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MG MGA - Race question Caster angle

Any thoughts on what optimum caster angle I am looking for, for track use I have just got some new Moss shocks and the arms are different lengths, so 1 of them will have to be 'adjusted'

CP
Colin Parkinson

changing the length of the shock absorber arm will not change the caster angle. It will however change the camber angle
Bob

Answered that at work and thought others would give follow ups. Not to worry, yes changing the length of the shock arm ie shortening the top link will give the front suspension more negative camber.
How much you want csn be influenced by many thing not least of which would be how much cornering are you doing compared to straight road. With general circuit use I would expect 5 to 7 degrees would be a good starting point.
Bob (robert) I am turning? yes I once owned an MGWasp!!

Colin, AFAIK there is not an easy way to change the caster angle on a MGA. The camber angle is usually changed by using longer or shorter lower A arms, not modifying the shock arms. If the arms on your shocks are not the same length, I would check with Moss, I'm not aware of any changes in arm length on MGAs, you might have a shock from another type car.
Bill Young

Thanks everyone. It was late when I wrote that!! Of course it is camber that would be altered!!

The current shocks from Moss are the Australian ones for the B with different arms fitted for the A.

Production tolerences for these arms are not good.

Bob are you quoting 5-7 degress of caster, or camber??

I have already fitted neg camber lower arms. engine is not in yet, so geometry not checked.

Thanks for all your help

CP
Colin Parkinson

I was quoting Camber. I too have negative arms on my A and it turns in as if on rails but is only a road car. Not too sure how much is the camber or how much is the big anti roll bar. At lower speeds it must be the camber doing the work though I think. With a rear wheeled drive car I think caster is not as necessary as with a front wheeled drive car and other items ought to come first.
Bob (robert) I am turning? yes I once owned an MGWasp!!

Bob 5-7 degrees is a lot of neg camber!! Cannot measure mine until body on and engine in.
Which anti roll bar are you using?

I am using a B 3/4 for a start, with rose jointed links, and solid alloy mounts.

CP
Colin Parkinson

Respectfully suggest that 7-8 degrees camber is way too much. Will reduce ability to brake by rudcing contact patch size, and even in roll, it's unlikely you'd be at maximum grip du to being to far negative.

Bob- Can I ask what basis you have for believing this much camber (I am assuming it's negative camber) is good?
greg fast

Naturally it is a balancing act and you are correct Greg in your thoughts on braking. The more upright the wheel the better the braking grip in a straight line will be.
On the other hand no negative at all and the contact patch of the tyre when the car is going around a corner is drastically reduced and therefore corner speeds are reduced.
In my original post I made mention to this specifically when I said how much is totally dependent upon the ratio between straight road and corners. On a race circuit it is mostly corners and thus a lot of negative could be an enormous advantage but it is a balancing act. Grand prix cars have an awful lot!
I have not specifically measured mine but with the negative bottom arm it certainly looks like at least 5 degrees and I think that the car turns extremely well on the road. Perhaps I don't push the braking too hard but hard enough.
Bob (robert) I am turning? yes I once owned an MGWasp!!

Modern radial tyres are much more forgiving when running negative camber than the old bias ply tyres. When these cars were designed the bias ply tires wouldn't run well with much negative camber, as the stiff sidewalls caused a significant reduction in contact area when running straight. The reduced sidewall stiffness in radials allows for reasonable negative camber in a straight line and perform better with some negative camber when cornering.
Bill Young

My racer is set up with 3deg total that's 1.5 per side and a Addco 3/4 or 7/8 anti roll bar can't remember which.

Look up Barney Gaylord's site for bar fitment details.

It all works REALLY well together!

j
JohnB

This thread was discussed between 04/04/2006 and 06/04/2006

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