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.

Bink Industries · 05-22-2014, 05:56 PM

[QUOTE=n2o_matt;5640384]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.

drifting is a new motorsport being only 11 years old professionally in the states. I am finding that this sport is vastly different than road racing. road racing for the most part you can buy a book (carrol smith series etc) follow whats in print and have a pretty successful race car IMO. You cant apply these things to drifting as the cars are doing something else and there for asking for something else. driver feedback is so important because we are still finding and learning what set up is required for drifting. what you set up for drifting WILL be different than a road racing car period. example being what your saying about SAI vs caster settings. driver feedback has told me otherwise for drifting.

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?

it can effect it, yes, based on the fact that you can have different contact patches at or near lock on your trailing tire that is scrubbing (on cars with ackerman) giving the scrubing more or less effect.

this is scrub. if your talking about scrub from Ackerman that is simply the difference in angle from your leading and trailing tire. more angle difference more scrub, simple. I could get into pneumatic trail and stuff and it effects but I will just tell you to go buy a book haha

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...

no that looks the same as stock. 5/16 offset forward like a bicycle, not backward like a shopping cart. (if my memory correct)

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...

I can not comment on laser alignment after SAI change as I don't use one. I have been using tape measures and bubble type camber gauges for 6 years. they have there quirks and there is better but that's just what ive been using. works great ive set up winning time attack cars using this method down to my street car. works great. if you have moddiffed knuckle you will lose mechanical advantage of your pivot so yes it will be hard to turn car off. if its doing that with the car on I have no comment as I don't know.

hope this helps
N8

05-22-2014, 05:56 PM	#6389
Bink Industries Leaky Injector Join Date: Oct 2008 Location: Southern California Posts: 86 Trader Rating: (0)	[QUOTE=n2o_matt;5640384]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. drifting is a new motorsport being only 11 years old professionally in the states. I am finding that this sport is vastly different than road racing. road racing for the most part you can buy a book (carrol smith series etc) follow whats in print and have a pretty successful race car IMO. You cant apply these things to drifting as the cars are doing something else and there for asking for something else. driver feedback is so important because we are still finding and learning what set up is required for drifting. what you set up for drifting WILL be different than a road racing car period. example being what your saying about SAI vs caster settings. driver feedback has told me otherwise for drifting. 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? it can effect it, yes, based on the fact that you can have different contact patches at or near lock on your trailing tire that is scrubbing (on cars with ackerman) giving the scrubing more or less effect. this is scrub. if your talking about scrub from Ackerman that is simply the difference in angle from your leading and trailing tire. more angle difference more scrub, simple. I could get into pneumatic trail and stuff and it effects but I will just tell you to go buy a book haha 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... no that looks the same as stock. 5/16 offset forward like a bicycle, not backward like a shopping cart. (if my memory correct) 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... I can not comment on laser alignment after SAI change as I don't use one. I have been using tape measures and bubble type camber gauges for 6 years. they have there quirks and there is better but that's just what ive been using. works great ive set up winning time attack cars using this method down to my street car. works great. if you have moddiffed knuckle you will lose mechanical advantage of your pivot so yes it will be hard to turn car off. if its doing that with the car on I have no comment as I don't know. hope this helps N8 __________________ [email protected]