Davey D
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| posted on 16/4/09 at 11:30 AM |
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Self Centering
One of my fail points at SVA was lack of self centering... so i got all my other jobs done to it last night, then took it out to a
"private" carpark to test it out.
Suspension/ Geometry is as setup by MNR with Contina based front end and usual castor angle. The tyres are set to about 30psi.
i was doing some figure 8 in the carpark, and found that it was starting to self centre when steering to the right.. from full lock the wheel would
slowly make a 1/3 turn back on its own, but there was no self centering from a smaller turn of the wheel. There was absolutely no self centering at
all steering to the left.
when turning the wheel it feels quite sticky so to speak. it isnt difficult to steer, and i can steer the front wheels by pushing/pulling on them easy
enough.
Anyone have any ideas what would be best to look at?
could my rack be a bit tight?
ive also read on here about problems if your steering column top mount doesnt bolt upto the bracket on the car at 90deg, and causes extra friction on
the steering column.
mine doesnt bolt up at 90deg, and the action of bolting it up bends the bracket on the car so it nips up.
anything else i should look at, or do you all think that it will be one of the things ive listed?
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alistairolsen
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| posted on 16/4/09 at 11:32 AM |
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1) jcak up the front of the car and check you can turn the steering by moving the wheels by hand, if you cant, something is too tight.
2) unless youre a bodger, you WANT self centring, in the conditions in which you would drive the car, so get your tyre pressure back down and set the
tracking to something sensible
3) if its like any of the locost kits you will need to get new top wishbones to induce some castor as ultimately this is why none of them self centre
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Davey D
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| posted on 16/4/09 at 11:42 AM |
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quote:
Originally posted by alistairolsen
1) jcak up the front of the car and check you can turn the steering by moving the wheels by hand, if you cant, something is too tight.
2) unless youre a bodger, you WANT self centring, in the conditions in which you would drive the car, so get your tyre pressure back down and set the
tracking to something sensible
3) if its like any of the locost kits you will need to get new top wishbones to induce some castor as ultimately this is why none of them self centre
1) i can turn the wheels by hand when it is on the floor, so i will be able to do it when jacked up, as above
2) tracking setup by MNR, as above
3) it has cortina geometry with castor angle, as above
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Mr Whippy
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| posted on 16/4/09 at 11:45 AM |
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it's amazing this is such a common complaint
try lowering the rear and raising the front as this will increase the caster angle
[Edited on 16/4/09 by Mr Whippy]
Fame is when your old car is plastered all over the internet
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bassett
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| posted on 16/4/09 at 12:40 PM |
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Hi, i went up to 40psi and 1-2mm toe out or what ever it says in the manual and that worked for me.
Adam
My MNR Blog Updated Jan 2010 - Track Day Prep Begins!
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Mr Whippy
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| posted on 16/4/09 at 01:06 PM |
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hmm to me 40psi on such a light car is about 20psi to much and not really addressing the problem of the castor angle being wrong. Also having the
tyres so much out of shape do to the pressure you'll only be using the center of the tread and both reducing your grip for turning and braking.
If you raise the front an inch and lower the rear an inch it will make a huge difference in the self centering. On the old vw beetles, shims are put
behind the front suspension to tilt the front suspension back to restore caster after the fronts been lowered otherwise the car handles awful
Fame is when your old car is plastered all over the internet
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alistairolsen
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| posted on 16/4/09 at 01:11 PM |
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Whippy: Indeed,high tyres pressure, valve springs, weird tracking angles etc are a bodge to get some self centring for an sva pass. None of them
actually address the issue.
The SVA rule is there for a reason and a car that doesnt self centre is fundamentally unsafe imo.
When Mine gets to that stage I want to see proper self centring at 18 psi and a fraction of toe in before I present it for a test, whatever is
required!
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craig1410
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| posted on 16/4/09 at 05:29 PM |
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Hi,
It sounds like you have covered the obvious although it is worth checking everything again so be sure. One thing I don't think has been
mentioned is whether you have the correct offset wheels fitted and/or whether you have spacers. This can affect what is commonly known as the scrub
radius and might be part of your problem. To evaluate this, try to visualise a straight line through your upper and lower balljoints and extend this
line to the ground. Ideally you want this line to intersect the ground just and the inboard shoulder of your tyre. If it intersects the ground any
further inboard then your steering will be jittery over bumps and if it is towards the centre of your tyre contact patch then the steering may feel
lifeless and lack feedback. This could be your problem.
Also, a lot of people will tell you that toe-out will produce more self-centering but Des Hamill in his book on suspension design says that on rear
wheel drive cars it is toe-in which promotes self-centering so don't neglect to try this out. Also, try it at normal inflation pressures (18-20
psi) as this will alter your tyre contact patch.
I hope this helps,
Craig.
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bassett
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| posted on 16/4/09 at 05:52 PM |
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I agree 40psi is only to get through the test. Im getting mine fully set up once finished but things like this need to be done so you can drive it
somewhere to get sorted plus its at an incorrect ride height to pass the ligths.
