Sagaris steering arms and bump steer
Discussion
It still amazes me that people think the steering arms from a different model in the range, with different suspension pickup points, is going to help them.
Have you measured your geo? Do you actually have any bump steer that's affecting the way it handles?
My tuscan came burdened with all the usual miracle cures (rack spacers, hub spacers, wheel spacers) and it never handled as well as when I took them all off, returned it to standard, and set the geo properly.
Have you measured your geo? Do you actually have any bump steer that's affecting the way it handles?
My tuscan came burdened with all the usual miracle cures (rack spacers, hub spacers, wheel spacers) and it never handled as well as when I took them all off, returned it to standard, and set the geo properly.
spitfire4v8 said:
It still amazes me that people think the steering arms from a different model in the range, with different suspension pickup points, is going to help them.
Have you measured your geo? Do you actually have any bump steer that's affecting the way it handles?
My tuscan came burdened with all the usual miracle cures (rack spacers, hub spacers, wheel spacers) and it never handled as well as when I took them all off, returned it to standard, and set the geo properly.
Well done Jules - words of wisdom!Have you measured your geo? Do you actually have any bump steer that's affecting the way it handles?
My tuscan came burdened with all the usual miracle cures (rack spacers, hub spacers, wheel spacers) and it never handled as well as when I took them all off, returned it to standard, and set the geo properly.
Nick
Well ummmm.
If the arc of the track rod and wishbone don't coincide,then you are going to get bump steer .
If,if if if! fitting Sagaris steering arms, moving the track rod ends and possibly shimming the rack does allow these arcs to coincide then it will illuminate bump steer.
It's a fundamental issue and no geo adjustment or tyre pressure changes etc will alter a basic design fault ( feature?).
Stiffening the spring rates,as I have done will massively reduce whatever bump steer there is , because the suspension travel is massively reduced ( front rates increased by 150%).
I think " tail slide", said the difference after Sag arms etc was pretty subtle for a T350, but for a MK1 Tuscan It's rather more than that?
You only have to drive 50 feet to realise that a Sagaris is much less nervous to drive than a T350.In fact it's almost boring!
In my case,upping spring rates and fitting Nitron dampers has made the T350 much more Sagaris like ( it now feels easily capable of handling another 100 bhp for example).
So,I'm interested in getting bump steer to as near to zero as is reasonably possible.
But the Sagaris arms do seem bizarrely expensive?
If the arc of the track rod and wishbone don't coincide,then you are going to get bump steer .
If,if if if! fitting Sagaris steering arms, moving the track rod ends and possibly shimming the rack does allow these arcs to coincide then it will illuminate bump steer.
It's a fundamental issue and no geo adjustment or tyre pressure changes etc will alter a basic design fault ( feature?).
Stiffening the spring rates,as I have done will massively reduce whatever bump steer there is , because the suspension travel is massively reduced ( front rates increased by 150%).
I think " tail slide", said the difference after Sag arms etc was pretty subtle for a T350, but for a MK1 Tuscan It's rather more than that?
You only have to drive 50 feet to realise that a Sagaris is much less nervous to drive than a T350.In fact it's almost boring!
In my case,upping spring rates and fitting Nitron dampers has made the T350 much more Sagaris like ( it now feels easily capable of handling another 100 bhp for example).
So,I'm interested in getting bump steer to as near to zero as is reasonably possible.
But the Sagaris arms do seem bizarrely expensive?
Here's the thing, and I didn't appreciate it until a lotus suspension engineer pointed it out to me many years ago.. you don't necessarily want zero bump steer. You want the geo that's going to get you a fast stable predictable consistent handling. Good luck with that on any car! They can't even manage it in F1.
What you probably want is a slight trend to toe out in bump (though you may well also be starting with toe in to start with it depends on your preferences, and keeping that toe in during bump, but the effect of bump is to add some additional toeing out ie static you might have 30 mins toe in total, full bump you might have 5 mins toe in total), as that gives roll understeer and is generally accepted as the safe way to set up a powerful rear drive car.
Guess what the tvr has as std on every modern model I've measured .. toe out in bump.
I've seen some horrendous bump steer kits, I posted some pics once of the worst, you might be able to google it.
If you think you know what you're doing then please crack on. But it sounds like you've not measured anything yet or you'd have given us the facts ? so that would be a good first point to do (accurately).
What you probably want is a slight trend to toe out in bump (though you may well also be starting with toe in to start with it depends on your preferences, and keeping that toe in during bump, but the effect of bump is to add some additional toeing out ie static you might have 30 mins toe in total, full bump you might have 5 mins toe in total), as that gives roll understeer and is generally accepted as the safe way to set up a powerful rear drive car.
Guess what the tvr has as std on every modern model I've measured .. toe out in bump.
