Steering and Suspension Alignment

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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! (cf. is short for compared to or relative 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

Suspension alignment settings should be adjusted in the folowing order:

1) Caster; 2) Camber 3) Toe


From the workshop manual

2WD T25 alignment settings
Setting Empty (800 kg axle load) Half load* (1000 kg axle load) Max load* (11~1200 kg axle load)
Front
Toe per wheel (degrees° & minutes') + 0° 10' +/- 15' + 0° 10' +/- 15' 0° +/- 15'
Total toe (degrees° & minutes') + 0° 20' +/- 30' + 0° 20' +/- 30' 0° +/- 30'
Total toe (mm) + 2.0 +/- 3.5 mm + 2.0 +/- 3.5 mm 0 +/- 3.5 mm
Total toe (inches) + 0.08 +/- 0.138" + 0.08 +/- 0.138" 0 +/- 0.138"
Camber (wheels strt. ahead) 0° +/- 30' + 0° 15' +/- 30' 0° +/- 30'
Total angle diff. over 20 deg. lock, left to right (non-adjustable) 1° 10' +/- 20' 1° 10' +/- 20' 1° 50' +/- 20'
Caster (vehicle on level)** + 7° 15' +/- 15' + 6° 30' +/- 15' + 6° 0' +/- 15'
Caster above corresp. to camber diff. of wheel on lock from 20 deg. left & right + 4° 50' +/- 10' + 4° 20' +/- 10' + 4° 0' +/- 15'
Caster diff. (max.) between left & right
Rear
Setting Empty (700 kg axle load) Half load* (1050 kg axle load) Max load* (13~1400 kg axle load)
Toe per wheel 0° +/- 10' + 10' +/- 10' + 10' +/- 10'
Total toe (at specified camber) 0° +/- 20' + 0° 20' +/- 20' + 0° 20' +/- 20'
Camber - 0° 50' +/- 30' - 1° 30' +/- 30' - 2° 10' +/- 10'
Camber Max diff. between left & right 0° 30' 0° 30' 0° 30'

* Measure unladen if possible; Some later models, have a reduced suspension height: use 'half-load' settings as equivalent 'empty' settings for those lowered from factory models.

** If vehicle is inclined to front or rear 10' must be added to or subtracted for each 15' angle off of level (measured in sliding door opening) This saves levelling floor of vehicle fore/aft by jacking.

e.g. Angle measured 6 ° 40'

Correction angle for inclination to front by 1 °

Actual caster angle 7° 20'

NB. Angling front down then add correction figure; angling rear down then subtract correction figure


Other relevant data (2 WD models 1983-1989.):

Wheelbase 2460 mm

Front track 1570 mm

Rear track 1570 mm

Wheel nut torque 180 Nm (130 lb-ft)

Track rod lock nut 71 Nm (51 lb-ft)

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

Syncro

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...

Alignment Settings (works manual)

See here for Derek Drew's (USA) syncro steering alignment synopsis

Forum discussion

Simon Baxter: Cutting to the chase!

Camber on the zero's; 1 degree of tolerance left to right; Tracking, toe in 2mm.

Thats all you need to know.

What do the various settings do?

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)

Toe-in/out determines resistance to disturbance by road surface irregularities and works with camber to ensure good straight-line stability. Front and rear-wheel drive vehicles vary, and suspension bush compliance helps determines a safe basic setting as undriven wheels will drag back with speed and driven ones pull forward. Normal, is slight toe-in for undriven front wheels

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.

Camber & toe settings affect tyre wear more than other geometry settings

Caster (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.

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!

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.

A DIY approach can be found over on the Samba: http://www.thesamba.com/vw/forum/viewtopic.php?t=396113

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' )

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.

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! 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.

Damien: Can get these magnetic protractors for under £10 posted. see here:

5977500keps large 01.jpg

Cromwell Magnetic alignment protractor

I set them up with that then drive them 10 miles to get them set up properly, never been far off the mark.

Suspension Modifications

Hypnovan: I'd like to check out what effect different suspension configurations have before buying into it.

It's not an urgent job so i'm just canvassing opinions/taking advice, so thanks for yours.

