Wheel Tracking Dilemma

[woo]

So I went to get my front wheel tracking adjusted armed the details in the manual, i.e. 3/32 inch or 2.5 mm toe in, and they want the measurement in Degrees! Does anybody know how many degrees toe in the Moggie needs. I'm using 145 x 14 radials.

Thanks

Robin

[Cam]

Well, a 2.5mm toe in gives a single wheel movement of 1.25mm a 14" diameter rim moves 7" from the centre to the end. 7" = 177.8mm.

That's assuming that they use the edge of the rim to adjust the 2.5mm toe in which I think they do.

Using sohcahtoa, the angle we are after is given by the inverse tangent of opposite over adjacent.

Inv Tan (1.25 / 177.8 ) = 0.403

So they should want to move EACH wheel inwards at the front by 0.403 degrees relative to the centreline of the car. If they are measuring relative to the other wheel, then have them ajust it so that there is 0.806 degrees between the front wheels.

I think................

[woo]

Cam,

'some old horses can always have their own apples' that takes me back a bit...

Thanks

[Cam]

I was showing someone how to do it today actually!! They were working out 2-D constellation points for a communication system, but the principle is the same!!

[woo]

Cam,

Presumably you were using your old school copy of 'Five Figure Logarithmic and other tables' By F. Castle.

Or did you cheat and use a calculator

[Welung666]

Well, a 2.5mm toe in gives a single wheel movement of 1.25mm a 14" diameter rim moves 7" from the centre to the end.

It was at this point you lost me! I'll be in the corner if I'm needed

[Cam]

Cam,

Presumably you were using your old school copy of 'Five Figure Logarithmic and other tables' By F. Castle.

Or did you cheat and use a calculator

Erm........... I cheated. It's been a long time since I used tables, although I used a calculator BEFORE I used the tables!!

See! I'm not THAT old! Honest!

Actually, all I have here is the built in calculator in Windows2000. My calculator and books are either at work or at home, so I'm lucky I could work it out at all!! Don't fancy trying an inverse tangent in my head!

[Cam]

It was at this point you lost me! I'll be in the corner if I'm needed

Hopefully stripping Doris! Oooer! Matron the screens!!

[woo]

Cam,

This is a long way back for me, I'm interested to know why you use the Inverse tangent, and I'm prepared to be blown out of the water so please be kind to me

Presumably we are trying to calculate the angle that the centre of the wheel turns through, So if we assume that with a triangle ABC the 177.8mm represents the Adjacent AB (with A at the hub) the 1.25mm represents the Opposite BC. With AC representing the Hypotenuse (which we are not using). Wouldn't a Natural Tangent provide the angle at A?

[Cam]

The natural tangent of the angle gives the opposite/adjacent.

So the inverse tangent of the opposite/adjacent gives the angle.

we know the opposite (1.25mm) and the adjacent (177.8mm) so we divide them and take the inverse tangent to get 0.403 degrees.

[woo]

Ahhhh, I see.

As I said, It's a long way back. I did trigonometry with chalk and slates.

Thanks

[Kevin]

Thanks for working that out Cam, as for years I have been led to believe it short be set to parallel so it wont be far out then, and even I remember Log tables although the last ones I used were i think 7 figure ? and as for the other master piece the slide rule (blimey that was a long time ago)

[Cam]

Yeah, 0.4 or 0.8 degrees is not a lot is it? Parallel is a close approximation.

Just because not many people use ready reckoners, log tables or slide rules does not mean that they don't work anymore!!

[Kevin]

Cam you are right of course its just that brains like mine that dont function as well mentally as they used to

[Pyoor_Kate]

What's this calculator nonsense? In my day you had to count using pebbles! And you were lucky if you got two pebbles!

....Although, these days I've got a sliderule and very good it is too; although I do own a 'Sinclair Programmable' calculator.... now, where did I put the mains adaptor.

[somewhere around on the interweb is a print-and-cut-out-sliderule too].

[Willie]

Out of interest, I have made my own tracking gauge(don't laugh)
after an upsetting incident with Quick Fit, and set my t racking
last week after fitting a new grease nipple type track rod end.
Yes tracking is measured at the wheel rims and should be 3/32"
toe in. It transformed my car, changed from a tendency to slight
wander to 'goes where you point it'.

[woo]

Willie,

Could you share with me how you made it?

[Willie]

I hesitate to explain my method Woo as you seem to be a very
precise gentleman. However I spent my working life dealing
in thousandths of an inch and am quite confident with my rig.
I used a length of the narrow plastic pipe sold for waste pipes
in the home with planed timber inserted inside it which was
sanded until it was an 'interference fit' i.e. no discernable play.
One end was fixed and located permanently by screws through
the pipe. The other end was able to be slid into and out of the
tube to do the measuring and to this end I screwed a 12 inch
ruler marked in millimeters (2.5mm =3/32"). The uprights
on each side were screwed and glued wood with inwards projecting
knobs(these are the pieces which actually touch the wheel rims
AT THE SAME HEIGHT AS THE CENTRE OF THE WHEELS
when doing the measuring). Obviously there is no play or looseness
anywhere which would nullify the measurements. I am happy with
this arrangement but replacing the wood and plastic pipe with a
METAL pipe within another pipe and welded uprights would be even
more robust. One thing is sure, I make a better job of the tracking
than Quick Fit did!!!

[rayofleamington]

Hi Fred - didn't completely follow your description as I can't visualise how you get the pipe to touch the wheels at the front and rear centre height as the bodywork would be in the way I'm guessing when you say 'uprights' that you had dog-leg ends on the wooden bits?

One of these day's I'll knock up my idea for a DIY tracking guage - made from a couple of bits of bent wood some screws and a tape measure....
I'm sure everyone will be astounded!

[woo]

Willie,

That sounds interesting, perhaps you should set up a cottage industry making them for classic car owners since building one would be beyond me.

Wasn't a tracking guage produced once that you put on the floor and drove over? I don't see them for sale anymore so perhaps they weren't all they were cracked up to be.

Your home made job seems to have equalled the rig at my local Jet Tyres which used 3 lasers to show the measurements and cost £29.38 to reset my tracking. But I do get a free checkup after 500 miles time, but then so do you!