Rear Strut Re-Design? (was: the need for 33 or 35 spline stub axles....)

[pparaska]

(split from http://forums.hybridz.org/showthread.php?t=100758)

 

Jaime - build it and they will come! Not sure how many, but if it's not break-the-bank over-the-top expensive, I can see my Z sporting these rear pieces.

 

I had a thought on the strut (re)design. This modification of the stock Z rear strut is intriguing to me - it radically changes the camber curve and roll center height of the rear.

 

http://www.classiczcars.com/photopost/showphoto.php?photo=14036&cat=500&page=1

http://www.classiczcars.com/photopost/showphoto.php?photo=13695&cat=500&page=1

http://www.classiczcars.com/photopost/showphoto.php?photo=13688&cat=500&page=1

 

Incredible work!!!!

 

You could adapt a similar idea (lowering the outer control arm attachement point on the strut assembly) EASILY since you're starting from scratch. Just make those two vertical-ish tubes longer and probably at a different angle viewed from the rear.

 

Yes, I know he's copyrighted the design, but all you'd be doing is using the idea of lowering the outer suspension pickup point. Last time I checked that kind of idea grabbing is not illegal, even in the US.

 

Thoughts? New thread?

[260DET]

Beautiful work but Jamie's seems to have more merit, strong five stud hubs and axles for a start.

[Guest JAMIE T]

Pete I remember those. It seems like you'd have to raise the diff also. Or, does that just make the LCA angle down? Hmmm. Maybe I'll try that. Like I've said. The one pictured is the "prototype". Anything can happen!

[pparaska]

Beautiful work but Jamie's seems to have more merit, strong five stud hubs and axles for a start.

 

I was only pointing those out for the LOWERING OF THE STRUT/CA attachment point, not to say the entire thing should be copied. OBVIOUSLY, Jaime's path is a stronger route to persue for stub axle strength. I was just showing that SINGLE DESIGN element that Jamie might want to consider, not saying that the 280Z stub was the way to go.

[pparaska]

Pete I remember those. It seems like you'd have to raise the diff also. Or, does that just make the LCA angle down? Hmmm. Maybe I'll try that. Like I've said. The one pictured is the "prototype". Anything can happen!

 

Not sure why you'd say that (the first sentence). Keeping the diff where it is, but lowering the outer attachment point of the CA relative to the stub axle centerline would make the CA angle down more, making the camber curve slower in a lowered Z, and raising the roll center.

[Guest JAMIE T]

Yeah, Pete. I realized that afterwards...

[JMortensen]

I'm not sure I care for Panchovisa's design. Seems too complicated and hard to adjust. Looks VERY expensive to make. But like Pete said, it would be EASY for Jamie to move the stub up in relation to the control arm attaching points, which would be basically just the same as a drop spindle setup. I guess the question then becomes how much would you raise the stub axle? I know most people think the front roll center is way more important than the rear. Then there are people like Cary who think that a roll center below ground is faster (at least at autox). So does it come down to a preference thing? Could it be made adjustable with maybe several sets of mounting holes?

 

Interesting possibilities there...

[pparaska]

I think the lowering of the attachment point and it's changing of the camber curve is probably more of the advantage. It seems on a lowered Z, the stock suspension presents a quick camber vs bump change. Making this less so seems advantageous, especially when alot of power is available. It certainly would help the straight line acceleration. I'd LOVE to have a totally camber compensating setup back there (http://locost7.info/mirror/dax.php), but that's a BUNCH of work.

[JMortensen]

I think the lowering of the attachment point and it's changing of the camber curve is probably more of the advantage. It seems on a lowered Z, the stock suspension presents a quick camber vs bump change. Making this less so seems advantageous, especially when alot of power is available. It certainly would help the straight line acceleration. I'd LOVE to have a totally camber compensating setup back there (http://locost7.info/mirror/dax.php[/url']), but that's a BUNCH of work.

We're saying the same thing Pete. You raise the stub axle in relation to the bottom of the strut. Or as you said, you lower the attachment point in relation to the axle. Same difference.

[cygnusx1]

I am fairly un-studied in suspension geometry so here is a question. When I look under my Z from the rear which has been lowered by 1", the control arms are only a few degrees off of horizontal with the inner end slightly higher. As I see it, when the car leans on that side (outside wheel), the control arm gets to "horizontal" and then goes past horizontal where the inboard end is lower than the outboard end. The horizontal point of the LCA is the point of maximum negative camber relative to the chassis. Anything before or after horizontal is robbing the wheel of negative camber. So by lowering the outer LCA point, you are on the "gaining" side of negative camber as the car leans. So as you lose negative camber to body roll, the LCA gives it back through it's swing arc. Am I close?

[JMortensen]

This one took me a while to get, but Terry explained it best. Maybe he still has his diagram, but the jist is this: When the suspension goes past horizontal it still continues to get more negative camber (or lose camber whichever you prefer) as the suspension compresses, because the strut gets shorter. What does happen is that the rate of camber change drops off, which now that I look at it is counter to what Pete was saying earlier. At least that's my understanding of it...

