'....osf +6d 13'

Toe.......nsf 0.............osf 0

KPI/SJI.nsf 4d 40'.......osf 7d 27'

Included angle.... you can maths that one

 

Rear

Camber nsr... -1d 10'....osr -1d 25'

Toe.......nsr 0...............osr 0

Thrust..0

Clue: Remember the parallelograms and there is no point trying to triangulate since the car is naturally adjustable.

 

So indeed a bit more difficult but can you suggest whats happening to this car when driven?

[Tony]

ok i think the car would be wearing front tyres on the inside, the steering wheel may not be straight (slighty left) and the car pulling to the right. mostly all down to the rear toe being at -20' and +20'

Correct... well done... the -20' and +20' rear toe displaces the cars centre line (Thrust angle) so the driver needs to compensate through the steering position to manufacturer a new thrust position.

 

 

One more example then we will move on to modifications....

 

Example: This car is camber/castor/toe adjustable

Front

Camber nsf -45'........ osf -40'

Castor nsf +5d 59'....osf +6d 13'

Toe.......nsf 0.............osf 0

KPI/SJI.nsf 4d 40'.......osf 7d 27'

Included angle.... you can maths that one

 

Rear

Camber nsr... -1d 10'....osr -1d 25'

Toe.......nsr 0...............osr 0

Thrust..0

Clue: Remember the parallelograms and there is no point trying to triangulate since the car is naturally adjustable.

 

So indeed a bit more difficult but can you suggest whats happening to this car when driven?

Answer: This example is difficult so i am not surprised it went unanswered but if you want the wim logo then it's school time

 

From the above example the only visible disparity is the KPI (King Pin Inclination) This angle is very misunderstood so conveniently ignored but vital to diagnostics...... So what is it?..

 

The KPI is the inclination of the front lower swivel pin, it exists in three planes (vertical, perpendicular, longitudinal) and is the recipient of the upper parallelogram of the cars weight.

 

What is hard to understand about this angle is it's measured position ver force... Since the angle is measured in a 3D plane then true vertical would read as 0 KPI as the pin is declined the measured angle increases but is reactive influence decreases... The longitudinal position is due to the mechanical castor trail by design.

 

So in the example above the nsf has 4d 40' inclination and the osf 7d 27' inclination, as explained this then suggests the nsf pin is more inclined than the osf so supporting more weight from the upper parallelogram of the vehicle.... Agreed?

 

To the consequence.... By design the inclination is compressed pushing back down the cars weight, but both the front King Pins want to be at rest, this resting opportunity is available through the steering rack turning the front wheels until both pins share the same inclination..... So in answer to this example the car is pulling to the left and by the drivers defensive reaction the steering position is right hand down.

 

An area to note is the fact this example is 'multiple adjust' Geometrically so in essence this masks the real reason why the KPI has this disparity....most times it's soley due to a bend at the wishbone, most times the bend would take the camber with it... unless it's been adjusted correcting the angle?.... Now the shop are wondering why is the car pulling?..... We know

[IanF]

ok i think the car would be wearing front tyres on the inside, the steering wheel may not be straight (slighty left) and the car pulling to the right. mostly all down to the rear toe being at -20' and +20'

Correct... well done... the -20' and +20' rear toe displaces the cars centre line (Thrust angle) so the driver needs to compensate through the steering position to manufacturer a new thrust position.

 

 

One more example then we will move on to modifications....

 

Example: This car is camber/castor/toe adjustable

Front

Camber nsf -45'........ osf -40'

Castor nsf +5d 59'....osf +6d 13'

Toe.......nsf 0.............osf 0

KPI/SJI.nsf 4d 40'.......osf 7d 27'

Included angle.... you can maths that one

 

Rear

Camber nsr... -1d 10'....osr -1d 25'

Toe.......nsr 0...............osr 0

Thrust..0

Clue: Remember the parallelograms and there is no point trying to triangulate since the car is naturally adjustable.

 

So indeed a bit more difficult but can you suggest whats happening to this car when driven?

Answer: This example is difficult so i am not surprised it went unanswered but if you want the wim logo then it's school time

 

From the above example the only visible disparity is the KPI (King Pin Inclination) This angle is very misunderstood so conveniently ignored but vital to diagnostics...... So what is it?..

