Unwanted toe out by Ackermann is said to be corrected by changing the tie rod angle. One means of achieving this is altering the steering rack's location on a rack & pinion steering. Has this been done by anyone here with Integras or Civics?

 

i'm trying to find about the way realtime fixed their bumpsteer.

i have thought of the way moroso makes a tierod kit for drag civics. but make it where it places the tierod below the knuckle,instead of above it.

 

Exactly. Tie rod mounts to the bottom so the angle is level instead of upward? Has anyone drilled out their knuckle to do this without any added slop on the steering?

 

woah. are we discussing ackerman or bumpsteer? ackerman can be changed by moving the rack fore/aft. bumpsteer by changing the arc the tie rods transcribe to coincide with the arc the spindle transcribes. changing one should have little change on the other. all that aside, i'm not sure we need to screw around with the ackerman on these cars. especially since there seems to be some disagreement about how much ackerman you need.

nate

 

thanks nate. I was talking about Ackermann. just didn't know if anyone has taken any measurements of the tie rod angles and played with the idea of taking out the angle. I noticed that the NSX has a different layout on the steering arms from the Civic/Integras and thought it might be n area to tackle to get a little crisper precision on the steering input.

judging by your reply it sounds like "a leave well enough alone...if it ain't broke..." kinda deal. thanks again.

 

how much ackermann do civics have stock? im assuming less than 100%... but im kinda curious what it actually is

 

Ackerman is an "effect" seen in 4 wheeled (not 4WD) cars. During a turn, each tire follows a different arc length about some center. It is dependent upon the horizontal tie rod angle (seen from the top). To be honest, I don't really understand it that well, even after reading the steering chapter in Tune To Win, where Carrol Shelby basically tells me to leave it alone.

So I'll leave that question unanswered.

 

from what i understand, having more ackermann results in better low speed handling. im not completely sure what is going on though. i suspect its the fact that the front tires will try to follow more extreme radii when you increase the ackermann, for a given degree of steering wheel angle.

BUT, im probably wrong. some one that has read the Milikan (sp?) book would be able to answer this correctly

 

Ackemann effect isn't too hard to visualize. Calculating it is quite a bit more difficult. Basically, if your car had 100% Ackermann geometry then the front wheels would turn such that if there is 0 slip on the outside front tire, there is 0 slip on the inside front tire - or in other words, they each follow the exact arc that they are turing on. This is good for tire wear and reducing stress on suspension components, but it isn't always best for racing. High Ackermann is very similar to having toe out, but it doesn't have the straight line drag associated with toe. In this way, being close to 100% Ackermann helps low speed / tight handling like autocross. Road racing needs lead you to exactly the opposite conclusion. In higher speed corners with lower steering angles, less Ackermann seems to be faster. Some say it's because the inside tires operates closer to optimum slip angle, others think there's less drag and that's why it works better.

At the end of the day, it's not something that's particularly easy to change anyway, and there's a lot of differing opinions about what you'd want to do anyway, so you might as well just leave it alone.

-Chris

 

Here are a couple of pictures showing the front bump steer correctors from RealTime's cars circa 1997-1998. Difficult to say if they did anything about Ackerman. There is a free piece of software available from Race Tech magazine's web site that computes Ackerman.






I have an album on imagestation with more ITR pictures from Realtime here:

http://www.imagestation.com/al...73631

 

I guess I don't understand. You want the tie rod as close to level as possible when the car is on the ground- right? In those photos, it looks like the fittings for the spherical rod ends would put the tie rod angle would be uphill(toward the knuckle) when the car is put on the ground.??? If i'm wrong, please edumacate me.

 

you want the tie rod to be as parallel as possible with the control arms.

 

That pic is definately opposite of my Civic's geometry. In order to fix bump steer on my 86, I would have to do basically the same thing but pointing down. Maybe they raised the position of the rack on that car? The tie rod looks pretty parallel to the control arm, but I'd assume the pic is taken at full droop, not ride height. I actually went through and measuered the actual bump steer on my car at several steering angles, and found that it was not very much at all, and not really worth worrying about.

