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MG MGB Technical - 660 lb front springs on RB

I am considering using the 660 lb front springs on my rubber bumper MGB. I have to imagine that this has been discussed here, but I couldn't find a clear answer in the archives.
I am setting up a '76 MGB with a 3.5L for Solo and Time Trails, and I’m curious why Moss US does not recommend PN 264-335 for rubber bumper MGB's. Moss UK has the same part (TMG40707) and lists it as applicable on these models. The drop (approx. 2”) appears to be the same as the 550 lb spring.
Given the fact that each of these shorter springs are putting the front suspension closer to the bumpstops (modified of course) I would think that the 660 lb springs would help keep the car off the bump stops under load.

Any thoughts or experience?
JCL Lagasse

I have the 550lb springs on my chrome bumper roadster which is used in sprints and on the road. Have you tried 550s? My feeling is 660s would be too hard. What have you done with your ARB and damper rates?
Are you using negative camber arms?
David Witham

David,

The shocks are rebuilt 25% uprated units and the sway bar is 3/4". I suspect that both of these will be stiffened further once I begin testing next season. I installed adjustable camber bushings in the shock arms and negitive camber A-arms. The car will not be street driven, so ride quality isn't a significant concern. Althought I have not put the car on a scale yet, I suspect the weight is about 1850 lbs., so I need to factor that in as well.
JCL Lagasse

I am very much in favour of the soft spring stiff bars school of thought. I would make an ARB change before a spring change. What is it that you don't like with the handling of the car at the moment?
J Phillips

You do realise that the Rover 3.5V8 is lighter than the 4 cylinder 1800?
Roger T

Bare engine maybe. According to the BL publications the 4-cylinder 5-bearing GT kerbside weight is 2401lb and the V8 GT 2442lb. The bottom line is it doesn't make much difference either way.
PaulH Solihull

It all comes down to how YOU want your car to feel
If you go the 650lb way you will probably need to keep the size of your front bar to 3/4 max.
If you go 550 the 7/8 bar seems to work ok but again it will depend on your driving style
A friend has 600lb springs and 7/8 bar and it tends to be a little pushy unless its getting plenty of throttle
The bump stops need plenty of clearance they should not touch at all during any event just there for emergency limit if they are too close and touch during cornering efectivespring rates go sky high
Willy
WilliamRevit

Thanks for all of the responses. I opted to install the 550# springs as a staring point. They effectively lowered the front of the car an additional 1 1/4" compared to the 480# spings that I had originally installed. This was surprising, since the uncompressed length of the 480# spring was only about 1/2" longer.
The car has not been driven since I installed the V8, so this setup is simply a starting point for next season. Obviously, I want to get the car as low as possible and still have a working suspension. With the 550# springs, dropped spindles and a slightly shorter tire (23"OD) I think I am 2 1/2" to 3" lower than a stock RB.

Joe


JCL Lagasse

This thread was discussed between 28/09/2010 and 07/10/2010

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