IVA test fail: Steering turning circle correction

[WillF71]

Hi all.
I have recently had a fail on the IVA turning circle self-correction with my GBS Zero. At the low speed turn, taking my hands off the wheel has bo change at all in the turning circle. It simply stays on track with the same turning radius. Any ideas on what I could do with the front geometry to try and initiate self- correct?
I have over-i flated front tires. Steering rack is a new Mk2 escort unit and seems free with eh front wheels in the air so I don't think there is any binding.
Thanks in advance

Will

[Hawkshaw]

It sounds as though there isn't enough caster - but that is simplistic, as all the steering angles are inter-related so the problem may originate somewhere else. Is it set up to the manufacturer's spec (if there is such a thing)? How much adjustment do you have in the wishbones, etc. and what sort of measuring equipment do you have?

[WillF71]

Hawkshaw said:

It sounds as though there isn't enough caster - but that is simplistic, as all the steering angles are inter-related so the problem may originate somewhere else. Is it set up to the manufacturer's spec (if there is such a thing)? How much adjustment do you have in the wishbones, etc. and what sort of measuring equipment do you have?

No manufacturer figures to reference and there doesn't seem to be any adjustment forward or back for the wishbones. Only adjustment i have is for stearing arms and upper wishbone rose joint. No proper measuring gear. Just setting up equally for both sides.

[Nigel_O]

I had the same issue with a Westfield - zero self-centring effect, which meant constant steering input. In the end, I had some custom adjustable top wishbones made to allow me to dial in some caster.

One thing to check (as it applies to Westfields and a few owners have made this mistake) - are the top wishbones ‘handed’? If they are, you might find you’ve fitted them the wrong way round and removed all the caster.

[WillF71]

Nigel_O said:

I had the same issue with a Westfield - zero self-centring effect, which meant constant steering input. In the end, I had some custom adjustable top wishbones made to allow me to dial in some caster.

One thing to check (as it applies to Westfields and a few owners have made this mistake) - are the top wishbones ‘handed’? If they are, you might find you’ve fitted them the wrong way round and removed all the caster.

Thanks for the reply.
I did think of the 'handing' issue last night and shall check into this. Initial inspection is that there seems to be no markings on the wishbones to indicate this, but worth a call to the factory

[Gemaeden]

Try a bungee cord.

[Nigel_O]

WillF71 said:

Nigel_O said:

I had the same issue with a Westfield - zero self-centring effect, which meant constant steering input. In the end, I had some custom adjustable top wishbones made to allow me to dial in some caster.

One thing to check (as it applies to Westfields and a few owners have made this mistake) - are the top wishbones ‘handed’? If they are, you might find you’ve fitted them the wrong way round and removed all the caster.

Thanks for the reply.
I did think of the 'handing' issue last night and shall check into this. Initial inspection is that there seems to be no markings on the wishbones to indicate this, but worth a call to the factory

Of course it could just as easily be the bottom wishbones that are the wrong way round - I have no idea what they look like on the Zero

[Hawkshaw]

According to this
https://paul94-gbs-zero-build.blogspot.com/2012/08...

Caster angle on a Zero should be 11 degrees. That is a large angle for a car of that type (commonly 4 to 6 degrees) and if it is present, it should be visible.

Edited by Hawkshaw on Wednesday 5th April 03:51

[Equus]

Caster is very much the first and obvious thing to check, but it also might be worth checking you are using the correct wheel offsets: in combination with the King Pin Inclination (AKA Steering Axis Inclination), which is fixed by the design of the upright, the wheel offset dicates the scrub radius, and that can also influence self-centring.

[schmokin1]

If all else fails, springs on the rack, hidden by the rack boots have been used…!

[johnpsanderson]

I’d suggest you get into the Locostbuilders forum, probably been well covered in there. I think increased tyre pressure (which you’ve already mentioned) and increasing toe out are the two go-to recommendations…