Blooze Own: An F355 Six Speed N* Build Thread (Page 80/126)
Will SEP 06, 09:51 AM

quote
Originally posted by Bloozberry:

Flipping the knuckles has a few other advantages:
a. it keeps most of the geometry intact, though I'd like to get a simulation done to see actual changes (if any). Although Will hasn't commented specifically about this approach, he has led me to believe there may be hidden problems.
b. it moves the shock bell crank further backwards giving me more room for the front shock mount;
c. it moves the rear calipers closer to the cabin making it potentially easier to find cables that are long enough;
d. it would be dirt cheap to implement.




Flipping the knuckles will make your lower links into a parallelogram, but since both ends are coaxial, that shouldn't cause any problems with unwanted toe changes. It will transfer some of the lateral loads into the trailing link, however.
It makes the trailing link slightly longer.
I don't see anything hideously wrong with it. Just analyze the new geometry to make sure you're not losing anything.
Zac88GT SEP 06, 10:49 AM

quote
Originally posted by Bloozberry:
One problem with using high misalignment rod ends at their limits is that a greater component of the load acts axially though the rod end, essentially pushing the ball out of the side. Most companies only state the radial load capacity (along the axis of the pushrod) but a general rule of thumb is that a rod end's axial load capacity is about 10% of the radial load capacity. If I went this way, I'd have to be certain that the loads wouldn't be too great in the axial direction.



With separate links, like you have, only pure axial loads can be supported through the link. The rod ends will only have radial loads (unless they bind). If you change to an rigid A arm then you will have to consider the axial load rating of the rod ends.
eph_kay SEP 06, 10:51 AM
Dare I say custom knuckle?


ccfiero350 has done something of the sort with laser cutting if I remember right.
http://www.fiero.nl/forum/F.../000094-10.html#p385

I know it might add quite a bit of cost to it, but you should be able to do all the assembly work, and you are really only wanting to change the relative position of the "strut" mount in relation to your axle centerline to not negatively effect the rest of your suspension points.

Chris
Jefrysuko SEP 06, 11:35 AM

quote
Originally posted by Will:

Flipping the knuckles will make your lower links into a parallelogram



You're assuming that he wouldn't shift the inboard locations.

Keep up the good work blooz. Remember that if this was easy everyone would do it!

[This message has been edited by Jefrysuko (edited 09-06-2013).]

Bloozberry SEP 06, 12:15 PM

quote
Originally posted by ccfiero350:
Another alternative is to swap locations of the upper a-arm tie in point to the lower OEM strut hole and move your vertical transfer link tie up a little. You will get more camber gain out of it to boot.




quote
Originally posted by Will:
Can you lower BOTH pivots of BOTH links? You should be able to do that while preserving your camber and forward view instant center behavior.



Somewhere back around page 12 or so I had originally considered using the lower hole in the knuckle for the upper control links, but it was impossible to make the roll center behave in that configuration. I played around a LOT trying to make it work exhausting a dozen or so ways to salvage the idea back then, but it just falls flat. I'm nearly certain that using the lower hole would mean major concessions in the kinematics.


quote
Originally posted by Will:
That would also make you build a pocket into the frame rail for the inner pivots. If you do that, you dramatically reduce the twisting load on the frame rail that you have now, replacing it with a pure bending load



I've decided to strengthen the frame rail in that area with 2" angle over 10 or so inches in length. It will also restore the decreased cross section in that area due to the bite taken out for the stock spring clearance), returning it to a rectangular shape. As for the magnitude of the twisting load on the frame, you also have to consider that the center of the rod end is only 38mm above the top of the rail... so the moment arm isn't very long.

Thanks also for the explanation of the anti-squat behavior... I'll still need to go over it in my head when I have more time. For now it seems the best alternative is the one suggested by ccfiero350 to swap the knuckles side to side. I'll put together a set of coordinates for Zac to (pretty please) analyze this scenario. For the record, as Jefysuko mentioned, I will move the inboard lower link mounts to line up with the lower knuckle mounts.

Here's a quickie modified drawing (I've shifted the lower inboard mounts and upper inboard mounts, but haven't changed the trailing link nor the forward shock mount. Rather than lengthening the trailing link, I'll probably just move the mount backwards and keep the same angle):
Yarmouth Fiero SEP 06, 01:31 PM
There....... that wasn't so hard now was it.....

Great job Blooz. Nice to see so many knowledgeable PFF members sharing their wealth of knowledge as well. All the more reason to post our build thread on this forum.

[This message has been edited by Yarmouth Fiero (edited 09-06-2013).]

FieroWannaBe SEP 06, 07:48 PM

quote
Originally posted by Will:


Two separate links should not be analyzed like an A-arm.



This. What you have assembled resembles a 5 link suspension. None of the links are fixed relative to each other. They only provide the suspension the control of one degree of freedom each.
Bloozberry SEP 06, 09:55 PM
Yep... understood.

I've just fired off the suspension coordinates with the flipped knuckle to Zac88GT to run on his Lotus Suspension Analyzer program. With any luck, he'll see my email and have a chance to run them before too long. :fingers crossed:
kennn SEP 07, 10:58 AM
Blooze,

Does your latest proposal shorten the wheel base, or are you relocating the forward trailing link pivot to the rear to compensate for switching the uprights? If I understand correctly, you wanted to maintain the stock length of the trailing links. The discussion you have opened seems very productive. It's good to see so many well thought out ideas and suggestions.

Ken

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'88 Formula V6
'88 GT TPI V8

kennn SEP 07, 11:00 AM
By the way, beautiful work, and very instructive.

Ken

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'88 Formula V6
'88 GT TPI V8