Vixen chassis height
Discussion
To minimise bump steer which way should the steering arms be facing - downwards a bit/level/up a bit?
This is assuming adjustable shocks and obviously the chassis chassis height from a flat floor determines the arm orientation.
Be ready interesting to see the likely differences people have. Mine are currently upwards slightly.
This is assuming adjustable shocks and obviously the chassis chassis height from a flat floor determines the arm orientation.
Be ready interesting to see the likely differences people have. Mine are currently upwards slightly.
Hi, I have done all this with the Griff, plus Scimitars, but not a Vixen (yet..). So, general words. I would expect to aim for level lower links when under normal load (I.e when on its wheels) at most. Not leaning up to the upright. Depending on ground clearance issues, more leaning down to the uprights. Normal ground clearance at the chassis often dictates more than anything else.
You can, and I have, measured bump steer. Some setups don’t have any, so,you,may not have an issue. It’s a bit of a fiddle, I did it with fully assembled suspension with no shocks or springs. Car on axle stands all round and all level. I attached an aluminium sheet to the hub, which extended forwards, I then articulated the suspension from low to,high with a jack, whilst recording any movement at the al plate with a dial gauge.
Bit of fun, if you like that kind of thing!
I am sure someone has specific Vixen experience.
Best
Nic
You can, and I have, measured bump steer. Some setups don’t have any, so,you,may not have an issue. It’s a bit of a fiddle, I did it with fully assembled suspension with no shocks or springs. Car on axle stands all round and all level. I attached an aluminium sheet to the hub, which extended forwards, I then articulated the suspension from low to,high with a jack, whilst recording any movement at the al plate with a dial gauge.
Bit of fun, if you like that kind of thing!
I am sure someone has specific Vixen experience.
Best
Nic
V6 Pushfit said:
To minimise bump steer which way should the steering arms be facing - downwards a bit/level/up a bit?
This is assuming adjustable shocks and obviously the chassis chassis height from a flat floor determines the arm orientation.
Be ready interesting to see the likely differences people have. Mine are currently upwards slightly.
IIRC the general rule is the steering arm should be parallel to the lower wishbone. This is so under compression and droop they stay parallel which therefore keeps the geometry similar throughout suspension travel.This is assuming adjustable shocks and obviously the chassis chassis height from a flat floor determines the arm orientation.
Be ready interesting to see the likely differences people have. Mine are currently upwards slightly.
I believe bump steer results when the steering arm and lower wishbone go out of parallel causing the geometry to change as the wheel drops into a pot hole or compresses due to a lump in the road surface.
Moto
Edited by Moto on Sunday 25th September 19:28
Moto said:
IIRC the general rule is the steering arm should be parallel to the lower wishbone. This is so under compression and droop they stay parallel which therefore keeps the geometry similar throughout suspension travel.
I believe bump steer results when the steering arm and lower wishbone go out of parallel causing the geometry to change as the wheel drops into a pot hole or compresses due to a lump in the road surface.
Moto
Yes ideally they should scribe the sams arc. The point is that with a standard vixen are the rods up/down/straight? With adjustable shock platforms it can be whatever angle you want but best to get it as original. I believe bump steer results when the steering arm and lower wishbone go out of parallel causing the geometry to change as the wheel drops into a pot hole or compresses due to a lump in the road surface.
Moto
Edited by Moto on Sunday 25th September 19:28
Parallel with the lower arms would mean a very high chassis.
V6 Pushfit said:
Yes ideally they should scribe the sams arc. The point is that with a standard vixen are the rods up/down/straight? With adjustable shock platforms it can be whatever angle you want but best to get it as original.
Parallel with the lower arms would mean a very high chassis.
OK, my setup is not standard but this photo may be of interest :Parallel with the lower arms would mean a very high chassis.
Don't look too closely at the dust cover - I know it's shot and new ones are on the bench waiting for me to fit. The one in the photo was brand new in March this year. How 'crap' is that !
Moto
Moto said:
OK, my setup is not standard but this photo may be of interest :
Don't look too closely at the dust cover - I know it's shot and new ones are on the bench waiting for me to fit. The one in the photo was brand new in March this year. How 'crap' is that !
Moto
Interesting, what’s your dimension from floor to underside of chassis corner strengthening plate (ie under your right foot). I’ve got 185mm. Do you get bump steer?Don't look too closely at the dust cover - I know it's shot and new ones are on the bench waiting for me to fit. The one in the photo was brand new in March this year. How 'crap' is that !
Moto
V6 Pushfit said:
Interesting, what’s your dimension from floor to underside of chassis corner strengthening plate (ie under your right foot). I’ve got 185mm. Do you get bump steer?
Approx 160mm. It used to suffer from bump steer but last winter the chassis & steering rack were modified by Nigel Reubens. Now it is virtually non-existent.
Moto
Dollyman1850 said:
Moto said:
Approx 160mm.
It used to suffer from bump steer but last winter the chassis & steering rack were modified by Nigel Reubens. Now it is virtually non-existent.
Moto
You have hit the nail on the head. The angle of the rack is a factor only if the centreline of the suspension and steering pivot point is the same It used to suffer from bump steer but last winter the chassis & steering rack were modified by Nigel Reubens. Now it is virtually non-existent.
Moto
Edited by anonymous-user on Tuesday 27th September 16:18
Dollyman1850 said:
V6 Pushfit said:
As they aren’t the same on a standard setup, the height of the chassis dictates the angle of the steering rods - which in turn will determine how much bump steer there is. Hence the original question as to what angle or chassis height do people have that has minimised it.
