OT: Wheel tracking - how accurate does it have to be?

I have just had my car serviced. The garage sends out videos showing inspection of the underside, and in mine the technician showed the front kerbside tyre as having only 3mm tread but said will probably be all right till my next service as I only do 2000 miles per year.
I then got a call from the garage owner saying I needed the tyre to be changed, and that the tracking was out and needed tow-in adjustment to prevent one-sided wear observed on that tyre, which I agreed to.
When I got the printout from the tracking machine I was astounded at the manufacturer's limits on the settings. The front wheel states tow limits of 0°00' to 0°10', and my wheel before adjustment was 0°23'.
After adjustment it read 0°05'. In other words they adjusted it by 18 minutes of arc, about a third of a degree.
I cannot believe that such a small adjustment will have noticable effect on tyre wear. It seems to me that manufacturers have such limits because they are easy to achieve, but users should be given much wider limits before adjustment is needed.
I've now researched this interesting subject, but can find no scientific treatment. The first 10 pages on Google are filled with garages offering tracking, laying it on thick about how important it is. The tracking machine's website has two videos of garage owners saying how quick and easy it is to check alignment and offer customers adjustment, and the added income paying for the machine many times over.
I was charged £145+VAT for it, and looking at my video again, there was no characteristic toe-in wear. I think I've been had! Any thoughts?
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Dave W wrote:

I think you have at that price, F1 Autocentres will do the alignment check for free and something like £30 to re-align if needed.
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On 24/05/2019 11:50, Andy Burns wrote:

DIY is quite possible all you need is a measuring tape some spanners and perhaps some knowledge of trigonometry. Long time since I last did this though.
--
Michael Chare

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On Fri, 24 May 2019 12:13:36 +0100, Michael Chare

I believe you, but it wouldn't be to within a few minutes of arc. Until I have evidence to the contrary I don't believe such accuracy is needed.
--
Dave W


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On Fri, 24 May 2019 11:39:12 +0100, Dave W wrote:

8
I wouldn't like to bet on it. Though compared to tyre pressure it's probably lower. Incorrect tracking normally shows itself as the car pulling slightly to the left or right. Correctly aligned and on a straight, flat road, and decent speed (50mph+) the car should go in dead straight lilne with hands off the steering wheel. The chances it will slowly drift left or right as roads aren't flat, repeat a few times on different stretches of "flat, straight road" and see if it consistantly drifts left/right at about the same rate. Oh and make sure all the tyre pressures are correct (note that might not be the book value, "correct" to produce even tyre wear).

At £145+VAT for a simple tracking check and alignment, you've been had. But was it a full 4 wheel alignment check and adjustment? Bear in mind that a full 4 wheel alignment means putting the car in a jig and bending it to align the wheels, normally only done after an accident.

At the begining you say there was...
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Cheers
Dave.
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Dave Liquorice laid this down on his screen :

Never heard of that, my car has proper adjusters for the rear alignment.
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On 24/05/2019 13:26, Harry Bloomfield wrote:

More accurate would be that come cars only give you the option of replacing (or re-aligning (bending!)) bits- for instance many FWD cars have non-adjustable rear axles. (Golfs 1-4, IIRC, for example)
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I took my SD1 (rigid rear axle) to a four wheel alignment place once. I'd fitted a new steering rack and wanted it done properly. So not the likes of Kwikfit. The rack has a centre finder, so I'd fitted the steering wheel in the straight ahead position with the rack central - as per the BL manual.
The computer print out said I'd too much rear wheel toe-in. ;-)
After they'd finished (and charged rather a lot) the steering wheel was miles out when going straight.
My guess is it's all very well buying expensive sensitive equipment. But like all such likely needs the calibration checked regularly to give the best results.
--
*Do paediatricians play miniature golf on Wednesdays?

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Fri, 24 May 2019 13:04:03 +0100, Dave Liquorice wrote:
<snip> > At £145+VAT for a simple tracking check and alignment, you've been had.

