Steering and Suspension Alignment

Sign-convention for steering geometry settings

HarryMann: It's not always obvious what the sign convention is i.e. which way things point when the setting says +ve or -ve. And of course it matters - a lot!

NB. cf. is short for compared to/ referenced to

Toe +ve Toeing-in (front of wheels is closer than rear, pigeon toed!). Toe-in mainly reduces tendency to diverge into a turn when wheel deflected by irregularity, unless excessive. It complements the straight-line stability due to +ve caster.

Front-wheel drive vehicles tend to run with a bit of toe-out and rear-wheel drive a bit of toe-in. Excessive toe of course wears tyres out. Rear wheel toe-in/out is important on independently suspended rear-wheel drive vehicles (T25/T3) which can become unstable with excessive toe-out at the rear.

Camber +ve Should be top of wheel leaning out cf. bottom. Camber controls the lateral spread of the tyre contact patch during cornering, -ve increases cornering forces. As with all settings, affects understeer/oversteer, more directly than toe or caster though. Toe and camber affect tyre-wear more than caster.

Caster +ve The steering axis of left front wheel slopes from bottom left to top right when viewed from left side; right front wheel, from bottom right to top left when viewed from right side. This would usually be the angle of a McPherson strut or the angle between the upper and lower ball joints; the actual point of contact Vs the camberline is not taken into account, just the angle, whether it leads or trails. On T25/T3s the forward radius rod alters the caster angle (as well as the fore-aft position of the front wheel)

Note: The slope of whole van, front to rear can affect caster a bit. Heavy slope has more effect on roll-centres and the front-rear roll-axis than caster, with regard to handling (picture an overloaded Tranny pickup truck, high at the front, low at back swaying all over the road, also contributed to by under-inflated rears Vs fronts, for the load carried)

Then there's SAI (Steering Axis inclination), like caster but viewed from the front.

Scrub Radius/Kingpin Offset - preset. Where the steering axis strikes the road cf. the tyre contact patch centroid. (-ve implies the tyre patch centroid is outside of the extended line of the steering axis) VW were early adopters of -ve scrub radius (whilst lightening the steering for manoeuvring and when tyre is under-inflated, also allows you to be totally unaware of a tyre going flat - great!)

Thrust Angle: If this isn't zero your vehicle will 'crab' (drive sideways whilst going straight). Thrust angle is normally non-zero due to chassis damage, though with some 4-wheel independent wishbone suspension even rough 'kerbing' can cause this.

Setting for T25/T3s

Baxter's Brickyard Info on T25 geometry settings (Includes 2WD, Syncro 14 and Syncro 16)

There has been some confusion by VW over the years about correct Syncro settings, information appears on the Syncronauts Website from various sources. Some mfrs of alignment equipment even programmed in the wrong figures

Here's one set of figures from Nigel in SA

I have 235/75/15 tyres. Alignment specs used at my alignment shop are below (with my syncro's actual values in brackets):

FRONT

Caster: 4.41 to 4.91 (L=5.00, R=4.01)

Camber: 0.66 to -0.40 (L=0.18, R=0.08)

Toe: no spec (L=-0.2, R=-0.2)

REAR

Caster: no spec

Camber: -0.42 to 0.25 (L=-0.66, R=-0.39)

Toe: -0.5 to 1.6 (L=-0.2, R=0.4)

Regards Nigel, SA

What do the various settings do?

On cost and quality... Bearing in mind what we find with some garages today, and esp. quality of staff in some tyre-centres, I might be happy to have all the settings checked and reported by an alignment service, but would be pretty circumspect before allowing them to re-set any... Unfortunately, they are not always of like mind and seem to want to dive at everything with spanners before sucking their teeth quite enough for my liking (e.g. a few minutes of error in a setting angle is better than loosening a wickedly corroded bolt holding a wickedly naff bush and then re-setting it wickedly wrong!) Just my take, I may be getting cynical in my old age... but I'd rather pay to at least find out if settings are basically within tolerance or some are way out - and then think about why?

The normal setting home mechanics do themselves would be toe-in (or out), and even then takes a fair time to get it right, as needs to be done (or checked) about 3 times rolling vehicle back and forth between checks. One reason is wheel rim deformation, another is any play in rack or tie-rod ends or wheel bearings. Also, it used to be quite common to find the rack has been de-centred when doing toe-in amateurishly, by not adjusting both tie-rods and it does matter if it's well out (gives bump steer). Fortunately, unless the steering box splines have been off, T25 steering wheels and racks are very accurately centred and will be noticed.

2WDs have very slight toe-in, Syncros parallel to slight toe-out, but dependent on suspension height (dist between wheel centre and wheel arch lip above)

Camber generally not done at home, but like the kit MaxStu* :)

Again, rolling about back & forth and re-checking/re-doing is also recommended for camber. Waste of time if the top or bottom wishbone bushes are knackered or a ball-joint has play in it. If the eccentric pin doesn't look central in the top bush, that's a clue.

