whats needed for ultimate handling?

[gixxerdrew]

Yah its totally position sensitive (among other things). So I cant tell you what to do and not be wrong in some cases. You gotta know the details of the situation. God I wish I even kept a list of everything we did now, theres so much I know I cant even remember it anymore. I designed and built some parts and getting involved with robi was huge.

Robi and I were in constant communication... all this stuff is in his head too. On my end I did a lot of simulation and modeling work, robi and andy were really ingenious how to build it, he brought a lot of great ideas to the table for what the car needed and everything moved us in the right direction.

 

[jdsoza]

@ cinder: I'm still gathering info as to how much we will be moving arms in total when we build a sub-frame. My fabricator thinks he can get away with building a set of arms that will give about 4 degrees of positive or negative camber. i also have no problem cutting a hole through my floor for the compression arm, the cars an experiment. I got a cost for a custom knuckle to be cnc'd, looking about 3K so I'm trying to avoid that. Would you suggest having the upper lca mounts being moved up or left in a factory location? I'm confused if your talking about the eyes on the knuckle being lowered or the eyes on the upper lca itself.

 

[eclipse420ags]

I didnt read thru it all but having your directional tires going the right way would help haha

 

[jtmcinder]

@ jdsoza

I was talking about extending those eye-bolts that hold the upper LCA to the chassis. By moving the eyes (and, therefore, the inboard end of the upper LCA) downwards, you add static negative camber and also steepen the camber curve (i.e., more added camber in roll). But, as pointed out by Andrew, angling the upper LCA downwards (from top of knuckle to chassis) will lower the roll center on a car with a good set-up for the lower LCA. So this cheap-and-easy way to get camber should probably only be done on an over-lowered car that hasn't had it's lower LCA redone and/or on a car that is so stiffly sprung that the roll center isn't very important ... but then why bother with a steeper camber curve?

@ the joker above

Actually, on dry pavement, running directional tires backwards often gets you more grip. (Old AWD drag-racer trick: snow tires on backwards.) Directionality is for rain or snow, only. I know that you were joking, but some jokes can be rather misleading.

 

[greengoblin]

Wow. This is a great example of how you have to think "system" not individual part, isn't it? If your lower LCA is angling down, as on a over-lowered 2G with OE subframe, then lowering the eyes of the upper LCA actually helps the roll center, as well as steepening camber. But if your lower LCA is still pointing where it should, then lowering the eyes hurts. I never connected those dots before. Thanks.

Are you saying it will move the RC down?
I played around a paint and I only saw the roll center move up when the inboard pickup on the upper arm is moved down. Am I missing something here. That being said it may bring it up to high. I don't know since I'm just playing around with no really data.

Thanks
Kevin

 

[jdsoza]

Just got good news from my fabricator. He recommended an off-road shop that will modify the knuckle to raise the points. can anybody give me an idea of where they want the knuckle to be raised? I'm going to pick up a spare knuckle from the salvage yard and ship it to him to see whether or not it can be modified and be safe. if not he will use it as an example and cnc a new one, for a lot cheaper than what I have been quoted. Im not good at the math portion of what points and how high they should be raised or dropped. i just thought I'd let everybody know of a possible solution.

 

[jtmcinder]

@Kevin

By my paper-napkin model (since I still can't find my real one), a sharper angle to the upper LCA will raise the roll center if (and only if) the lower LCA is angled down from knuckle to chassis, as on an over-lowered and not corrected 2G. You basically catch the lower LCA's line at an earlier point, moving the instant center up a little. In contrast, if your lower LCA is flat or better (i.e., angled up from knuckle to chassis), then angling the upper LCA down more will hurt, because catching the lower LCA's line sooner will now lower the instant center.

Make sense?

I've been thinking about over-lowered 2Gs for so long that I had it ingrained that angling the upper LCA more would be all good. But, of course, it's not what you want when the lower LCA is still angled correctly. And, as you know, you really really really want the lower LCA to be angled correctly.

Here's a really dumb idea: people should look at how much of the thread of the ball-joint's post on the lower LCA sticks up through the nut. Whatever you see there is "wasted." Pop the post out of the knuckle and put some washers on there and re-install. Yeah, you'll lose a little camber, but you'll make a decent gain in roll center height for the effort. Same goes for the compression arm's ball-joint post to get some more anti-dive. This is - in effect - the poor-person's WhiteLine RCK.

 

[snowborder714]

By looking at the pictures I posted on the first page of this thread, it doesn't look like there's much wasted thread to play with. Although I can't be certain without finding a picture with a different angle or just popping my head in there and looking.

 

[jtmcinder]

By looking at the pictures I posted on the first page of this thread....

Ooo. That one left a mark.

 

[greengoblin]

Good suspension post in another forum I think.

Moment Centre / Instantaneous Roll Centre - Fully Explained (anti 56k)

 

[snowborder714]

Thanks for that link, Kevin. That clears up some of this stuff for me, since I'm just starting to learn about how it all works together.

Makes me want to go collect data now!

