Excessive camber gain

[cushionbumper]

what would happen under this scenario:
You have a shorter and a longer RF upper A-arm. The static camber is the same regardless of which upper A-arm is being used. Would the shorter upper A-arm produce more dynamic camber gain than the longer?
CB

[9WRACER]

Shorter the arm the faster the reaction, so it will gain negative camber faster.

[cushionbumper]

@9WRACER, but will the shorter upper a-arm gain more dynamic camber?
CB

[MasterSbilt_Racer]

@9WRACER, but will the shorter upper a-arm gain more dynamic camber?
CB

More dynamic negative camber gain for the same amount of travel. The travel available may have changed.

[Matt49]

If you want the same amount of static camber but more nagative camber gain on suspension bump travel (which is what I think you mean by "dynamic" camber), then you need a shorter upper control arm but you need to space/shim it away from the chassis by the same amount that you shorten it.
This will accomplish more nagative camber gain on suspension bump travel.
But you need to be careful doing this as you can quickly get the upper control arm in contact/interference with the shock body.
When we play with this stuff here is what we do:
* put the car on jack stands
* take the RF spring off
* put the RF shock back on by itself
* set the RF at ride height using a jack
* measure the camber
* jack the RF up 1/2 inch and measure camber again
* jack the RF up another 1/2 inch and measure camber again
* etc.
Chart this out in Excel and then do the same thing with the shorter upper spaced out (e.g. 1/2 shorter upper with 1/2 spacer between upper and frame).
Repeat the process and compare the two. This will give you a nice visual representation of what is going on with camber gain for the different upper control arm lengths.

All of this could also have an effect on bump steer but that is an entirely different conversation...or is it?

[cushionbumper]

@Matt49. Thanks for your response. That certainly has helped a great deal.
We already are running an 8 1/4" RF upper a-arm with a 3/4" spacer. Do you have an opinion as to how much bigger the spacer could be before you may compromise strength?
CB

[Matt49]

@Matt49. Thanks for your response. That certainly has helped a great deal.
We already are running an 8 1/4" RF upper a-arm with a 3/4" spacer. Do you have an opinion as to how much bigger the spacer could be before you may compromise strength?
CB

I've seen people use as big as 1" without any problems. Honestly I don't know of anybody that makes a one-piece shim/spacer bigger than that. There shouldn't be a lot of shear stress on those bolts so lengthening them isn't really hurting you. If you think about it the upper is really just locating the ball joint with reference to the chassis. The only forces there should be pushing the upper INTO the frame (holding the spindle/wheel up) with very little shear force. The lower control arm on the other hand has to support the weight of the car because that is where the shock and spring are connected. Hence the much larger bolts and sturdier mouting locations of the lower control arm.
Just really pay attention to your shock clearence and make sure your ball joint isn't binding at extreme bump travel. A slightly bent ball joint is almost unoticeable without taking the spindle off and it's a gremlin you don't want to chase.

[F22 RAPTOR]

@ Matt49, I have to disagree with on your point about the upper not being stressed. The more the suspension moves thru travel down on the RF, the harder the angle is in the upper control arm. Which in turns makes it more stressed due to getting closer to 90 degrees with the track surface. I think this is why we have more control arm failures now than we did in the 90's. Just some food for thought.

[Matt49]

@ Matt49, I have to disagree with on your point about the upper not being stressed. The more the suspension moves thru travel down on the RF, the harder the angle is in the upper control arm. Which in turns makes it more stressed due to getting closer to 90 degrees with the track surface. I think this is why we have more control arm failures now than we did in the 90's. Just some food for thought.

It's not that I don't think it's being stressed, it's the direction of the stress that I am wondering about. I just don't think that the bolts that hold the uppers to the chassis are under a lot of shear stress. I think the majority of the stress is compression of the control arm between the upper ball joint and where it mounts to the frame. But I certainly see your point that as the angle increases, that is moving toward shear stress on the bolts. I think overall the lower is under a lot more stress as a whole because of the shock/spring mounting there (the engineers must agree based on size of bolts and larger ball-joint).
But bottom line, I don't think running a 1" spacer with good high strength bolts should create any issues there.
What types of "failures" are you refering to? Outside of crash damage, we've seen some of the bolt in ball-joint upper controller arms fail where the tab meets the tubes and we've seen bent tabs. Which is one reason we are switching to screw-in uppers next season.

