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Tracking tool recommendation
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welshrover



Joined: 09 Aug 2011
Posts: 326

PostPosted: Wed Mar 13, 2013 10:00 am    Post subject: Reply with quote

Kelsham wrote:
Jim, when I centralised the rack on my XJ-S, I held the steering wheel in the position indicated by the drill bit inserted into the rack.

I supposed that the wheels could be running differently as the wheels were being held in a set position by the rack.

I can't remember what the readings were on both sides of the car, it is a long time ago, but it seemed sensible at the time.

I think we are all agreed that the Trakrite is a simple tool that delivers.

I had a Rover 100 that kept pulling to one side. I applied the Trakrite without improving the driving experience.

I decided to take the car to a four wheel alignment specialist, I told him I had set it up with the Trakrite and he was amused. Almost sneered in my face.

I watched him adjust the tracking, he fiddled about and made a miniscule adjustment to the trackrod ends.

He then admitted he did not think it would make much difference to the pulling problem. Only improvement was to his bank balance.

I took the car home and after further thought realised that one rear swinging arm had worn bearings.

I could just see the lean on the back wheel, I was surprised the four wheel alignment had not identified it.

The trakrite was innocent of blame. Pre war I believe it was not unusual to drive over a sheet of paper and see which way it twisted as the tyres ran over it.

Kels

the other one was with tyre pressures . a chalk line across the treads
to see if they were right , you'll be amazed how far out the handbook can be using this method , Shocked
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Jim.Walker



Joined: 27 Dec 2008
Posts: 1229
Location: Chesterfield

PostPosted: Wed Mar 13, 2013 12:50 pm    Post subject: Reply with quote

A lot to answer there Kelsham.
But centreing the rack as you describe if fine.
The second point to note is that all results are checked from a datum. In this case the "datum" is the wheel on the floor.
Using degrees to facilitate my explanation: if the tracking gauge says the wheel being checked is (say) 5 degrees different to the datum, it follows that changing the "datum" to the other side wheel (by swapping the gauge to the other side) will now say the original datum wheel is 5 degrees out. Perhaps a similee is that if you are walking one pace BEHIND a friend ,He can be said to be walking one pace in FRONT, but who is in the correct position?

You might have taken the car to a "claimed" wheel alignment specialist, but in reality he was a "numpty"! And I would have no hesitation in saying so to his face. Too many people are trained to use expensive equipment with no idea how it works or even why it is necessary. He probably even believed wheels ran toe-d in like a Red Indian.

It is most unlikely (if not impossible) that a "pull" on the steering is caused by faulty tracking. Which obviously causes excessive tyre wear but can cause "wooley" feeling with toe out and (surprisingly skittishly sensitive steering with excessive stationary toe in.
Perhaps the simplest cause might be a binding brake At ANY WHEEL.
To that you can add incorrect camber or caster angle with wrong king-pin inclination (Even if you have no king-pins Very Happy) or even, as you say a rear wheel/suspension fault. To sort out from that lot WOULD probably need a "specialist"! But a COMPETENT ONE!
I could lecture for hours on steering geometry and tracking. I used to have to for a living!

Jim.
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Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!
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Jim.Walker



Joined: 27 Dec 2008
Posts: 1229
Location: Chesterfield

PostPosted: Wed Mar 13, 2013 1:00 pm    Post subject: Reply with quote

Missed your comment about the paper test Kelsham. You are correct.
If you run your fingers ACROSS the tread of a tyre in both directions, any "feathering" due to a tracking fault is easily detected too.
I tend to do that quite frequently and on friends cars too as I pass. It has confounded many when I have told them to get the tracking checked. Especially when it was confirmed it needed attention.

