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MG MGB Technical - Rear Coil springs

As you know the MGB was originally designed for trailing arms and coil springs. A prototype was tested with such, then abandoned for cost reasons. Those oversize bump stop locations were in fact the spring seats. I want to set up trailing arms and coils in the original locations. I'm looking for information on coil springs fitted to the rear of MGB's. Dimensions, ratings, free standing height, compressed height etc. anything useful when I head off to the spring manufacturer. Getting the ride height will be a trial and error process I think.
I am aware of Costellos kit, but it is way too expensive and I would prefer to fit the coils where they were meant to be. Four trailing arms and a set of coil springs. I figure I can set this up for under $700 Australian.
Can anyone help?


Peter


One example at the following site. I do not think it can be done by following the factory initial steps.


Onehttp://www.vord.net/cars/mgb_mods/rear_susp/coil_over_damper_mounting.htm

Pete
Pete

Peter, Wasn't the coil spring abandond when they flipped the car in tests? Anyways similiar ideas have floated through my mind and a three bar plus panhard rod with coil-over dampers is probably the easiest way to go. Look up pictures for the 05-06 Mustang rear suspension for a similar setup sans-coil-overs.

I just think that the coils if placed as you suggest would be too small to be effictive(too small) I don't know for sure. Coilovers will be easier to find in varying spring and load rates and their slight adjustablity might help. Try mounting them from the original damper mount, just remember the angle will decrease effectivness of damping and sprining.

Cheers
Patrick
Patrick

A suspension engineer friend of mine once said, "a spring is a spring is a spring . . .".

A spring that's coiled is not necessarily better than a spring that's flat, especially if the rest of the system is set up to accept the flat one. Now, one can do things with coiled springs that may be helpful - they can be made progressive by varying either the distance between coils or the thinkness of the wire, they can be barrel-shaped as well to increase travel as well. All of this requires some fettling and engineering and cost, you understand, of course.

There are flat spring alternatives as well. Composite leaf springs are available which provide a useful weight savings and I understand have progressive rates as well. Info in the archives.

You may be right about an intent to do IRS on the original MGB brief - but the prototype they built had trailing arms, coils and a panhard rod with a live axle. Like most of these designs, they can wind up and discharge their load in something called "snap oversteer", which is as awful as it sounds.

The MGB rear suspension is primitive, to be sure, but it works. Improvements can be made - but most of what's out there can make matters worse. You might try the relatively easy (and effective) composite leafs.



John Z

I think a coil setup can be made a little lighter than a leaf setup, but other than that, what's the point? 75 blazing HP at the wheels isn't exactly going to roll up your leaf springs.

Anyone tried those parabolic springs from MGOC? Any difference from the standard springs? Ride height issues?
Matt Kulka

These issues have been discussed at length various times on this board over the years. There are some facts that are fairly non-controversial.

1. An rear irs system is heavier than the live axle system, although the sprung weight is usually less.

2. Designing an irs that gives stable predictable handling is more dificult than a leaf spring system.

3. modifying the unitized frame on the MGB for an irs system is a major project and engineering challenge.

Some other facts.

The leaf spring is relatively heavy and has substantial internal friction. The single leaf metal or fiberglass spring is lighter and has virtually no internal friction. However the mono spring is not progressive and has virtually the same spring rate throughout it's range of travel. Arguably a progressive spring rate would be better to control the live rear axle.


The mono leaf spring is challenged with a hi horsepower application and a "traction rod" or other anti windup device is needed to stop wheel hop off the line with hi power. Doug at MGBMGA.com is now advising that the springs will fail if abused in a high power situation without a traction rod.

Having said that, I find that the ride on my MGB GT is dramatically improved with a mono fiberglass spring set. My experience appears to be typical. I'm using the stock rear shocks with a little heavier fluid. I'm planning to install a panhard rod to stop my wide tires from occaisionally rubbing in aggressive handling situations.

