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  • Projekt Kastor

    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.
    Cheers'en, AndyC
    1994 ABY Coupe - Projekt Alpinweiss

  • #2
    I've been having a little design this morning and have got a nice offset top mount sorted, it uses a monster bearing so should last (max axial load is 10.4 tons), I've got to get it priced but but am not expecting it to be remotely cheap, one of the biggest things is the bearings, a PTFE coated motorsport spec bearings is twice the price of an industrial spec one and represents over 1/3 of the build cost. As the design takes a specific size of bearing I should be able to offer a couple of options for this.

    The offset gives around 1 degree of additional castor (I can't go any more with the stock strut top ) and helps to move the wheel backward if you're using offset subframe bushes (also on the drawing board) and so minimises the chances of interference with the bodywork (not an issue with stock but might be with 18/19s).
    Cheers'en, AndyC
    1994 ABY Coupe - Projekt Alpinweiss

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    • #3
      Originally posted by Rusty View Post
      The offset gives around 1 degree of additional castor (I can't go any more with the stock strut top ) and helps to move the wheel backward if you're using offset subframe bushes (also on the drawing board) and so minimises the chances of interference with the bodywork (not an issue with stock but might be with 18/19s).
      Isn't moving the wheel backwards in the arch going to reduce the caster angle, and thereby cancel out the offset bushes?


      Kieron
      1994 URS4 Avant RS2+

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      • #4
        What if you modify the brackets on the suspension leg so that you can alter the angle it bolts to the hub?
        Audi Nut!!!

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        • #5
          I like the lower Ball joint idea, is their any lower ball joint in the audi range which could be used ?
          sigpic

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          • #6
            You need to read more books Andy!
            Increasing castor then gives more camber in roll. Have you factored that in?
            I have a picture of the suspension changes Staniforth made to that hillclimb S2 if that helps? Might get you scratching your head though!
            Rob..
            94 RS2 Noggy,LHD,MTM map,18"cup 1s,245/35/18,Bilsteins,RS2 H&Rs,Cup splitter.
            87 UR 20v ABY
            97 S6 Avant
            96 A6 C4 2.5 TDI quattro avant,Ming,Wietec/eibach,chipped
            1967 Ford Mustang,Eleanor,460ci v8

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            • #7
              An interesting topic this. The way the top mounts work doesn't allow for much adjustment without getting happy with the grinder and welder and altering it drastically. Like you say its possible to play around with things at the bottom of the strut, but then it alters where the wheel sits in the arch. It would be interesting to hear what just 1 degree extra castor did to the steering feel.

              When you look at the rear struts on a quattro they have quite a bit of castor very noticable over the fronts which are almost vertical.

              If you want to see some extreme camber then have a look at the front struts on a focus wrc car! Also the new s2000 Fiesta has huge castor of the rear struts, it looks funny seeing the strut at such an angle but i suppose it puts it towards the impact of whatever is coming towards the wheel.

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              • #8
                Why not seek out a B4 or B5 touring car to get some front geometry measurements from that as a reference... That must be surely be setup for best handling with custom mounts etc - they won't be friendly towards tyre wear I should imagine but will give some useful data.
                Paul Nugent
                Webmaster http://S2central.net
                Administrator http://S2forum.com

                1994 S2 Coupe ABY - aka Project Lazarus
                2001 A6 allroad 2.5TDi - family tank
                2003 S4 Avant 4.2 V8 - daily burble

                Purveyor of HomeFries and Exclusive agent for Samco hose kits (S2/RS2)

                There are only 10 kinds of people that understand binary - those that do, and those that don't

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                • #9
                  You can Buy up rights here http://www.touringcarspares.com/part...at=trans#thumb from the BTCC and STW's
                  Chef

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                  • #10
                    On paper morecastor is the perfect suspension mod to these cars, more straight line stability, more steering weight and feel and self-centring forces + dynamic camber gain which should also benefit the car no end.

