Self Centering?

[Guest Taffy Rob]

SVA Retest is Tuesday

And...

everything is sorted except the self centering steering

So far, I have greased the rack, added much toe in (wheel arches now touch headlamps on full lock), and added as much castor as possible. I have read how people had over an inch or more of space between the lower back wishbone mount and where the wishbone naturally ends, on mine there was a bare 1/4 inch. I've now spragged it out and squeezed some washers in but it doesn't seem to have helped. Has anyone got any more ideas to try???

Cheers

Rob

[Jon Bradbury]

Yes.

 

I am assuming you are not going to move the rear mount point for the bottom wishbones to get more castor as Richard says in his video. If you do decide to try this you'll have to make a plate up and the original chassis hole would have to be drilled out to make a slot, if you get my meaning.

 

Otherwise...

 

Make sure the steering rack isn't stiff (mine is) and grease it well, and that the other parts are moving freely (steering bush / universal joints / ball joints / etc). Check for minor obstructions (for example, on mine the steering column shroud mount bracket (a small bent piece of metal atop the column) got bent and rubbed against the steering wheel - this gave stiffer steering. Best way to do all this is to get the front wheels off the ground and have a good play. You might also try raising the rear (this will have the effect of altering the castor angle slightly in your favour) and perhaps increasing tyre pressure at the front to reduce turning friction (that is turning about the steering axis). As a last resort you might try increasing the weight over the front axle - so that the self centering effect overcomes the friction in the steering, although I wouldn't drive back to the SVA centre too "enthusiastically" with this setup if I were you...

 

Check this out for more information: Automobile Ride, Handling, and Suspension Design

 

I think there's something else you can adjust to affect the self centering - camber? Can't remember because I haven't read it for a while.

 

 

 

Cheers

 

JonB

 

(Added later) Sorry that should have "read steering axis inclination", not "camber". If you read the article you'll get the gist...

Edited April 11, 2003 by Jon Bradbury

[Guest Daz]

I also believe that if you give the car a little bit of toe-out instead of toe-in it helps the self-centring also. (That's what I did to make sure!).

 

I would be careful about having any part of the wheel assembly touching any part of the main body of the car when it is on full lock. I think it may be a fail point, even if it is only the cycle wing touching the light.

 

Daz

[Longboarder]

Not sure which way you have moved the wishbone. You need to produce 5-7 deg positive castor by moving lower wishbone forward and upper wishbone backwards. Phone around to find a garage that can competently measure suspension angles. Second set camber to zero to minus one degree. Then toe in to half a degree. Important to do in that order. These are very much baseline sort of figures but should give some self centering and a reasonable drive. You then tune the angles to suit yourself after you have driven it a bit.

[Jon Bradbury]

Longboarder -

 

That is a very good answer. I was wondering what I shoud set the suspension settings to intially.

 

Thanks!

 

JonB

[Guest Ant]

How is the caster angle adjustable on a 2B wishbone set up?

 

Surely both wishbones are fixed at the front with the box section mounts. On mine there's no spacers in there - the box section is a tight fit on the wishbone bush.

 

Ant

[Jon Bradbury]

Ant,

 

This is from my admittedly limited experience of the 2B DOHC kit. so apologies if it isn't appropriate to your chassis.

 

Here's what Richard says on the second build video:-

- the top wishbone isn't adjustable

- the bottom one is, by drilling the rear mounting holes inboard or outboard relative to the front mount holes. This has the effect of moving the bottom ball joint fore / aft in an arc. Move the rear mount holes for the bottom wishbone inboard to increase the castor and outboard to reduce it.

- 5 degress +ve camber is the target

- This is what they have drilled the front (of the box section) holes for

 

As I said, some of these holes are already drilled for you so that is why I mentioned making up a plate (to cover the already drilled holes). Its not really that difficult, but a pain in the arse if you have to do it in the short term, because you'll be dismantling the front suspension. Try those other ideas first (especially steering friction reduction and jacking rear end up).

 

As a rough guide, level the chassis (with jacks / axle stands), make both wishbones horizontal (probably helps to remove the shockers and wheels) and line a plumbob (or a nut on the end of a piece of string) against the middle of the top balljoint. If the same point on the bottom one is behind the string (ie, on the side nearest the rear of the car), then you're in +ve camber. On the other side, its -ve. If you had a protractor and straight rule you could actually measure it (albeit roughly).

 

I could post a diagram if its any use...

[Longboarder]

Sorry mine's a series three. I hadn't realised you 2b boners had no adjustment at all. Has any 2B boner had castor measured by someone who knows what they're doing and if so what was the result? Changing castor would have to involve remaking one of the wishbones or welding on new wider brackets to the chassis to allow shimming one of the wishbones fore or aft. Probably safest to do the upper wishbone as its the least stressed but it should be done by an expert. Still not adjustable so get the maths right. (I went this route on my three because the geometry was so bad even with adjustable top and bottom wishbones!) Would be interesting to measure a few 2B's to see what sort of figures emerge.

As a rough guide, level the chassis (with jacks / axle stands), make both wishbones horizontal (probably helps to remove the shockers and wheels) and line a plumbob (or a nut on the end of a piece of string) against the middle of the top balljoint. If the same point on the bottom one is behind the string (ie, on the side nearest the rear of the car), then you're in +ve camber. On the other side, its -ve. If you had a protractor and straight rule you could actually measure it (albeit roughly).

Jon I think what you are describing here if I correctly understand you is negative castor. You need positive like bicycle forks.

Nigel

[Guest Taffy Rob]

Cheers everyone for the help

As above, the castor angle is pretty impossible to change, I have moved the top back and the bottom forward by a washers thickness each (all I could squeeze into the mounts), and altered the steering inclination (by altering the neutral camber), and hey presto I have self centering. If you are VERY enthusiastic about testing it. The bloke said that he only wanted to see a small 'tendancy' to self centre, so hopefully this will be ok. If not, the only other thing I can think of is that I noticed when checking over the entire system the bottom uj (splined shaft out of the steering rack) works at quite a tight angle, so maybe some kind of angled spacer could be in order to make the rack meet the steering shaft better?

Thanks again

Rob

[Jon Bradbury]

Jon I think what you are describing here if I correctly understand you is negative castor. You need positive like bicycle forks.

D'oh!