ae86 steering geometry.

[BEAMS_86]

I am trying to wrap my head around the whole steering geometry thing and how it effects your steering as I am having a few minor steering issues.
I have been searching and reading for a few hours now and nothing has come up with specific explanations so if you have some please link me or explain. thanks.

Suspention specs:
diy coilovers, xt130 lca's, 30mm rca's, cut and shut knuckles, extra lock rack ends, stock ae86 rack.

So I drove my car at friday night prac last night and my troubles were.
When I initiate drift to enter the corner the car was fine but it seemed at a certain angle it had a some what dead steering feel but with a littlle more angle I have steering again.
Now my vague understanding of what is causing this issue is it is when the steering rack and tie rod are dead straight. Is this correct? If so, doing some measurements and having a some one machine up some rack spacer could possibly fix this so that the knuckle side of the tie rod is all ways facing the back of the car? or put some more toe out in to it?

Also on the faster corners it feels as if the inside wheel is skipping which I assume is due to the fact that it doesnt have as much angle as the out side wheel? will adjusting the accarmen fix this issue? if so what is the "ideal" accerman angle for an ae86?.

And last what is the ideal angle of the lca to be?. Just threw the digi level on mine and they are at 3.3 degree's with the ball joint side being the higher point.

Thanks in advance for any help/advice.

Cheers, Sam.

[Jimmee1990]

The vagueness in the middle of the rack travel isn't the tie rod end and the steering arm being inline, if this was the case the steering would bind rather than get better if you wind some more lock on. The ball joint should be lower than the mount on the cross member, so the geometry there is far from ideal and might also be contributing to the dead steering feel and the inside wheel feeling like it's skipping as you could just be suffering from bump steer. The ackerman I'm not sure on as I've never really played around with it personally.

[BEAMS_86]

ok cool. So I just done a few measurements and for me to bring the centerline of the ball joint to the same level as the centerline of the lca mount ( center of the bolt hole) I would need to go to an 80mm rca, thats with it being inline and not lower than, in that case I would have to got to say 85 or 90mm rca would that be correct? They are only rough measurements to try and get a better understanding as I dont think they will be an off the shelf item and I can have a mate machine them for me cheaper than I could buy any way. GOD DAMN LOW CAR haha.

As for the ackerman situation, I just found a pretty interesting read http://www.rctek.com/technical/handling/ackerman_steering_principle.html which explains how it is measured and the differant effects it has on steering. From what I get out of this is that from a drifting POV the ackeman should be at 0 as the C/L of the rear wheels is on the opposite side of what it should so in turn would be ideal for drifting as both wheels are pointing in the exact same position.
I was thinking the skipping feeling I was getting may be caused more so by the ackerman angle as I made the knuckles myself and they were the first pair I made ( have been skooled by my old employer on making knuckles but always nissan stuff) and not having a full understanding on ackerman angles and if it were bump steer I would feel it in both front wheel? it feels as if it is only the inside tyre being dragged and catching causing it to skip and jolt the wheel and the lead wheel is fine.

Also when my car is on lock my tierod's end up facing forward of the C/L on the steering rack? is this normal?

thank's for your reply.

[Delazy]

Shinji Minowa/Hey Man steering knuckles aren't quite 0 Ackerman...just saying :)

[BEAMS_86]

Yea, I dont think any one would actually run 0 ackerman as the steering would be bad in other aspects like turn in and transition, was more of an in theory sort of thing.
you wouldnt happen to know the ackerman angle they run at all Delazy? If not I suppose ill find some pics and measure them.
And thanks for the reply.

I will make my own knuckles again and this time take in to account ackerman angles and pinion angle for the tierod end ball joint specifit to my car this in turn should eliminate most if not all bump steer and wheel skipping.

Now to figure out what the dead steering feeling is as I want to run short track for matsuri and its certainly not a track to have steering issues on haha.

[Jimmee1990]

I don't think running that big of an RCA would be possible, wouldn't fit in the wheel. Fit the biggest possible RCA you can, and then raise the car from there. Super low cars and great handling don't generally go together, so it's really one or the other.

