Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum - View Single Post - This is the roll center, suspension pickup, and steering angle modification thread.

n2o_matt · 05-22-2014, 01:40 PM

Thanks! Wish this forum had rep/karma/etc to give.

Your trailing wheel has a small effect on front grip. its your leading wheel that's pointing you around the track So trying to set up your geo for more contact patch on the trailing tire would be counter productive. you want to dial in your lead wheel.
SAI is a source of self steer. but having too much of it causes geometry problems and makes it hard to get all of your other things like RC and scrub in check. and SAI does not cause scrub it causes jacking just like caster. it rasies the car so naturally the car wants to go to its lowest point and that's what returns the steering.
Interesting suggestion to have a bit more SAI than castor. For track I've seen many people say you need at least half as much castor as SAI to fight the positive camber gain of the (normally) outside wheel. This is why I was thinking it might be beneficial even for the leading tire, since I'm assuming it would add dynamic negative camber, or at lest lessen the positive camber gain from castor on the leading wheel.

SAI, doesn't cause scrub but it does effect it doesn't it? Scrub is like the trail of SAI in a front view right?

Thanks for the help on ackerman, just realized it was answered on the previous page. This thread is quite something to get your head around, wish it had its own section rather than a single, endless thread.

this is caster trail/ mechanical trail. what wise fab has done is added steering axis offset which increses your caster trail. so a car with 9 degrees of caster stock knuckle has lets say 5 inchs of caster trail. if you offset the hub more you can now run 3 degrees of caster and have the same 5 inches of caster trail. make sense? that's how they get selfsteer with almost no SAI and caster. this reduces jacking and keeps the contact patch more flat through angle. unfortunately the self steer is now speed sensitive with this set up so the hair pin at longbeach requires hand over hand to steer the car but at higher speeds it steers its self on transistions.
Ah, that's what i've always heard it as, "mechanical trail." Makes sense, been a while since i've looked this deep into suspension geometry.

So is the GK Tech knuckle loosing steering axis offset? Maybe to allow road racers to gain more (-) camber through more castor with out the disadvantage of increased steering effort...

Also, do you have any insite on the accuracy of laser alignment racks once SAI and such has changed? My recent firestone alignment showed my SAI at 14.0 and castor of 6.5 yet my wheel is very far forward in the wheel well. I'm running keisler knuckles (zero ackerman) and PBM rack spacers. My steerign is smooth but after about 30deg of angle it gets very difficult to steer, but it doesn't completely stop. Almost feels like its binding, but it steers smoothly when off the ground. If I'm going slow and turn the wheel hard it wants to keep on turning and not self steer, but it does seem to get better with speed. I haven't really tried it while drifting though...

Thanks agian!

05-22-2014, 01:40 PM	#6387
n2o_matt Join Date: Aug 2002 Location: tn Posts: 35 Trader Rating: (0)	Thanks! Wish this forum had rep/karma/etc to give. Your trailing wheel has a small effect on front grip. its your leading wheel that's pointing you around the track So trying to set up your geo for more contact patch on the trailing tire would be counter productive. you want to dial in your lead wheel. SAI is a source of self steer. but having too much of it causes geometry problems and makes it hard to get all of your other things like RC and scrub in check. and SAI does not cause scrub it causes jacking just like caster. it rasies the car so naturally the car wants to go to its lowest point and that's what returns the steering. Interesting suggestion to have a bit more SAI than castor. For track I've seen many people say you need at least half as much castor as SAI to fight the positive camber gain of the (normally) outside wheel. This is why I was thinking it might be beneficial even for the leading tire, since I'm assuming it would add dynamic negative camber, or at lest lessen the positive camber gain from castor on the leading wheel. SAI, doesn't cause scrub but it does effect it doesn't it? Scrub is like the trail of SAI in a front view right? Thanks for the help on ackerman, just realized it was answered on the previous page. This thread is quite something to get your head around, wish it had its own section rather than a single, endless thread. this is caster trail/ mechanical trail. what wise fab has done is added steering axis offset which increses your caster trail. so a car with 9 degrees of caster stock knuckle has lets say 5 inchs of caster trail. if you offset the hub more you can now run 3 degrees of caster and have the same 5 inches of caster trail. make sense? that's how they get selfsteer with almost no SAI and caster. this reduces jacking and keeps the contact patch more flat through angle. unfortunately the self steer is now speed sensitive with this set up so the hair pin at longbeach requires hand over hand to steer the car but at higher speeds it steers its self on transistions. Ah, that's what i've always heard it as, "mechanical trail." Makes sense, been a while since i've looked this deep into suspension geometry. So is the GK Tech knuckle loosing steering axis offset? Maybe to allow road racers to gain more (-) camber through more castor with out the disadvantage of increased steering effort... Also, do you have any insite on the accuracy of laser alignment racks once SAI and such has changed? My recent firestone alignment showed my SAI at 14.0 and castor of 6.5 yet my wheel is very far forward in the wheel well. I'm running keisler knuckles (zero ackerman) and PBM rack spacers. My steerign is smooth but after about 30deg of angle it gets very difficult to steer, but it doesn't completely stop. Almost feels like its binding, but it steers smoothly when off the ground. If I'm going slow and turn the wheel hard it wants to keep on turning and not self steer, but it does seem to get better with speed. I haven't really tried it while drifting though... Thanks agian!