Whilst I understand that correct, aren't there also vehicles that have 4 wheel tracking / geometry adjustments under normal use?
Such adjustments being required after parts were replaced (suspension related bushings) or the ride height changed etc?
After a minor accident on the kitcar, I noticed excessive rear wheel 'tracking' type tyre wear and when KF couldn't measure the error themselves, they let me use their kit and measure it myself. ;-)
1.5 deg toe-in (when it should have been zero) knocked out a fairly big / new tyre in less than 1000 miles.
Cheers, T i m
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On 24/05/2019 13:04, Dave Liquorice wrote:

That's not true far all cars. My last 2 cars have had independent and adjustable rear suspension- and indeed there have been revised settings issued after the cars were made. https://en.wikipedia.org/wiki/Volkswagen_Group_A_platform#PQ35_(A5)
£145 seems a bit steep for full alignment compared to my independent garage, but at dealer charges it doesn't seem too bad, I suppose. It's not a five minute job.
FWIW I'd never allow one of the cruddy tyre-fitting places that do tracking for £20-30 near my car as historically they've fucked it up every time, and/or neglected worn/damaged components.
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On 24/05/2019 13:04, Dave Liquorice wrote:

No, it doesn't.
Most cars have adjustments on the rear wheels.
--
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and people tell those stories because everyone important believes them.
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On 24/05/2019 17:39, The Natural Philosopher wrote:

Bollocks. Usual nonsense from you.
Astras and Corsas and many other makes have torsion bar rear suspension. If the rear wheel is out of alignment, then the car has had an 'off road experience' and something is bent.
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On 25/05/2019 12:17, Andrew wrote:

small cars froma single manufaqctuirere of cheap nasty cars
and many other makes
like?
have torsion bar rear

Corsa has coils
http://www.megavaux.co.uk/part-rear_axle_corsa_d_a12xer_with_suspension-14650.aspx
If the rear wheel is out of alignment, then the car

Bollocks from you as usual.
If its independent rear trailing half beam then chances are there is a link as well. Its hard to ensure algnment on a single canyilever.
--
The New Left are the people they warned you about.

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On Sat, 25 May 2019 13:21:16 +0100, The Natural Philosopher
<snip>

Irrelevant, other than trying to gain you some wriggle room.

Many and not for others to prove but for you to disprove. [1]

Yes, to provide the actual suspension but both trailing links are joined by a substantial torsional section and so for the *tracking* of the rear wheels (the point of the conversation) to be out, 'something would have to be bent'.

Fact in this case as it happens.

Is that some sort of smart Scottish suspension?
Cheers, T i m
[1] A lorry squashed our Astra against the kerb (whilst parked, at night) and that bent the rear axle / trailing arms.
A mate lost the back end of his Fiesta though some muddy road works and sideswiping the kerb bent the rear axle / trailing arms.
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On 24/05/2019 13:04, Dave Liquorice wrote:

Most likely left. Most roads have a camber - higher in the middle of the road than at the kerbs - to make rain run off.
Andy
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On Fri, 24 May 2019 21:14:06 +0100

Indeed - if you want to check your car is running straight you need to drive along the middle of the road, straddling the centre line.
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On Fri, 24 May 2019 13:04:03 +0100 (BST), "Dave Liquorice"

Wear, but not the corner wear typical of toe misalignment. They only adjusted the toe on the front wheels - none of the other adjustments that would have been needed to make the printout results all green.
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Dave W

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On Fri, 24 May 2019 13:40:53 +0100 (GMT+01:00), Jim K.. wrote:

in a

an

It is when there is no adjustment on the rears and has suffered an accident or "off road experience". There's far more to wheel alignment than just simple toe in/out relative to front wheels only. That also needs to be "inline" with the toe in/out "direction" of the rears as well, then there are castor angles. Any or all of which could be out after a car has suffered a whack.
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Dave.
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On 27/05/2019 11:13, Dave Liquorice wrote:

and all of which is either preset or adjustable.
Or both. Shimming suspension pickup points is standard practice
--
There is something fascinating about science. One gets such wholesale
returns of conjecture out of such a trifling investment of fact.
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I've often heard this and wondered. Why would poor tracking do this? It might well put the steering wheel off centre. But why would it make it pull to one side?
With R&P steering, if the rack was vastly off centre, the geometry will be wrong. But then few tracking places will sort that out 100%.
--
*Pentium wise, pen and paper foolish *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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