smart51
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| posted on 28/7/12 at 03:37 PM |
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Self centering
Enough of the car was finished this afternoon for a test drive  The good news: it goes and it stops. All the electrics work, bar a slightly dodgy
starter relay. Bad news: the speedo stays on zero and there's not a trace of self centering.
What do I have to do to the suspension geometry to induce self centering? Is there any reason why a 3 wheeler would be different (single rear
wheel)?
[Edited on 28-7-2012 by smart51]
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plutos3
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| posted on 28/7/12 at 03:49 PM |
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If every thing is square and alighned its probably just needs more caster angle
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renetom
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| posted on 28/7/12 at 04:17 PM |
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self centering
Hi
Our indy R1 had no self centering whatsoever
We changed the top wishbones to rose jointed ones and this allows you to set the caster angle at pretty much whatever
you want.
We set the caster at a bit over the top at 8 degrees , it now self centers a bit.
Good luck
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David Jenkins
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| posted on 28/7/12 at 05:49 PM |
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Before you muck around with castor etc. just check that all the ball joints are working nice and freely, and that there's no drag in any joint
or steering gear.
new ball joints can be very tight, and can make you think that there's a geometry problem - there may be a geometry problem, but check the basic
things first!
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rusty nuts
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| posted on 28/7/12 at 06:06 PM |
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I agree with David , I found my self centering vastly improved when I fitted a self aligning bearing instead of the normal Sierra steering column bush
due to it binding slightly
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smart51
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| posted on 28/7/12 at 06:08 PM |
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Thanks All. Just has a look and there's very little castor. I can only assume ai put the wishbone brackets in the wrong place. The steering
is extremely light - mosly because the whole thing weighs about 220kg. There isn't any noticeable stiffness in the joints. Looks like I need
to do some cutting and welding.
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snapper
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| posted on 29/7/12 at 06:22 AM |
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At a couple of IVA's we attended a touch of toe out got us the self centering g required fora pass
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eddie99
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| posted on 29/7/12 at 11:57 AM |
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As snapper said, toe out dramatically improves self centering.
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RichardK
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| posted on 29/7/12 at 01:55 PM |
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Pumping up the tyres can help too if this is just for Iva.
Cheers
Rich
Gallery updated 11/01/2011
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smart51
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| posted on 29/7/12 at 02:48 PM |
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Wishbones now cut and rewelded. Just waiting for the paint to dry. We'll see if castor makes a difference. What effect does camber have?
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smart51
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| posted on 29/7/12 at 07:31 PM |
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aw crap! Cutting and shutting the wishbones produced zero difference. A plumb bob and ruler measure 5 degrees of castor but there's absolutely
no return off the rack end stop. Damn.
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Hellfire
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| posted on 29/7/12 at 08:14 PM |
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Can you not fit rod ends to the top wishbone to make it more adjustable? That way, you can alter the castor (within range) until it feels
right.........
Phil
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smart51
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| posted on 3/8/12 at 05:34 PM |
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I've made another mod, shifting the top ball joint back be 12mm. Again it's had no affect. With just 70kg of sprung weight (laden) on
each wheel, I suspect there's not enough weight on the wheel to force it it centre.
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Dangle_kt
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| posted on 3/8/12 at 06:04 PM |
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quote:
Originally posted by smart51
I've made another mod, shifting the top ball joint back be 12mm. Again it's had no affect. With just 70kg of sprung weight (laden) on
each wheel, I suspect there's not enough weight on the wheel to force it it centre.
can you fit skinnier tyres?
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smart51
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| posted on 3/8/12 at 06:26 PM |
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It already has 135s on the front. I don't think you can get less than this.
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britishtrident
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| posted on 3/8/12 at 08:00 PM |
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Tyre pressures is the first thing to look at the self-aligning torque generated by the flexing of radial tyre treads generate a lot
self=centering torque, too high a tyre pressure for the weight carried by the front wheels will give very light steering but not give good
self-centering
.Most bubble car style vehicles used trail (in addition to caster angle) on the front but that brings potential problems including weather
cocking.
