17 replies to this topic

[Pavel]

My car seems to tilt the wheels outwards at the top (increase positive camber) as the wheel turns in!!!

As far as I know castor must be set the other way round, so the wheels tilt into the corner, not out of it!

Firstly, what is this castor called (positive or negative)?

Secondly, is there anyway to fix it?

[Woody]

Basicly the bottom of the wheel is further forward than the top (the pivot points ), if it was the otherway round you would have negative castor (this can hapen if the subframe is bent and the tie-rod pushes the bottom arm back )

[Pavel]

Well thats what i said, seems like i have negative castor, but im pretty sure my sub is straight!

Could it just be that my car has positive camber up front and it is exagerated when turning the wheels?

[siggy]

CASTOR and CAMBER are NOT the same.

Camber is the the angle that the wheel is tillted at from the vertical.

Castor is the angle that the wheel sits on the road compared with where the centre line of the swivel axis would be

Siggy

[Pavel]

yeh i know

castor increases negative camber as a wheel turns in..

on my car, it seems like the negative camber decreases as the wheel turns in, and im wondering whether this is because of negative castor or whether i just have a lot of positive camber on the front wheels

[siggy]

But it looks like Woody does not.

Basically if the castor is out the front end is bent. I would have thought that the drivability of it would be terrible. if it was that far out. IIRC the steering would be very easy to turn in but you would need a 6ft steering wheel to straigten it up. otr the opposite.

It sounds like there is nothing wrong, the camber angle will change on a lock

Siggy

[Pavel]

Drives fine, must just be me then

[siggy]

The moral of this story is If it an't broke don't fix it' ))))

Siggy

[Woody]

Yea guys i do understand (i have certificates to prove it )but i dont have certificates in explaning it ,even your explanation Siggy seems baffling (but i know what you mean !)
In the garage i worked in until last year we had a Bear 4 wheel alignment system (lazer beams and all that )and where adjustable i could set Caster , Camber,Toe and camber and toe on the rear as well as checking set back and S.A.I or K.P.I as we used to call it .

[siggy]

When you completed your NVQ, if you used the 'Brooks' book, a good explenation is in the Chassis Transmission book level 3.

Siggy

[Pavel]

camber and castor is really much easier to explain with a picture

if you re-read woody's original explanation, it actually is correct

as they say, a picture is worth a 1000 words

[siggy]

re reading it, his explanation is not too good. As you say a photo is worth a 1000 words. Its phyisically impossable for the bottom of the wheel to be further forward than the top.

If you were able to draw a line throught the centre of the Kingpin or ball joints. This line would touch the ground in front of the contact area of the tyre. If you then drew a line from the top to the bottom of the tyre. the angle between the 2 is the Castor angle.

Siggy

[Pavel]

granted this is for RC, but the idea is the same:

What it does: Caster is the angle of the steering kingpin in relation to a vertical plane perpendicular to the ground. With the top of the kingpin angled back towards the car you have negative caster. Positive castor, with the top of the kingpin would be angled towards the front of the car, is never used. Negative castor makes the car more stable to drive in a straight line. Without it, the car would feel very twitchy, react very quickly to steering inputs and easily spin out. The more negative caster you have, the more steering you will have in high speed sections, during turn in, and the more stability you’ll have in the straights. With less caster, you’ll have more low speed steering with less stability in the turns and less steering during turn in.

Attached Files

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[siggy]

It is exactly the same.

Thinking about it if you look at the front forks and wheel of a motorbike, you can see it clearly.

Sigygy

[bluebottle]

the other benefit of having more castor, is that it helps the steering self centre as well