IVA test - failed on steering self-centring

[ian papworth]

Need help- I have my BMW Sportster with a kit car builder to set front suspension etc but they are unable to effect any self-centre into the steering after 3 days of trying ! Due for retest on Wed so I am under the hammer a bit! Tried new steering rack ,all kids of casor angle /tracking/etc but no result , Wheels are 7x17. Any help much appreciated!

[Dane_Rescueman]

Re: IVA test - failed on steering self-centring

If you have tried all the settings such as camber castor and tracking, could it be that your wheels have the wrong offset - with the tread centre well outside the extended camber line. Borrow a set of narrower wheels and see if that makes a difference.
Good luck with the next IVA.

[danny_nelson]

Re: IVA test - failed on steering self-centring

And put plenty of pressure in them for the test.

[Peterx]

Re: IVA test - failed on steering self-centring

Hi Ian,
the trick is to use 2 or 3 degrees of Toe-OUT. Yes, I said toe out. It was against all my logical thought processes but Robin suggested it and it worked a treat for my SVA. After the IVA you should put it back to about 0.5 degrees toe-in. As Danny mentioned, pumping up the tyres to about 28 psi helps as well, because it reduces the friction of the tyre at the contact with the road.
Good luck!
...peter

[ian papworth]

Re: IVA test - failed on steering self-centring

Hi Guys,
Thanks for all the tips. I have got hold of a pair of original wheels to try today. I noticed that Marlins demo car came in for comment with its lack of self centring in a Daily Telegraph road test, so is there an inherent design flaw, and if Wildmoor Kit Car Builders can,t fix it .....? Keep you posted.
Ian

[ian papworth]

Re: IVA test - failed on steering self-centring

Change of wheels made no difference. Car on trailer to Marlin next week- Mark to sort out. Hopefully if another builder has these sorts of issues there will be expertise in the club to assist without having to trailer it to Devon . I will let you know how things go.
Ian

[Peterx]

Re: IVA test - failed on steering self-centring

Hi Ian,
did you try what I suggested in my post above? If your suspension is assembled correctly, it really does work! My car passed its SVA first time with absolutely no issue with self centering. If Wildmoor can't make it work, they are not trying hard enough. Patrick Short , Robin Martin and I all passed SVA with no reference back to Marlin for help!
regards
Peter

[tim hawkesworth]

Re: IVA test - failed on steering self-centring

Hi Ian,
Sorry to note that you still have a problem
You are welcome to borrow the wheels off my Sportster [Weller Racing supplied by Marlin] although the tires fitted are probably too old to be taken anywhere near an IVA Test Station. I also have my Hunter wheels which you are welcome to.

[greatoldone]

Re: IVA test - failed on steering self-centring

Sorry to hear about another fail, Ian. As I told you over the phone, mine would have failed as the inspector said it didn't self centre, but that was down to way too much toe in.

After winding the rods out on the test day by a couple of turns on each side it passed. This was all done by eye, and as it feels fine on the road, I've left it like it is.

I doubt that there is an inherent design flaw, as many BMW based sportsters have now passed the SVA / IVA.

If the suspension looks the same as the pictures I sent you, I can only assume that the suspension mounting points are in a different location to ours...

If I recall correctly, you mentioned something to me about one side being slightly more forward than the other?

[ian papworth]

Re: IVA test - failed on steering self-centring

Thanks for all the advice on the self-centring problem I have. I have tried withe standard bmw wheels 15x5.5 and no difference.I wonder if your wheels Tim would be any different? I tried toe out and that made no difference. The only way I could get any self centre effect was when I removed one track rod and that wheel would s-centre. (The rack has been rebuilt)
THe difference in wheelbase has been adjusted out by resetting the top wishbones. I have also tried a variety of tyre pressures.
The set up looks the same as the pictures from Jason and the Marlin dvd and I took measurements from Graham Chiltons car, but still no effect.
Is there someone closer than Marlin where I could trailer the car to cast an eye over it?

Regards

Ian

[Peterx]

Re: IVA test - failed on steering self-centring

Hi Ian, sorry to hear you're still having problems. You should make sure your top wishbones are not on upside down. I understand that it is possible to fit them the wrong way up and it plays havoc with the geometry. I'm sure you've checked that already, so just a thought as your running out of ideas.
Here's mine....
http://www.flickr.com/photos/peters-bmwmarlin/1175188960/in/set-72157601555879061/

good luck,

Peter

[martinclan]

Re: IVA test - failed on steering self-centring

Have you tried some positive camber - that is the top of the wheels stick out more than the bottom. You are welcome to come and take a look at my car and take some measurements if you want. I am in Bedfordshire SG17

Robin

[jon_cox]

Re: IVA test - failed on steering self-centring

Ian,
I know this must be very frustrating for you, to get this far and then to have these problems. If the above advice does not fix the problems then I would recommend a company that I know well and would no doubt cure the problem. They are Track Developments near Castle Combe in Wiltshire. I know they are a long way from you but it would be worth it if they cured it. I used to work with one of the directors and he was a very knowledgeable chap. They have done a significant amount of rework to the suspension on the Marlin 5exi which I believe they now sell as an after market upgrade to fix all the issues with that design. Ken's car has been worked on by them so you might ask him for some feedback.
www.trackdevelopments.co.uk
Good luck......

[greatoldone]

Re: IVA test - failed on steering self-centring

Just a thought - how many packing washers do you have forward and aft of the top wishbone mounting? If you have too many to the front, that would pull the wishbone to the front of the car, making the upright more "upright". This would reduice how positive the castor angle is, which is what gives you your self centering.

I (and I bet everyone else who's steering is working) have one washer to the front, and 3/4 at the back.

[ian papworth]

Re: IVA test - failed on steering self-centring

A big thanks for all the advice from fellow Sportster owners.The visit to see Mark at Marlin went really well and I have to say that most of the tips given went into the front end rebuild.
The main issue seemed to be the ride height and angle of the track rods , and fitting shorter springs dropped the rods to horizontal. The track rod ends were swapped over and the upper wishbone spacers were evened out 3 per side- much to my surprise.
Mark was meticulous in his measuring of the upper wishbone settings and ride height. We used 1 degree of neg camber and 3mm toe-in and 18.5 psi all round. After some 3 hours the car now self-centres and rides in a very controlled way-hooray!
He also suggested not bothering with the anti-roll bar- any comments on that?
Once again thanks for all the advice. If you know of another builder that needs the "add-ons" get pass Iva I will be glad to help. Retest on 4th Oct !
Ian