One thing that will improve self-centering is ackerman (toe-out in turns) you can get toe-out in turns by moving the steering rack rear wards in
relation to the track-rod ends.
Static toe-out should be avoided at all cost it can put you into a ditch very quickly.
[Edited on 3/8/12 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
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[/I]
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austin man
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| posted on 3/8/12 at 09:14 PM |
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are you sure the top wishbones are on the right side this can cause the self centering proble as it throws the Castor out
Life is like a bowl of fruit, funny how all the weird looking ones are left alone
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smart51
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| posted on 3/8/12 at 09:31 PM |
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Good food for thought there BT, thanks.
Top wishbones push the inboard suspension. Can't go on the wrong way, but a good suggestion.
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Steve Hignett
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| posted on 3/8/12 at 09:36 PM |
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I wouldn't be at all surprised that at 200 odd kilos, you didn't need even as much as 12 or more degrees of castor...
I will try and dig out one of my chassis dynamics books that has that info in it as I'm not experienced enough to remember it off the top of my
head, sorry...
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smart51
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| posted on 6/8/12 at 08:11 PM |
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Another day, another mod. This one took the castor up to 10 degrees on one side (but only 7 on the other. I'll have to check that). On the 10
degree side, the steering moved off the end stop by about 10 degrees. So some progress. How much self centering does the man from the ministry want
to see?
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smart51
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| posted on 15/8/12 at 08:07 PM |
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Well I phoned the man from the ministry who said there does need to be evidence of self centring, despite the MSVA manual not mentioning it. So
I've a carried on making adjustments. There is now some evidence of self centring in one direction but not the other. A little more should
hopefully do it.
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craig1410
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| posted on 15/8/12 at 08:54 PM |
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When trying to understand steering self centring, go and have a shot on a go-kart as they have it in spades due to extreme amounts of scrub radius.
When you turn the steering on a kart, scrub causes it to "jack up" the kart on one side and this rise in height, coupled with gravity is
what produces a lot of the self centring torque. Now you wouldn't want that much scrub radius on a car as it would dart all over the place when
you hit a puddle or went over the crown of the road etc but you might want to have a little bit to amplify the castor/trail effect you already
have.
In my opinion, wheel scrub radius is as important as castor and camber and toe all come into it as well. Your narrow tyres might actually be reducing
the centring effect. If you have at least 6 degrees of castor then castor is probably not your problem so look elsewhere for answers. If your steering
gear is moving freely and not binding then it may be worth systematically looking at scrub, camber, toe and tyre pressures.
I would start with sensible tyre pressures for the weight of the car (compare with a similar weight road car) and I would start with zero toe and 1
degree of negative camber. If possible, try and vary wheel offset using spacers or different wheels or even by reversing the wheels you have (if
poss.) and see what effect this has. I'm assuming you are testing at manoeuvring speeds only by the way so temporary spacer measures should be
safe, especially with the low weight of the car. Try measuring one thing at a time and note which measures help or hinder self centring. Then just try
to optimise for maximum centring.
HTH,
Craig.
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smart51
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| posted on 15/8/12 at 09:24 PM |
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Good suggestions. Wheel spacers might be the next step.
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Doctor Derek Doctors
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| posted on 15/8/12 at 09:53 PM |
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How much King Pin Inclanation do you have in the front uprights? KPI affect static self centering quite a lot especially when added to the effect of
Caster angle.
You can see the KPI on this pic of a Go-Kart (which we know has pretty extreme self centreing)
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mad4x4
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| posted on 16/8/12 at 06:33 AM |
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Met these guys at Stoneleigh - they know most things about suspension and could be able to assist this
problem
Scot's do it better in Kilts.
MK INDY's Don't Self Centre Regardless of MK Setting !
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