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With advances in suspension design it was possible to reduce the kingpin off-set to almost zero but although this made construction more economical a problem with road shocks evolved, the logical solution was to tilt the SAI to a perpendicular position (remember the kingpin was vertical) thus increasing the castor position, inevitably this made the steering weight heavy since the weight is no longer over a vertical pivotal point. The castor off-set although more productive needed assistance to reduce driver fatigue, hence the need for power assisted steering.

 

So is it castor per-se or the positiong of the kingpin (either literal or theoretical kingpin) that dictates steering weight ?

Does it impact upon steering "feel" too ?

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KPI/SAI position is matter of fact and in my opinion one of the most valuable tools in chassis dynamics in controlling steering weight, migration and return. The castor position is "theoretical" since it cannot be measured directly, it's theoretical position can only be measured by the camber migration.

 

KPI/SAI is deemed as a diagnostic non-adjustable angle, in fact this is not the case since and unsprung camber change will inevitably change the inclination/ declination of the KPI/SAI.

 

Castor has a mechanical law, that being the wheel is being pulled, if the castor trial distance is extended the stability increases but so does the need to add weight to yaw, for most drivers this additional effort is not welcomed.

 

Point to really, really remember about the KPI is the "perpendicular pins length", it's the lower pivotal point and during yaw it's lifted or declined, the lifted pin lifts the sprung chassis so now it holds that corners weight, since the pins are linked via the steering rack and their natural desire is equilibrium, meaning the unsprung chassis wants to share the vehicle's weight, this transition is done via the steering rack and returns the steering position after yaw.

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Did a '99-ish Volvo V70 yesterday. Jeez, the front cross-camber tolerance was so big it was absurd. Nearly a degree allowed by OEM, so -15" N/S and (+)35" O/S was "acceptable". When the target positions are undermined by big tolerance it makes me wonder why they bother petting any target positions in.

Wasn't just cross-camber either. :rolleyes:

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Hey not had much tp put up on here for a while. I've been pondering suspension roll v suspension travel recently, specifically why something like an Omega runs -2.0 OEM camber but something like a Ford Ranger 4x4 (IIRC) mild positive camber.

 

I think I may have been mistaking the two (travel & roll) ?

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