4 replies to this topic

[JonnyAlpha]

OK so I am now working on the front of my Mini and as with everything so far I am learning as I go.

 

What are the bottom arms? Are these the long metal round bars that are bolted to the the front hubs and run to and fit under the front lip with a large round bush?

 

My LH side has a slight kink in it should these be straight and can I hammer it out?

 

Edit

 

Sorry being lazy just checked it up on Mini Spares, the piece I am looking at is the front Tie Rod:

 

http://minispares.co...91.aspx|Back to

Edited by JonnyAlpha, 07 May 2016 - 09:02 AM.

[blackbelt1990]

They are the tie bars. I've had bent ones before.

[Steve220]

They're made of the weakest steel ever and do bent. Get yourself a set of adjustable ones, they're made thicker.

[tiger99]

NEVER straighten one of these. It will fail, some time later, and you may be going fast at the time. As I explained about a year ago they are subject to bending loads during braking or acceleration, because the centre of the bottom ball joint is some distance above the neutral axis of the lower arm. So, the backward pull of heavy braking tries to twist the lower arm and bend the tie rod upwards in the middle. However it is almost always impact with something that bends them, they are OK for all normal usage. However adjustable tie rods enable the castor to be set exactly, which is a good thing. They are thicker and more resistant to bending, but nothing is free and the downside is slightly higher unsprung mass. The standard item is made of relatively mild steel because it has to be welded to the fork end without risking hydrogen embrittlement or any other weld- related problems. I would be extremely wary of any aftermarket part which is made of high grade steel and welded. As for alloy parts, don't even think of going there. The fatigue life might take you round a few race tracks, but not for many thousands of miles on the road. (I do hope you all use your Minis for many, many miles on the road, not just on special occasions!) An aftermarket part (or a home - made one if you have a machine shop) can have a machined fork end, no welding and no stress raisers if thought out properly, which in the case of this particular part is not all that difficult. Should not be all that expensive to do it right.

[MRA]

Impact ?  more likely somebody used it for towing or as a jacking point !

 

Tie bars are subjected to various forces, ie tensile, compressive and bending moments, however of very special concern is where people fit super hard tie bar bushes, these are often made of nylon and are only for racing, not for road use.

 

Under heavy braking or to some extent acceleration the tie bar is under tensile/compressive and bending moments (forces) heavy duty tie bars will reduce the impact that these forces have on the geometry.

 

An often overlooked mode of failure is the area just at the point of transition from 1/2" diameter to the larger 5/8" diameter of the uprated tie bars, which is by default a fatigue failure area that is not such an issue on the standard lighter duty tie bars, this is why careful design and manufacture is so important, whilst careful consideration of the tie bar bush is also taken into account.

 

Think of it like this, as your suspension goes up and down over the bumps in the road, the tie has to change angle, if the bushes are too stiff this small section of tie bar will be held rigid and therefore the tie bar will bend up and down at this point, a heavy duty tie bar is more likely to bend at this point being the smallest diameter, whilst also having a stress raiser corner.

 

Something about the standard tie bars....

 

They will fail at about 65kN which is about 6600 kg and will almost always fail at the bolt interface to the bottom arm under direct tensile loading.

Edited by MRA, 08 May 2016 - 01:21 AM.