In the sixth part of our handling series, Neil reveals all you need to know about tie rods and how they can effect your Mini.
In the sixth part of our handling series, Neil talks about tie rods, and how they have a massive impact on how a Mini handles…
Tie rods are often replaced on Minis. One reason is that the original parts often end up bent by people jacking the car up on them, but I suspect that a lot are uprated simply because they don’t look very sturdy. Happily, the standard part is up to the job in normal circumstances as most of the forces acted on it are pulling along the length of the shaft rather than trying to bend it. If you are using the Mini in more aggressive situations then you may find the need for stronger tie bars but you are also adding more weight.
The tie rod does more than supplement the bottom arm mounting, it also sets what is known as the castor angle (or ‘caster’ for our American cousins). You will be familiar with castors on shopping trolleys and how important the mounting point is to where the wheel wants to go and how it “self centres”.
The tie bar completes a triangle formed with the bottom arm and
“If you are using the Mini in more agressive situations you may need stronger tie bars”
subframe, so changing the length of the tie bar alters the angle between the bottom arm and the subframe. Thinking about this triangle, you can see that putting longer bottom arms on, for example, will need longer tie rods to keep the same angle between the bottom arm and the subframe.
ADJUSTABLE TIE BARS
It’s the self centring effect which we can change with adjustable length tie bars and this adjustment becomes a must when you modify other aspects of the suspension. The steering self-centring is generally a good thing, but like everything else it can get to a point where it just causes problems. If you moved the front wheels too far forward they would want to turn in every direction apart from straight, where if you move them too far back, then they would resist your desire to go around any corners.
A good starting point when you fit adjustable tie bars is to match the standard length items. That will give you a point to compare adjustments to. Make sure that any measurements are made from the mounting points of the
bars, not the overall length as the replacement tie bars may have different length threads on them and therefore differ in length even if the suspension geometry is the same.
There are a couple of different ways of mounting tie bars on to the front of the front subframe. The factory units use a threaded end with rubber either side. This allows a little movement at the subframe end which is needed as it also acts as a bearing for when the wheel moves up and down. There are alternatives to rubber, including stiffer bushes. These stiffer bushes are okay, and may be a solution if you find that the tie rod is moving too much under braking for example, however these firmer bushes can permanently deform and I’ve seen them split and fall off entirely when used on the top of rear dampers. Although they are trapped better in the tie bar mount you really don’t want that to happen there. I would recommend that you check any bushes made of different materials on a regular basis to ensure that all is well.
For circuit work and tarmac rallying, rose-jointed tie bars are available. These give free vertical movement to the tie bars and zero play. This is great in the competition environments as you can maintain your geometry precisely whilst making sudden changes from hard acceleration to heavy braking. As ever though, there is a trade off; mainly that any hits your wheels take will get transmitted straight through to the tie rod mounting points on the front subframe. It’s entirely possible for these to bend, altering your geometry quite drastically or even for them to break. Competition cars which use these re-enforce the tie bar mounting points, this is also worthwhile on a rally car using any type of mount, particularly if you are venturing into the forests.
The forces transmitted into subframes and body shells by using firmer and solid mounts is a factor which is always worth serious consideration. Solid
mounts also make the ride less pleasant over any surface imperfections, although I suspect that most Mini owners are more influenced by handling and steering response.
Tie bar length can cause your car to pull in one direction under acceleration and braking. The first thing to do is check that the mounting points are okay. The most likely cause is the tie bars are unequal in length for some reason. If one is bent, you would be better to replace it as you don’t want one failing, and if you don’t know why it’s bent then consider a stronger version. If the bushes have too much movement then you can experience pulling and it’s always possible for a subframe to be twisted in some way. You can carry out a degree of adjustment to counter issues, but if you find you have to make big differences from one side to the other, or you need to keep making adjustments then further investigation would be quite urgently required.
Adjustable tie rod.
Rose-jointed tie rod.
Standard mounting for a tie rod with uprated bushes.
Re-enforcement on subframe mounting.
Tie rod geometry.