Geometric stagger

[Tony]

Geometric stagger is a gentle disparity in the front camber/ castor positions that helps to belay the drifting effect of the UK road crown pulling the car left. The Hunter machine has a data pool of 25k cars and on choosing a car sometimes the fields asks for information like where in the world are you? then some fields open the data release for the UK/ Japan, in this event the front camber/ castor positions end results asks for a stagger.

 

I find it really odd only some manufacturers recognise the need to stagger the angles for the UK?....

[jammy]

isnt it standard reg or somthin for uk roads to pull you to the left :S

[Tony]

isnt it standard reg or somthin for uk roads to pull you to the left :S

 

Donno mate, i don't understand the question...... Your brain and fingers need to work as a team

[keithsto]

I've just had my 2008 TT done and the right camber was -0 26' and the left -1 02'

 

As I understand it the greatest positive will create a pull in that direction. The car drove beautifully but now they have set both sides to -0 55'

 

The printout said there was a cross camber tolerance of +/- 0 30'

 

I haven't driven it enough to be certain yet, but it seems to be drifting to the left a bit more.

 

I'll post the full printout when I get to take a photo.

[CIH]

The higher negative cambered wheel pushes against the less negative/positive

[adam_r]

surely the car should be set up as evenly as possible ?

[Tony]

surely the car should be set up as evenly as possible ?

 

It reads like now it is..... On some cars ( mainly German ) we have to allow a geometric stagger to belay the road crown pushing the car left. The stagger should use the permitted tolerance so there's no tyre wear.

[Rich]

isnt it standard reg or somthin for uk roads to pull you to the left :S

 

That's just mondeo's mate, a common problem apparently!!

[Tony]

Not to be confused with an "eventual drift"....

 

No car however calibrated is immune to the road crown, simply because the crown distorts the NSF/OSF tyre sidewalls, this conical deformation means the tyre walls have different circumference. Nascar race cars run a huge tyre stagger on the ovals so the crown doesn't throw the car off when it hits the bank.

 

Most decent!! manufacturers offer a distance where the car should resist the crown, this is called an "eventual drift", the actual distance differs from manufacturer to manufacturer but it's around 20yrds on average, oddly enough manufactured cars with known pulling problems don't offer a distance in the UK but they do for the continent

[keithsto]

Does this imply that the steering wheel must be held at an angle on a cambered road to go in a straight line for any distance?

 

Basically my car now drifts a lot earlier than it used to, now the camber has been set to tolerance.

 

Although the cross camber was out of tolerance by a large percentage the front tyres wore beautifully.

 

The steering feels a lot lighter now, which is a bit of a shame to be fair, I like more of a sporty feel.

 

On a seperate note the steering wheel is now a bit crooked.

 

The Hunter machine calculated that the total toe was fine but each wheel was out by around 0 40' thus to adjust 'to the machine' the steering wheel dead ahead position has been moved relative to the wheels.

 

Does the alignment rely on the steering wheel to be clamped dead ahead to start with, or is it more sophisticated than this?

 

Thanks

[keithsto]

[Tony]

The steering position is immune to the road crown so if this is off they have not centred it correctly during the calibration, it's an easy fix and to some extent cosmetic, nevertheless you should return that car and have this fixed.

 

Your also a victim to "adjustment blindness" simply because the castor on your car is not adjustable it wasn't measured, measuring the castor unlocks loads more information about the steer axis, but without this data i cannot fully confirm or deny the real chassis status. In truth you have been robbed because you paid for a full geometry but only got a partial geometry.

[keithsto]

Thanks for the response

 

So you don't get the machine to work out the straight ahead position by letting it know each full lock for example? It's totally reliant on the operator clamping the wheel dead ahead?

 

I'm guessing you mean the rear castor as the front is on the sheet? How is this measured out of interest please?

[keithsto]

Another printout I received. Does the grey mean it wasn't measured?

 

Are the castor and SAI done as part of a separate procedure involving rotating the wheels? The SAI difference on the first printout looks quite a lot?

 

[Tony]

The grey numbers means it was measured but there's no target data, hence the grey shade. For some reason BMW/ Audi have not released the castor positions, to date i cannot found out why so in the absence of numbers we simply look for symmetry ot in the event there's a drift a stagger.