How light does your steering feel?

[Fen]

I agree that track control arms would affect precision, but I wonder if what Charles describes is wandering due to imprecision. The design is such that a miniscule amount of play in the joint at the rack end can translate to a lot more at the hub.

Castor has everything to do with steering weight - it is the forward and back of the wheel in the arch (like camber but longitudinally) and clearly the further forward it is the greater angle on the strut and the more self-centring effect there will be. Steering weight is largely if not entirely due to self centring effect.

 

[zcacogp]

Fen,

Track control arms - good point. Quite agree about the amplification of any play, due to the design.

Yes, castor will make a HUGE difference to steering weight (I had a discussion with a chassis expert the other day to the effect that the only reason modern small cars need power steering is because they run very aggressive castor angles, which is necessary to make them 'nippy'), but this is a function of the castor setting, not of the condition of the castor mount. Charles will have had his castor set correctly when he had his geo done (or it should have been done, if they were doing a half-reasonable job), so this should be OK (and thus not making his steering overly heavy or light.)


Oli.

 

[Fen]

Have you seen how much of the standard 944 castor mount is rubber compared to the 968 one. Add 20 years of degradation of that rubber and it will be about as effective as custard skin of a similar age at keeping the angle at the static setting while the car is being driven.

I believe it's factory a technical bulletin recommendation that the castor mounts should be replaced with uprated versions when 17" wheels are fitted to a 944.

 

[zcacogp]

Oh great. Another thing I need to be spending the pennies on! Better stop Mrs zcacogp's chocolate budget for the next couple of months so I can afford it ...

Ho humm Boys and Girls. Whoever said that Porsches was cheap was either hallucinating or lying.

(Imprecise castor mounting won't necessarily lead to permanently light steering - the castor mounts on mine are 19 years old, and the steering isn't at all light. That's not to say that there won't be a significant improvement in handling feel on the road if they were to be changed, but I doubt they would make the steering light all the time on Charles's car. Having said that, I don't know what other factors may be at play here - we have discussed the geo and tyre pressures, which are the prime suspects. Could it be an over-active PS pump, perhaps? Is there such a thing? Or some restrictor valve that is jammed open? Or just that Charles has spent too many evenings in the gym and his biceps are rippling more than he thought possible?)


Oli.

 

[Fen]

Could be the gym option. Or maybe Charles fitted a Routemaster steering wheel and neglected to mention it []

In all seriousness I agree that I don't know if the castor mounts are the sole cause, but I bet it's geometry or as Mik suggested a dodgy wear pattern on the tyres due to previous dodgy geometry. What I can say for sure is that any 19 or 20 year old suspension bits that flex or mover and haven't been replaced will not be performing as they should and getting rid of any slop then setting the geometry again should cure it.

I think I'm right in saying that you went with the 1989 geometry and the more aggressive end of that theory and you felt it made a huge difference? There are a number of different sets of figures for different years (which I don't understand, one set for early and one for late (ABS offset) cars is all that's needed) and perhaps the ones used on Charles' car were less aggressive or tended toward the less aggressive end of the tolerance. I bet that would make a difference in itself to the plantedness of the car.

 

[charles.y]

OK. The tyres are quite new. Here are the geo settings done a few weeks ago ...

LEFT RIGHT CROSS
<Front>
Castor: Before 2 degree 55' 2 degree 54' 0 degree 01'
After no change no change no change
Cross no change no change no change

Camber: Before -0 degree 14' -0 degree 02' -0 degree 12'
After -0 degree 54' -0 degree 58' 0 degree 04'

Toe: Before -0 degree 01' 0 degree 08'
After 0 degree 25' 0 degree 26'


LEFT RIGHT CROSS
<Rear>
Camber: Before -1 degree 48' -1 degree 04' -0 degree 44'
After no change -1 degree 06' -0 degree 42'

Toe: Before 0 degree 10' 0 degree 10'
After 0 degree 11' 0 degree 11'

 

[zcacogp]

Both quite possible. Or maybe he fitted 155-profile front tyres (lower rolling resistance) and is also now enjoying 45mpg fuel economy (and chronic understeer)!

