Eggy
|
| posted on 26/9/08 at 07:31 PM |
|
|
Self centering....
Ok, it's driving me mad!
I've read loads of posts, looked on the net, and asked at the Speed Trials. All with diferent answers - what's correct?
Is there a definate fix for this (raising the rack, using valve springs, over inflating tyres etc).
What's been done before that works??
Photo's would really help too!!!
Cheers,
Kev.
|
|
|
|
|
Paul TigerB6
|
| posted on 26/9/08 at 07:37 PM |
|
|
trial and error seems to be a good starting point - see what works on your car!! 
Start with a bit of toe out and see how that goes
|
|
|
blakep82
|
| posted on 26/9/08 at 07:37 PM |
|
|
then a bit more castor
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
|
|
|
chrisg
|
| posted on 26/9/08 at 07:45 PM |
|
|
Note to all: I really don't know when to leave well alone. I tried to get clever with the mods, then when they gave me a lifeline to see the
error of my ways, I tried to incite more trouble via u2u. So now I'm banned, never to return again. They should have done it years ago!
|
|
|
blakep82
|
| posted on 26/9/08 at 07:46 PM |
|
|
mmm worms on toast
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
|
|
|
jacko
|
| posted on 26/9/08 at 07:56 PM |
|
|
What car you building ie MK / locost /MNR / it may help us help you
|
|
|
paulmw
|
| posted on 26/9/08 at 08:38 PM |
|
|
I got really pi$$ed off with this when building my Indy. Most answers to the problem were either sarcarstic or wrong.
In the end I added some valve springs to the rack and on the SVA the steering would magically spring back.
....... step away from the soap box................
|
|
|
simonk
|
| posted on 26/9/08 at 09:02 PM |
|
|
Some sensible tips would also be appreciated here also. Castor is the obvious one but that's set by the front end geometry for most of us. I can
rotate the mushroom to drop the upright back a bit to get a little more trail and was planning some toe-out and 40lbs of tyre pressure. I have already
juggled wishbone washers to move the bottom bone fully forward and the top one fully back and on my exploratory drives down the lane it's still
not great.
Any other practical tips would be very welcome.
|
|
|
Eggy
|
| posted on 26/9/08 at 09:25 PM |
|
|
quote:
Originally posted by paulmw
I got really pi$$ed off with this when building my Indy. Most answers to the problem were either sarcarstic or wrong.
In the end I added some valve springs to the rack and on the SVA the steering would magically spring back.
....... step away from the soap box................
I've heard about this but can't get my head around it, anyone got some pictures?
|
|
|
NeilP
|
| posted on 26/9/08 at 09:45 PM |
|
|
Some trailing hub helped mine a fair bit after shuffling the wishbones as far as washers would allow - From my experience, toe in/out and tyre
pressure seemed to have a very limited effect...
If you pay peanuts...
Mentale, yar? Yar, mentale!
Drive it like you stole it!
|
|
|
whitestu
|
| posted on 26/9/08 at 09:48 PM |
|
|
Valve springs in the rack were the only things that made a difference on my Indy as well.
I think the proper fix is to make new top wishbones with more castor.
Stu
|
|
|
mark chandler
|
| posted on 26/9/08 at 11:14 PM |
|
|
Caster is the key, look at any motorbike, the forks always lean backwards, the principle is exactly the same.
So twiddle the mushroom, pack the bottom bones forward with washers and the top bones backwards or better still make some new top ones, they are easy
to make, you just need a bit of board and some nails to make a jig.
Regards Mark
|
|
|
zetec7
|
| posted on 27/9/08 at 04:09 AM |
|
|
Or, maybe it's possible to cut the upper a-arm mounts off and move them rearward, ideally 1" or so. We designed our a-arm mounts to be
adjustable for caster angle - we can add as much as another 1" rearward displacement of the upper 'bones.
And, yes, caster is the ONLY right way to add self-centering. Toe-out = twitchy steering, toe-in = rapid tyre wear & rapid onset of understeer in
corners.
As for valve springs in the steering rack...well, I suppose it works, but it strikes me as fundamentally wrong for some reason...probably because
self-centering is suppose to occur automatically as a result of good suspension design and adjustment. I suppose you could use bungy cords on the
steering column...
http://www.freewebs.com/zetec7/
|
|
|
David Jenkins
|
| posted on 27/9/08 at 07:00 AM |
|
|
quote:
Originally posted by paulmw
I got really pi$$ed off with this when building my Indy. Most answers to the problem were either sarcarstic or wrong.
The fundamental problem is that nearly all the kit manufacturers are selling chassis & front suspension with a design flaw built in - for road use
anyway.
The original design with minimal castor is fine for the race track, where self-centering isn't a major concern and the lightness of the steering
is a bonus. For the road a lot more castor needs to be built into the design, and no amount of fiddling about can rectify its omission. People worry
about it for the SVA, when in reality it's essential for comfortable and safe road driving.
The fix is really easy for the kit manufacturers - make a minor adjustment to the top wishbone jig, so that the top pivot is about 22 - 24mm behind
the lower pivot - and a lot of people will be a lot happier.
Until builders put a significant amount of pressure on the chassis makers, the issue will continue to come up here, and the silly answers will
continue, as everyone here who's built a commercial kit knows that the fundamental error is built-in and can't be fixed by half-arsed and
potentially dangerous bodges.
And that's my 2p's worth for the morning!
[Edited on 27/9/08 by David Jenkins]
|
|
|
flak monkey
|
| posted on 27/9/08 at 07:24 AM |
|
|
My GTS self centres brilliantly. Not sure what the offset is on the top wishbones, dont think I ever measured it.
