Castor - seems off

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wennbom
Posts: 137
Joined: Tue Apr 29, 2014 12:09 pm
Location: South Sweden

Putting my suspension back after a refresh and replacing the rubber bushed with bearings.
I assembled using an even distribution of shims 3mm front and rear on all positions.
I thought I'd be ending up with something close to nominal. But nooooo.

When I now measure I get FL +4.8° and FR +4.5°
The manual says + 3.5° to + 4.1° with +3.8° being optimum

My first guess is that I'm doing the castor measurement the wrong way.

I turn wheel -20° and read Camber, turn wheel +20° and read Camber
Calculate the delta and multiply by 1.5
Right or wrong?

/Michael
tlracer
Posts: 647
Joined: Mon May 26, 2003 11:00 am

I have never come across the 'multiply by 1.5' before. Simply add the 20 deg. left lock to the 20 deg. right lock figures.

That gives you figures of 3.2 and 3.0 respectively.
wennbom
Posts: 137
Joined: Tue Apr 29, 2014 12:09 pm
Location: South Sweden

Approximation formula is like this
Caster = 180/pi * (Delta Camber/2*TurnAngle)

180/(pi*40)=1.43 so not really 1.5

Switching to excel and using this formula I get 4.7 and 4.4.
tlracer
Posts: 647
Joined: Mon May 26, 2003 11:00 am

There are conflicting methods for castor, not least as it is not an easy direct measurement to make.

What are the camber figures you have for the two wheels, each at 20 deg. left and right steering lock?
wennbom
Posts: 137
Joined: Tue Apr 29, 2014 12:09 pm
Location: South Sweden

Readings as follows:

FL-20°: 0°
FL+20°:-3.2°

FR-20°:+0.5°
FR+20°:-2.5°
wennbom
Posts: 137
Joined: Tue Apr 29, 2014 12:09 pm
Location: South Sweden

Camber readings straight ahead
FL: -2.3°
FR:-1.8°

The manual says 1mm shim alters camber by 0.25°.
So I planned to remove 1 shim from RH and add 1 shim to LH.
Started with the RH one and read new camber to -2.3° ?? Either my gauge is very inaccurate or 1mm shim alters more than 0.25 - probably my gauge
tlracer
Posts: 647
Joined: Mon May 26, 2003 11:00 am

Thanks for those. If they were mine, I would first adjust until the left and right values for the wheels agreed, ie. similar +20 and -20 figures for the left and right wheels and also that the camber values themselves were equal.

Make sure your gauge is accurate and repeatable, and that you properly settle the suspension after any changes.
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