anyone fitted these yet ?
Discussion
https://delta.securesslhost.net/~shenglt/catalog/p... wedge tie rods £77 plus vat (inc carriage .)
Edited by combine on Friday 22 February 22:06
combine said:
Question is do they do things better than whats on there already , I presume so or Steve wouldn't have bothered ?
Yes. I was putting big bends into the originals (for some reason... 
) and was repeatedly having to take them off and straighten them. The problem is that when they bend, they change the rear geometry so the two sides are very different. BTW this was before the supercharger. By having the adjustment in the centre, it puts a weak point in the bar so that when force is applied, it tends to bend at that point. Once that happens the bar will bend as far as it will go. As it is very important part of the suspension as it stabilises the rear wheel position during braking and acceleration, the bending is not a good idea and eventually they will snap and break. So, I've moved the adjustment to the ends and used rose joints to remove unwanted flexing. They are also offset so that the bar is further away from the wheel edge which helps those cars fitted with Tuscan racers. They can also be adjusted in situ which the originals can't. So all in all a big improvement.
Ordered and waiting, Great idea Steve 
Easy to find go here, then go to Wedges
http://www.shpub.co.uk/
Easy to find go here, then go to Wedges
http://www.shpub.co.uk/
Edited by BadRedWedge on Monday 25th February 15:27
I know that this is a weak point in the A-frame design. RT made up some stronger versions a while back IIRC.
I don't see how two things work in this design though:
1)the offset appears to create a four pin mechanism and
2)the rubber bushes in the original are necessary because it swings in an arc which is perpendicular to the arc of the A-frame; the rose jointing removes this vital flexibility for those who do not have suspension harder than rock.
It appears that the rose joints ( 2) ) are being negated by the offset ( 1) )
I don't see how two things work in this design though:
1)the offset appears to create a four pin mechanism and
2)the rubber bushes in the original are necessary because it swings in an arc which is perpendicular to the arc of the A-frame; the rose jointing removes this vital flexibility for those who do not have suspension harder than rock.
It appears that the rose joints ( 2) ) are being negated by the offset ( 1) )
That's what I thought originally but the reality is very different when I started modelling and investigating the suspension in detail.
As the tie rod moves in an arc, it effectively shortens a little so when the suspension is in droop or compression, the effective length of the tie rod reduces. The distance needed to compensate is way beyond the actual amount of compression that the tie rod bushes can support. However if the A frame bushes give a fraction of a mm, the effective change at the hub end of the A frame is a lot more because of the length of the frame. In other words, if the A frame is needed to move 10mm, then the system has two choices: compress the tie rod bushes by 10mm or let the A frame bushes distort less than a mm and the A frame move forward. Guess what? The tie rod bushes don't compress and the A frame twists slightly on its bushes to compensate.
To see this in action, get a 21 inch length of wood or a ruler. Place it horizontally on a table. Move one end forward 10mm and look at the other end. The angle change from the perpendicular is very small.
The whole idea of the tie rod is to stabilise the A frame so that the rear wheels are held in a consistent position and don't wobble.
If you do the calculations then the A frame bushes move by very little to give the movement that is needed to cope with the arc movement. I have hard poly bushes and when the tie rods bent and effectively shortened the tie rod by about 1-2 inches, the A frame simply moved forward. I only noticed something was wrong when the wheel had moved so far forward it was nearly touching the wheel arch.
The offset simply moves the tie rod in a bit so that instead of being central (ish as mine certainly aren't ) the tie rod is moved across a few mm. The rose joints take care of any alignment issues. the resulting forces are transmitted using the existing pick up points on the hub and chassis.
As the tie rod moves in an arc, it effectively shortens a little so when the suspension is in droop or compression, the effective length of the tie rod reduces. The distance needed to compensate is way beyond the actual amount of compression that the tie rod bushes can support. However if the A frame bushes give a fraction of a mm, the effective change at the hub end of the A frame is a lot more because of the length of the frame. In other words, if the A frame is needed to move 10mm, then the system has two choices: compress the tie rod bushes by 10mm or let the A frame bushes distort less than a mm and the A frame move forward. Guess what? The tie rod bushes don't compress and the A frame twists slightly on its bushes to compensate.