Camber is nominally 0 degrees, each wheel to be within 1 degree of the other. Slight +ve camber on Syncros.  Weight and ride height of course affect camber.
Camber affects the oversteer/understeer, load/temp across the tyre width and ultimate cornering forces more than any other parameter.

[b]Caster [/b](Castor is oil from the castor bean, you remember Castrol 'R' )

This is set by the forward radius rods, sometimes called tie-rods so if those big rubber bushes at the front have had it, and the sleeve inside is rotten to the core, then caster will be changing a bit as you brake and accelerate and negotaite corners, much as camber will with a badly worn wishbone bush or ball-joint.

Caster affects straight-line stability and steering weight, as well as changing camber angle as the wheels are turned, increasing neggy camber on the outside wheel with tighter turn radius, a +ve effect.

Critical point here is that they are the same (provided the thing hasn't been badly bent, when it may well require them to measure differently to drive straight and true, ditto camber; until its been straightened!)

Recent discussion about changing these bushes and their sleeves in Tech Advice, makes a lot of difference to steering accuracy, stability and response... at least accurately mark the rear backing nut on the rod, before moving it, this is what sets the position & hence caster angle.

With rear-wheel drive vehicles it is extremely important that the rear toe and camber angles are checked as well. The toe especially!

Effect of tyres and pressures Oversteer/understeer/stability etc.

Notes: These settings are not just about tyre wear, they affect steering as well as handling characteristics and they interact to an extent.

These are 'static' but change dynamically with load, load distribution, roll, cornering forces and acceleration and braking. The dynamic changes are set 'by design' and also affected bush compliance.

[b]With independent suspension rear-wheel drive vehicles it is important that the rear toe and camber angles are checked as well. The toe-in especially, as toe-out can cause instability![/b] T25s have very slight toe-in (10'), but the +/- tolerances allow a smidge of toe-out.

NB. If using setting gaps rather than angles, then wheel size will affect the measurement.

Home mechanic alignment possibilities

Safety, likely accuracy, workshop services, Brickyard charges £35 for basics, etc.

Always tighten suspension bolts up with WoW (weight on wheels), esp. rubber jointed ones like top and bottom wishbones and shock absorber bolts; a 2nd lightweight trolley jack comes in handy at times like this.

T25s are very robust IMHO, it always amazes even some of the Synro die-hards that after a thorough battering of the worst kind, they can have their tyre pressures checked/reset and then be driven on tarmac again without pulling or behaving erratically nor requiring much attention thereafter. There are of course things that wear out quicker or do sometimes get damaged, but overall, they are very resistant to being seriously damaged or misaligned in the suspension department.

Tyre centres & alignment services... Bearing in mind what we find with some garages today, and esp. quality of staff in some tyre-centres, I might be happy to have all the settings checked and reported by an alignment service, but would be pretty circumspect before allowing them to re-set any... Unfortunately, they are not always of like mind and seem to want to dive at everything with spanners before sucking their teeth quite enough for my liking (e.g. a few minutes of error in a setting angle is better than loosening a wickedly corroded bolt holding a wickedly naff bush and then re-setting it wickedly wrong!) Just my take, but I'd rather pay to at least find out if settings are basically within tolerance or some are way out - and then think about why?

The normal setting home mechanics do themselves would be toe-in (or out), and even then takes a fair time to get it right, as needs to be done (or checked) about 3 times rolling vehicle back and forth between checks. One reason is wheel rim deformation, another is any play in rack or tie-rod ends or wheel bearings. Also, it used to be quite common to find the rack has been de-centred when doing toe-in amateurishly, by not adjusting both tie-rods and it does matter if it's well out (gives bump steer). Fortunately, unless the steering box splines have been off, T25 steering wheels and racks are very accurately centred and will be noticed.

2WDs have very slight toe-in, Syncros parallel to slight toe-out, but dependent on suspension height (dist between wheel centre and wheel arch lip above)

Camber generally not done at home, but MaxStu and xxx have been using the following method, like it :)

Rolling about back & forth and re-checking/re-doing is also recommended for camber. Waste of time if the top or bottom wishbone bushes are knackered or a ball-joint has play in it. If the eccentric pin doesn't look central in the top bush, that's a clue.

Camber is nominally 0 degrees, each wheel to be within 1 degree of the other. Slight +ve camber on Syncros.  Weight and ride height of course affect camber.
Camber affects the oversteer/understeer, load/temp across the tyre width and ultimate cornering forces more than any other parameter.

Caster (Castor is oil from the castor bean, you remember Castrol 'R' )