                    I'd definately be interested to see the pics of that hillclimb car Rob

                    I've got a solution to the rotation problem of the offset subframe bushes Andy, did you get my mail about that?
                    Panthero Coupé quattro 20vt
                    Indigo ABY coupé
                    Imola B6 S4 Avant

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                    • #11
                      GBP2000 for a pair - bargain - LOL
                      Paul Nugent
                      Webmaster http://S2central.net
                      Administrator http://S2forum.com

                      1994 S2 Coupe ABY - aka Project Lazarus
                      2001 A6 allroad 2.5TDi - family tank
                      2003 S4 Avant 4.2 V8 - daily burble

                      Purveyor of HomeFries and Exclusive agent for Samco hose kits (S2/RS2)

                      There are only 10 kinds of people that understand binary - those that do, and those that don't

                      Comment


                      • #12
                        Its a pic of the design changes.
                        I'll get it of the camera asap...
                        Rob..
                        94 RS2 Noggy,LHD,MTM map,18"cup 1s,245/35/18,Bilsteins,RS2 H&Rs,Cup splitter.
                        87 UR 20v ABY
                        97 S6 Avant
                        96 A6 C4 2.5 TDI quattro avant,Ming,Wietec/eibach,chipped
                        1967 Ford Mustang,Eleanor,460ci v8

                        Comment


                        • #13
                          cool, really sueful thanks mate
                          Panthero Coupé quattro 20vt
                          Indigo ABY coupé
                          Imola B6 S4 Avant

                          Comment


                          • #14
                            Cheers guys, should do well.

                            Kieron, the mounts move the top of the strut backwards and so add castor.

                            Rob, castor on the S2 is tiny, 1.5-2deg and with the two small scale mods will only be 4deg or so. Compare this to a BMW running 9deg. Effects on other geometry are small and although doubled will still be small. Are you referring to the camber induced by the steering or natural roll of the car in cornering, or a combination? As my car is lowered the macpherson design will mean that the suspension geometry in roll will act to give more positive camber in roll, something I see as unsatisfactory, thus I see any small scale change towards negative camber as quite welcome for cornering, I'll have to put up with any additional tyre wear...

                            I'd be very interested if you have any pictures to share or indeed any additional knowledge on chassis setup, it's an area that interests me because I feel there's a lot to be gained over the stock S2 and it can only increase my enjoyment of my car if I get it right. Driving a similar spec S2 and E30 BMW is an interesting comparison in chassis and layout differences, just need a mk.2 Golf now, complete the German set, then an S1 Elise.
                            Cheers'en, AndyC
                            1994 ABY Coupe - Projekt Alpinweiss

                            Comment


                            • #15
                              Castor, which gives the self centering steering effect is about having the contact point of the wheel behind the line of the king pin (or strut). If you draw a line down the strut so that it touches the floor, the distance from that point to the contact point of the tyre is the trail. More trail = more stability at speed and more self centering. Problem with leaning the strut back further (more rake angle) is that as you turn the steering the tyre leans over onto its side wall, not a good idea when you're trying to get power down though it. So front wheel and all wheel drive cars cant have as much castor as your BM or Merc (yes check out a Merc turning a tight circle!) unless you get very clever with the steering and add extra links to try and keep the tyre flat on the road (check out the A4) the other way to get more castor is like a supermarket trolley, by mounting the wheel behind the pivot point and letting it "trail", there may be some scope here but now there's another problem, any amount of rake angle at this point makes the wheel want to flop to one side, its become unstable again, 2 mins in a supermarket or airport watching the wheels wobble will prove this point. So how much extra rake angle can you add to the humble Macpherson strut in an AWD car before losing drive and wearing the tyres into round profiles (a typical sportsbike has 23-24deg or rake!) I would hazzard its not very much, a degree or 2 at most maybe. Extra rake also causes more weight transfer under braking as the suspension is more easily compressed (bikes are bad for this)

                              S2 Coupe 3B Project


                              Ur quattro restoration

                              S2 Avant

                              Boost is the new rock and roll!
                              sigpic

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