[BEAMS_86]

I reckon I could fit a 100mm rca in there if it needed to be, fair bit of room. But with measuring from the C/L of each and going down a touch on the ball joint side would be ideal.
the only problem I see with buying off the shelf items is most the time its not a one size fits all kind of deal if that makes sence.

I really dont want to raise the car hence trying to figure it out and perhaps leave some info for other who want to go low and keep geometry correct. If anything I would go lower but my current chassis isnt worth putting equal lenghth 4 link and boxing the floor like brett's old purple machine.

[Jacobxxx]

You couldn't run a 100mm RCA unless you had 17's and adm brakes.

Try a 50mm RCA but i doubt thats your issue, i had 30mm and my car was stupid low and i never noticed a handling issue like you're describing.

I'd say it's your custom knuckles. Who made them? What are you wheel allignment settings?

[BEAMS_86]

Jacob, you are right, after a few more precise measurements this morning with a clear mind ( few late nights and early morning last week lol ) the most I could get in there is an 80mm rca with out getting to close to the rim but I think 50mm would be fine, that would bring the lca angle to around a 2.5 degrees downslope the correct way.

As I said in an above post I made my own knuckles with out the proper understanding of how ackerman works and how to measure it correctly, I know understand it with more detail so I will get some new knuckles and give it another go.

Wheel allignment settings are
Camber: -4.5
caster: maxed out
Toe: 3mm total toe out ( from memory was a few months ago )
Pretty happy with this allignment.

I am thinking that with new knuckles and some 50mm rca's this should bring the geometry back a bit better and eliminate all my problems.

Know what I need to know is, Does any one know ackerman angle of say the HEYMAN knuckles? I could get some pictures and measure them and work it out from there but thats time consuming haha.

thanks for your replies guy's.

[BEAMS_86]

Also I will get some offset rack spacers made up and test them out as I cant find any for the ae86. Having my motor mounter where it is rules out moving the rack mounts forwards.

[drift kid]

Yeah, I have my car sitting stupid low and I run a very similar setup and have never felt this in my steering, I would also say the knuckles, how much shorter are they? Do you have any photos of them?

[Jacobxxx]

I don't really think an ackerman adjustment is necessary

[BEAMS_86]

Drift kid, they are 15mm shorter than p/s knuckles. I dont have any pic's but I will go down and take some in a min.

Jacobxxx, Why is that? I will get some pic's of the car on lock while I am in the garage. you can clearly see the differance in angle between the wheels ( it is quite bad ). I will also take some measurements while I am down there.

I will report back soon.

[BEAMS_86]

29432

so thats the knucles.

at full lock the wheels are 4° apart with the trailing wheel being the lesser angle. Now it doesnt sound that bad but at speed it would be causing my wheel to skip.

not trying to say whats rite or wrong to my own question here, just more getting others opinoins ect. If you have to improve your set up why not :).

[BEAMS_86]

Ok after going through and measuring pic's of most of the knuckles every one rates, they all seem to run 0 ackerman.
Just watched a vid on youtube of TOXIN and it says his knuckles have 0 ackerman aswell.

[Delazy]

http://img.tapatalk.com/d/13/09/22/3ara6e2e.jpg

Heyman, sorry for the crap photo...they also retain the standard "twist"...

[BEAMS_86]

So are they HEY MAN knuckles? standard "twist"as in the king pin angle were the tierod end ball joint goes in.

Adjusting the KPI ( King pin inclination ) would also have the same effect as installing RCA's although the geomitry of the LCA still wouldn't be correct.

[Delazy]

Yeh, they are genuine hey man, bought them a few years back...KPI is what I meant by "twist"...I remember quite a length thread maybe 18 months ago discussing knuckle variety/designs...worth finding

[BEAMS_86]

Ok cool, I think I will mod the KPI to my specific need's. I can understand why they leave it stock on "mass produced" items though.

yea I had a look through that thread, has some great info.

