Toe Changes for Track Use

[heavy85]

So if short vs long steering arms don't significantly affect ackerman then what are the major advantages of each beyond the obvious fast steering vs easier to steer?

 

Figured this fits here since steering arms control toe.

 

Cameron

Edited January 17, 2011 by heavy85

[JMortensen]

You've pretty much got it, it's a trade off between effort and quickness.

[260DET]

My present Z has power steering, after getting used to it and some lack of feeling its the only way to go in my opinion. For a track car you want fast steering particularly in an impending emergency situation, fractions of seconds count and power steering can gain those fractions.

[cygnusx1]

Let me summarize/clarify/ask some things about what I read here in this looong thread>

 

 

 

 

1)When the car leans to the side in a corner, the inside (fronts) wheel toe's-in and the outside wheel toe's-out (bump steer?) I see this when I jack up the car.

 

2)Negative camber causes the tires to "steer" inwards toward the cars centerline, as a result you can run more static toe out to make them go straight ahead..so to speak.

 

3)Parallel steer means that the wheels follow the same X radius around a curve? or do they follow each others (left and right radius) radii?

 

4)On a basic Z, static toe-in adds anti-Ackerman characteristics in corner, and static toe out adds pro-Ackerman.

 

5)Lengthening the TC rods increases caster angle and does what to the handling and Ackerman?

 

 

 

 

 

[JMortensen]

1)When the car leans to the side in a corner, the inside (fronts) wheel toe's-in and the outside wheel toe's-out (bump steer?) I see this when I jack up the car.

Yes. You are seeing the bump steer when you jack the car up.

 

2)Negative camber causes the tires to "steer" inwards toward the cars centerline, as a result you can run more static toe out to make them go straight ahead..so to speak.

There is camber thrust which is close to equal when the car is going straight. When you turn, the weight transfers to the outside, and the camber thrust from that side becomes dominant. If you have negative camber, the camber thrust is pushing the car in the correct direction to continue the turn. Not sure I follow you with the toe bit. I don't think the goal should be to counter the camber thrust, the goal with the toe setting should be to affect the way the car turns in, and this in large part has to do with the angle of the inside tire when initiating the turn.

 

3)Parallel steer means that the wheels follow the same X radius around a curve? or do they follow each others (left and right radius) radii?

Parallel steer means that the wheels turn at the same angle. If the left wheel turns 20 degrees, the right wheel turns 20 degrees. Z's do not have parallel steer, much to my surprise.

 

4)On a basic Z, static toe-in adds anti-Ackerman characteristics in corner, and static toe out adds pro-Ackerman.

Kind of. You get the improved turn in with toe out, but it's a fixed setting and isn't progressive like Ackerman is. In the case of a Z you'd have to have an unreasonable amount of static toe out to maintain an Ackermann type of effect during a sharp corner at an autox, for example. So you get the Ackerman effect at first, but then that effect trails off and even with an aggressive toe out setting it turns into an AA effect in a very sharp turn.

 

5)Lengthening the TC rods increases caster angle and does what to the handling and Ackerman?

Increasing caster increases Ackerman in a Z.

 

 

 

[260DET]

S30's need more caster than most people run. One of the characteristics of a modern strut front suspension is big caster, it's not the only thing of course but S30 owners should take note. And move into the present century

[Zmanco]

S30's need more caster than most people run. One of the characteristics of a modern strut front suspension is big caster, it's not the only thing of course but S30 owners should take note. And move into the present century

I'm using the TechnoToy Tuning LCA and TC parts and have found the most caster I can obtain is about 3 degrees before the tire edge begins to rub on the valence in front. This is with a 16 x 7 Panasport and 225/50 tires such as Dunlop Direzza Star Specs, so nothing radical. I'll probably slot the strut towers to gain a little more, but wonder if anyone has found another approach to gain more caster? I don't want to cut up the fender/valence lip as this is a mostly street driven car and I'd like to maintain its otherwise mostly stock appearance.

[cygnusx1]

I suppose that the S30 engineers kept caster angle shallow to keep steering effort down?

[1 tuff z]

nice summary in posts 84-85, thanks.

 

oddly enough, my steering effort appeared to become lesser when we 'moved the front wheels forward' [caster] and on turn in the tires had a better bite at the track.

 

i run coilovers and mike kelly's zf racing adjustable front lcs's on my z.

[JMortensen]

oddly enough, my steering effort appeared to become lesser when we 'moved the front wheels forward' [caster] and on turn in the tires had a better bite at the track.