 

The KPI is the inclination of the front lower swivel pin, it exists in three planes (vertical, perpendicular, longitudinal) and is the recipient of the upper parallelogram of the cars weight.

 

What is hard to understand about this angle is it's measured position ver force... Since the angle is measured in a 3D plane then true vertical would read as 0 KPI as the pin is declined the measured angle increases but is reactive influence decreases... The longitudinal position is due to the mechanical castor trail by design.

 

So in the example above the nsf has 4d 40' inclination and the osf 7d 27' inclination, as explained this then suggests the nsf pin is more inclined than the osf so supporting more weight from the upper parallelogram of the vehicle.... Agreed?

 

To the consequence.... By design the inclination is compressed pushing back down the cars weight, but both the front King Pins want to be at rest, this resting opportunity is available through the steering rack turning the front wheels until both pins share the same inclination..... So in answer to this example the car is pulling to the left and by the drivers defensive reaction the steering position is right hand down.

 

An area to note is the fact this example is 'multiple adjust' Geometrically so in essence this masks the real reason why the KPI has this disparity....most times it's soley due to a bend at the wishbone, most times the bend would take the camber with it... unless it's been adjusted correcting the angle?.... Now the shop are wondering why is the car pulling?..... We know

 

Will the 3 degree difference in included angle change the scrub radius enough to cause the car to pull under breaking?

 

Hmm fully adjustable geometry is that a curse or a blessing. To adjust anything other than toe on the Senator requires the use of an engine lift so that the front cross member can be loosened and moved. Makes fixing the geometry a pain once it is wrong. None of the local alignment /geometry shops are willing to do anything other than the manufacturer adjustable toe. Which does nothing for the underlying problem.

 

BTW how is adjustable castor implemented?

[Tony]

In reply to Ianf

 

The scrub radius is born by the perpendicular position of the KPI and the true vertical, the intersection of these imaginary lines determines the scrub radius....... The included angle is a perpendicular line drawn through the KPI and the actual camber angle projected through the tyre and form a diagnostic position and the dynamic value the camber/KPI will swap during compression/release..... these two are not easy to differentiate.

 

A 3 degree difference in the included angle over the front axle under braking is disastrous. If the KPI is inclined... under compression the conical camber needs to swap values with the KPI, if there is a disparity over the axle then the massive compressive force acting on the KPI will violently pull the car to one side.

 

Fully adjustable is a blessing for the most desperate of Geometry problems.... reading the results is the issue?

 

Cradle adjustment on the Senator is very unusual.... to my knowledge the camber has available adjusters within the two front strut pinch bolts?...What is the 'underlying problem?'

 

Castor if adjustable opens many opportunities.. since the angle by marriage with the camber and controls the turning radius then it is possible to change the radii, position the Ackerman angle, extend/reduce the mechanical trail.....All with massive consequences regarding driver feed-back.

[IanF]

In reply to Ianf

 

The scrub radius is born by the perpendicular position of the KPI and the true vertical, the intersection of these imaginary lines determines the scrub radius....... The included angle is a perpendicular line drawn through the KPI and the actual camber angle projected through the tyre and form a diagnostic position and the dynamic value the camber/KPI will swap during compression/release..... these two are not easy to differentiate.

 

A 3 degree difference in the included angle over the front axle under braking is disastrous. If the KPI is inclined... under compression the conical camber needs to swap values with the KPI, if there is a disparity over the axle then the massive compressive force acting on the KPI will violently pull the car to one side.

 

Fully adjustable is a blessing for the most desperate of Geometry problems.... reading the results is the issue?

 

Cradle adjustment on the Senator is very unusual.... to my knowledge the camber has available adjusters within the two front strut pinch bolts?...What is the 'underlying problem?'

 

Castor if adjustable opens many opportunities.. since the angle by marriage with the camber and controls the turning radius then it is possible to change the radii, position the Ackerman angle, extend/reduce the mechanical trail.....All with massive consequences regarding driver feed-back.