To see this in action, get a 21 inch length of wood or a ruler. Place it horizontally on a table. Move one end forward 10mm and look at the other end. The angle change from the perpendicular is very small.
The whole idea of the tie rod is to stabilise the A frame so that the rear wheels are held in a consistent position and don't wobble.
If you do the calculations then the A frame bushes move by very little to give the movement that is needed to cope with the arc movement. I have hard poly bushes and when the tie rods bent and effectively shortened the tie rod by about 1-2 inches, the A frame simply moved forward. I only noticed something was wrong when the wheel had moved so far forward it was nearly touching the wheel arch.
The offset simply moves the tie rod in a bit so that instead of being central (ish as mine certainly aren't ) the tie rod is moved across a few mm. The rose joints take care of any alignment issues. the resulting forces are transmitted using the existing pick up points on the hub and chassis.
Edited by shpub on Monday 25th February 19:42
BadRedWedge said:
Ordered and waiting, Great idea Steve
Easy to find go here, then go to Wedges
http://www.shpub.co.uk/
Looking forward to taking mucky stuff off the wedge and putting shiny stuff on !Easy to find go here, then go to Wedges
http://www.shpub.co.uk/
Edited by BadRedWedge on Monday 25th February 15:27
I had similar concerns re. tie rod and A frame arc's etc. but understand Steve's logic.
As part of the rear upgrade I have removed some recently fitted hard black (nylon-ish) bushes and fitted the red poly bushes. Playing with the A frames on the bench there is certainly more movement in the poly bushes vs the nylon - which are very harsh (too harsh) for road use.
I hope the new tie bars plus poly bushes is the best balance.
Hope the bars arrive soon.
David
As part of the rear upgrade I have removed some recently fitted hard black (nylon-ish) bushes and fitted the red poly bushes. Playing with the A frames on the bench there is certainly more movement in the poly bushes vs the nylon - which are very harsh (too harsh) for road use.
I hope the new tie bars plus poly bushes is the best balance.
Hope the bars arrive soon.
David
shpub said:
Lots and lots..
Taking all of that on board it seems to me that your harder A frame bushes may have contributed to bending the tie rods? Not criticizing just trying to understand the mechanism involved here. I guess for your hard-core requirements that the better location provided by the harder bushing is necessary but I wonder if for less extreme use i.e. road tyres as opposed to slicks, a more compliant bush (specificially the inboard A frame bushes) would be advisable?More by luck than judgement I have, for the moment, arrived at rock solid outer A frame bushes and standard inboard bushes. This seems to be quite a good compromise but the time will come when I need to replace the inboard ones. Question is do I stick with standard or do I fit the solid ones I have in the draw? Obviously I can and will suck it and see but I'm interested to hear your thoughts. It would also be interesting to hear what type of bushes you recommend to go along with your rose jointed links.
The bending was due to the stresses going through the tie rod and the built-in weakness caused by the adjustment in the middle. Also bear in mind I have changed the rear suspension and limited the amount of suspension movement to keep it in the sweet spot. As a result the tie rod arc movement is very limited and the effective change in length is mm compared to the 1-2 inches I saw. Also remember that the wheel moved forward so there was no gap. This movement is far in excess of any needed to compensate for the tie rod arc.
Even with the harder bushes I could move the A frame enough to take the tension off the tie rod so that I could unbolt it, straighten it and then refit it. With the new ones I can adjust the tie rod length and position the hub where I want it so I can't see any issue with the hard ones except they are a bit harsh. Not really a problem with the 520SE especially as the front is rose jointed anyway. And the suspension is very hard...
BTW I supplied a set to a Wedge owner at Christmas who had just broken a tie rod. It had bent and snapped in the middle so the problem is not just limited to nutter cars...
Even with the harder bushes I could move the A frame enough to take the tension off the tie rod so that I could unbolt it, straighten it and then refit it. With the new ones I can adjust the tie rod length and position the hub where I want it so I can't see any issue with the hard ones except they are a bit harsh. Not really a problem with the 520SE especially as the front is rose jointed anyway. And the suspension is very hard...
BTW I supplied a set to a Wedge owner at Christmas who had just broken a tie rod. It had bent and snapped in the middle so the problem is not just limited to nutter cars...
