MGB GT Handling

[Martin Green]

Any suggestions of how to improve the handling of my 1970 MGB GT. At a recent MGs on track day I found that it under steered into the tight bends and when I tried to bully it to turn in the rear end still gripped solidly while the front end hopped around!
Car has already has Gaz adjustable shocks, uprated strings, anti roll bar and fully poly-bushed.
I have thought of fitting the lower wishbone arms which give some negative camber to the front wheels but have been advised that they are really just for racing and not for the road.
Any advice from more experienced owners would be most welcome.

[John Watson]

Hi Martin. I am a great believer in experimenting with tyre pressures. It sounds as if your rears my be down. Also how is you suspension set sometimes it is better to be soft rather than to hard.
John

[Peter Cresswell]

Hi Martin
I think you have discovered that a car set up for the road doesn't perform well on a track and the vice versa is also true. It is also the subject of a talk I give about Modifying Production Cars for the Road and Competition, which might appeal to some of the larger natter meetings or groups of MGs on Track people. Most road cars will inherently understeer because this is considered to be safest for most car buyers.

Suspension design is also a huge subject which can take up entire books - all of which describe the science of suspension objectively. How the car reacts to your driving style is subjective and is described as handling. Modifications to a basic design will also fill a number of books!!! Hence a lengthy reply to your question!

To start, and apologies for being blunt here, if you try to 'bully' the car into a corner it will almost always understeer as the steering and braking action throws the weight onto the front axle which overloads the tyres and they lose grip. Braking incidentally is the hardest skill a driver has to learn - much harder than acceleration and steering. But all three of these skills of driving are about managing weight transfer. So there may be nothing wrong with the suspension set up at all!

John W comments about tyre pressures can go some way to dialling out understeer. The higher the pressure (within reason) the more grip the tyre can generate as this stiffens the sidewalls of the tyre so it doesn't deform. I use 27psi front and 24psi rear on the road using 185/70 x 14 tyres, which is in the range recommended in the Special Tuning Booklet for the MGB. The Owners Handbook pressures for the MGB of 20 -21psi front (+6psi for high speed) and 24psi rear (+6 for high speed) were for 1960s radials and tyre technology has moved on enormously over the intervening 50 years! I have attached a slide from my talk showing a simple way to optimise tyre pressures to suit your driving style.

The first thing to realise is that all the suspension components interact with each other so it is very easy to end up with something much worse than the standard car, but with some knowledge you can make it better for a particular application. I can summarise the main effects of suspension for you (and hopefully the formatting will stay in place to allow this to be read easily!):

Antiroll bars - Increasing the stiffness at the front increases front roll stiffness, increasing understeer, or decreasing oversteer.
Decreasing the stiffness at the front, decreases front roll stiffness, decreasing understeer or increasing oversteer.
Increasing the stiffness at the rear, increases rear roll stiffness, increasing oversteer or decreasing understeer.
Decreasing the stiffness at the rear, decreases the rear roll stiffness, decreasing oversteer or increasing understeer.

Camber: Zero and negative camber improves tread footprint when cornering. Increases steering effort.Improves turn-in and
reduces understeer. You can get negative camber without using the negative camber bottom arms by lowering the
car and/or by using the offset top trunnion bushes (they have an offset hole) Part No. 8G621O/S from B&G. I
haven't seen these listed elsewhere. You need to aim for the tyre to be flat on the road under maximum cornering.

Castor: Increasing castor improves turn-in. Increasingly adds to camber angle as more lock is applied. Increases steering effort,
and makes the car reluctant to change direction. The MGB is generally considered to have too much castor as standard
and kits to reduce it to 4 degrees are available, but you have to correct the steering column angle as well.

Toe: A small amount of front Toe – out reduces understeer. A small amount of rear Toe – out increases oversteer.
Toe – out makes the car unstable.

Springs and Dampers
These must work in harmony, so if you increase the spring rate then the damping rate normally has to be increased as well.
Don't use springs or dampers to control roll - that is the job of antiroll bars. However class regulations may force you
to do this - e.g. the standard classes in sprints and hillclimbs.

A final thought for now! The MGB like many cars from the 1950s to 70s used independent front suspension and beam axle rear. This is just about the worst combination for a rear wheel drive car as the design gives a high roll centre at the rear (the roll centre is in the centre of the diff casing) and a low roll centre at the front. Again this inherently makes the car understeer!

[David Witham]

A lot of good information there from Peter.

An additional point I would make is that increasing the stiffness of rear springs on an MGB increases the tendency for it to pick up its inside rear wheel on a tight turn. This limits when you can get the power on coming out of that turn.

[Jeffrey Lister]

Hi Martin,
I fitted negative camber lower wishbones plus Superpro poly bushes, 7/8th anti roll bar (front only) and uprated lever arm shock absorbers.
Tyre pressures set at 26-28psi front and 28-30psi rear. These mods transformed the handling. The front bites into the corner with very little wallowing and using the old technique of slow in, fast out the car is balanced and brings a smile if executed properly.

It also helps to have decent tyres mine are Yokohama's, I also have a similar set up on my V8 GT except I installed Telescopics and again the car is stable and a pleasure to accelerate through a corner.

Ultimately its personal preference as to achieve the fastest cornering speeds you will probably have to sacrifice some of the compliance and softer ride during normal road use.

Good luck in quest.

Jeff Lister

[Martin Green]

Thanks for all the information and advice. Lots of things to try.