This is the roll center, suspension pickup, and steering angle modification thread.

[MY_S14_SR20DET]

like 10 hours of reading later. this thread is amazing!

[singlecamslam]

Originally Posted by SoSideways

Meh... either way.

So are your's seriously in the dumpster but still sitting around? Or have they been picked up by the trash people already?

I'm asking because I want to see if those cups can be opened up for the bigger bearings that I wanted to run without any ill effects, or if it will make the cups too thin, and thus dangerous to do so.

If you still had those arms sitting around, I was gonna see about taking them off your hands for this purpose.

Sorry dude i seriously chucked them. But they were cut in half so i dont think they had anymore use to them.

[SoSideways]

Meh, it's all good.

I'm almost considering either cutting mine down and rewelding the bearing cups on with less of an angle, or sending my knuckle out to PBM so they can weld the FLCA mounting point 2" lower, and using stock arms or something.

[swiftmini]

Quick update on my setup.

I just removed a huge amount of ackerman. Car feels really nice, better grip, less tyre wear, car felt quickerthrough mid drift. Didn't notice any negative affect on turn in grip.

Had to extend my ikeya tie rods by 50mm because I ran out of thread. Also had to remove the 7mm lock spacers and fit 10mm because I ran out of rack travel.

Steering is just locking out slightly when on full lock with heavy loading on the leading wheel.

Not sure whether to move the rack forward a snatch or just run less lock

[Slidin' Sam]

NORIYARO » A MASTERPIECE: Takurou Watanabe’s ultimate knuckles

Discuss.

[PoorMans180SX]

Just another modified knuckle. Just took it to the extreme.

[Slidin' Sam]

Yeah, I really wanna see some pictures with the wheel off. Alexi said that the guy removed his bump stops all together. I don't think it's anything special really. I'm happy with the PSM knuckles for now.

[swiftmini]

He uses ikeya formula fla without the stops fitted.

Max stuff is capable of the same angle :nod:

I have a youtube link of him driving that car at nikko if anyones interesteyoud

[articdragon192]

Wow, super camber loss at full lock.

[nieko]

Yeah wtf? He either needs less caster or more negative camber from the get go... lol

[swiftmini]

He runs a 205 16 tyre, I doubt he cares about front grip. After all he is 4 wheel sliding and backing it in on every corner.

Also he has shortened the steering arm so much that he needs caster to make it less twitchy. I'm pretty sure he knows what he is doing

[Z33dori]

video plz
msglgth

[swiftmini]

YouTube - ???????????? ?DRIFT?NIKKO?CIRCUIT

[SicBastard]

Can anybody confirm that a car with a independent rear suspension calculates anti squat with a line through the instant center and the center of the wheel, rather than through the rear tires contact patch? And if so why? I found this textbook page, but I've seen a lot of contradicting information stating that IRS cars' anti squat is calculated the same as a sprung 4-link. HELP!



The difference is dramatic. Using the contact patch, as is standard when calculating antisquat in sprung 4 link drag cars you get about 200% [BLUE LINE] antisquat for an s14 and a completely rediculous >300% in an s13. But Using the textbooks wheel center method for an s14 gives a makes-no-sense 0% antisquat [ORANGE LINE]. 120-150% [GREEN LINES] is standard for a road race car, and of course it's possible that my pic is a bit off, but this isn't making any sense.

[singlecamslam]

Originally Posted by SoSideways

Meh, it's all good.

I'm almost considering either cutting mine down and rewelding the bearing cups on with less of an angle, or sending my knuckle out to PBM so they can weld the FLCA mounting point 2" lower, and using stock arms or something.

Yea i hear ya. I'm actually in the prosses of welding in my bearing cups in my stock arms at a different angle. They will be angled at the top more towards the wheel so i wont have so much bind when the car sits on the ground. Pictures will come soon.

[Def]

Originally Posted by SicBastard

Can anybody confirm that a car with a independent rear suspension calculates anti squat with a line through the instant center and the center of the wheel, rather than through the rear tires contact patch? And if so why? I found this textbook page, but I've seen a lot of contradicting information stating that IRS cars' anti squat is calculated the same as a sprung 4-link. HELP!



The difference is dramatic. Using the contact patch, as is standard when calculating antisquat in sprung 4 link drag cars you get about 200% [BLUE LINE] antisquat for an s14 and a completely rediculous >300% in an s13. But Using the textbooks wheel center method for an s14 gives a makes-no-sense 0% antisquat [ORANGE LINE]. 120-150% [GREEN LINES] is standard for a road race car, and of course it's possible that my pic is a bit off, but this isn't making any sense.