[F22 RAPTOR]

It's not that I don't think it's being stressed, it's the direction of the stress that I am wondering about. I just don't think that the bolts that hold the uppers to the chassis are under a lot of shear stress. I think the majority of the stress is compression of the control arm between the upper ball joint and where it mounts to the frame. But I certainly see your point that as the angle increases, that is moving toward shear stress on the bolts. I think overall the lower is under a lot more stress as a whole because of the shock/spring mounting there (the engineers must agree based on size of bolts and larger ball-joint).
But bottom line, I don't think running a 1" spacer with good high strength bolts should create any issues there.
What types of "failures" are you refering to? Outside of crash damage, we've seen some of the bolt in ball-joint upper controller arms fail where the tab meets the tubes and we've seen bent tabs. Which is one reason we are switching to screw-in uppers next season.

I agree that the lower probably sees more stress overall, but ever since the inception of the, "on the hook" setups I've noticed a rise in control arm failures, upper & lower ever since. At first it was LF failures from the dramatic falls on decel, but as the setups have evolved to keeping the LF down, but rolling over hard on the RF, the failures have moved to the RF. I think the 1" spacer will probably be fine, but the shorter you go on that arm length the faster it gets into a critical failure angle during body roll. My personal view is I think most of this stuff has gone to far to an extreme, but that's the nature of racing, we push the limits, sometimes too far. JMO

[Ghopper]

Hello all

F22, Matt49 - Since the upper aframe has no other connections than the spindle and the frame, the loads at the ball joint and frame bolts are essentially equal and opposite.

An interesting point on aframe loading.....
- the upper aframe is under the most load in the straight away. That is in the orientation of the mounting bolts it has a combined loading across both bolts of ~80lbs tension, ~650lbs vertical shear, ~300lbs fore/aft shear in the straightaway (Gray front Rocket).
- In the corner the upper aframe load is reduced at the frame.....down to a >100lbs for X,Y,Z because of the overturning moment.

Maybe this is easier to explain that static load would be higher. Under lateral force from cornering the force creates a moment around the lower ball joint that reduces the load on the upper aframe.


Ghopper

[Matt49]

Hello all

F22, Matt49 - Since the upper aframe has no other connections than the spindle and the frame, the loads at the ball joint and frame bolts are essentially equal and opposite.

An interesting point on aframe loading.....
- the upper aframe is under the most load in the straight away. That is in the orientation of the mounting bolts it has a combined loading across both bolts of ~80lbs tension, ~650lbs vertical shear, ~300lbs fore/aft shear in the straightaway (Gray front Rocket).
- In the corner the upper aframe load is reduced at the frame.....down to a >100lbs for X,Y,Z because of the overturning moment.

Maybe this is easier to explain that static load would be higher. Under lateral force from cornering the force creates a moment around the lower ball joint that reduces the load on the upper aframe.


Ghopper

Interesting. Where did this data come from? How was it acquired? Or was it calculated by a ME?

[Ghopper]

Matt49 - this is on an average smooth track, without ruts. Clearly if you hit a wall or other cars there would be some force spikes.

I used LMS Virtual.Lab-Motion which a multi-body simulation program. You can google it so that I dont make a shameless company plug. This model is correlated with test data for accelerations only because I did not have time domain force data from my data acquisition (strain gauges). I work with AutoOEMs to simulate handling/ride/comfort/durabililty events.....So of course I have made some latemodels The real challenge is how to apply it. Simulate an idea to gain understanding of the mechanism and its limitations, then physically test test test test.



Ghopper

[zeroracing]

Why does it have to be a ME? Many airplane manufactures hire structural engineers with civil engineering degrees. Us structural guys can figure some of this out too.

All jokes aside, has anybody on here used strain gauges on a car on the track? I have been looking at trying it some but trying to do it on a budget, any tips where to buy components for good prices?

Cool looking program but would venture to say it's out of my operating budget.

[Ghopper]

Zero - You dont need a degree to make calculations. Just a "library card" and some common sense for checking for errors. Of course a ME is a natural fit to do this work (I am a ME).

Strain gauges and proper post processing is a lot of work to get motivated for. The company that I work for does phyical testing for AOEMs and I have not barrowed the equipment yet. But I also feel pretty confident that we can simulated the forces. It would require tire data for a really good virtual prediction of handling behavior......but 10-15k for the test is outside my budget as well.

And the program is cool....but the clients that own licenses have cars that race on TV or they produce at least 500 units per year.


Ghopper