Slimy38
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| posted on 29/9/25 at 03:37 PM |
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Into the dreaded 'no self centring' ballgame
My car is 99% finished, with only a few bits of trim to add. Everything looks and feels ok... apart from steering. The car will go in a straight line,
and it will turn... and keep on turning.
Bearing in mind I can only get to just above walking speed in the little cul de sac I live in, but turning the wheel slightly off centre turns the car
and it stays in that direction when I release the wheel. If I turn it too far it'll actually go to full lock and stay there. Even typing that out
loud I know I don't want to be going any kind of speed and have that to deal with.
The first thing I think I should do is actually measure caster. How is it measured, what two points are used and what is the reference? I'm
assuming it's the floor rather than the chassis? I see anywhere between 6 and 10 degrees, is that about right?
I've checked the wishbone orientation, and toe in is slightly in from zero (I got it to zero then gave the track rods a 'tweak' so not
very scientific). The other consideration is that they're built with MX5 hubs with the Saturn wishbone design, but without the lower wishbone
adjustment.
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adithorp
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| posted on 29/9/25 at 05:39 PM |
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It's measured from vertical. 6-10⁰ should be ok.
First off; eyeball it.
Is the centre of the top ball joint behind the lower one? With the track rod ends disconnected, do the hubs turn easily? Similarly does the rack turn
freely?
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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Slimy38
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| posted on 29/9/25 at 07:10 PM |
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From vertical it's measuring 6 degrees, so it's at the bottom of the range. I went back through my blog and I can also see I calculated it
to be 6 degrees then, so I've built it to spec. It just drives horribly.
Everything is loose and easily moved, I can control the steering from a road wheel with very little effort.
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adithorp
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| posted on 29/9/25 at 07:42 PM |
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Then it should self centre to some degree.
Toe can affect it. How much was a "tweek"? A nudge of toe-out can help but shouldn't be necessary. Likewise a bit more tyre pressure.
What's your camber like?
I've got 6deg castor (from memory... might be 8) and if I put a 1/4 to 1/2 turn of lock on and push the car it trys the self centre.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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JC
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| posted on 30/9/25 at 06:12 AM |
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Double check everything!
For example, I discovered my (cortina) uprights were warped!
Measure vertically up from the centre of the bottom ball joint.
Measure how far back the top ball joint centre is from the vertical line.
Divide the distance the ball join is behind by the vertical distance between the ball joints and hit INV TAN on your calculator.
As a rule of thumb, if the vertical distance between the ball joints was 20cm, then the top ball joint needs to be 2cm behind the bottom one for 6
degrees of caster.
Sorry if I’m teaching you to suck eggs - whenever I encountered an inexplicable problem, I had usually made a really obvious error so I’m judging you
by my own low standards lol
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Slimy38
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| posted on 30/9/25 at 06:49 AM |
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quote:
Originally posted by adithorp
Then it should self centre to some degree.
Toe can affect it. How much was a "tweek"? A nudge of toe-out can help but shouldn't be necessary. Likewise a bit more tyre pressure.
What's your camber like?
I've got 6deg castor (from memory... might be 8) and if I put a 1/4 to 1/2 turn of lock on and push the car it trys the self centre.
For toe I went for roughly one revolution of each track rod, but I wound them in not out. I thought I was aiming for toe-in so I need to sort that.
Tyre pressures are 25 if I remember rightly.
Camber could be an interesting one, what should it be? Along similar lines I do need to look at ride height, at the time I was more interested in the
front wheels avoiding the arches rather than driving well.
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Slimy38
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| posted on 30/9/25 at 07:09 AM |
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quote:
Originally posted by JC
Double check everything!
For example, I discovered my (cortina) uprights were warped!
Measure vertically up from the centre of the bottom ball joint.
Measure how far back the top ball joint centre is from the vertical line.
Divide the distance the ball join is behind by the vertical distance between the ball joints and hit INV TAN on your calculator.
As a rule of thumb, if the vertical distance between the ball joints was 20cm, then the top ball joint needs to be 2cm behind the bottom one for 6
degrees of caster.
