Help design custom rear trailing arms

[RonM]

I have been butting up against the limitations of the 510 semi trailing arm as I'm sure many of you have. Undoubtedly the need for a better design exists. I'll say it right off the bat; I do not have the knowledge, or the tools to do this on my own. There is so much knowledge and talent gathered here I figured if we could collectively brainstorm this, I'm sure a kick ass design could come of it. I mentioned the desire for a custom arm to 510wizard and we started kicking it back and forth (posted below)

Here is what I propose. Break it down into parts: 1. A wish list of improvements, 2. How best to accomplish them, and 3. Drawings / plans. Fundamental questions such as traditional fabrication vs. CNC are open. I have a friend in San Diego with a CNC machine in his shop, so if we were able to provide 3D C.A.D. drawings maybe he could run a batch for cheap.

Here are some items for the wish list

1.set back on the outer edge to accommodate a wider wheel

2.use a bolt on hub/bearing assy., which will give 5 lug with cv's.

3. a bit of camber angle at the hub to help facilitate lowering


RonM wrote:
Side note: Would you consider making parts for sale? Say like a set of aluminum rear semi trailing arms?

510wizard wrote:
Thanks for the compliment. On the part thing, what do have in mind? I have a idea for rear semi trailing arms that use a bolt on hub/bearing assy., which will give 5 lug with cv's.

RonM Wrote:
Heres my situation; I'm building an SR swap and I anticipate getting a bit more than 400HP. I'm struggling to get as much rubber to the ground as I can while keeping stock fenders. With 7" rims I have more than an inch of space at the coil overs, but I don't think it's advisable to notch that much out of the stock arm. I was thinking of a trailing arm that is set back on the outer edge to accommodate a wider wheel. Also I was thinking it would be cool to incorporate a few degrees of camber angle at the hub to facilitate lowering. I'm not sure if this is even possible without screwing up the geometry.

510wizard wrote:
I wouldn't set the camber in the hub itself. You still have to deal with the toe anyway. If you change the ride height for any reason, you are screwed with the camber incorporated at the hub. I would recommend all adjustments for camber and toe remain at the crossmember. The 510's aren't super square anyway, (compared to newer cars), the settings for one side aren't the same for the other side. If you guys are game, we can start another thread on brain storming some custom rear arms. Could be fun stuff!

[510wizard]

Ok, some of my thoughts on this to start this off, first this isn't going to be a budget build, far from it, but I think it will solve a lot of the things that can be improved over the stock arms. It will require CV's ,(with no adapters on the hub side and depending on the diff. used will not require any adapters at all), which is needed for the high HP guys and also are a better set up all round over the half shafts( less noise , work better at large angles, lower friction) I would start with a hub that includes the bearing assy., most of the newer cars use these in one form or another. I would pick the rear hub assy. from say a 350Z. These are of coarse 114.3 x 5, bolt to the upright on the "Z" with four bolts. What nice about these is that you get a easily replaceable part, no preload spacers any more,no big frickin wrench to get the stock nut off, already set up for CV's( no adapter).
example


I would make a plate that this hub would bolt to, which also mount the brake caliper and the shock. This plate would be welded to the arm which could be a total new design or to a stock arm. If one of the goals is to fit larger tires in the stock wheel wells, then a new design is required that has the needed clearance for the tire/rim. This is a picture of a rear arm of a BMW "M"series coupe as a possible model. I think that studying the late model BMW's would be wise ,since they are still using the semi trailing arm suspension.



It might be possible if designing new arms, to include some form of eccentric at the pivot points for adjusting toe and camber.

Just some thoughts to think about

[S15DET]

I believe we may want to have a consensus on how far to take this. There are real limitations to a semi-trailing arm design, so do we want to simply redesign the arm, or perhaps the whole rear suspension? I will suggest that we at least consider looking at the whole rear suspension. Long nose differentials are harder to find than the common Nissan short-nose diff that’s in all the newer Nissan cars. Maybe we do away with the rear crossmember and the semi-trailing arms, and design a new mount for a short-nose, as well as a mating part that incorporates mounts for lower control arms, something similar to the Z-cars, LCA’s with struts to the stock unit-body upper shock mounts. I love what 510Wizzard is doing with the Miata hubs and suspension here…
http://www.the510realm.com/viewtopic.ph ... wagon+rear

If we decide to focus on just re-designing the arms, I really like the tubular arms that someone posted a while back that gave camber and toe adjustability and a better bearing/hub assy. but I can’t find that thread. And let’s not forget the billet arms that Matt made for the Ecotec project.
http://www.the510realm.com/viewtopic.ph ... iling+arms

Hopefully someone will find those tubular arms because it was a clever design and would serve as a good starting point. I like the idea of using the 350Z rear hub.