[SamsTA22]

The angle that the hole in the steering arm for the balljoint is on is not KPI. And it shouldn't have any change from factory. The only difference it makes is the allowable suspension travel without it binding.

It's probably a better idea to fix poor geomotry, than to mod components to suit screwed up geometry.

[blair]

What is restricting your lock? 15mm shorter than PS, with 4.5 deg camber and a heap of castor.... you must be running 7's -60 to clear everything??

[BEAMS_86]

The angle that the hole in the steering arm for the balljoint is on is not KPI. And it shouldn't have any change from factory. The only difference it makes is the allowable suspension travel without it binding.

It's probably a better idea to fix poor geomotry, than to mod components to suit screwed up geometry.

Ah ok, so what would the said angle and be referred to as? Just for future reference.

Was intending to fix geometry first obviously and then mod knuckles. What I was trying to find in the first place is, should the lca be at the exact same angle as it was from factory for perfect steering operation? As im sure toyota had to of made it that way for a reason. If this is the case then no I wouldn't have to modify the angle of were the ball joint goes but say I cant get the lca perfect with rca's due to space or what ever shouldn't the angle of the ball joint pin ( not sure on its exact name lol ) be at a 90° angle to the tierod for full movement in either direction?
That is a worse case scenario though.

[BEAMS_86]

Whst do you mean about restricting my lock?
Running 15x8 -0, tucks front tyre with no scrub on anything. Looks cool but now I need to make it work haha.

[blair]

well that doesn't make sense. i run xt130's same castor with power steering knuckles. around 3.5 camber. 8.5 -7 and 8 -15 (should have MORE clearance than you)

I'll get a photo of the rub marks and LCA angle... I have some jdi knuckles here that i can't run because shit will HIT not just rub lol.

My restriction is the tie rod end hitting the control arm (with lockstoppers removed - standard rack ends) and my front rail is 65mm from the deck?

What i'm getting at is, do you still have complete rack travel? or does something foul/hit to stop it?

[BEAMS_86]

Nah the rack has full travel and lock maxes out just mm before hitting the lca. Its weird how it works on one car but not another :s

[SamsTA22]

Ah ok, so what would the said angle and be referred to as? Just for future reference.

Was intending to fix geometry first obviously and then mod knuckles. What I was trying to find in the first place is, should the lca be at the exact same angle as it was from factory for perfect steering operation? As im sure toyota had to of made it that way for a reason. If this is the case then no I wouldn't have to modify the angle of were the ball joint goes but say I cant get the lca perfect with rca's due to space or what ever shouldn't the angle of the ball joint pin ( not sure on its exact name lol ) be at a 90° angle to the tierod for full movement in either direction?
That is a worse case scenario though.

If that angle has a name, I dont know it. Steering knuckle incline? It's not like it effects geometry at all.

Running the LCAs horizontal should be good enough, and that shouldn't require the incline of the steering knuckle to be modified...

I mean, yes, you wont have as much allowable movement. But if you're that low, you don't need extra movement because your car will bottom out first.

[BEAMS_86]

ok cool. not going to argue there as it will save me $150-+ for more rca's lol. The more I think about it though it wasn't suffering from bum steer so it shouldn't really need to be changed I guess.

As for the steering knuckle incline, I still need to cut the knuckles anyway to fix the ackerman so I may aswell change the angle for maximum movement since it's certainly not going to make it any worse the plus I couldn't remember the steering knuckle incline anyway so its going to be wrong haha.

Just hoping the the dead steering is due to the ackerman, I can't put it down to anything else. it's by no means un drivable but it's a thing that can be fixed so I will do it.

[Konakid]

If it were my car i would back the camber to 3.5 from 4.5 and run a 50mm rca, seeing as you are so low.
Cant help with the ackerman tho i imagine too close to 0 would feel weird .

[BEAMS_86]

Your just trying to make me buy some ajps rca's lol.

The car is track only so it would feel weird with normal street driving but not in drift. I think so dont hold me to that. I will let yous know how it goes any way.