Camber adjustment.

Post by **JimK** » Wed Jul 16, 2008 4:25 pm

I'm aware that the camber of front wheels can be adjusted by adding washers between the eyebolt and the chassis leg. I need to make some adjustments - -particularly as my front wheels have different camber, for some odd reason.

What I'd really like to know is this: has anybody worked out the relationship between washer thickness and the change in camber? I know I can work it out if I know the length of the lower arm and the swivel pin, but if somebody else has already worked it out...

Post by **MoggyTech** » Wed Jul 16, 2008 5:59 pm

Adding 3mm washer should add 1 degree of camber. Make sure there is enough thread on the eyebolt nut end, when it's tightened up.

Post by **bmcecosse** » Wed Jul 16, 2008 6:14 pm

Are you sure MT - I think 3mm will only add about 0.5 negative camber - if even that. There is a limit to how much can be added - because the nut on the other end of the eyebolt must have full thread. After changing camber - you must re-set the tracking!

Post by **MoggyTech** » Wed Jul 16, 2008 7:17 pm

bmcecosse wrote:Are you sure MT - I think 3mm will only add about 0.5 negative camber - if even that. There is a limit to how much can be added - because the nut on the other end of the eyebolt must have full thread. After changing camber - you must re-set the tracking!

Yes absolutely sure. KP distance between top and bottom trunnion centres (Pivot pin points) is 9.95 inches. Adding a .118 (3mm) washer gives 0.92 degrees 'shove' outwards. Just double checked it in a CAD/CAM program to make sure my maths is still up to speed.

Not quite a full degree, but pretty close.

Post by **bmcecosse** » Wed Jul 16, 2008 7:41 pm

Hmm - ok, well if it's been checked with MATHS!!!!!!!! But i added 1/4" thick plates to my Traveller many moons ago - and it only just set the wheels to slight negative - they had been very slight positive before. Checked on flat bit of road with spirit level.
Whatever does the trick - I would suggest no more than 1 degree negative for road use - or the inside edges of the tyres will take a beating.

Post by **JimK** » Wed Jul 16, 2008 9:34 pm

Thanks for that. I've yet to measure how much camber the wheels currently have, but the nearside looks about vertical whereas the offside clearly leans outward at the top of the wheel. I can't see any reason for the difference, either. Time to get out the ruler.

I reckon there's about a centimetre of thread on the eyebolt, which gives me some scope for adjustment.

Has anybody ever produced an eyebolt with extra thread? Or some other way of allowing for adjustment?

Post by **bmcecosse** » Wed Jul 16, 2008 10:21 pm

Yes - I think there were eyebolts with longer 'eye' section (not necessarily more thread) to give some negative at one time. But if your one wheel is leaning 'in' then there must be some chassis mis-alignement.

Post by **MoggyTech** » Wed Jul 16, 2008 11:58 pm

bmcecosse wrote:Hmm - ok, well if it's been checked with MATHS!!!!!!!! But i added 1/4" thick plates to my Traveller many moons ago - and it only just set the wheels to slight negative - they had been very slight positive before. Checked on flat bit of road with spirit level.
Whatever does the trick - I would suggest no more than 1 degree negative for road use - or the inside edges of the tyres will take a beating.

Yes if you added 1/4 Inch (6mm) that would change a 1 degree positive camber to 1 degree negative. So there you have the 1 degree per 3mm washer thickness added to the eyebolt. Definately not desirable to go beyond 1 degree on a standard road car.

Tracking will be out after camber adjustments. Changing to negative camber will tend to reduce toe in, and possibly even introduce toe out.

Post by **ian-s** » Thu Jul 17, 2008 2:10 pm

Surely the camber is controlled by the length of the bottom arm/the length of the shock absorber arm , packing washers behind the trailing arm will mainly alter the castor angle?

Post by **JimK** » Thu Jul 17, 2008 2:17 pm

ian-s wrote:Surely the camber is controlled by the length of the bottom arm/the length of the shock absorber arm

Yes, and that's what I propose to do; effectively change the bottom arm length by moving the pivot outboard.

packing washers behind the trailing arm will mainly alter the castor angle?

You're right, but I don't think anybody suggested that. And what do you mean by "trailing arm"? The tie-bar?

Post by **Alec** » Thu Jul 17, 2008 6:48 pm

Hello all,

theoretically, packing the eye bolt will alter both camber and caster, as the wheel will move slightly further forward. I would guess that it is minute so shouldn't be an issue.