[S15DET]

This isn't what I remembered, but it's the same idea.
From here...http://www.the510realm.com/viewtopic.ph ... suspension

[S15DET]

OR, maybe we can do a little of each, keep the rear crossmember and long-nose, but re-design the arm in a way that gets away from the semi-trailing design. Maybe the arm can have the forward link go to the inner pivot on the crossmember, and design a differential-mounted (Wizzard style) bracket to locate the other link, using a strut-type hub? With our low trunk floor there's no room for a SLA or a multi-link suspension, that's why I'm favoring a LCA/strut arrangement for our new arms, and it seems that we can do this with only the diff bracket to locate the rearward arm? Maybe a sketch is needed, off to the CAD cave!!

[S15DET]

Here's the concept, only a quick concept sketch, and I know there's lots wrong.

[S15DET]

I guess if we did this the strut would limit inner tire clearance just like the shock (or coil-over) does now? I doubt that we can get a consensus if it requires relocating the upper shock mounting point. If we design the arm to re-use the coil-overs that many already have, this makes the project more acceptable. This just makes the arm beefier as it needs to locate the hub/bearing in more axis. But there will be little cost difference because it eliminates the need for the pivot at the end.
The camber curve is the biggest difference, and this needs to be considered whatever is done. If we stick with the semi-trailing arm design then this remains constant. Does this crazy camber curve of the semi-trailing arm giv the car it's 510-ness?
Check these out for ideas from the Z world...
http://sth2.com/Z-car/Control_Arms.htm

[510wizard]

This isn't what I remembered, but it's the same idea.
From here...http://www.the510realm.com/viewtopic.ph ... suspension

Look at a few pictures up from that one, is that what you are talking about? It would be easy to mount the 350z hub to that.

http://www.the510realm.com/download/fil ... =11024&t=1

[510wizard]

I believe we may want to have a consensus on how far to take this. There are real limitations to a semi-trailing arm design, so do we want to simply redesign the arm, or perhaps the whole rear suspension? I will suggest that we at least consider looking at the whole rear suspension. Long nose differentials are harder to find than the common Nissan short-nose diff that’s in all the newer Nissan cars. Maybe we do away with the rear crossmember and the semi-trailing arms, and design a new mount for a short-nose, as well as a mating part that incorporates mounts for lower control arms, something similar to the Z-cars, LCA’s with struts to the stock unit-body upper shock mounts. I love what 510Wizzard is doing with the Miata hubs and suspension here…
http://www.the510realm.com/viewtopic.ph ... wagon+rear

If we decide to focus on just re-designing the arms, I really like the tubular arms that someone posted a while back that gave camber and toe adjustability and a better bearing/hub assy. but I can’t find that thread. And let’s not forget the billet arms that Matt made for the Ecotec project.
http://www.the510realm.com/viewtopic.ph ... iling+arms

Hopefully someone will find those tubular arms because it was a clever design and would serve as a good starting point. I like the idea of using the 350Z rear hub.

I agree with S15DET that we need some input on "wants" for these arms. Do we want coil overs or stock style springs or the provision for both? Bushings or Heim joints? Are these going on a street or race car? A total redesign of the rear suspension? What about the $$$ part of it, like what I mentioned in my previous post, this is not going to be cheap by any means, just doing the arms them selfs and the CV's are going to be big money, no junk yard parts can be used, every thing going to be custom. Going to have to make jigs, a least two, one for each side. Lots of time in design, in fabrication and testing and probably redesign.
The one big advantage to the semi trailing arm suspension is the packaging, it doesn't take up a lot of room,which probably why BMW is still using it, but as was mentioned by S15DET it has lots of limitations. These limitations is why I went with the Miata "A" arm style in the wagon project. I saw what others have done (using the sedan IRS or s13,14 multi link) in the wagon but decided to try the "A' arm suspension. IMHO, the only reason to use the sedan IRS in the wagon is it is already the right width. But, I have lots and lots of time in it so far and I am not done yet, not even close.
So lets get some input on the "wants", maybe in a list form, then we can discuss each one of them.