-Chris

 

Picture is ceratinly at full droop, as car is on jack-stands. But there is a very large machined spacer between the tie-rod end and the stock attachment point.

 

How do they machine this so that there is no play, does that spacer drop into the knuckle or is all dependant on how tight that nut and bolt is?

 

massively paraphrasing Paul Van Valkenburg in Racecar Engineering, since racecars are generally sliding around turns Ackerman probably isn't worth worrying about.

YMMV

IANAAE (I Am Not An Automotive Engineer [or even a mechanical engineer])

 

Mark Ortiz from RaceCar Engineering
http://www.auto-ware.com/ubbth...art=1

ACKERMANN RECOMMENDATION
I am modifying a road racing Formula Ford for SCCA Solo 2 [American autocross]. I am considering adding more Ackermann effect to make the car work better in tight turns. Is this a sound idea, and if so, what do you suggest for geometry?
Without writing a really long piece on Ackermann, yes you will probably help the car. I don’t know what geometry you have now, but as a general rule a car needs more Ackermann for events with tight turns, e.g. autocross or hillclimbs.
There isn’t a universally agreed way to express how much Ackermann (toe-out increase with steer) a car has. The closest thing we have is to take the plan-view (top-view) distance from from the front axle line to the convergence point of the steering arm lines, divide the wheelbase by that number, and express the quotient as a percentage. If the steering arms converge to a point on the rear axle line, that’s said to be 100% Ackermann. If they converge to a point twice the wheelbase back, that’s said to be 50%. If they converge to a point 2/3 of the wheelbase back, that’s said to be 150%. If they are parallel, that’s zero Ackermann. If they converge to a point twice the wheelbase ahead of the front axle, that’s said to be –50%.
Supposedly, with 100% Ackermann, the front wheels will track without scuffing in a low-speed turn, where the turn center (center of curvature of the car’s motion path) lies on the rear axle line in plan view. This is actually not strictly true, even for the simplest steering linkage, which would be a beam axle system with a single, one-piece tie rod. With either a rack-and-pinion steering system or a pitman arm, idler arm, and relay rod or center link, we can’t fully predict what the Ackermann properties will be at all, merely by looking at the plan view geometry of the steering arms. The whole mechanism affects toe change with steer.
Even knowing what instantaneous toe we want in a specified dynamic situation is not simple. We don’t necessarily want equal slip angles on both front tires. For any given steer angle, the turn center might be anywhere, depending on the situation. All the infinitely numerous possible situations will
have different optimum toe conditions. Therefore, there is no relationship between steer and toe that is right for all situations.
The toe we have at any particular instant results not only from Ackermann effect, but also from static toe setting and toe change with suspension movement (roll and ride Ackermann).
Because of these complexities, there is no single obvious way to define what constitutes theoretically correct Ackermann. It is possible to come up with a rationally defensible definition for your own purposes, but there is no standard rule, and it is unlikely that there ever will be.
Having entered these abundant caveats, I will now make some general-purpose recommendations for autocross and hillclimb applications:
1. In plan view, at zero steer (straight-ahead position) the steering arms should converge to a point somewhere between the rear axle line and the midpoint of the wheelbase. In traditional parlance, that’s somewhere between 100% and 200% Ackermann. The tighter the turns, the higher the percentage.
2. At all steering positions, the rack or relay rod should be either slightly behind the outer tie rod ends or even with them. This applies to both front steer and rear steer cars. With rack and pinion steering, it means that at zero steer, the rack should be a bit behind the outer tie rod ends on a front steer car, and about even with the outer tie rod ends on a rear steer car. Purpose of this is to assure that tie rod angularity adds Ackermann at large steer angles, rather than subtracting.
3. Angle between any arm and any link in the system should never be less than 30 degrees or greater than 150 degrees. This helps to assure that the mechanism cannot snap over-center due to deflections of the components. Alternatively, over-centering can also be prevented by provision of stops at appropriate points in the mechanism.

There is much more here;
Steering geometry; rack placement; bump steer as Ackerman mod; HP torque and axle tube, by M Ortiz

http://www.auto-ware.com/ubbth...art=1