That is odd, because when you increase caster you make it so that you are literally lifting the front end of the car when you turn the wheel.

 

When you add caster on most cars, some part of the turning is used to move the car vertically. To make the point, imagine if you had a really ridiculous motorcycle that had the front fork mounted straight up and down, 0 caster. The wheel wouldn't lean at all when you turned it, it would simply pivot to the left or the right. Now imagine a similarly stupid chopper that had 90 degrees of caster, with the handlebars at the front hub height. If you turned the front tire, it would just lean, it wouldn't actually turn.

 

Now imagine that the chopper had a rectangular profiled tire instead of a traditional rounded motorcycle tire. When you turn the wheel, you're putting that rectangle on its corner, and this makes the rectangle taller than it would be if it were flat. You are actually lifting the front end by turning the wheel.

 

That's a kind of crappy example, so I'll use what's handy to make the point. I have a soda can in front of me on my desk. It looks to be about 4 7/8" tall. If I tip it on the corner, I can manage to measure about 5 1/4" tall. Roughly estimating, that lift tops out at about 20 degrees, then goes back down. So similarly, a rectangular-ish tire is going to get taller as you lean it over until about 20 degrees of lean, then it will get shorter again.

 

When you turn the wheel of the car and it leans over, you are literally lifting the weight of the front of the car in the same way. People (I think Coffey is among them) have put a car on scales, turned the wheel and looked at the weight changes on each corner.

[1 tuff z]

jon, i think that is an excellent example and paints a nice 'word' picture in my mind. i am no expert in alignment or handling so i should be clear that when i say we changed my caster, i meant pushed the wheels forward-they are now pretty close to hitting my kaminari air dam when they turn. i don't pretend to know why, but the steering effort does feel less-both at parking speed and on the track.

 

i recall when i was a kid we'd cut forks off our parts bikes then add tubing to get the stupidly long chopper forks. looked ultra cool [think mid 70's] but were horrible to steer and had queen mary-like turn radius'. i also remember that the headset would rise when turning the handlebars with the bike at rest.

[johnc]

More positive caster adds weight to the outside front and inside rear wheel in a corner. The tighter the track the more benefit you get. There's no one best setting for toe, caster, camber, etc. and I think some on this thread forget that. I would run more of each at tight tracks like Streets of Willow and less of each at fast tracks like Willow Springs big track. Lap times and tire temps are your best quantitative measure.

[1 tuff z]

did a search on the net and some reading but am still not certain which way is positive caster. please don't flame me on this one...

 

is positive caster when the wheel is moved or adjusted forward from its normal position [on our s30 by extending the t/c length]?

[JMortensen]

Choppers have tons of positive caster.

[1 tuff z]

got it, the light bulb is now fully illuminated [for caster anyway...]

[jt1]

More positive caster adds weight to the outside front and inside rear wheel in a corner

 

ASSuming an understeering car and a positve scrub radius, isn't that reversed? Or maybe I don't understand?

 

jt

[johnc]

ASSuming an understeering car and a positve scrub radius, isn't that reversed? Or maybe I don't understand?

 

jt

 

With positive caster and a positive scrub radius the outside steered tire, as it rolls over, will push up on that corner of the suspension as the tire gains camber and tries to stand up on its inside edge. That's one of the contributing things in caster's self-steering effects - the weight of the car pushing down on the tire as you try to raise it with the steering wheel. Conversely the inside tire loses camber and drops. I checked this back when I had the ROD on a set of corner scales. Its real (at least with the car static on scales).

[cygnusx1]

With positive caster and a positive scrub radius the outside steered tire, as it rolls over, will push up on that corner of the suspension as the tire gains camber and tries to stand up on its inside edge. That's one of the contributing things in caster's self-steering effects - the weight of the car pushing down on the tire as you try to raise it with the steering wheel. Conversely the inside tire loses camber and drops. I checked this back when I had the ROD on a set of corner scales. Its real (at least with the car static on scales).

Here is a video that might help explain caster. It doesn't get into toe, camber, and ackerman, and how they are effected by caster, but maybe it will help to illustrate caster.

 

 

http://www.ehow.co.uk/video_2327628_caster-car-steering-system_.html

 

 

[260DET]

Friend of mine has just tested his S30 on the track with 6 degrees of caster, gained by modding the front strut towers so the strut tops could be adjusted rearwards. He likes it, a significant improvement particularly with turn in. All I have to do now is talk him into running 10mm rear toe in