OK so i've just got my MK on the road and when i hit 60mph the car seems to steer itself left and right!!! Quite alarming!!! It gets even worse when i'm doing between 60-80mph and i let my foot off the accelerator pedal? What does all this mean?

I have never setup self centering and the steering wheel never wants to pull back to the center, is this my problem? If so what shall i do about it?

Hello,

I've gotten the same.

Now i got the rideheight set too 110 mm front and 140 mm rear and it's compleet over.

Also check front wheels 0.5 degrees toe out.

Daniel

sounds like a lack of self centering to me, my car does this too. Are you sure the top bones are on the right side to give suitable castor?

quote:

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Originally posted by Smartripper
Hello,

I've gotten the same.

Now i got the rideheight set too 110 mm front and 140 mm rear and it's compleet over.

Also check front wheels 0.5 degrees toe out.

Daniel

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I think the top wishbones are ok, with that little mushroom, thats all in the right place.

Shall i just adjust the steering rack so that the wheels toe in? Whats the deal with adjusting the suspension, how can that affect how your car handles in a straight line?

Originally I set my front wheels with 0 degrees toe-in (i.e. straight) and that was a bit twitchy at all speeds. Setting a little bit of toe-in settled things down a lot.

However, that was at almost any speed - if it's only going unstable at higher speeds then it sounds more fundamental (like aerodynamics). Might be worth playing with ride height, if that's worked for Daniel.

David

Hello,

I got the numbers from snoopy on the forum here,

The Indy just likes toe out,

Ride height is important look at other post here, it affects everything,

By greater speeds my car felt like riding on ice it was going from left to right all the time.

now with the ride height set and little toe out, it's like the car is on rails.

With toe in, the car just didn't drive that great as with toe out, but it's easy too try it out..

Also setting corner weight is important, but not so easy.

Daniel

Proper castor angles will solve your problems. I am glad I took that advice on here. I remade my top bones to give adjustable castor and I am running 7 degrees (car is rear engined).
I can chuck it into roundabouts and know I am going to come out of the other side.
It is worth spending time getting this right.
Toe out is a bodge and I am pretty sure it is dangerous. After all the sevens made, you would think that this problem would be sorted by now!

Hello,

Toe out dangerous ???? explain please ??

http://www.locostbuilders.co.uk/viewthread.php?tid=43717

It's the post from snoopy, and it clearly says toe out 0-1 degrees.

I tried toe in from 0-1 degrees and it'was not so affective as 0,5 degrees toe out.

Drove the car on track also and it's great fun and like on rail also in the corners.

Daniel

I have the Des Hamill book on suspension - he states that anything between 1 degree toe-out and 2 or 3 degrees toe-in will work. With toe-out or straight-ahead it will be twitchy but will corner like it's on rails. With toe-in it will be more stable, but will not corner so well.

This matches my own experience.

David

Ahh, that sounds more like it. I knew toe in couldnt be all that bad.

Toe out might be ok for a circuit, but driving for a couple of hours on UK's roads will soon get to you. With toe in the car will be more stable at speed and predictable in corners.
The idea of toe in on rwd cars is that as the thrust comes from the rear of the car, it will force the front wheels outwards. Toe-in is there to compensate so that the front wheels effectively straighten up. Putting toe out in the fronts of rwd cars means that the toe-out increases under power and causes drag.
The effect is worn tyres.
But whether you have toe in or toe out, the problem of wandering is caused by lack of castor angle and even race cars have some.
Toe out is just an attempt to counteract the lack of castor in the book locost to give the feel of self centring and is a bodge.
The original post was not about race circuits or cornering, so my answer is related to the question.



[Edited on 20/8/2006 by nitram38]

The generally accepted practice for FWD is toe out and for RWD toe in. The reason behind this is the effect on teh suspension rubbers once driving. Front wheels on a RWD will be pushed so will strain teh rubbers backwards giving slightly more toe out (hnce the toe in start). The opposite will be true of FWD as the wheels are pulling the car along so will gain some toe in.
This is all well and good but the situation is more complex than that. The aim is to have the front wheels pionting in the correct direction on corners. Obviosuly the outer wheel needs a bigger radius of turn so teh wheel needs to turn less. Ackerman produced a method if achieving this and his system is widely used in Karting circles.
It may just be that the geometry on the MK prefers toe out to correct a situation.

The "situation" is lack of castor
MK's solution was valve springs on the steering rack to help self centering instead of addressing the problem...........modifying the top wishbones.

Read the last line on this webpage regarding confusing ackerman with toe out: LINK



[Edited on 20/8/2006 by nitram38]

but my indy always self centered perfectly.

i got it set up by paul at plays kool when he was still doing bits with cars. it was set up with toe in, and handled supremely. afaics, the lack of self centring, while attributable to too little castor, can be sorted by setting up correctly.

the valve springs are a blatant bodge imo!

tom

The other setting that will make your car wander is lack of toe in on the rears aswell!
I used to race hillman imps and I took the toe in out of the rear wheels. This made it slightly faster on the straights, but a bit twitchy.
Best to get your car 4 wheel tracked if you want to drive straight!!
I bought a 4 wheel tracking machine from ebay. It is old but it works!

