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MG MGB GT V8 Factory Originals Technical - Front suspension lowering
Iíve got factory V8 which, bluntly, does not go around corners as well as it might. I was looking thru the BB archive a couple of weeks ago and found a comment that the Factory V8 had the chrome bumper front cross member with spacers between the cross member and chassis to improve clearance for the V8 sump. So I looked under the car and yes it does! These are about an inch tall. With the net result that the car sits about an inch higher at the front than a standard C/B car. The aesthetics of this I donít have a problem with. What I do have a problem with is that this moves the centre of gravity at the front of the car up. Also the centre of mass of the V8 is higher than the 4 cylinder. The net result is that the CoG of the car at the front end is higher relative to the roll centre at the front end than it was originally designed for back in 1962. So I get lots of body roll from the front end and when driven hard into corners it leans really heavily on the front outside suspension, loading it up, so that if you hit a bump with front suspension gets unsettled, steps off line and my filling rattle. Basically this makes it less fun to drive. My idea is to lower the car at the front end using shorter springs which Iíve bought from the MGOC (their R/B to C/B conversion springs). This will lower the CoG the front, however it will also affect the position of the roll centre, because the lower wishbones will no longer be horizontal. This is the point where I need your help.
Will the roll centre move down as well?
In which case the problem wonít go away. Basic principles dictate that the lower the CoG the more equal the split of weight side for side whilst cornering and hence better control of the road wheels by the suspension, which is why the racers all lower their cars down to zero.
Does anyone know how to calculate how far the roll centre will move?
I know itís a really long post but this problem is going to affect every converted rubber bumper car, not just mine, and I want to try and understand the effect of what Iím doing rather than just bolt it on and see.
Its always more fun if you play with it.....
|You need a basic text book on suspension design - for instance the one by Colin Campbell published back in the 70's would be a good place to start. I think it was called 'Sports car design and performance'.|
I belive that because of the complications you mention, somebody has designed front uprights with the stub axle mounted higher up, to lower the front end and keep the geometry the same. It's been in recent threads.
Your answers can all be found in the HP series book, How To Make Your Car Handle, by Fred Puhn. Although I've read the book some years ago when heavily involved in Auto-X'ing a Big Healey, I can't remember enough of it to answer your question myself.
For the record, my wife picked up another copy of that book because she saw it on the "$1.00 table" at a local bookstore only 2 weeks ago. She knew I already had it 'cause she bought me that one too. She just can't pass up a sale!
|Phil what you have is a Geometrical problem.. If you draw of a cross section of the front suspension before the mod and extend the line of the lower wishbones in until they meet at the centre of the car, then repeat this with the angle of the wishbone changed to reflect the decrease in spring length|
you should be able to see the change in roll centre. However you will have lowered the c.o.g as well so the couple between centre of gravity and centre of roll will be the same!
I suggest you forget lowered springs, get uprated standard springs and the vertically offset stub axles that are available from my friends MG Ltd in Greenfield Wisconsin - 001-414-529-3200 ask for Dick.
I bought some and carted them home to the UK last Summer but havent got around to fitting them yet.
What you dont want is for the lower wishbones to angle up towards the hub. The offsetstub axle prevents this maintaining the correct geometry with the wishbones more nearly parallel to the road. Get some neg camber wishbones while you are at it from Ron Hopkinson or B and G and put poly bushes in all round at the same time!
I converted a 1977 roadster to V8 and also lowered it to chrome bumper ride height.
At the same time i fitted KONI telecopic dampers and made a bracket for this which has a plate which is fitted between the cross member and the damper. In your case you could fit a plate (=spacer) only between the damper and the cross member which leads you into the direction of the original suspension geometry.
The only problem which could occur is that the original damper touches the inner wing. My plate is is not an inchi thick but approx 12 mm which doesn't lead totally to the original geometry but in practice it goes well around corners.
Also i fitted bump stops from Moss without a spacer fitted and stiffer springs. Besides this the rear springs are replaced by lower and stiffer ones.
Hope this helps you any further
|Peter van de Velde|
|Philip, The above suggestions are very good. The book |
"How to make your car handle" Is the bilble on suspension set-up I got a copy of the first eddition
Don't ask what year, I am only....years old.
Since you live in the UK I would recommned to contact
Trever Tayler he has a web page on the BBS. I feel he is the expert on suspensions and MG V8 conversions in the UK. We just spend some time together this weekend while he was here in the USA on Bus. And we discuss MG's front ends etc... He builts a excellent modern front and rear set up that would take and MG into the next century. Classic looks with 21 first century handling. He can also help you with your MG needs.
r/ Bill G.
This thread was discussed between 31/03/2000 and 03/04/2000
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