Edited by shpub on Monday 25th February 22:15
leorest said:
harder A frame bushes may have contributed to bending the tie rods? Not criticizing just trying to understand the mechanism involved here. I guess for your hard-core requirements that the better location provided by the harder bushing is necessary but I wonder if for less extreme use i.e. road tyres as opposed to slicks, a more compliant bush (specificially the inboard A frame bushes) would be advisable?
I would go along with all of that.leorest said:
More by luck than judgement I have, for the moment, arrived at rock solid outer A frame bushes and standard inboard bushes. This seems to be quite a good compromise.
Not a compromise, that would appear to be the best solution. shpub said:
As the tie rod moves in an arc, it effectively shortens a little so when the suspension is in droop or compression, the effective length of the tie rod reduces. The distance needed to compensate is way beyond the actual amount of compression that the tie rod bushes can support. However if the A frame bushes give a fraction of a mm, the effective change at the hub end of the A frame is a lot more because of the length of the frame.
So far so good.shpub said:
In other words, if the A frame is needed to move 10mm, then the system has two choices:
Not so. If no rod were there the frame would move to a point which could be calculated. If both rod and frame are there the frame will move to a point between it's original location and it's fully distorted state AND the bushes in the rod will compress. Note that equilibrium positions(!) are not in the centre of the suspension movement as you would initially think but about 30% up and down.As I said... the tie rod bushes are not there to provide compression to compensate for the change in length as the tie rod pivots. There is simply not enough give/movement etc to do that. If they did, they would do a lousy job of locating the A frame.
Also consider the situation where the A frame move up and down and creates another arc. This requires the tie rod to move in towards the wheel arch but the tie rod is held in position at the chassis. This is done by twisting the bush which because of the tie rod length and the small amount of movement needed is not a problem. This is a similar case to the A frame but is a bit more complicated as the tie rod not only has to move in slightly but also rotate a little.
So the tie rod bushes distort to cope with the A frame arc and the A frame bushes distort slightly to cope with the tie rod arc. Make any of these joints solid and the system will lock up. Making the tie rod with encastre nodes at each end with no rotational/translational movement will lock the suspension. The original joints are not solid. Undo one end of the tie rod and it will move about as the bush distorts. If it was clamped with zero movement as suggested then the suspension would seize.
Replacing the tie rod bushes with rod ends does not mean the joint is solid. It means that instead of relying on the bush to distort, there is a nice spherical bearing to allow the tie rod to rotate/translate and move smoothly. If anything, it reduces the stress as it no longer has to rely on the bush being distorted to provide the required movement. The rose joint in this application works in the same way as the bush. It locates the A frame position while providing some movement to allow the suspension to move.
Also consider the situation where the A frame move up and down and creates another arc. This requires the tie rod to move in towards the wheel arch but the tie rod is held in position at the chassis. This is done by twisting the bush which because of the tie rod length and the small amount of movement needed is not a problem. This is a similar case to the A frame but is a bit more complicated as the tie rod not only has to move in slightly but also rotate a little.
So the tie rod bushes distort to cope with the A frame arc and the A frame bushes distort slightly to cope with the tie rod arc. Make any of these joints solid and the system will lock up. Making the tie rod with encastre nodes at each end with no rotational/translational movement will lock the suspension. The original joints are not solid. Undo one end of the tie rod and it will move about as the bush distorts. If it was clamped with zero movement as suggested then the suspension would seize.
Replacing the tie rod bushes with rod ends does not mean the joint is solid. It means that instead of relying on the bush to distort, there is a nice spherical bearing to allow the tie rod to rotate/translate and move smoothly. If anything, it reduces the stress as it no longer has to rely on the bush being distorted to provide the required movement. The rose joint in this application works in the same way as the bush. It locates the A frame position while providing some movement to allow the suspension to move.
Edited by shpub on Tuesday 26th February 08:48
shpub said:
BTW I supplied a set to a Wedge owner at Christmas who had just broken a tie rod. It had bent and snapped in the middle so the problem is not just limited to nutter cars...
I can vouch for that Steve, in the space of two years I have snapped two on the drivers side and one on the passenger side of my bog standard 400SE - the last one only about 4 months ago, just before selling it.I shall certainly be looking at swapping those on the 450 in due course!
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