So, in my travels I came across these two interesting pictures, comparing r32 and z32 front knuckles. It appears that the hub is offset around 15mm forward of the centreline, while the r32 is only 2-3mm forward of it. What impact/effect would this have on the steering and why would it have been designed this way?
Hard to say, as there are other variables to consider like king pin inclination/castor. However, if everything else is the same between Z32 and R32, then you'd expect the R32 to have a stronger self-centering effect on the steering.
From what I can gather everything else is the same. However the z32 runs more caster from factory than the r32 (which I'm guessing is to put the wheel in the same place).
Scrub radius is the first thought More castor the more the axle will have to move Need pics of both cars as fitted
The 'why' is almost certainly packaging, once the steering rack and A-arms are in the right place to leave room for the sump, alternator, intake etc. that's how they have to make the knuckle to clear the fenders and still get reasonable castor and wheels size. I can't get the effect on castor related stuff like wheel centering sorted in my head but if instamatic is right on the R32 having stronger centering then the extra castor on the Z is likely to make up for that. Assuming you're considering putting R chassis knuckles on a Z and don't mind running more castor what I would be more worried about is the effect on steering rate since the position of the hub relative to it's pivot point and the tie rod is different you may find the gearing of the rack is too fast/slow unless nissan set it so they have the same mechanical leverage.
Or is the reduced offset to permit AWD front drive-shaft CV to pivot on the steering (king-pin in old-school terms) axis and therefore not displace the CV over-much ?
Redactions and extra info I've realised that my suggestion that hub offset will affect steering rate is wrong, steering rate will be just the distance from tie-rod end to steering axis (which you should check if you want to run the knuckles). Hub position may still affect steering weight as it has a mechanical advantage at the steering axis. The property that reduces the centering of the Z32 knuckle at a given castor/all other things being equal is 'trail'. Trail contributes to/is a component of the usual effects of castor, it is measured as the distance between where the vertical centre axis of the wheel and the steering axis meet the ground. Moving the centre of the wheel forward moves it closer to where a positive camber steering axis meets the ground and reduces trail therefore reduces the mechanical advantage of the tyres centering/camber neutralising forces at the steering axis. So I'm guessing once you add the castor necessary to run the knuckles plus the increased trail from the hub position your car would hate turning without some big changes else where. Good for a drag car? Hopefully that's less wrong than my last one.
Pretty sure that's a GTS-t knuckle, the GTRs do run even less castor than either the Z or a GTS-t for that reason though.
Its to effect steering geometry, specifically in this case is the caster angle which as mentioned in this thread has a direct effect on the self centering of the steering - A good write up can be found here http://www.autek.dk/Articles/PrincipOfSteeringGeo_eng.pdf edit * I know traditionally that caster angle is thought of as the angle of the kingpin or macpherson strut or similar but this is just another way of increasing this and working in with other aspects of steering geometry
I will have some useful info on this very soon. Have just fitted up some r33 Modified Knuckles (extra lock) into my z32 and will let you know how it drives after I get a wheel alignment (So far it drives okay but definately needs some alignment done haha). Once its all up and running well ill let you know how I went around doing this.