Sorry if I’m teaching you to suck eggs - whenever I encountered an inexplicable problem, I had usually made a really obvious error so I’m judging you
by my own low standards lol
Keep the ideas coming, at this stage I need all the egg sucking that's available! In fact, just typing this response I've realised I've
made a mistake in measuring. I was measuring off the bit that is fixed to the wishbones, so the 'cap' that is on the back of the ball joint.
There's no guarantee that is actually in line with the pivot point, just thinking about it the bottom one definitely isn't because
it's horizontal. I need to measure from the parts that are fixed to the upright, IE the ball part. I think I'm going to have to try again.
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gremlin1234
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| posted on 30/9/25 at 09:02 AM |
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what tyre pressures are you using?
edit:
ah, I see you have answered that already
[Edited on 30/9/25 by gremlin1234]
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Slimy38
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| posted on 30/9/25 at 10:55 AM |
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quote:
Originally posted by gremlin1234
what tyre pressures are you using?
edit:
ah, I see you have answered that already
[Edited on 30/9/25 by gremlin1234]
Aye, is 25 about right for the car? It's a bit tubby for an average locost, if I understand my corner weighting method correctly I'm heading
for around 800kg.
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steve m
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| posted on 30/9/25 at 03:32 PM |
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My Locost, was 17-18psi on all 4 wheels, and was perfect, any lower pressure the tyre would creap on the rims, anything above 22psi (ish) it was like
driving on ball bearings
To help with self centering, i believe folk would put 30+ psi in the front only, and just to satisfy the SVA/iva self centering rule, and once passed,
reduce to 20
Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at
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adithorp
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| posted on 30/9/25 at 04:45 PM |
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[For toe I went for roughly one revolution of each track rod, but I wound them in not out. I thought I was aiming for toe-in so I need to sort that.
Tyre pressures are 25 if I remember rightly.
Camber could be an interesting one, what should it be? Along similar lines I do need to look at ride height, at the time I was more interested in the
front wheels avoiding the arches rather than driving well.
A full turn each side will be giving you about 1 to1.5deg toe-in. 0 to 0.5 would be more like it and even a touch of toe-out can give better turn in
though to me makes it a bit twitchy.
Camber probably 0 to 1 deg negative.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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jacko
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| posted on 1/10/25 at 03:32 PM |
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Just as a matter of interest do f1 cars have self cantering
Jacko
555
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coyoteboy
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| posted on 1/10/25 at 10:12 PM |
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quote:
Originally posted by jacko
Just as a matter of interest do f1 cars have self cantering
Jacko
Driver61 says yes. I can't imagine a car being pleasant without.
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Slimy38
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| posted on 3/10/25 at 09:09 AM |
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quote:
Originally posted by coyoteboy
quote:
Originally posted by jacko
Just as a matter of interest do f1 cars have self cantering
Jacko
Driver61 says yes. I can't imagine a car being pleasant without.
I can certainly attest to my car being quite unpleasant at the moment!
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JC
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| posted on 5/10/25 at 06:09 AM |
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Maybe post some pictures of your front suspension?
Someone may spot something you missed?
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jacko
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| posted on 5/10/25 at 02:08 PM |
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Who made the. Chassis did it come as a kit chassis body etc could the front suspension part be wrong ?
Is the top suspension arms on the wrong side pushing the top forward to much ?
Just thinking out aloud
G
555
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Slimy38
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| posted on 5/10/25 at 05:33 PM |
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quote:
Originally posted by jacko
Who made the. Chassis did it come as a kit chassis body etc could the front suspension part be wrong ?
Is the top suspension arms on the wrong side pushing the top forward to much ?
Just thinking out aloud
G
Haynes Roadster self build, and yes the suspension being wrong was my first thought. It's not the wrong way round but I do wonder whether
I've done something else wrong. Unfortunately the weather has limited what I've been able to try this weekend, I'll have to get back in
there during the week.
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jacko
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| posted on 6/10/25 at 06:06 PM |
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It’s not the Healy then ?
555
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Slimy38
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| posted on 6/10/25 at 07:48 PM |
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quote:
Originally posted by jacko
It’s not the Healy then ?
Yes but thats just a body on top of the haynes roadster.
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jacko
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| posted on 7/10/25 at 07:27 PM |
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Very nice , a mate of mine had a Serbring with a Nissan straight 6 engine
G
555
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