I'm in the process of setting my MK up as we speak.
The steering set up toe out was, I am sure, posted only for SVA purposes to get the thing to self centre, as was the valve spring bodge, as this would only work close to full lock anyway.
Mine starts to centre fine at this extreme anyway, but there is very little, read, none to speak of! at normal degrees of turning.
My front end was going very light at 60-70 , I raised the rear and dropped the front today and its made an immediate difference and feels planted up to top speed now.
I tend to agree that there could be more castor built in to the front end, but it's not just MK wishbones as i've got GTS adjustable top wishbones and I don't think they have any more..........?
Wether a heavier engine would help...
Bit slow but to add... I have seen mention before of rear wheel tracking. bt there is no adjustment on the Indy, only camber.

[Edited on 20/8/06 by ReMan]

The castor problem is caused by too many "copies" of the 7 without any thought for improvement. After you got the first one "wrong", then you would think that after all these years, it would be put right.
All that has to be done, it modify the top wishbomes.
As soon as my car didn't self centre, I asked questions on here and as soon as I got the answer, I changed my top bones.
Why spend ages building a car that is not right?
I find the whole situation bizarre, in that we are still discussing this in the first place, because this should have been sorted years ago!

[Edited on 21/8/2006 by nitram38]

Too much negative camber on the fronts will make the car 'self steer' to the undulations in the road surface. As will insufficient castor.

Give it as much castor as possible, more than 5degrees certainly, and pull the negative camber back to less than 1/2 degree.

Particularly if you are running wide, flat, low profile tyres. But no-one does that surely, do they?

Cheers,
Syd.

My car:
7 degrees castor
0.5 degrees negative camber fronts
0.25 degrees negative camber rears
1 degree toe in fronts (overall)
0.5 degrees toe in on rears (overall)

With the 4 wheel tracker, I also know that the wheels are correct in relation to each other i.e. the car does not crab.

As far as I understood it the valve springs on the steering rack were not a bodge to resolve self centering but as a means to limit the amount the wheels could be turned left or right to overcome problems with the front brake flexi hoses coming in contact with suspension components on full lock - an SVA no no, but a totally different issue.

I could be wrong.

It is used soley as a self centre measure.

I am also surprised that manufacturers haven't sorted this yet (and it's not just MK). I was fortunate in that I had heard about this problem way back, before I'd made my top wishbones. I took advice, and modified their design so that I had a fair bit more castor angle - not difficult in the slightest, just a re-jig of the jig...

I have driven a car with insufficient castor and thus little self-centering - I prefer mine, as it is a much more pleasant sensation. It is possible to take my hands off the wheel and still go roughly straight ahead, but being so light it is still easy to turn.

There's no argument as far as I'm concerned - don't do a bodge to get through the SVA - fix the problem.

David

quote:

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Originally posted by nitram38

I find the whole situation bizarre, in that we are still discussing this in the first place, because this should have been sorted years ago!

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As far as I am aware, the book is wrong.

Hi Chaz, my car does exactly the same as yours. Worst car i have ever driven. Found this post by snoopy but not tried it yet.


basic setup
tracking 0-1degree toe out
camber 1 degree in all round
caster mushroom inserts offset hole to front
tyre pressures 17 -18 p.s.i
damper settings around 7 clicks
ride height personaly about 4 inch

Will try this myself when i return from Hols.

Cheers Nige.

HI yes if the trailing arms on a live axle setup are to far of parralel that will also cause some rear steering problems. Witch means that cars such as the mk and luego need to run at about 5-6" ride hight at the rear .

cheers matt

It's an Indy (independent) so it's the rear wishbones in permanent droop by the sound of it.
Do you mean not parallel to the ground for the live axle trailing arms?, they must be parallel to each other to work or they will lock.

Hi for your average road going locost the arms parralel to the ground and each other will do. But if you want to take advantage of the fact that you have a live axle then no all i will say is do some research on mallock clubmans. If you can get the geo right then it's amazing what you can get the car to do. Get it wrong and the car has no grip and rear steers like a pig.

cheers matt

Hi rear ride hight is ussually messured just in front of the rear wheels.

cheers matt

A mate of mine has an MK Indy with the same 'wandering' problem.
He asks what tyres are you running?
He has 195/60/14 Yokohama A048's.

Hi would be worth try the 4" rh to see if the change in geometry has any benificial effect on the front. the rear needs to be level or up to 1/4" higher at the rear but all this will only work if you have the right amount of travell on the shocks ie not hitting the bumpstops or topping out . And don't forget that if you move the rh more than 4-5mm you will need to readjust the camber and tracking.

cheers matt

edit to say remember that all rh camber and tracking should be done with you or replacement weight onboard.

[Edited on 23/8/06 by procomp]

Are you sure that the lower rear wishbone slopes upwards from chassis end to wheel end when the car is at normal ride height?

If so then it sounds like an issue!

Rule of thumb is as follows:

Really the wishbones should move a roughly equal amount "above" and "below" horizontal in bump and droop.

They should also be somewhat divergent from the chassis end to the wheel end, and obviously the top wishbone will tend to need to be somewhat shorter than the lower one in order to pull on negative camber in roll.

The fact that they are divergent obviously means that the amount of movement of the upper and lower wishbones is not strictly equal above and below horizontal but you see the point I am making hopefully!

If all that is happening then the car should drive ok to a greater or lesser extent.

quote:

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Originally posted by David Jenkins
I am also surprised that manufacturers haven't sorted this yet (and it's not just MK). ........

There's no argument as far as I'm concerned - don't do a bodge to get through the SVA - fix the problem.

David

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Has anyone got a drawing for the correct wishbones, so I can make some. I am new to the site, will you need my E mail address?