Figure 1: the standard tie bar bush (arrowed)

Figure 1 shows a not oft-seen view of Andrew Phillips' MGF Scarlet Fever. In this view, one can see the rear subframe, the inside of the near-side rear wheel, the hub carrier, the driveshaft and gaiter, and the lower suspension components including the tie bar (the tie bar is the near horizontal bar running from the right of the picture, and passes through the lower suspension arm inside a rubber bush as arrowed). The white arrow points to part of the tie-bar bush. I wish to draw your attention to this rubber component. The car is raised on jacks for this picture, and the suspension therefore unloaded. There is a gap evident in the bush both top and bottom- but there is a significant difference evident here- there is compression of the top and expansion in the lower part of the bush. This is down to the compliance of the standard rubber bush. This poses no problem for a car on a lift, but on the road, this movement of the tie-bar relative to the hub represents a small but significant geometry change under differing loading conditions, contributing to passive rear-wheel steer.

An example of this anomaly is instability of the rear end under hard braking- and is especially evident if entering a corner. It is for this reason that those who competitively sprint or race their MGF are advised to fit RoverSport tie-bar bush spacers. These bushes may also be advantageous in other 'Fast-road' applications.

It should also be noted that problems associated with movement within the tie bar bush is exaggerated with age and wear (figure 1b); this will become more of a problem as even the youngest MGFs were built in the beginning of 2002...

Installation of the Tie-bar bush spacer

A closer view of the rear tie bar bush, this time of Paul Sharpe's car (figure 2). Here the white arrow points towards the tie-bar bush spacer. Significantly, although the car has been raised in precisely the same way as Andrew's car above, there is little evident compression/expansion of the bush. This therefore represents significantly reduced geometry change in this unloaded mode. This suggests improved geometry control on the road and hence better handling. From personal experience, I would vouch that there is a significant subjective difference in handling under extremis.

Better rear geometry control is of particular importance to those considering altering and experimenting with the rear toe-angles to alter handling characteristics. Without either a spacer or replacement stiffer bush, only toe-in angles are frankly advisable.

These simple components are available from a couple of sources. RoverSport sell them (but you have to have an MSA Race license to order them, and they cost in excess of 30 GBP), or they can be bought reasonably cheaply from Brown and Gammons and are available to anyone.

Polyurethane bushes are available for and may be fitted as direct replacements to all of the bushes found in the suspension system- including subframe mounts. On the MGF these bushes do not appear to dramatically reduce ride quality or increase NVH (noise, vibration, harshness) levels significantly - although if this option is potentially on your shopping list for your car, you are well advised to try a car so-equipped before making your final decision . This picture (figure 3) is of the now familiar rear tie-bar bush on Andrew Gillhooley's car. Again, like the bush in figure 2, there is no evident compliance in the bush in this unladen state- a positive sign for excellent geometry control. Andrew is delighted with this installation, reporting little deterioration of ride quality, but with significant improvements in handling and steering responses.

This particular installation was performed by Mike Satur, but polyurethane suspension bush kits are also available from Brown and Gammons, as well as other performance parts suppliers like Demon Tweeks. Note that not all kits are the same: some kits come with bushes with a stainless steel insert, whilst cheaper kits use mild steel. Mike Satur recommends the stainless steel option, and this is how the kits he retails are specified.

Polyurethane Bushes available for the MGF

Figure 4: Powerflex bushes for the MGF

As can be seen from figure 4, there is a comprehensive range of suspension bushes that can be fitted to the MGF- including the subframe mount bushes [not shown]. Perhaps the most dramatic effects can be observed will the full kit, although the best starting point for a 'bit-by-bit' approach is the rear tie-bar bush mentioned above. Andy has had his car modified with the full replacement kit, and is delighted with the results.

Many of the bushes are readily accessible to the DIY mechanic, but if you are not this way inclined then Mike Satur does offer a full fitting service.

If you fancy replacing your rear tie-bar bush, then Tim Woolcott has written full instructions, which can be downloaded  here. Note that the instructions are in PDF format, and you will need Acrobat reader to read them. If you haven't already got Acrobat reader, you can load the latest version for free from Adobe's website, as linked from the button, below right.