[two_68_510s]

Can you make a double sided jig? Flip it over to do the other side. Too much extra work? or could it be more likely to carry the symmetry/precision side to side?
(PS I am no toolmaker but I love that part of the problem.)

[510wizard]

Can you make a double sided jig? Flip it over to do the other side. Too much extra work? or could it be more likely to carry the symmetry/precision side to side?
(PS I am no toolmaker but I love that part of the problem.)

It could be possible if there is no camber correction build in to the arms, but still there is a lot of work just in the jig(s) if you are doing a production run and want any kind of precision and constantly.

[RonM]

For me, I was hoping this would be a bolt on improvement. My concern is that if it becomes too technically challenging and fabrication intensive it will put it out of reach for mere mechanical mortals like myself. That being said, I wouldn't want to be an anchor on any real advancements.



Here's list of wants so far. If you see anything you'd like to add please chime in.

*tubular arms that give camber and toe adjustability

*set back on the outer edge to accommodate a wider wheel

*use a bolt on hub/bearing assy., which will give 5 lug with cv's.

*ad a bit of camber angle at the hub to help facilitate lowering

*Heim joints

*coil overs PLEASE

*Billet aluminum CNC


Wizard, you mentioned a distinction between Race, or street. What would the actual difference be?

[S15DET]

The difference between race and street as it relates to this semi-trailing arm I believe are minor, and mainly related to the pivot points. For a racecar you'll want spherical bearings, for a street car you don't. Although I track my car a bit, it's not a racecar and I have rubber or poly bushings all around, no spherical bearings because I dont want to pay the NVH penalty, or the maintenance headaches. However, regarding the maintenance, I have seen a few places that sell rubber boots specifically made for spherical heim joints, so that would make them more practical for street use. And since my rear crossmember is still rubber mounted, you might could talk me into bearings. Street or race, both will want ease of adjustability, a positive way to lock the adjustments (no slotting that could be bumped out of adjustment), and tire clearance. If it were a 10/10ths race effort, then the arms would be light to the point that they wouldn't hold up to street use, but no one here is interested in that I don't think.

[510wizard]

Right on S15DET on the NVP, for me a street-able car has to be a lot quieter than a race car. I was thinking about using a delrin type material for the bushing with grease fittings. Also adding some type of adjustments for toe and camber that are non binding at the pivot points.

RonM, when you say "Billet aluminum CNC" what part(s) are you talking about? The arm itself or the complete assy. (arm, bearing/caliper bracket/shock coil-over mount) ? Billet= $$$$

[RonM]

RonM, when you say "Billet aluminum CNC" what part(s) are you talking about? The arm itself or the complete assy. (arm, bearing/caliper bracket/shock coil-over mount) ? Billet= $$$$

I was thinking just the arm itself, because it's the heaviest component. I figured it's a "want" list at this point, so why not put it on the table for further examination. My assumption is that it would be easier to develop the arm design in virtual environment. Hell, at this stage I don't even have someone to do the CAD modeling, but why not run it up the flag poll and see what comes of it? I'll contact my buddy in Dago and see if he can give me some idea of the cost to develop and eventually run a batch. My younger brother is an investment banker and might be willing to fund the initial investment. I'll speak with him as well.

This is an awesome learning experience for me, and I'm thankful to contribute anything I can. Hopefully in this process of vetting we'll be able to create a trailing arm design that will provide the most improvement bang for the buck. Ultimately this will also improve it's future marketability if that is the desire. Again I'm not as knowledgeable in this area as you, or Brad, so if I'm proposing something totally unrealistic please feel free to offer some perspective. I think it would help if in the beginning, we can assume to one degree or another everyone working on this will have their own subjective vision base on their specific needs, skill set, and and budget. In this process however, I will always defer to wisdom over want.

Thanks guys