I've seen some horrendous bump steer kits, I posted some pics once of the worst, you might be able to google it.
If you think you know what you're doing then please crack on. But it sounds like you've not measured anything yet or you'd have given us the facts ? so that would be a good first point to do (accurately).
Hi,thank you for that.Plenty of information to digest.
I don't know what aT350 usually has in terms of bump steer envelope,between static and a reasonable amount of bump.I don't know whether it has toe in or out on bump and how much.
The pictures I've seen suggest that the arc of the track rod can be made closer to the arc of the lower wishbone using the "Sagaris", model.
I was assuming that as Straight six had offered this tweek it was worth doing?
I'm keen to learn as much as I can.
Having discussed this with Andy at Power,I'm now lead to believe that there is no one standard initial T350 set up and that the factory introduced a number of variables to the components fitted over the production period!
That means checking the initial set up first,which is probably what you were suggesting?
I was hoping to simply fit the most desirable components myself and get it set up afterwards,that may or may not work apparently!
Best Wishes
Simon .
I don't know what aT350 usually has in terms of bump steer envelope,between static and a reasonable amount of bump.I don't know whether it has toe in or out on bump and how much.
The pictures I've seen suggest that the arc of the track rod can be made closer to the arc of the lower wishbone using the "Sagaris", model.
I was assuming that as Straight six had offered this tweek it was worth doing?
I'm keen to learn as much as I can.
Having discussed this with Andy at Power,I'm now lead to believe that there is no one standard initial T350 set up and that the factory introduced a number of variables to the components fitted over the production period!
That means checking the initial set up first,which is probably what you were suggesting?
I was hoping to simply fit the most desirable components myself and get it set up afterwards,that may or may not work apparently!
Best Wishes
Simon .
astonman said:
The pictures I've seen suggest that the arc of the track rod can be made closer to the arc of the lower wishbone using the "Sagaris", model.
.
That's your first mistake then..
You will only get zero bump steer in that case if the steering arm is actually in the same horizontal plane as the lower arm and your steering joints are in line with the lower arm pivots.
What I think you mean to do is find the centre of instaneous rotation between the upper and lower arms, and plant your steering arm axis on that same centre of rotation, and your inner steering knuckle joint on the line between the upper and lower arm inner pivot points. That would also give you zero bump steer. But I say again, you might not want that.
People always keep talking about making the steering rod parallel with the lower arm, completely forgetting that it's both upper and lower arms that describe the trajectory of the hub to which that arm is attached. They also keep on about making the lower arm horizontal at rest as that's somehow a magic formula, whilst completely forgetting the action of the upper arm (steeply inclined on our cars to give some camber compensation in roll) which causes the hub to move inwards at the top considerably during full travel.
Bottom line is : measure it all, plot it out, decide if you want to change it and why, and how.
astonman said:
It's a surprise that after all this time,that we don't have a definitive comparison of the Sagaris suspension geometry and the T350.
That's what I need first?
I can only assume straight six must have pretty much done this before they started offering the bump steer mod package ?
They haven't offered it for some time now though.......That's what I need first?
I can only assume straight six must have pretty much done this before they started offering the bump steer mod package ?
I have them fitted to my 2000 Tuscan along with the rack being raised and I can tell you on my car at least it is like night and day (also had full geo setup by HHC)
From before it would dart all over the road and find any rut and is now planted and can drive with one hand if need be.
This might not be the same for all T cars but have had mine over 10years and definitely know how mine has been improved. Also having driving a few of my friends this is very worthwhile.
Yes mine are Powers ones and the cost is for the pair.
G
Edited by boardinscotland on Friday 5th October 17:59
Edited by boardinscotland on Friday 5th October 18:33
astonman said:
It's a surprise that after all this time,that we don't have a definitive comparison of the Sagaris suspension geometry and the T350.
That's what I need first?
I can only assume straight six must have pretty much done this before they started offering the bump steer mod package ?
The Sag chassis suspension mounts are different to the T350, hence the need for the cranked arms.That's what I need first?
I can only assume straight six must have pretty much done this before they started offering the bump steer mod package ?
My '00 Tuscan with the later top wishbones, steering rack and uprights (ie as per T350) did have bump toe in with the rack mounted direct on the chassis. A combination of different track rod ends, which lower the outer steering rod pivot point, and 8mm spacers under the rack gives me c. 1.5mm bump out per wheel at 2 inch bump, which I find makes the car much more stable under braking and with mid corner bumps etc.
I did have a kit that was done as a group buy on the Cerbera forum that flipped the track rod below the steering arm, roughly equal to fitting Sag arms to a non-sag chassis, resulting in a lot of bump toe out. It made the car more stable over bumps but didn't do much for steering feel or tyre life...
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