Front geometry is set to the same as the caterham set up. Lots of camber and very little toe. Sticks brilliantly into the corners and get full tread
contact on the tyres running 17psi per corner.
David
Sera
http://www.motosera.com
|
|
|
britishtrident
|
| posted on 27/9/08 at 07:59 AM |
|
|
Rotating the Mushrooms will have no effect on caster
|
|
|
Mole
|
| posted on 27/9/08 at 08:03 AM |
|
|
Anyone would think you'd mentioned that before.
|
|
|
britishtrident
|
| posted on 27/9/08 at 08:03 AM |
|
|
Increasing the king pin inclination will help ----- this can be done by rotating the mushrooms.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
|
|
|
whitestu
|
| posted on 27/9/08 at 09:10 AM |
|
|
I got next to no difference in self centring however I adjusted mushrooms and toe.
I agree the bones should be made differently, and will be trying this next.
I used springs for SVA which worked [they also limit lock which helps to prevent brake pipes fouling as well], but I took them off straight after.
They are a bodge and I'm surprised MK recommend it [which they did to me when I phoned up for help].
I'm sure someone could make a few quid if they started selling modified top bones. as most people who buy kits do so cos they don't want
to start making chassis bits.
Stu
|
|
|
t.j.
|
| posted on 27/9/08 at 06:32 PM |
|
|
quote:
Originally posted by britishtrident
Rotating the Mushrooms will have no effect on caster
you don't have to scream...
My caster is adjustable by moving the mushrooms/shims in the brackets in the lower and upper wishbones.
So pictures could be helpfull, to understand each other.
I want to know which mushroom is pointing at? KPI adjustable?
[Edited on 27/9/08 by t.j.]
Please feel free to correct my bad English, i'm still learning. Your Dutch is awfull! :-)
|
|
|
mad-butcher
|
| posted on 27/9/08 at 07:43 PM |
|
|
Just a couple of observations, not that I know what the F**K I'm talking about.
1. By rotating the mushrooms would this not make the problem worse. my nut is a the front meaning that the upright is fully adjusted to rear, if I
rotate the mushroom it will push the upright forward, surely the opposite effect to what we are looking for.
2. if by moving the adjustment towards the the rear of car. by moving brackets rearwards or by remaking the top wishbone, is this not going to put too
much strain on the ball joints.. my bottom one alresdy looks at a frightning angle.
3. the use of springs to induce self centering seems a bit weird to me, my transit, my 7.5 ton works vehicle and the wifes pajero all self centre from
very little movement of the steering wheel, so what benefit do springs serve, or are we saying that for the sva they only test for self centering on
full lock.. (a position of the steering that I think most people would rarely use) when are you ever on full lock in normal motorway driving.
Tony
[Edited on 27/9/08 by mad-butcher]
|
|
|
simonk
|
| posted on 27/9/08 at 10:21 PM |
|
|
Agree, the ball joint on my mushrooms is currently directly adjacent to the wheel - if yours if fully forward then whatever you do will reduce trail.
I will try moving the mushroom round to push the upright back as far as possible.
To clear up the discussion and agree with Triton adjusting the mushroom has no effect on caster or king pin inclination. All you can do with the
mushroom is add or reduce trail (how far the contact patch is behind the point where a line drawn through the upper and lower pivot hits the ground)
by moving the axle position in relation to the line described above. Increasing caster angle adds trail in addition to adding to the jacking effect of
adding lock.
I won't be getting new top bones made by next SVA date so will be adding max trail (with the mushrooms) and will be upping the tyre pressures.
Will let you know what happens.
Thanks
Simon
|
|
|
MikeRJ
|
| posted on 28/9/08 at 11:27 AM |
|
|
quote:
Originally posted by mad-butcher
3. the use of springs to induce self centering seems a bit weird to me, my transit, my 7.5 ton works vehicle and the wifes pajero all self centre from
very little movement of the steering wheel, so what benefit do springs serve,
It's a total bodge to get the car through the SVA.
|
|
|
t.j.
|
| posted on 28/9/08 at 07:22 PM |
|
|
quote:
Originally posted by simonk
Agree, the ball joint on my mushrooms is currently directly adjacent to the wheel - if yours if fully forward then whatever you do will reduce trail.
I will try moving the mushroom round to push the upright back as far as possible.
To clear up the discussion and agree with Triton adjusting the mushroom has no effect on caster or king pin inclination. All you can do with the
mushroom is add or reduce trail (how far the contact patch is behind the point where a line drawn through the upper and lower pivot hits the ground)
by moving the axle position in relation to the line described above. Increasing caster angle adds trail in addition to adding to the jacking effect of
adding lock.
I won't be getting new top bones made by next SVA date so will be adding max trail (with the mushrooms) and will be upping the tyre pressures.
Will let you know what happens.
Thanks
Simon
I don't know what, but you can increase your caster by moving the upper wishbone to the rear and the lower wishbone to the front.
wishbones seen from above
[Edited on 28/9/08 by t.j.]
Please feel free to correct my bad English, i'm still learning. Your Dutch is awfull! :-)
|
|
|
David Jenkins
|
| posted on 28/9/08 at 09:17 PM |
|
|
An alternative would be for the chassis builder to fit extra-wide top pivot points - the builder could use washers or spacers to put the wishbones
precisely where he/she wants them.
So, as I said earlier, the kit makers could remake their top wishbone jig, or the pivot point jig, or the shape of the pivot points, to permanently
solve the self-centering problem. None of these are hard or big jobs.
So why don't they?
|
|
|