Several people have mentioned -40mm and -50mm and at first this seemed reasonable (to me 40mm isn't that big a difference) but after realising that I spend some of the time off road on bumpy,muddy tracks and fields, that clearance is an issue. A 4x4 is becoming increasingly tempting though we have now grown attached to our Atlantic following a rocky start. I just read someone's blog and they only changed their dampers and bought huge rims with low profile tyres.

HarryMann: Read up on it from a good source, there's a fair bit of twaddle around... 

Differentiate stiffer springs from stiffer dampers.. once the wheel mass for a given spring stiffness is being controlled adequately in bump and rebound, there's no point in increasing those rates much - if at all; in fact increase bump damping and you start to lose grip (understeer if front, oversteer if rear)...

Std. T25 shockers seem pretty well specced, so unless significant changes to wheel/tyre mass or stiffer springs fitted, little point, other than maybe greater retention of damping as shockers get worked hard and thus get hot, which is mainly an off-road situation.

Additionally as soon as you're on a rough road (e.g. pitted B road) roadholding can get worse, not better, with stiffer shocks.

What can create an improvement is changing in bump to rebound characteristics. Generally, this whole area is one for design and development engineers, who not only understand the mechanics at work, but have the tools at hand to analyse the results and interpret them meaningfully..

Stiffer springs will augment anti-roll and pitch reduction, at the expense of bump and harshness transmission into the body e.g. scuttle shake. If much heavier wheels and tyres are fitted, then a correspindingly stiffer spring might be required. It's finding the right combination of spring and damper if they are required. Main thing is not to go too far... Lowering the nose cf. rear can help turn-in and reduce wind effects, even reduce drag a bit. 10 ~20mm? I recently raised the back of my Syncro Doka a bit (20mm) and noticed a bit more directional stability and turn-in, just noticeable I'd say.

Unless a lot of good R&D has been done on a particular combination for a particular van type, it's all a bit of a guessing game and you won't find everyone being particularly forthcoming about any downsides when they've spent a fair wedge... to be fair some won't be noticing them as any change might seem to be +ve; it takes a large mileage to really weigh up and find exactly what the change has done across the board, under all conditions.

Remember also often changes are not from new to new, but from old to new!

Some examples:

+ve A heavy Syncro camper often running well-loaded: Syncro.org springs (stiffer) with corresponding HD Syncro shockers can improve the ride, pitch and roll to a degree that it's worthwhile. Well designed springs aimed at a very particular vehicle and configuration.

-ve Over-raising a vehicle to garner maximum ground clearance... with the best setup, driveable, but will almost always compromise cornering. particularly with enormous wheels that put loads into body and shockers that are hard to handle...

-ve Over-lowering and over stiffening... crash bang wallop, fine on glass smooth tracks, even then maybe not well balanced for controlled understeer at departure, but overall not suitable for bumpier surfaces.

Often the best initial step is to check all the wear points in suspension meticulously, and check the geometry settings accurately back and front.

Fit a front spoiler for long distances if it hasn't got one, but be prepared to remove it or sacrifice it off-road :wink:


Lowering: Lowering the front cf. the back will make the vehicle turn-in better, but also oversteer more at the limit (unstable situation). Lowering at the rear will do the opposite. Lowering both will reduce body roll and consequently sharpen the steering up, provided the alignment angles are kept much the same... Lowering of course, reduces suspension travel and with stiffer springs, upset the shock absorption, and handling on poor surfaces (bump thump and bump-steer). Slight lowering of the front or raising of the rear (esp. if sagging) can add a good deal of immediacy and response to the steering and improve roadholding slightly.

Wider wheel, lower aspect ratio tyres etc.

This trend reduces some of the compliance (opposite of stiffness) of the tyre, so the suspension becomes more critical in supplying that required compliance. The advantage being that the road forces are transmitted into the suspension more directly, and provided the system is tailored for it and responds accurately, better roadholding and handling can be achieved. The downisde is that without adequate engineering in the suspension and chassis/body area, NVH increase (Noise; Vibration & Harshness)

Further reading links

More about alignment and their effects

Everything you ever wanted to know about tyres (hopefully!)

More on alignment and vehicle handling and stability

Derek Drew (USA) writes on syncro steering alignment and the pitfalls