I am sorry but I don't understand the question you have posted. Edited by anonymous-user on Tuesday 27th September 16:18
So what chassis height do people have which minimises bump steer? Or what is the OE height if fixed spring platforms ?
Make sense?
Dollyman1850 said:
V6 Pushfit said:
I can’t rephrase it much clearer - the chassis height on a vixen determines the angle of the tie rods, non?
So what chassis height do people have which minimises bump steer? Or what is the OE height if fixed spring platforms ?
Make sense?
Not really. Ride height is dynamic as is the change of the angles.So what chassis height do people have which minimises bump steer? Or what is the OE height if fixed spring platforms ?
Make sense?
N
You know exactly what I'm saying so either continue to make an issue out of a straighforward question or actually add something positive for a change. The choice is yours.
Dollyman1850 said:
V6 Pushfit said:
Christ on a bike - are you suggesting the pivot points change too in which case we're really in trouble.
You know exactly what I'm saying so either continue to make an issue out of a straighforward question or actually add something positive for a change. The choice is yours.
Alistair. Can I suggest that rather than try to have a pop at me you first understand what bump steer is and what causes it. Winding your suspension spring platforms up or down does not cure bump steer !! go read a few books. You know exactly what I'm saying so either continue to make an issue out of a straighforward question or actually add something positive for a change. The choice is yours.
N.
Edited by Dollyman1850 on Thursday 29th September 11:29
If you want to post your usual negative or obtuse comments please start your own thread on shortened adapted racks, realigned arm pivots or whatever engineering or fabrication work you consider vital but totally non standard but as usual without divulging any helpful information.
I must apologise for this post but someone has to say it.
Edited by anonymous-user on Thursday 29th September 20:57
Too much going on in that picture, the lower wishbone is upside down, and rose jointed (from previous pictures I have seen) the upper one is upside down and rose jointed too, AND, even if it were on the car as standard they are not true M series (on this era car the top wishbone as designed could not give enough camber and it was changed for the M proper) the steering arm mod almost brings it in-line with later M's.
A thought here, is that the pictorial in the M series parts manual shows the lower wishbone as upside down in error. I have always thought that this was turned upside down for no other reason that it was seen to be incorrect IN that pictorial and copied onto the car, I might be wrong.
For the sake of the topic. I think I would be pointing people off at either Neil or Nigel over how the cars are taken back to Thurner's OE design on the Grantura Mk3, rack and steering arms (OR, shortened rack and longer Vixen steering arms with a modified top wishbone to allow better camber) which will address the short comings of the TVR compromised version.
It might be that you invest in shortening the steering rack and modifying the wishbone yourself (as I have done on myself on my Vixen S3) but to do that the chassis has to be changed. I found in moving the rack I needed a one piece lower steering shaft (so it missed the engine) as these are welded together three piece as OE. A@
(edited to add the pictorial comment)
A thought here, is that the pictorial in the M series parts manual shows the lower wishbone as upside down in error. I have always thought that this was turned upside down for no other reason that it was seen to be incorrect IN that pictorial and copied onto the car, I might be wrong.
For the sake of the topic. I think I would be pointing people off at either Neil or Nigel over how the cars are taken back to Thurner's OE design on the Grantura Mk3, rack and steering arms (OR, shortened rack and longer Vixen steering arms with a modified top wishbone to allow better camber) which will address the short comings of the TVR compromised version.
It might be that you invest in shortening the steering rack and modifying the wishbone yourself (as I have done on myself on my Vixen S3) but to do that the chassis has to be changed. I found in moving the rack I needed a one piece lower steering shaft (so it missed the engine) as these are welded together three piece as OE. A@
(edited to add the pictorial comment)
Edited by Adrian@ on Friday 14th October 08:52
The difference between running on low profile against balloon tyres will of course make a difference to the 'chassis height' so in fact the ideal question would have been what angle is the rod - which is difficult to measure which is why I asked what peoples chassis height was.
Instead of discussion you are still determined to go to extremes and I think most will be well familar with the fact there are two arcs the question is what is the best point for setting at rest nearest where the two arcs cross.
Its best leaving it there otherwise you will no doubt conntinue in your critical-negative way of disagreeing with this due to the need to go not where the arcs cross but on the droop side of the cross because compression.
Only PH can make such a f
king fuss out of a simple question and wreck any potentially useful and informative replies.
Instead of discussion you are still determined to go to extremes and I think most will be well familar with the fact there are two arcs the question is what is the best point for setting at rest nearest where the two arcs cross.
Its best leaving it there otherwise you will no doubt conntinue in your critical-negative way of disagreeing with this due to the need to go not where the arcs cross but on the droop side of the cross because compression.
Only PH can make such a f
king fuss out of a simple question and wreck any potentially useful and informative replies. Hi, let me just add a note for anyone searching in the future. Vixen bump steer as standard is appalling. 5 degrees per wheel. 0.5 would be okay…. The absolute fix would be to contact Nigel Reubens who does indeed have solutions.
On a standard car the bump steer is most pronounced when the car is riding high. As the car gets closer to the ground, it is still bad but not as bad.
If you want to improve, lower your car.
If you want a better fix, use solid mounts on your rack with no strengthening plate, this lowers the rack a bit, which helps. But not fixes.
More complete threads are available!
Nic
On a standard car the bump steer is most pronounced when the car is riding high. As the car gets closer to the ground, it is still bad but not as bad.
If you want to improve, lower your car.
If you want a better fix, use solid mounts on your rack with no strengthening plate, this lowers the rack a bit, which helps. But not fixes.
More complete threads are available!
Nic
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