Toe geometry

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Charles H
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Toe geometry

#1 Post by Charles H » Tue Nov 28, 2017 5:04 pm

I have been using my new Gunson tracking tool on the Mk1 rally car. The front wheels each read 0.25 degrees toe out. I reckon that that should be as near as damn it parallel or just toe in. The rear wheels are adjusted by shims on the rear shackles. The readings are 1.00 degrees toe in on the offside, and 0.5+ degrees on the nearside. The manual appears to advise that the car should toe in front and rear from 0 to 1/16". What advise can anyone give me as to adjustment, even if it is to just leave it alone.
The car is on a standard spring and shock set up, the only change is a CW slightly deeper spring insulator to maximise the ground clearance.
Charles Harrison
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Re: Toe geometry

#2 Post by johnnydog » Tue Nov 28, 2017 8:13 pm

Hi Charles,
My understanding of the Gunsons set up is that it gives you a reading whilst the car is moving over the tracking plate. The settings of 1/16th toe in at the front is whilst the car is static.
The Gunsons trackrite gives a reading of 0 degrees or parrallel whilst moving and any movement in the steering is taken up and the front wheels are correctly tracked at 0 degrees as when the car is moving.
I've used the Gunson trackrite on all my Triumphs and none suffer from any abnormal tyre wear setting them up to 0 when rolling the car over the plate
The rear is more fixed, and assuming there is no wear in the rear bushes, it needs to be equal on both sides. Ideally the rear needs to be set correctly and equally on both sides before the front is set up, otherwise the rear will travel in a different line to the front and any adjustments to the front will be a waste of time, and when you test drive the car you will find the steering wheel will be off centre!
There are purpose made shims to alter the rear tracking which fit behind the shackles on the subframe. I've removed these from cars in the past when I've scrapped them.
This is just relative to the toe, and not camber.
Does that make sense?!?
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Clifford Pope
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Re: Toe geometry

#3 Post by Clifford Pope » Fri Dec 01, 2017 8:54 am

That makes sense to me. I've always understood that rear wheel drive cars have very slight front toe in (static) because when they move the wheels tend to splay out a bit as joints and bushes and things compress a bit, so the effect is to put the wheels parallel.
(conversely on front wheel drive cars the wheels tend to splay outwards under drive, so there is the opposite effect. I've never been entirely convinced by that argument, because the wheels won't be in drive all the time - often on over-run or coasting)

I've also been unimpressed by all the hype about laser tracking. The toe-in figures in the book typically say something like 1/16" +/- 1/16", or 2mm +/- 1mm.
It doesn't take precision instruments to measure to that accuracy. I've always used a home-made device with a length of timber and two wooden uprights with long bolts threaded through nuts clamped in the wood.

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