Alec

Post by **MoggyTech** » Thu Jul 17, 2008 6:59 pm

ian-s wrote:Surely the camber is controlled by the length of the bottom arm/the length of the shock absorber arm , packing washers behind the trailing arm will mainly alter the castor angle?

The camber is set about the following points. The top trunnion pivot pin to Kingpin. As the top damper arm is of a fixed length and in no way adjustable, it doesn't enter into the equation when adjusting camber. When you add washers between the eyebolt and chassis, you increase the active length of the lower wishbone assembly, effectively pushing the bottom trunnion further away from the centre of the car. The castor angle is set by the Kingpin inclination. Changing camber by adding washers, will have zero effect on castor angle. To change castor angle, you have to move the eyebolt along the chassis, or bend the top damper lever arm.

Post by **bmcecosse** » Thu Jul 17, 2008 8:00 pm

Dragginmg the tie-bar forward will increase the castor - done on Minis to give better traction and better 'turn in' - but not necessary on Minor with rear wheel drive. Yes - increasing the castor will v slightly increase the castor - but the Minor steering is v light anyway, so not a problem - in fact a GOOD thing! The more castor - the more negative on lock which is exactly what you want. Look at any modern car parked on full lock - the outside wheel will have lots of negative camber - but they have power steering to allow you to turn the wheel! You would need to shorten the tiebar to increase castor - can be done by slightly reducing the thickness of the inner rubber bush - but i don't suggest this for a road car. Correct way to do it would be to have adjustable length bars - v popular on Minis.

Post by **jonathon** » Thu Jul 17, 2008 9:00 pm

Not a problem BM as we already do adjustable uprated tie bars

Post by **Alec** » Thu Jul 17, 2008 9:42 pm

Hello Moggytech,

"Changing camber by adding washers, will have zero effect on castor angle."

No so, but as I said probably minimal. As the wheel moves outward by spacing the eye bolt, the tie bar will pull the arm forward so increasing the caster. To properly understand the effect, imagine doubling the length of the bottom arm , the tie bar will rotate outward and pull the arm forward. Draw a geometric diagram and tell me I'm wrong?

Alec

Post by **MoggyTech** » Thu Jul 17, 2008 10:10 pm

If you do a CAD/CAM diagram with the pivot points and standard geometry and add a 3mm washer between eyebolt and chassis, the tie bar will not be further stressed enough to cause forward movement of the lower wishbone assembly, unless all the bushes are shot for the trunnions and there is slop in the suspension.

If we want to get pedantic, ECAM gives a castor increase of 0.000001208 inches for a camber alteration of 2 degrees (6mm washer/plate on eyebolt)

I wouldn't even classify that as any movement as part of a suspension geometry change.

Further, the tie bar is free to move within the front bushings to some degree, side to side.

If it will make everyone happy, I will amend my statement to: Increasing camber by 1 degree will not cause any perceptible change to castor angle.
If you double the length of the lower wishbone, the castor will change briefly, just before the tie bar snaps, the Kingpins hits you in the face, and you wonder why you would do something quite so silly.

I'm also beginning to wonder why I bother with this Forum.

Post by **Alec** » Fri Jul 18, 2008 7:27 am

Hello MT,

Thank you.

Alec

Post by **JimK** » Fri Jul 18, 2008 9:19 am

MoggyTech wrote:I'm also beginning to wonder why I bother with this Forum.

In any forum, net-based or otherwise, there are those who will hold their own position and will disregard any evidence that contradicts it. It's like that now, it was like that on USENET in the eighties and I suspect it was like that in the Areopagus in Athens 2500 years ago

Don't let it wind you up.

Thank you very much for your information; actual calculations rather than guesswork is exactly what I was hoping for. I think I can disregard the castor change ;-)

Post by **Peetee** » Fri Jul 18, 2008 10:24 am

Jim if your front wheels are currently displaying a different static attitude and you apply more spacers to one eyebolt don't forget to check the wheel to car centreline as you may end up with even worse handling.

Post by **JimK** » Fri Jul 18, 2008 11:07 am

Peetee wrote:Jim if your front wheels are currently displaying a different static attitude and you apply more spacers to one eyebolt don't forget to check the wheel to car centreline as you may end up with even worse handling.

Fair point. Obviously, there's a significant difficulty in moving wheels in or out without changing the jommetry - could the dampers be moved in any way? I haven't got a Minor handy to have a look.

How much tolerance in wheel-to-centreline is allowable?

I strongly suspect that the chassis legs are slightly different, and that by spacing out the eyebolt I will bring the wheels back into line. I will also check the rest of the front suspension to make sure all is well.