A-arm adjustability

[Jon_Dal]

I'm looking at rod ends vs sphericals for our inboard a-arm mounting points. Yes, I realize there are many threads about this and the topic is half beaten to death. Rod ends in bending is bad and so on.

Most people seem to say that sphericals are better and you can simply adjust camber/caster with shims. How do you adjust caster without changing the distance between the inboard points? Do you just force the arms out to fit? If so that doesn't seem like a good idea. With a rod end you can screw one end out (say the back) and one end in (say the front) to change caster without changing the distance between the 2 points.

How do people address this?

[Jon_Dal]

I'm looking at rod ends vs sphericals for our inboard a-arm mounting points. Yes, I realize there are many threads about this and the topic is half beaten to death. Rod ends in bending is bad and so on.

Most people seem to say that sphericals are better and you can simply adjust camber/caster with shims. How do you adjust caster without changing the distance between the inboard points? Do you just force the arms out to fit? If so that doesn't seem like a good idea. With a rod end you can screw one end out (say the back) and one end in (say the front) to change caster without changing the distance between the 2 points.

How do people address this?

[Jon_Dal]

Just to clarify...I am using sphericals on the outboard points, there is no question about that. Also as kind of a side question...has anyone had issues with crimping the tubes down to size for the spherical bearing mount? Is there a better way to do this? Thanks

[Mike Cook]

On our outboard pickup points, we use a sleeve that houses the spherical bearing. It is 5/8" long which accomadates both .5 and .625" A arms. It has a snap ring groove. WE also ream it to spec after welding. We don't crimp our tubes down at the end.

About caster: pick it and live with it. I think you could make up a seperate set of a arms to try a different setting if you really wanted to.

[Jon_Dal]

That's kind of the direction I'm leaning towards (non adjustable caster). Do you use spacers on your bolts that attach your sphericals? I was looking at the high misalignment auroras and was hoping to avoid spacers if I can.

[kwancho]

Good question. I actually had a conversation about this the other day. Speaking from my zero experience, I figure that the upper A-arm takes significantly less load than the lower, and so we're going to use sphericals on the lower and rodends on the upper, and we're going to adjust caster by some manipulation of all three rodend lengths. Also keep in mind this'll move your steering tierod location as well.

As for crimping, I saw in that thread you're referring to a team that had some good looking inserts. Makes even more sense if you're using sphericals because the insert can function as the capture too.

[Mark TMV]

Wouldn't it change your effective suspension arm length if you start manipulating rod end lengths.
For our first car I'm trying to compensate for lack of caster adjustment with buttloads of camber adjustability.

[kwancho]

Well, think about it. Really, you have 3 points of a triangle. To move the outboard point foreward, you'd lengthen the rear inboard rod end, shorten the front inboard rod end, and lengthen the outboard. Yeah? If you do it right, the front view will be exactly the same.

[TG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mark TMV:
Wouldn't it change your effective suspension arm length if you start manipulating rod end lengths.
For our first car I'm trying to compensate for lack of caster adjustment with buttloads of camber adjustability. </div></BLOCKQUOTE>

Plug it into a suspension calculator and look at the sensitivity your specific suspension would have to such a change.

[Mike Cook]

Yes I use spacers on the outboard points. Since the sleeve is .625 long and the ball height is only like .375" there is no way around it. However on the inboard side of the car all of our spacers are brazed in to our square tubes. It was the single biggest improvement on the car from last year to this. I was so sick of loosing spacers, dropping them on the ground, shit not fitting right..grr.

[BStoney]

As the late Carroll Smith would say...

Using rodends at the outboard location is essentially a sin and puts the threads in bending...a big no-no. Using sphericals is really the only way to go.
.....
Think about the large loads that are transferred through the tire to the suspension linkages during braking and acceleration.

[RacingManiac]

We use outboard shims on the upright to change camber and inboard shims on the a-arm pickup point to adjust caster(never really used that much), we have to live with the point change when we do change the caster though. On the Formula BMW cars I've see they use spherical on one side of the inboard a-arm and a rod end on the other to accomodate for the caster adjustment....

[Cement Legs]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Jon_Dal:
Yes, I realize there are many threads about this and the topic is half beaten to death. </div></BLOCKQUOTE>

NO... all the way to death... its so dead... it thinks its alive....

And another point that is often overlooked is weight. We were glad to switch from rod-ends to sphericals for our outbaord joints because of safety and proper design.... we were just as happy to switch to sphericals on the inboard joints for the 3-5 lbs it saved us http://fsae.com/groupee_common/emoticons/icon_biggrin.gif. I think the fact that you eliminate so much weight going with the better design ends the debate forever.

[Mike Cook]

3-5lb? .5" rod ends???? smoking crack??

[Jon_Dal]

Smoking crack eh? That sounds like trouble....
So do most people just deal with the caster that they've picked? If so what's a decent amount of caster? I know it depends on the rest of your geometry and your whole design. Is 5 degrees reasonable or is that way too much? That might actually be -5 degrees....I can't remember which way is which. I mean the way that gives you favourable camber gain though. Thanks for all your help.

[B Hise]

It is almost impossible to throw out a number for caster. Given the interdependance of your suspension design parameters you cant say one single number is "good". I have seen equally fast (who knows about drivers though) FSAE cars with vastly different suspension geometries. In short, go to start&gt;programs&gt;matlab 7.0...


Bryan

[Mike Cook]

Matlab??? Whats that?...I prefer the eyeball method.. I mean it works for our baha team.

[Jon_Dal]

Haha....yeah our Baja team has been burned on that many times.

[Jon_Dal]

By the way, I have already designed the suspension, modelled it and so on. I was just curious about other people's caster because I've never designed a suspension system before. 5 degrees seems to be reasonable to me and works with our design nicely, I'm just not 100% sure.

People on this form seem to be pretty arrogant towards anyone who hasn't designed 10 cars or whatever. I know what Matlab is and I've used it plenty. I'm not asking anyone to hold my hand through the design. A simple "yes that seems like a fairly typical number" or "no I've never seen a car with a caster greater than x" would've worked.

[B Hise]

haha, take it easy boss.

Didn't mean to offend, but your question is fairly subjective. I've seen caster setups from 0 deg to 9 deg or more. Yes, 5 degress is right about in the middle of that and yes your car will probably handle just fine.

If you're concerned that you're making the wrong choice, you can always build adjustability into your suspension mechanical design.

Bryan

[Jon_Dal]

Sorry, I'm not trying to pick on you. That just seems to be pretty common on these forums. There seems to be quite a few people looking for a simple response that get more of a "research it you idiot" answer. My appologies if that came off harsh.

[Blake_DFSAE]

Research you idiot.

[Blake_DFSAE]

Dammit it's on a new page.

Now I look like an ass. Happy jon?

[Jon_Dal]

YESSSSSS! I am happy.