 

 

argh too ....much...... information

 

On my Senator the front crossmember /cradle isn't square. I think its about 5mm set back on the nearside. Car pulls to the left The standard pinch bolts don't allow for camber adjustment, some friends have modified their cars to allow adjustment though I think the tinkering is reserved for the Lotus Carlton's which have much more expensive tyres. The topic of alignment comes up every now and then, but none of us knows of a decent shop that is trustworthy. I suspect that the Lotus boys would be quite happy to trek some hundred miles to ensure that their cars are just right. There is quite a market out there for a decent geometry allignment shop.

[Tony]

In reply to Ianf

 

The scrub radius is born by the perpendicular position of the KPI and the true vertical, the intersection of these imaginary lines determines the scrub radius....... The included angle is a perpendicular line drawn through the KPI and the actual camber angle projected through the tyre and form a diagnostic position and the dynamic value the camber/KPI will swap during compression/release..... these two are not easy to differentiate.

 

A 3 degree difference in the included angle over the front axle under braking is disastrous. If the KPI is inclined... under compression the conical camber needs to swap values with the KPI, if there is a disparity over the axle then the massive compressive force acting on the KPI will violently pull the car to one side.

 

Fully adjustable is a blessing for the most desperate of Geometry problems.... reading the results is the issue?

 

Cradle adjustment on the Senator is very unusual.... to my knowledge the camber has available adjusters within the two front strut pinch bolts?...What is the 'underlying problem?'

 

Castor if adjustable opens many opportunities.. since the angle by marriage with the camber and controls the turning radius then it is possible to change the radii, position the Ackerman angle, extend/reduce the mechanical trail.....All with massive consequences regarding driver feed-back.

 

 

argh too ....much...... information

 

On my Senator the front crossmember /cradle isn't square. I think its about 5mm set back on the nearside. Car pulls to the left The standard pinch bolts don't allow for camber adjustment, some friends have modified their cars to allow adjustment though I think the tinkering is reserved for the Lotus Carlton's which have much more expensive tyres. The topic of alignment comes up every now and then, but none of us knows of a decent shop that is trustworthy. I suspect that the Lotus boys would be quite happy to trek some hundred miles to ensure that their cars are just right. There is quite a market out there for a decent geometry allignment shop.

That's better now we can see why you have explored this topic.... The car pulls left.... Belay any attempt to counter the pull by off-setting the camber since this agitates the cornering, it's best to deal with the reasons first then the resolve.... How have you concluded the cross member is set back?

[IanF]

That's better now we can see why you have explored this topic.... The car pulls left.... Belay any attempt to counter the pull by off-setting the camber since this agitates the cornering, it's best to deal with the reasons first then the resolve.... How have you concluded the cross member is set back?

 

I suspected that the garage muppets had taken the car out for a "spin" and hit the nearside wheel on an obstruction in the road. The garage of course denied it and the extra miles on the clock were my imagination too They also denied that the car pulled left when the steering was released claiming that that was all down to road camber. I stopped using that garage shortly afterwards.

 

Some time later whilst underneath the car changing oil and filters I noticed a shiny ring around the bolt that holds the cross member to the chassis. I took the car to a local geometry shop who gave me a printout showing set back which when I asked what does it mean they didn't have a clue! They adjusted the toe on the front, didn't adjust the rear thrust line and charged me money. MORE DISILLUSIONMENT.

 

So I borrowed some optical allignment kit and reset the rear thrust and toe then set the front alignment to the rear. Car still pulled left but at least tyre wear was okay. Since that time I've hid an obstruction in the road whilst trying to avoid the lorry comming down the middle of a country lane. Unrelated to this I've also had to replace the front wishbones (old rubber bushes = MOT fail) and I'm getting edge wear on the front tyres. So the car needs fixing once again. I'd like it to be done properly this time. So here I am.

[Tony]

That's better now we can see why you have explored this topic.... The car pulls left.... Belay any attempt to counter the pull by off-setting the camber since this agitates the cornering, it's best to deal with the reasons first then the resolve.... How have you concluded the cross member is set back?

 

I suspected that the garage muppets had taken the car out for a "spin" and hit the nearside wheel on an obstruction in the road. The garage of course denied it and the extra miles on the clock were my imagination too They also denied that the car pulled left when the steering was released claiming that that was all down to road camber. I stopped using that garage shortly afterwards.

