Lowering MGF Suspension
When to lower/ Methods of lowering/ Conclusions/ Motorsport notes
See also: DIY Lowering

Because of the Hydragas suspension design, your MGF is actually exceptionally easy to raise or lower through addition or removal of Hydragas fluid. But is it advisable, and can one do it ones self? The answer is depends and yes respectively. You can lower your car- but you must proceed with caution. And ideally you should have easy access to a hydragas pump.

When does lowering make most sense?

Why might you consider lowering your car? Firstly, there are many MGFs that have unnecessarily high ride heights. Essentially any ride height above 368mm is regarded as acceptable, and most dealers will not touch your car to lower it even if the ride height is over 395mm (like mine was - pictured back in 1998, right) because of the problems associated with the lowering process. But suspension this high is detrimental to handling. You can, therefore, lower your car within the manufacturers' limits to the benefit of handling (lower centre of gravity) and appearance without excessive geometry change or insurance implications so long as the car remains above 358mm. Any back street garage that services Metros can alter your car’s ride height. The Hydragas valves (that look suspiciously like tyre valves) are located in the front bonnet under the black shroud [for pictures, click here]. With due care with a friendly mechanic, you can lower the car for as little as ten quid. ALWAYS have the tracking rechecked once the ride height has resettled (leave at least 3 hours, ideally after a short drive over some speed bumps and a cooling off period). It is not uncommon to find that one side has been lowered more than the other has, so you may have to head back to your friendly mechanic friend to get the car pumped back... Id warn you that this is a tricky and potentially lengthy process to get spot on.

Measure ride height from the front wheel centre to the wheel arch lip vertically above it.
Manufacturer's specification: 368mm +/- 10mm @ 17C.
Temperature corrections: 0.4mm per degree celcius from ideal reading temperature, therefore:

Temperature

"Ideal" ride height

15 C

367.2 mm

17 C

368 mm

19 C

368.8 mm

Due to manufacturing tolerances, you may find that the camber is out by up to a degree even with the ride height within the normal range. On my car @ 340mm (17C) the rear camber is out between 30 minutes and one degree; so far after over 60k miles, there is no discernible uneven tyre wear (3 sets of tyres; no uneven wear detected). [TIP: always park with full steering lock- not only does it make it more difficult for a thief to tow your car away, it also means you can always observe tyre tread casually and regularly]

Methods of lowering an MGF

There are two methods of lowering a F. Hydragas depressurisation and/or installation of lowering knuckles.

Hydragas Depressurisation

Depressurisation of Hydragas by extracting some of the fluid medium from the suspension system is a widely used approach to lowering the MGF's suspension - as has been discussed above. But depressurisation in this fashion will have effects both on the damping characteristics and on the spring rates of the Hydragas spheres (read more here). Put simply, the lower the pressure of the fluid, the softer the damping and springing - ultimately reducing suspension control. This is why companies that lower MGF suspension systems in this way (like Motobuild) strongly advise the fitment of up-rated dampers. MG advise a Hydragas pressure of 400psi - and suggest that damage can occur to the Hydragas units if this is significantly reduced. Therefore you are well advised to opt for the other method of suspension lowering if a ride eight of less than 358mm is desired - as 350mm equates to approximately 300psi...

If you fancy giving the depressurisation lowering approach a go, then proceed with caution, be aware of the problems mentioned above, and follow the link below:

>> How to lower the suspension myself <<

Lowering Knuckles

The alternative to depressurisation is to use lowering knuckles, as marketed by Mike Satur, Brown and Gammons and Moss International. Tech-speed take their own approach, but effectively they shorten the combined knuckle/displacer cone length. The knuckle is a simple mechanical rod that connects the Hydragas sphere with the upper wishbone (pictured right: A - standard knuckle, B - Trophy 160 knuckle). Putting in a shorter link or knuckle will lead to a correspondingly lower suspension height, but with the advantage that the pressures within the spheres, and therefore spring and damper rates, are unaltered. Read more here. Lowering the suspension in this manner will lead to a dramatically lower chance of damaging the internals of the sphere that can result from depressurisation.

Given the relatively low unit cost of lowering knuckles, and the potential longevity benefits to the Hydragas spheres, I’d certainly recommend anyone who is seriously looking into lowering their car to take this route.

Frankly, having tried both methods: lowering to 340mm on pressure and lowering to 340mm with knuckles, the difference in ride and handling is appreciable. The knuckle approach is massively superior. Actually, I found the handling superior with a standard ride height compared to depressurisation because the suspension doesn't spend the whole time banging along on the bump stops!!!

Conclusion

The suspension of an MGF is a marvel of productionisation that will give many thousands of miles trouble free service with excellent ride and handling characteristics. But it is essential that the tracking be set up correctly to avoid unnecessary tyre wear.

Lowering the MGF is a surprisingly simple process that even can be done easily by a DIY novice, but unfortunately the pitfalls are many, and are equally easy to fall into. ALWAYS get the tracking checked after your car has been lowered.

When lowering the car, two rules apply:

  1. When lowering the car within the manufacturer’s specified range, no suspension modification need necessarily be considered. Lowering knuckles may be a good idea, to the benefit of the Hydragas sphere longevity. Always ensure exacting depressurisation methods and checking of tracking after any suspension height change.
  2. When lowering the suspension further than the recommended range (lowest, 358mm), one should always use lowering knuckles, consider up-rating the dampers and bear in mind issues relating to camber adjustment. If no camber adjusters are available then you may have to accept increased rates of tyre wear.

You should note that your insurance company will certainly want to be informed of any suspension modifications that necessitate new parts or bring the car's suspension outside manufacturer's tolerances.


Competition note for Speed and Race events following MGF Abingdon Trophy regulations.

Lowering the car to within manufactures specified limits IS allowed under the standard class regulations for the Abingdon Trophy and the Moss International Speed Chamionship. Similarly the fitment of non standard dampers are allowed, so long as they are non adjustable. Current ride height limit is four inches as measured from the ground to the bottom of the sill (4/5/99).

As of the start of the 2000 season, lowering to a ride height of 320mm is permissible, and lowering knuckles are allowed to be employed to achieve this.

Any other modification - and that includes up-rated, non-standard suspension bushes - are unlikely to pass the scrutineers inspection.