I'm with you - geo is top suspect. Tyres I would be inclined to doubt - I can believe that a pull to one side or the other could be explained by funny wear patterns on tyres, but overly light steering is something that is not to do with balance (as in, it's not explained by a pull to one side or another) so I'd doubt it is tyre-related. It *could* (perhaps) be due to very new tyres, which have very large (tall) tread blocks that move around a lot, thus offering less resistance to the twist of steering, but I doubt this would make enough difference to be noticable.

(On the topic of tyres, this is very interesting and makes a good read:

http://www.carbibles.com/tyre_bible.html

Look about 5/6ths of the way down on Page 1, at "What about the coloured stripes in the tread?" I am semi-wondering whether this is relevant to Charles's situation as well, but slightly doubt it as it says it leads to a pull to one side rather than general lightness.)

General comment about changing rubbery and wobbly geometry bits after 20 years and 140,000 miles - yes.

Your memory serves you correctly in terms of the geo settings I asked for. (Yes, I can't understand why Porsche offered so many different factory-settings, unless they simply had a team of designers who changed their minds as to the favored behaviour of the car as the years passed.) However, Charles went to the same geo place as I went to, and asked me what settings he should ask for before he went, and I sent him the print-out for mine. So he should have something that's pretty close to that which I have.

Yes, I felt it made a huge difference, but I never directly compared old geo with new geo. I had old shocks with old geo, then changed everything and set the geo as best I could at the side of the road with a spirit level and bit of string, then took it in to be fully re-geo'd. (Apparently my attempts at getting the geo right ended up with wheels doing impressions of satellite tracking dishes, they were so far out.)

I do sometimes wonder how much of the handling improvement I experienced was due to the new shocks and bushes, and how much to having correct geo, but that's a different thread.


Oli.

 

[zcacogp]

OK, the '89 manual lists castor as between 2.3 and 3 degrees (Porsche manual Vol 3, page 44-03), so Charles's posted settings (2degree55' and 2degree54') are well within spec.

I'd be pretty sure that is therefore not the root of the problem.


Oli.

 

[charles.y]

I DON'T go to the gym. [8|]
Maybe its just me. I am now driving my wife Merc E-Class v6 more often (family thing) than I drive the S2 and probably get used to the well weighted Merc's steering. I have owned four Mercs since the 80s from the smaller 190 to the v12 where the ride and steering are always very sweet and reassuring..

Oli,
Since you are not too far from where I live maybe we can meet up to compare the steering feel on our S2s.

 

[Fen]

OK, we seem to be ruling lots out. Maybe you should compare steering feel as Charles suggests?

Excellent tyre info on that link; I didn't know any of the coloured dot or stripe stuff.

 

[zcacogp]

Charles,

Good idea - very good idea actually. You'd be very welcome to drop 'round for a cuppa, you can have a shufti at how heavy my steering is and I'd quite like a nose around a cab as well. If you are insured to drive other vehicles (and promise to behave - I know the rumours!) then you are more than welcome to drive it.

Excellent idea.

Dates are going to be the tricky one, I am coming up to a horrendously busy patch. Can you do Friday daytimes? Or Monday daytimes? If we are looking at weekends then Sunday 20th would be an option. Or else we are looking into early September.


Oli.

 

[charles.y]

Oli,
Thanks for the invite. Will check my diary and PM you directly later.

 

[zcacogp]

Charles,

No problems ... I'll get the kettle on ...


Oli.

 

[TTM]

ORIGINAL: Fen
Steering weight is largely if not entirely due to self centring effect.

The size of the front ARB affects steering weight too - this is actually the reason why I took off the 30mm bar from the S2 and fitted back the original 26.8mm. M474 shocks with CS springs are too "soft" for the 30mm bar.

 

[zcacogp]

Very interesting. Charles - did you fit a bigger ARB to your cab? (Although I would have thought that a bigger bar would make the steering heavier rather than lighter.)


Oli.

 

[charles.y]

ORIGINAL: zcacogp

Very interesting. Charles - did you fit a bigger ARB to your cab? (Although I would have thought that a bigger bar would make the steering heavier rather than lighter.)

Oli.

Not yet. This week. Hope the bigger ARBs will give a bit of weight.