The GT with it's extra rear weight tolerates the stock leaf springs better than the roadster. The low friction mono springs provide an even greater change in ride and rear spring compliance with the roadster. Of course, the problem with the momentum of that heavy live axle over a bump is even more acute with the roadster.
Barry
Barry Parkinson

If you are interested in a well designed IRS set-up for the "B" take a look at the set-up by Hoyle Engineering out of England. It will hit your wallet heavy, especially if you need to purchase all the components and are unable to souce them locally. About 5.2 K US dollars.
Frank

Coincidentally, I was watching Legends of Motorsport, the MGB story today and Don Hayter was discussing this very thing. He said that they found that their test car driver who drove these cars very spiritedly actually tore the panhard attachment point away from the car under continuous heavy cornering. He also stated that the car had a tendency to wander from the rear end from this arrangement and that is why it was found unsuitable. Don also stated that he had to extend the rear of the car one inch to accommodate a spare that laid flat due to the leaf spring arrangement.
mwhitt

This conversation has wandered around a bit. I trust we all understand that:

1) Coil springs does not imply IRS. Some IRS system cleverly use transverse leaf springs (Spitfire and Corvette) and some use coil springs with live axles (early RX-7, TR-7 and MGB protoype)

2) the entire back end of the original MGB prototype was chalk and cheese to what made production. The leaf spring did lengthen the car by about an inch (it was, afterall, a long, flat spring), which permitted a flat spare, similar to the MGA. What with spring towers, a different fuel tank, panhard rod and more vertical spare, the prototype B's rear structure was completely different than the production car's. It could not be duplicated without a similar reconstruction of floor pan, fuel tank, etc., etc., a huge undertaking.

3) Logically, sufficient travel with a coil spring would be difficult without significant modifications in the florrpan to permit its vertical travel.

The easiest way to spring weight savings in an MGB is still the composite spring (per Barry). I have a friend who autocrosses a B GT, he uses the composite spring. Also, he has tried the Panhard rod, and has had the attachment point tear out during load. To work, the attachment must be strongly reinforced.
John Z

I think Peter's aim here ( I seem to remember from another thread) is better axle location. Agree with points re a spring is a spring but the good old leaf spring does no locate the axle very well, allows axle tramp, torque steer etc. A four bar trailing arm setup will positively locate the axle and separate the functions of axle location and sringing.........a good thing. If a panhard bar was added this would be a significant improvement over stock. Especially when, as in Peter's case, you have a v8.
Grant Stubbs

Aha! When I was younger, I thought meaning was important.

Now I know context is much more important.
John Z

In moments of day dreaming an innovative rear suspension design, I considered an independent rear suspension using fiberglass springs to provide suspension and wheel location, with a traction type rod going forward from the lower part of the axle/wheel hub to the chassis and a second diagonal rod from the top of the axle/hub connecting at the drive line tunnel terminus to provide lateral location and torque twist resistance.

A mount for the differential would have to be fabricated. The irs differential does have torque twist loads but no side thrust. The glass springs would not have torque twist loads, except for braking.

The major challenge would be to keep the wheel stable in a vertical axis (i.e. not wobbling) under varying side loads. A de dion solution could be used. That of course has clearance challenges and weight penalties and would probably impinge on the fuel tank.

Barry
Barry Parkinson

Barry,

Have a look to the TR6 IRS design! The rear wheels moves on a vertical axis, the differential is tied to the car body , no need to modify the petrol tank ! But I agree the lower triangle is strongly maintained in place.
A nice british design ... for once.
Renou

Has anybody tried the 'A' frame route. This is a link from the axle case to the front of the leafsprings. Tickford used it on the Capri and we all know the rear axle problems that effected them. I have also heard it used on other leafsprung cars?
Brian
Brian

Yes, I have tried an A frame to locate the axle - it was a nightmare, the handling became decidely twitchy with the car flipping sideways as if the rear tyres were flat and it snapped the spring centre bolts twice!
Chris at Octarine Services

If I remember correctly they did a lot of experiments with the MGB, ABS IRS Airbags Collapsable steering wheel, etc. Remember seeing it on an automotive show once, very facinating, Ill try to do some research on it, find website's etc. If anyone remembers, would love to hear some info on it again. If my memory serves me it was on the late model B's
James

This thread was discussed between 26/09/2005 and 15/10/2005

MG MGB Technical index

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