I'm about to put the tie bar brackets on my modded subframe and have rose jointed heavy duty tie bars. The hinge point on these is in a different place to the Mini rubber mounted jobbies due to the brackets needed to mount the rose joints on the original subframe, all the ones i've seen are similar. I'm wondering what effect this has on geometry as the suspension arcs. To get all the pivot points in line the tie bar would need to be moved some bit or longer tie bars would be required. Any thoughts or experience on the subject welcome

It's an interesting point, I suspect on the front of a Mini any effects, caused by the change in castor angle as the suspension moves, would be lost in the torque steer etc.
On the rear of a gtm where the wheels are supposed to stay pointing forward! it could I suppose become more of an issue. I guess you've got to try it and see whether it's an issue in practise or just a theoretical problem?

Thinking about it no castor angle should be required on the rear Basically i only want one end to steer

Indeed, what I was trying to suggest was that as the suspension moves, the bottom arm is pulled forward/pushed back by the tie bar. Maybe it's not actually castor, but it's a change in geometry.
Thinking about it a bit more I don't see how the front Mini setup, with tie bars ,can ever keep the wheels pointing straight ahead, as the end of the bottom arm doesn't move vertically up and down. It describes an arc centered on the tie bar pivot point, whereas the top arm can move straight up and down.
Yes that seems like a good idea

In fact the geometry is a lot better than it looks as if it might be.
When I was making a jig to produce my own tubular subframes I did a lot of measuring and lining up and I found that on a standard Mini front subframe the inner pivots for the bottom suspension arm and the hole for the tie bar rubbers line up exactly!

When the whole thing is bolted up solid the bottom arm and tie bar form a wide based solid wishbone which pivots pretty much parallel to the centre line of the car.

If you fit a rose jointed tie bar then, as Tim suggests, you do move the pivot point out of line and it will affect the geometry.

I raced minis for years and we did away with the rose jointed tie bars and went instead for a ball joint setup. It uses the internal rack end from a steering rack threaded into a tube attached to the bottom arm. What this gives is perfect alignment, oncar adjustment (only need a RH thread) and incrediably strong. (I have proved this with a number of heavy crashes to the front and never once did the unit break) I have adopted this for my Coupe also for both front and rear because the STD tie bar arms can differ in length effectively placing one rear wheel further forward or further back than the oposing one. Similar systems are used on doble wishbone single seater race cars. I agree that you do not need to have the ability to change the caster angle in the rear but you do need the ability to align the wheels.

This pic is not the best but you can get the general jist,

Should anyone wish to get the dimensions and parts used I can forward this information

John is spot on, pass a rod centrally through all 3 holes and they all line up. This is something i want to keep

Andy, this appears to be a sensible solution, i for one would be interested in more info.

Yes agree with the above that idealy you want to keep them lined up, but saying that with the rose jointed tie bars the movement from ideal is minimal and not anything to really worry about , especially if you start to find out where other things are for instance you may be surprised to the amount of angle on the top arm rotation axis when looking from the side., If the tie bar pivot was over an inch from where it shuuld be then you may want to look into things. as always with suspension its a compromise you cannot have all you want. Even i am struggling to get a pickup point where i want it on my new rear suspension mainy due to the space available or lack of it.

I do like the solution with the rack ball joint.

WEST

I will check my measurements tonight and post later but from memory the rack end was from a Mercedes the thread was 14mm (std sparkplug tap) the tube was 20mm solid which I bored to suit threads and the connection to lower arm is STD mini swaged and welded into tube. You have to turn the end of the rack end down slightly to fit into the 19mm hole in the subframe. The only additional thing I added to the coupe version over the mini was a dust cover over the joint. (racing-road use) This was a STD mini ball joint cover with a cable tie securing it. I built 4 units for the same price minispares want for 1 pair of their's. They are also a lot lighter than the minispares setup.

Right I have drawn this up in autocad but not sure if it will be readable on here but here goes, The inner rack end used was from a Mercedes not sure of type but I have two part numbers which should help (Qunitin Hazel QR3011S or Equlivant MTR3011) the rest is either STD mini fittings or 20mm steel rod.

Should anyone have access to autocad and wish a copy just ask and I will email.

This is not a given unit and can be adapted to suit any available rack end, you just have to make sure that there is enough thread to make it adjustable, you can get hold of the taps for threads and also that the end piece will fit through the subframe hole.

Hope this helps

Thanks Andy, thats great, should be able to put my brackets where i want them now without having to cut up my existing tie bars
Anyone want some rose jointed tie bars

They are Merc 210 chassis E class

Just bought 4 Merc rack ends from Eurocarparts pt no str4743, total including greedy Gordons slice £52.88 The threads on these are 14mm x1.5.

18" of 20mm solid £2 as an offcut from my local machine shop. Actually i raid their alloy scrap bin when the need arises, there's solid up to 1" (25.4 mm for the younger members ) to be had for peanuts