TEDSgrad

iTrader: (4)

I was under the impression that a 17" would not fit: with Racecraft spindles, Wilwood 13" FSL, and bumpsteer kit. Am I wrong? - be good news if I am.
I thought 18's would be very close.
Here's pics with my stock formula 16's:

//<86TA>\\

iTrader: (14)

We are talking about stock spindles. My origional thought was to use racecraft spindle and cut them up and modify them, but after trying to deal with them I gave up.

Pablo

iTrader: (1)

Bringing this back because I have learned some new information concerning our steering system that is important to consider.

The assumption that our cars have anti-ackerman may be incorrect. I (and I think others) based this assumption upon the fact that our steering arm points are inboard of the ball joint pivot. Many web pages offer a simplified explanation to ackerman geometry stating that the angle of the arms relative to the balljoint is what determines ackerman.

This is an oversimplified explanation and only really correct for a steering system with a single drag link connecting the two steering arms... something like this:

Obviously our steering system is different, here is a visual:

There is an important thing going on here that affects ackerman. As you turn, the pitman and the idler turn which moves the inner tie rod pivot points forward. At the same time, the outer tie rod pivot points move rearward (depending on position, one always moves rearward at least). Since we do not have a solid link between the two tie rod outer end pivots, the effective length between the two tie rod outer pivot points changes.
If you started out with the tie rods without any angle as viewed from above, the distance between the two outer tie rod end points would have to shorten as the centerlink moves forward.

In our situation though, the tie rods look like the image above. So what happens is the angle between the tie rods decreases. As this angle
decreases the overall length between the two outer tie rod end points increases.

This effect counter acts the angle between the balljoint pivot and the outer tie rod end pivot. To what degree would only be known if we measured everything. With the steering arms angled inward, the distance between the two outer end points has to increase if we want to maintain the same change in angle at the wheels.

So you can see the angle of the tie rods looking from above is pretty important.

Now what does this mean for shortened steering arms? Well when you shorten the arm, you are flattening the angle of those tie rods when looking from above. As you turn the wheel and the tie rod outer pivots move rearward and the inner pivots move forward. The gain in length for a given degree change in angle is not as great. There is more lateral travel at a steeper angle for a given degree change. This is the same idea why the angled steering arms change ackerman.

Shortening the steering arm with no other changes will decrease ackerman. It can multiply if the arms end up angling rearward such that the inner pivots are ahead of the outer pivots.

So then how do we improve the situation to gain ackerman? Well there are a couple of ways but they will yield different ackerman curves. You could most easily space the inner tie rod end rearward. In looking at my car it appears as though you may have a half inch or so to work with before hitting the K member.
I believe this would end up giving you an ackerman curve with a greater rate gain from center but the rate would slow the further away you get from center. It may still be more than stock through the entire range. It would have to be measured or modeled to know for sure.

The second way is to move the outer tie rod pivot outward. This will give you an increasing ackerman curve. I believe this is preferable to the decreasing gain ackerman curve of angling the tie rods more by spacing their inner pivot rearward.

Since we can't move the outer tie rod point outward without shortening the effective length of the steering arm, the solution is to shorten the arm as little as possible to allow the tie rod end room so it doesn't hit the wheel. Any shortening of the arm will have to be accompanied by spacing the inner tie rod pivots rearward to maintain the same tie rod angle as viewed from above. Even doing so, you will not maintain a stock "angle curve" of the tie rod because you've changed where its end point is and where it moves.

Ultimately, you'd have to model or measure the result of changes in order to know how well they worked. I think the first step in doing that is getting accurate measurements of our steering linkage, ball joint centerlines, and steering arm angle and length. (I believe I have accurate specs for the center link, pitman, and idler arm so far)

tvc 15

I know what you are talking about but I think your wrong. At least I hope you are, after all the time I spent on my spindles. Your diagram is out of proportion the line between the tie rod ends and the drag link is more straight. I don't belive the arcs are going to cause as much change as you think, but unfortunatly I am months away from getting mine on a alignment rack to find out. I will let everyone know if I'm a hero or a zero.

Pablo

iTrader: (1)

I didn't realize you were expecting me to post a scale drawing of our steering. Sorry.

I'm not really sure what your spindles are going to prove or disprove. If all you did was shorten them while maintaining the same angle I think you most likely have less ackerman. I say most likely because there is the possibility that the shorter throw of the arm is in proportion to the reduced toe out gain from the tie rods. At some point they will be short enough to definitely guarantee reverse ackerman as the tie rods angle rearward from the center pivots. The only way to know is to measure.

I can tell you this, the angle of those tie rods is important enough that spacer kits for steering racks are quite common, and you can also find several circle track articles that mention spacing the inner tie rod ends rearward to increase ackerman on parallelogram steering cars like ours.

Roostmeyer

iTrader: (3)

The rack spacers I've seen are for adjusting bump steer.

The modded spindle 86 ta has done should move the steering arm out enough to counteract this. The other method I'd prefer is to move the LBJ/front axle centerline forward one inch. It would improve weight distribution and keep the back of the tire off the fender well.

TEDSgrad

iTrader: (4)

I'm hoping that I can do this (probably not 1 whole inch) by lengthening the back ear of the a-arm (firewall side), in order to move the LBJ forward. Having the swivel spring cup will help w/any spring issues. For those with stock spring perch, will spring bind be an issue with moving LBJ?

Also, will track width be effected by this?