My MNR Blog Updated Jan 2010 - Track Day Prep Begins!
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marc n
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| posted on 16/4/09 at 06:37 PM |
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tyres do not need inflating that high 16 front 18 rear
as long as the rack and link are ok movement wise should be fine, you dont need big camber toe etc with all cars on escort new racks there are no
worries its the modified sierra ones that are a pain in the ass with the preload adjuster and are too tight
cheers
marc
please email rather than u2u
direct workshop email ( manned 8am till 6pm )
www.mnrltd.co.uk enquireys to :-
chrismnrltd@btinternet.com
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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Wheels244
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| posted on 16/4/09 at 06:45 PM |
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quote:
Originally posted by marc n
tyres do not need inflating that high 16 front 18 rear
as long as the rack and link are ok movement wise should be fine, you dont need big camber toe etc with all cars on escort new racks there are no
worries its the modified sierra ones that are a pain in the ass with the preload adjuster and are too tight
cheers
marc
Hi Marc
Is that what was wrong with mine ?
See you tomorrow afternoon.
Rgds
Rob
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Davey D
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| posted on 17/4/09 at 08:19 AM |
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quote:
Originally posted by marc n
tyres do not need inflating that high 16 front 18 rear.....
so all the other Cortina front end VortX have passed SVA with tyre pressures around these figures?
ill drop my pressures tonight, and see how it does
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Davey D
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| posted on 18/4/09 at 11:36 PM |
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Woot! I've got my self centering all sorted. In the end it was the steeing column causing the problems.
With the front end jacked up I could move the front wheels with 2 hands. When I disconnected the column at the triangle clamp I could move the wheels
with 1 hand, showing that there was loads of friction there. So I pulled it all to bits, and oiled the bearings. The sticky feeling was from the
sierra plastic bush, I sanded if down a fraction, and lithium greased it, and now the sticky feeling is gone. I then bent the mounting bracket a
little where the column bolts to so there is no twist on it.
I took it back to the carpark, and it self centres fine with no adjustment to the geometry :-d
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Mark G
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| posted on 25/4/09 at 05:32 PM |
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quote:
Originally posted by Davey D
Woot! I've got my self centering all sorted. In the end it was the steeing column causing the problems.
With the front end jacked up I could move the front wheels with 2 hands. When I disconnected the column at the triangle clamp I could move the wheels
with 1 hand, showing that there was loads of friction there. So I pulled it all to bits, and oiled the bearings. The sticky feeling was from the
sierra plastic bush, I sanded if down a fraction, and lithium greased it, and now the sticky feeling is gone. I then bent the mounting bracket a
little where the column bolts to so there is no twist on it.
I took it back to the carpark, and it self centres fine with no adjustment to the geometry :-d
Thats a very interesting solution, I'll have to try that on my Indy to see if it works. What pressures did you run in the end?
Mark.
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Numb nuts
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| posted on 26/4/09 at 07:27 PM |
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I read this all last night...went out in the garage this morning and ransacked my steering...it's never been right since I bought the kit
(built) 
The vehicle has been transformed It drives like I always imagined it should.
Thanks guys Steve
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dan8400
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| posted on 29/4/09 at 06:13 AM |
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Just to throw something else into the mix... had sva retest (Tiger Supercat) on self centring yesterday (and a few other jobs) but couldn't make
it go. Most things i have read suggest toe in. However the sva man (nice guy called Dennis at Norwich) said try toe out. And after a bit of tinkering
in the sva carpark i had a pass. Not sure if it's the same for all cars.....?
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Mark G
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| posted on 29/4/09 at 09:44 PM |
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you do want a bit of toe out for self centering but ideally for a rear wheel drive which is light on the front (BEC) you'd want a little toe
in.
I disconnected my collumn the other night and it made a little difference, disconnected the track rods too and noticed that the rack is solid to turn.
Problem found.
Removed the rack, stuck it in a vice and stripped it to pieces. Cleaned out all of the grease and relubricated it all, adjusted the load on the
pinion and it made all the difference. The load on the pinion was far too strong and having fitted the rack and setting the toe to parallel by eye it
self centers better than I've had yet.
Looking forward to setting the steering properly this weekend. Problem sorted.
A dicky rack was to blame, as supplied and modified by MK! Cheers guys.
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MikeRJ
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| posted on 30/4/09 at 10:32 AM |
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Very refreshing to see a thread where people are actually investigating and correcting the causes of self-centring problems rather than fitting valves
spring to rack etc!
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craig1410
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| posted on 30/4/09 at 10:47 AM |
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quote:
Originally posted by MikeRJ
Very refreshing to see a thread where people are actually investigating and correcting the causes of self-centring problems rather than fitting valves
spring to rack etc!
I'd like to think that, even if self centering was "fixed" for SVA, as soon as the builder drove the car on the road they would
realise that all was not well with the steering. My car passed SVA without valve springs or similar but SC is almost non-existent and definitely not
good enough in my opinion. I think I have a sticky rack so will be stripping it down at the weekend.
Cheers,
Craig.
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