You also mentioned the chalk test. Very useful if different sized wheels or tyres have been fitted. Though many people think the original pressures are still correct (AND the original toe-in figures too).
Jim.
_________________
Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!
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Bitumen Boy



Joined: 26 Jan 2012
Posts: 1733
Location: Above the snow line in old Monmouthshire

PostPosted: Wed Mar 13, 2013 7:04 pm    Post subject: Reply with quote

What's this chalk test then? Sounds useful and I always have a bit of chalk handy in the garage... Smile
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Jim.Walker



Joined: 27 Dec 2008
Posts: 1229
Location: Chesterfield

PostPosted: Wed Mar 13, 2013 7:35 pm    Post subject: Reply with quote

Bitumen Boy wrote:
What's this chalk test then? Sounds useful and I always have a bit of chalk handy in the garage... Smile


Well. It seems I found this before Kelsham.
This is a method often resorted to when no specific tyre pressure recommendations can be found. Of most use to builders of "specials" etc. it can be used to determine a suitable pressure if different wheels or tyres have been fitted or an axle loading has been changed significantly.
First it is necessary to understand that the optimum pressure gives the biggest floor contact area (footprint) possible with minimum "tread huffle", which is the main factor in tyre wear.

With the normally loaded vehicle stood on level ground with sufficient room to be moved forward several wheel revolutions; draw a chalk line across the full width of the tyre tread.
Push, or gently drive the vehicle foward until the chalk line begins to disappear.
If the line is disappearing faster at the edges the tyre is too SOFT.
If the line is disappearing faster in the centre the tyre is too HARD.
If the line is disappearing equally across the tread the pressure is correct.

Obviously, several tries with adjusted pressures may be necessary to find the optimum pressure for fronts and rears.

I built a one off car about 1984. With bigger wheels and fatter tyres than the donor chassis usually had.
Tyre pressures, as obtained in the manner above and with Front AND REAR toe in set with a Gunsons Trakrite (necessary with the swing arm rear suspension) has produced at least 30,00 miles per set of tyres averaged over four or five sets.
Jim.
YES it is the car in the avatar. Now nearly 30 years old from the date of building from (mostly) scrap.
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Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!
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Bitumen Boy



Joined: 26 Jan 2012
Posts: 1733
Location: Above the snow line in old Monmouthshire

PostPosted: Wed Mar 13, 2013 11:30 pm    Post subject: Reply with quote

Thanks Jim, I'll have to try that one on the Herald. Fronts seem to be pretty much spot on but last tyres on the rear wore in the centre, so I dropped the pressures a little - I was thinking only time would tell but should be able to figure it out a lot sooner with this method. I assume the tyres are chalk tested warm, after a run, but pressure tested cold as usual?
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Jim.Walker



Joined: 27 Dec 2008
Posts: 1229
Location: Chesterfield

PostPosted: Thu Mar 14, 2013 12:43 am    Post subject: Reply with quote

Bitumen Boy wrote:
Thanks Jim, I'll have to try that one on the Herald. Fronts seem to be pretty much spot on but last tyres on the rear wore in the centre, so I dropped the pressures a little - I was thinking only time would tell but should be able to figure it out a lot sooner with this method. I assume the tyres are chalk tested warm, after a run, but pressure tested cold as usual?


I must admit that testing tyres warm is obviously best. though I have never thought about it! Obviously I should have done!

You mentioned Triumph Herald.
The fairly uncommon swing arm suspension raises two problems.
The first is the angle of the wheel and tyre on the road, which is constantly changing and can only be perpendicular very rarely. It follows that wear on the rear tyres must be rather different to the wear of a tyre on a wheel held perpendicular most of the time as on a live axle.
The second, I know from experience that as the rear suspension sags under loading or just because of age the rear wheels tend to toe-in quite a lot and periodic checking/adjustment is wise. Adjustment is usually by shims, though adjustable track control arms are available.
The rear wheel alignment can be checked with the Trakrite too, but it is best to gently drive the car over to simulate normal drive displacement of the wheels.
It is a personal theory of mine that excessive toe-in on the rear of these cars probably increases the chance of the dreaded tuck-under. Which once experienced is never forgotten,

Jim.
_________________
Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!
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