Pablo

iTrader: (1)

Yes there are rack spacers for bump steer but there are also rack spacers for ackerman. Like these: http://www.miracerros.com/mustang/rack.htm

I agree that moving the ball joint forward has potential but as TEDs said, the spring pocket alignment needs to be considered.

I think there is no way to know whether or not Phil's steering arm bracket has moved the pivot out far enough unless we model it or he actually measures the ackerman.

If someone can get me the stock steering arm length and angle from the ball joint and the distance between the ball joint centerlines at a typical ride height, I could probably figure this out

87350IROC

iTrader: (2)

I did exactly what you are proposing with the Spohn a-arms. Adjusted the back mount longer. I did it for wheel fitment since my tires are tight. Probably moved it forward 1/4" or so. I don't currently have springs in the car to tell if it will be a problem. I suspect no issue with just 1/4"

tvc 15

The shortening of the steering arm on my spindles was purely a side effect. It's hard to tell in the pics I posted but the LBJ and outer tie rod are now inline with each other. The only clean way I could relocate the mounting point was to shorten the arm. Right or wrong the performance cars I have been around have had the LBJ and the outer tie rods inline.

//<86TA>\\

iTrader: (14)

I have been rather busy lately and haven't had much time to mess with this more.

I'm planning to pickup a set of turnplates and from there I can get some real world measurments or inner/out wheels angles and see what exactly this mod has done vs a stock spindle. I can get measurements of the stock spindle and measurements of my modded one.

Pablo's thoughts have got me thinking, I'll have to do some drawings and maybe model the steering and see what's happening

SlickTrackGod

I applaud your guys efforts, but messing with steering arms is a serious issue in safety. This is an inherent flaw that the chassis designers missed back in the 80's along with a whole handful of other things. Just too damn hard to reengineer things with this wheel offset and front steer- everything is gonna be a bandaid fix and will never be correct. Its a fine line weighing saftety against getting closer to proper ackerman

I just kept 8" wheels on my car and tried to keep my scrub close to zero thrugh SAI mod and moderate camber. My car turned fine in sharp parkinglots

What Pablo shows on the last post is how they try and help to anti aclerman effect by swinging the drag link in the forwad arch, but its still not enough to compensate for the front steer spindles. Ackerman is done fom the rear center diff -forward through the ball joints period. Anything else is a bandaid fix. All the real performance cars had rear steer spindles like the Vettes. But in comparison, the Vette had a motor that sat more rearward off the kmember so this allowed room for the rear steer splindle and draglink setups. The 3rd gens do not have the room for rear steer in the chassis platform configuration and suffered much worse weight bias then the vettes also for those years. All in the name of back seat passengers

tvc 15

I think it depends on your skill level. Just like I'm sure not everyone can set up a racecar like you can.

Pablo

iTrader: (1)

I was lucky enough to visit the Ferrari Museum and factory in Maranello the other day and got some interesting pictures that show how Formula 1 used to do it and currently does it.

Note that all of the Formula 1 cars that I saw use front steer and what appear to be straight steering knuckles.

iirc 1986 F1, note the angle of the tie rods, looks like pro ackerman.:

Nigel Masell's 1989 F1, appears to have gone to anti ackerman:

2000 F1, looks like anti ackerman:

iirc 2008, the foremost carbon fiber bit is the tie rod, it's hard to tell from the pic but it does appear to angle back slightly and the gap between it and the control arm gets wider as it gets closer to the wheel. This appears to be anti ackerman:

I found it interesting that in Formula one it appears as though the primary means they use for setting ackerman is in the tie rod angles. I also thought it was interesting to see that it looks like they went from pro ackerman in early cars to anti ackerman in later cars. This supports some of the things I have read online about their use of ackerman. I'm not sure why they have done this, I suspect between tires, aero, suspension enhancements, and rules, the relative slip angles of the tires has changed considerably.

Just some food for thought. If nothing else, I feel reassured about playing with tie rod angles.

TEDSgrad

iTrader: (4)

Nonchalance and off-handed comment

OK, Pablo Montoya

Seriously...way cool!
Yeah, things have changed over the years. Don't know the vintage of the Ferrari, but the CART car is '02. Seriously, the driver is Jim Beam .

Pablo

iTrader: (1)

It was pretty cool. I also got to visit the Fiorano test track and the factory grounds. Got to really look at some formula 1 engines. Throttle body injection, and the sliding runners were very interesting. The engines themselves are dimensionally huge even though at most they were 3.5 liters depending on the year. Like big block Chevy width and length but a bit shorter.

The suspension stuff caught my eye and I tried to take decent picts with my cellphone. I forgot my camera SD card at home

I'm not so sure that first car you posted is an actual Ferrari

TEDSgrad

iTrader: (4)

Yeah, Faux Vintage!

The ALMS Jag looks like rear steering, but my pic is far away. Five guys looks front - but I don't always know what I'm looking at.

SlickTrackGod

Just for the record, I would not consider a F1 car with a rack steering to be what I was refering to as "Front steer". I was talking about drag links, pitman and idlers, and the way they swing in arch.

F1 cars do not see have such great tight corner downforce that they are creating such a tire slip angle as you stated Pablo. The inner tire which turns the car has much greater grip on a non-rolling 9lkaterally) heavy nose downforce car. The inner wheel has a much greater weight load so less ackerman is needed

Alot of ackerman on an open wheel car with alot of downforce has shown to destroy the inside front tires