 

The "bad" part about a low RC is that once the control arm goes past horizontal then side loads (cornering g's) will compress the suspension, making the body roll that much worse. So you can run low RC's with very stiff springs or very stiff anti-roll bars, or you can raise the roll center and run softer springs and smaller sway bars.

[cygnusx1]

I think I see. The negative camber loss due to swing arc of the LCA does not really become detrimental untill the LCA goes past the point of being perpendicular to the strut tube-which is probably never the case. When the LCA goes past horizontal or parallel to the chassis horizon, with the outer end higher, lateral load, inwards, will cause further suspension compression load. So the "easy way" to set up a Z for stability and handling is to keep everything from moving too much i.e. heavy springs and bars. The "right way" is to tweak the geometry.

[JMortensen]

I think Cary would take issue with you saying that tweaking the RC up is the "right" way. I think both can be made to work, but IMO the softer setup with the higher RC is preferable for the tracks and the autoxes that I've done personally. If your track that you frequent is smooth as glass maybe the other way is better. Also most racing classes don't allow you to change the suspension pickup points, so any mods to RC are verboten. Even in ITS and BSP I believe it is illegal to use bumpsteer spacers. So changing it puts you in the insanely fast class.

 

I should point out that all of my arguments are theoretical. The only RC I changed was my front to fix the bumpsteer, and that made a huge difference, but I couldn't say what percentage of the difference was the bumpsteer going away and how much was the roll center changing. If I had to venture a guess I'd say it was mostly the lack of bumpsteer that I noticed, because the biggest difference was the lack of a big twitch around one particular corner.

[Guest JAMIE T]

FWIW, my car will only be allowed to run in stupid fast racing classes anyway since not a single component has been left untouched. Everything is modified except the exterior(other than ZG flares and front and rear spoilers). I completely understand the reason that will work, but I don't have time Pete to change my current prototype by the weekend. I was busy tonight mocking/jigging my LCA up. Also, I forgot to run by the machine shop and pick-up my hubcentric rotor spacers for the Cobra rear rotors to fit the ZXTT hubs. Damn it. Someone mentioned making multiple pick-up points on the strut housing. I like that idea. It would allow fine tuning on the fly, even at the track as easy as my set-up will be to take apart. Also, I didn't have time to buy the QA1 adjusters so I'm using the old Mikelly ones. I had four left for my arms. I think I want to replace them with the QA1 ones for alittle better packaging.

[tube80z]

Then there are people like Cary who think that a roll center below ground is faster (at least at autox). So does it come down to a preference thing? Could it be made adjustable with maybe several sets of mounting holes?

 

For the record that was the front roll center. I have never used a rear RC underground. I should also point out that my car was using 20 inch tall tires at the time. With the current 22 inchers the RC is actually above the ground.

 

It seems to be a common notion that getting better camber compensation will solve a lot of problems with our cars. I have tried this numerous times and never seen the results it would indicate. What I have found is that you're better off not worrying about that and trying to keep the tire from laterally scrubbing. At least in my experience that did more for grip and overall driveability. If you can go with a longer link then you have a little more freedom to play with this.

 

What ever you do in the back of a Z think really hard about making the outer strut pickups double shear. In the stock setup you can see a lot of flex that changes the toe setting. If you have an automatic car (stick would probably work too) try adusting your rearview mirror to watch the tire and powerbrake the car. What you see may surprise you.

 

Instead of alternate holes make the design so that you mount it using spacers. This is a quick and easy way to make changes.

 

Cary

[tube80z]

I think Cary would take issue with you saying that tweaking the RC up is the "right" way. I think both can be made to work' date=' but IMO the softer setup with the higher RC is preferable for the tracks and the autoxes that I've done personally. If your track that you frequent is smooth as glass maybe the other way is better. Also most racing classes don't allow you to change the suspension pickup points, so any mods to RC are verboten. Even in ITS and BSP I believe it is illegal to use bumpsteer spacers. So changing it puts you in the insanely fast class.

 

I should point out that all of my arguments are theoretical. The only RC I changed was my front to fix the bumpsteer, and that made a huge difference, but I couldn't say what percentage of the difference was the bumpsteer going away and how much was the roll center changing. If I had to venture a guess I'd say it was mostly the lack of bumpsteer that I noticed, because the biggest difference was the lack of a big twitch around one particular corner.[/quote']

 

In ITS you can get around the BS rule by making sure the spacer is attached to the strut and can't be removed. I don't think that is legal in SP though.

I don't really have an issue with rasing the RC. As you pointed out both can be made to work. In the other thread I just wanted to point out that you don't necessarily need to do this. And for some setups I think the underground RC works better. Granted what I do is different than what most everyone else does.

 

Cary

[Mike Mileski]

So how does one acquire a set of GTR hubs if one is so inclined to do so? I haven't checked eBay but I'm assuming these things are as rare as a hens' teeth in this country.

 

Mike Mileski

Tucson, AZ