This thread follows on from the steering weight and feel thread here.
Been having a little chat with Error404 and lind4hl on here about castor and how to get more of it, the aim being to improve the steering weight and feel. From looking into the problem there seems to be a number of methods of gaining castor and each has its good and bad points. The S2 has around 2 degrees of castor on the front, compare this to my E30 BM that has between 8.5 and 9.5 and a few of the Audi steering traits become a little clearer.
Below are the methods I can think of and their relative advantages and disadvantages:0
Adjusting Lower Ball Joints
+ This method was used by my local alignment place to get the castor in spec and it worked rather well, I'm not sure on the total movement but there's at least a degree here.
- Will cost to have it all adjusted.
Offset Subframe Bushes
+ These should allow the subframe and thus lower arms to be moved forward somewhere in the region of 10mm, this equates to around and additional 1 degree of castor.
- Moving the subframe forwards may cause issues with other mounting points. Finding a suitable method of holding the bushes in rotation hasn't really been found, the method of dowels and notching the subframe isn't a great plan and leaving them free could put extra load on other mounting points if the subframe is hit sideways.
Offset Top Mounts
+ There's not much adjustment here, 5mm sensibly, 10mm at most (additional 0.5 - 1 degree) but if your top mounts are tired and need uprating then it's a good start. 2Bennet make some of these but they're a small fortune.
- Offset top mounts need some form of fixing to the strut top to prevent rotation and there's not many neat methods for this that I've seen. Drilling the strut top isn't ideal TBH.
Reversing Lower Ball Joints
+ This is a rather extreme method but one that could give potentially 4-5 degrees more castor.
- The lower ball joint is approximately 25mm offset so reversing it will movethe wheel forward around 40mm and will foul the bumper and could cause other issues with driveshaft clearance. The ball joint is also angled approx 10 degrees towards the rear of the car and reversing this will angle it slightly forward.
This method needs a bit of incestigation as the gains are large for a little head scratching.
Other Custom Parts
Tubular lower arms with custom ball joints or rod ends are one option, these would do well but are expensive.
Moving the strut tops rearwards is another method but this is certainly for the more advanced chassis fabricator
So overall there are a few combinations of methods that can gain 2-3 degrees castor and one method that can gain around an additional 4 degrees. With all mrthods added together (and no strut movement or chassis cutting) there is the possibility of getting around 8 degrees of castor.
Been having a little chat with Error404 and lind4hl on here about castor and how to get more of it, the aim being to improve the steering weight and feel. From looking into the problem there seems to be a number of methods of gaining castor and each has its good and bad points. The S2 has around 2 degrees of castor on the front, compare this to my E30 BM that has between 8.5 and 9.5 and a few of the Audi steering traits become a little clearer.
Below are the methods I can think of and their relative advantages and disadvantages:0
Adjusting Lower Ball Joints
+ This method was used by my local alignment place to get the castor in spec and it worked rather well, I'm not sure on the total movement but there's at least a degree here.
- Will cost to have it all adjusted.
Offset Subframe Bushes
+ These should allow the subframe and thus lower arms to be moved forward somewhere in the region of 10mm, this equates to around and additional 1 degree of castor.
- Moving the subframe forwards may cause issues with other mounting points. Finding a suitable method of holding the bushes in rotation hasn't really been found, the method of dowels and notching the subframe isn't a great plan and leaving them free could put extra load on other mounting points if the subframe is hit sideways.
Offset Top Mounts
+ There's not much adjustment here, 5mm sensibly, 10mm at most (additional 0.5 - 1 degree) but if your top mounts are tired and need uprating then it's a good start. 2Bennet make some of these but they're a small fortune.
- Offset top mounts need some form of fixing to the strut top to prevent rotation and there's not many neat methods for this that I've seen. Drilling the strut top isn't ideal TBH.
Reversing Lower Ball Joints
+ This is a rather extreme method but one that could give potentially 4-5 degrees more castor.
- The lower ball joint is approximately 25mm offset so reversing it will movethe wheel forward around 40mm and will foul the bumper and could cause other issues with driveshaft clearance. The ball joint is also angled approx 10 degrees towards the rear of the car and reversing this will angle it slightly forward.
This method needs a bit of incestigation as the gains are large for a little head scratching.
Other Custom Parts
Tubular lower arms with custom ball joints or rod ends are one option, these would do well but are expensive.
Moving the strut tops rearwards is another method but this is certainly for the more advanced chassis fabricator
So overall there are a few combinations of methods that can gain 2-3 degrees castor and one method that can gain around an additional 4 degrees. With all mrthods added together (and no strut movement or chassis cutting) there is the possibility of getting around 8 degrees of castor.
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