 

[greengoblin]

Brian,
If you have not read the Carroll Smith books you should. They have a lot of really good info and do a good job of explaining most things. Also dare I say this, the circle track magazine website also has a lot of good info on stuff too. It has helped me wrap my head around a few things in the past.

 

[snowborder714]

I just started going through Carroll Smith's books (and others) and putting together a list of ones I want. Dang there are a lot!

 

[turboking15]

found this little gem.
Carroll Smith - Tune To Win.pdf - 4shared.com - document sharing - download

should be a good read.

 

[snowborder714]

And to think, I just ordered that book from Amazon yesterday

Actually, I had downloaded a PDF version of it over the weekend, but I want a hard copy as it's easier to read (compared to a 12" laptop screen during the week). But the PDF will be very nice when I have to go back and find certain things I read. You just can't Ctrl + F a real book yet.

 

[snowborder714]

Another article to add to the collection:
It?s All in the Geometry- Part One, The Roll Center

 

[Getritch]

I know this is pretty necro, but i haven't found another thread like this in the forums. I picked up my 2G GSX in September for road race and the knuckle, i've found, is one of the major limiting factors in several suspension geometry problems. Specifically if the linkages could be moved around it could balance the effects of the anti-dive on lowering, as mentioned, but also the camber curve could be increased greatly (in conjunction with a shorter Upper arm) without many drawbacks at all.

it would literally optimize the suspension for shorter travel/stiffer operation while keeping most of the geometries oE

I know a guy who does CNC stuff and he is willing to machine me some new knuckles for way less than the 3k mentioned. literally just the cost of the chunks of aluminum it'd come from, so i've been working on a CAD modeling of what I think it should have been out of the factory.

any of you uber-experienced DSMers got any specific points other than the ones mentioned for correcting other connection points or steering angle stuff? (and obviously keeping the LCA at OE spec. Harder than it sounds, cause it DOES have to clear the front axles, )

 

[jtmcinder]

The only inboard points that I've ever seen anyone move are those for the lower front LCA. I don't see how you'd move the compression arm's pick-up (to fix the anti-dive), nor how to move the eye-bolts for the upper front LCA.

I've not seen enough effort put into the outboard end, IMO. That's the way we fix things on Evos. Long-stalk outer ball-joints, FTW!

As to shortening the upper A-arm. I was one of the first to do this and it was freakishly easy. (Those two things go hand-in-hand, you know: I did it and freakishly easy.) You just drill new holes on the ears (about 1/2" over), weld washers around the new holes for strength, and grind off the tips of the ears so they don't scrape. It did exactly what it was supposed to do.

 

[greengoblin]

I have to agree that the outboard pickup points on the front are really the ideal place to move things around on our cars. I think before too long there will be after market lower controll arms that are lighter than stock and have adjustable height on the outboard ends. There has been plenty of talk about it and I have seen some promising cad drawings.


Kevin

 

[jtmcinder]

Has anyone tried to use WhiteLine RCK ball-joints? I mean, it would be sad if the parts meant for Evos would fit but you all re-invented the wheel, as it were. tee hee

 

[lowell]

Has anyone tried to use WhiteLine RCK ball-joints? I mean, it would be sad if the parts meant for Evos would fit but you all re-invented the wheel, as it were. tee hee

Evo ball joints are zero taper with a pinch bolt.

 

[Ludachris]

On the 1g, I found the an S13 240sx ball joint to have the same taper. Just don't know if the body of the ball joint is the same as a DSM to fit into a control arm. Unfortunately, it doesn't look like Whiteline makes roll center adjustment ball joints for the Nissans. Other companies do though. I just never pulled the trigger on a set for testing. Don't know that I'm the best person to do the R&D. Wish someone with more technical experience would try it though.

Not that this applies to the 2g, but I would bet there's a ball joint out there from another car that would do what we need while requiring little modification to make work.

 

[Tyeler18]

On the 1g, I found the an S13 240sx ball joint to have the same taper. Just don't know if the body of the ball joint is the same as a DSM to fit into a control arm. Unfortunately, it doesn't look like Whiteline makes roll center adjustment ball joints for the Nissans. Other companies do though. I just never pulled the trigger on a set for testing. Don't know that I'm the best person to do the R&D. Wish someone with more technical experience would try it though.

Not that this applies to the 2g, but I would bet there's a ball joint out there from another car that would do what we need while requiring little modification to make work.

I've got a set of both at work. I'll break out the mic's and see what I can find out. Does the s13 use a c-clip like the 1g's do?

 

[Bud92gsx]

This has been weighing on my mind lately..

In our upgrade paths, it says don't lower the ar more than aboot 1.5 inches..Is there a obvious answer why that doesnt stick out in my head?

Yes I know too high too /low can defeat the purpouse..But why is the question???????

 

[Tyeler18]

The angle of your lower control arm should never aim "up" towards the ball joint. By overlowering the body will sit lower than the ball joint, making the control arm angle up. This defeats all anti-dive geometry and will upset the car. You want it as close to parallel with the ground as possible.