Your suspension arm IC is calculated wrong. One line goes through the lower arm mounts on the subframe, the other goes through the top mounts(camber/traction). That'll give you an IC that is much farther forward. The line from the contact patch to the IC is your anti-squat line.

Your IC line is calculated off the middle of the wheel it looks, so it is artifically close to the contact patch.

Going off memory on all this, been a while since I've done an analysis, but I'm pretty sure that's right.

[SicBastard]

I double checked gsracer's original image that I stole. The instant center IS calculated correctly through the lower arms/ traction+RUCA.



Originally I stated that I've been getting conflicting reports as to whether the anti-squat line should originate at the contact patch or the center of the rear wheel. The more I read, the more certain I am that the contact patch is only used to create the antisquat line in solid axle designs, and that the orange line is indeed the correct line to use (rear wheel CENTER to IC) to calculate the antisquat line in IRS designs.

Here's a link to a Professor of race car dynamics at Florida State agreeing

http://www.racetec.cc/shope/

Clarification: I refer to 100% antisquat line (no induced force) as the pink line (a lot of discussions will refer to the blue line as 100%. I call the blue line 200% antisquat.

Further evidence that the s14 has ~0% anitsquat: I remember the one time I drag raced my s14 at the track and at launch the rear would squat so much that I was a fraction of an inch from draging my stock tow hook! Any car with 200% anti-squat (as the blue line starting at the contact patch would indicate) will actually lift the rear end of the car on launch like a properly set up drag car. It's obvious that the 240 doesn't lift the rear on launch.

Here's a s14 running real QA1 drag shocks, with noticeable squat
YouTube - LS1 Nissan 240SX (S14) on QA1s at Beech Bend Drag Strip for some shakedown passes and testing.

Here's a mustang. While the guy struggles to stage you can see how softly sprung the car is, it wobbles all over the place. But whatch his launch around 1:12, a couple times. Even though he has enough power and traction to lift the front wheels completely off the ground THE GAP AT HIS REAR TIRE NEVER SHRINKS... no squat... That's how a car with 200% antisquat should behave on acceleration.
http://www.youtube.com/watch?v=Lq4FzEWdDNM


Finally here's a paraphrase from Herb Adams book "Chassis Engineering"

Chassis engineering - Google Books

Only real downfall of a IRS is the anti-squat, practical limit is about 25%. While a drag/live axle car can get 100% or more

[SoSideways]

Good info.

Thanks!

[Csomme]

I have a problem:

PSM steering angle kit welded up by a local machine shop. Lowered akerman(or so I thought) alignment is toe: 0 caster: 6.6 and camber: -3.2

What is going on? Why is my trailing wheel so fucked up and hardly getting any angle?! My leading wheel is fine, idk what to do.

Better pictures:








It's the same both directions. gahhhh. What do I need to do?

[SoSideways]

Do you have any pictures of the knuckles themselves, like, of the work done by the shop?

Mine is kinda sort like that, but I think my trailing wheel gets a little more angle than that.

[nieko]

Do you have tie rod spacers? PSM usually puts them in too.

ALSO, is your rack centered? or is it really off not letting the other side go in as far?

pictures of knuckles!

[Csomme]

I have rack spacers, PSM's that I put in. Rack is centered, it does this when I turn both ways on the trailing wheel. I will get pictures of knuckles up ASAP!

[Jonnie Fraz]

If I had to guess I would say they added ackerman.

[Csomme]

No, I can visually see the decrease in Akerman. The mounting point of the tie rod is inline with the mounting point of the FLCA, almost parrallel with the brake disk.

[PoorMans180SX]

Looks like your tie rods are too short. What are you running?

[Slikk Logic]

this is a epic thread.

[Csomme]

I'm running wicked tie rods. How are they too short? My alignment is dialed in. If they were longer wouldn't I be toed in? I really don't understand what's going on here. Lol

[PoorMans180SX]

Wicked tie rods for S13? S13 tie rods are too short. You need S14 tie rods. And PSM spacers.

And their tie rod ends suck btw.

[Csomme]

I have PSM spacers. How are these too short? If they were longer I would be toed in. These aren't even close to being fully extended. They may suck, but they're all I have. Kind of don't have a choice right now. Lol pretty damn broke.

[PoorMans180SX]

Trust me. S13 tie rods are too short. Look at any good website and they will recommend S14 tie rods for modded knuckles.

You can still get zero toe alignment, you just have to adjust them in farther. I know I know it doesn't make a lot of sense until you see it, but I know what I'm talking about. Everyone else in this thread and Kuah (from SPL parts) and Dan (from Parts Shop MAX) will tell you the same thing.

Check out PSM's new tie rod inners/outers. Cheap and strong.