 

Some time later whilst underneath the car changing oil and filters I noticed a shiny ring around the bolt that holds the cross member to the chassis. I took the car to a local geometry shop who gave me a printout showing set back which when I asked what does it mean they didn't have a clue! They adjusted the toe on the front, didn't adjust the rear thrust line and charged me money. MORE DISILLUSIONMENT.

 

So I borrowed some optical allignment kit and reset the rear thrust and toe then set the front alignment to the rear. Car still pulled left but at least tyre wear was okay. Since that time I've hid an obstruction in the road whilst trying to avoid the lorry comming down the middle of a country lane. Unrelated to this I've also had to replace the front wishbones (old rubber bushes = MOT fail) and I'm getting edge wear on the front tyres. So the car needs fixing once again. I'd like it to be done properly this time. So here I am.

That printout could you post the image here... type the front end after figures..

[IanF]

That printout could you post the image here... type the front end after figures..

 

 

these figures are from a couple of years ago...

 

All numbers a before left before right then === the after figures for left and right

 

F CAMBER -1o 02' -1o 08' ==== -0o 58' -1o18'

F CASTER 4o 19' 4o 50' ==== 4o 19' 4o 50'

F TOE 5.0mm -8.4mm ==== 1.0mm 0.7mm

F SET BACK left 0o 13' ==== left: 0o 15'

INC ANGLE 13o 25' 13o 52' ==== 13o 29' 13o 42'

SAI 14o 27' 15o 00' ==== 14o 27' 15o 00'

 

R CAMBER -1o 37' -1o 46' ==== -1o 34' -1o 46'

R TOE 2.0mm 0.4mm ==== 1.5mm 1.0mm

R SET BACK right 0o 07' ==== right 0o 03'

THRUST LINE right 0o 07' ==== right 0o 03'

 

 

I don't know what the correct figures for caster SAI KPI should be. The printout did indicate that the Caster angle was out of spec both before and after adjustment. I am suspicious of the CAMBER figures as they did not check either the fuel level in the tank or use any weights in the car. Something that I was later told should have been done.

 

I have to locate another geometry shop and get the car remeasured. So here I am engaged ina crash course on geometry LOL. A little knowledge may be dangerous but no knowledge is far worse.

 

The car is a 24V 3.0 Senator 1994.

[Tony]

That printout could you post the image here... type the front end after figures..

 

 

these figures are from a couple of years ago...

 

All numbers a before left before right then === the after figures for left and right

 

F CAMBER -1o 02' -1o 08' ==== -0o 58' -1o18'

F CASTER 4o 19' 4o 50' ==== 4o 19' 4o 50'

F TOE 5.0mm -8.4mm ==== 1.0mm 0.7mm

F SET BACK left 0o 13' ==== left: 0o 15'

INC ANGLE 13o 25' 13o 52' ==== 13o 29' 13o 42'

SAI 14o 27' 15o 00' ==== 14o 27' 15o 00'

 

R CAMBER -1o 37' -1o 46' ==== -1o 34' -1o 46'

R TOE 2.0mm 0.4mm ==== 1.5mm 1.0mm

R SET BACK right 0o 07' ==== right 0o 03'

THRUST LINE right 0o 07' ==== right 0o 03'

 

 

I don't know what the correct figures for caster SAI KPI should be. The printout did indicate that the Caster angle was out of spec both before and after adjustment. I am suspicious of the CAMBER figures as they did not check either the fuel level in the tank or use any weights in the car. Something that I was later told should have been done.

 

I have to locate another geometry shop and get the car remeasured. So here I am engaged ina crash course on geometry LOL. A little knowledge may be dangerous but no knowledge is far worse.

 

The car is a 24V 3.0 Senator 1994.

That report suggests no reason for a pull..... you do indeed need a new report to conclude the current problem.... The loading although neccasarry so the comparative positions comply with the mid point suspension compression to the manufacturers overlapped data bares no real concern to me?.... under whatever load symmetry is the real issue, addition-subtraction of load would still allow a real image in symmetry.