Shock placement on a-arm. Very odd, makes me wonder…

[Dan B.]

I was just reviewing this Raz video again before I reply to his email, and I had totally forgotten about this. Go to 5:25 in the video and see what he says about shock placement on the lower front a-arms. I’m kind of scratching my head here…
Also, I just watched him try to wiggle those arms after they were installed and I don’t think there is any way that the ones I got were made in the same factory, or by the same methods. Too bad. At the time, I was really excited to try them out.

 

[Steve B in Vegas]

Oh dear...... and 171k subscribers.

 

[blaster27]

I thought aluminum A Arms were bad.

 

[Dan B.]

I thought aluminum A Arms were bad.

I don’t run them on any of my off road rigs, but I run them on some of my street bashers and all of my speed runner builds.

 

[danny1202]

My old nitro cars have that type of shock adjustment, it’s my understanding is that the steeper the shock angle the harder it is to compress it so would give you less squat I guess?
Also when he wiggles the A arm it looks to me like he’s moving his wrist a lot and not actually trying to move the arms…

I bought a set anyway

 

[LibertyMKiii]

I don't know the answer to this but wanted to talk through it because there are 2 things going on.

When you move the shock outwards more, there is a difference in leverage 100% true.
The other thing that changes is that you are no longer directly moving the shock towards compression and instead it pivots more and has less compression per distance of the arm travel. What amount of difference is there in leverage vs compression change ratio?

In my MS Paint example the image on the left when the arm moves the shock compresses almost the same amount as the arm movement.
For the right side image due to the shock angle the shock compresses less per distance of the arm travel.

 

[NitroK]

I thought aluminum A Arms were bad.

Only if you hit stuff. More for onroad use...rigid and less torque

 

[Garcbomber]

After watching his in-car video with suspension compression/extension, I'd personally run all composite arms/solid locked shocks and let the arms do any articulation near 200mph+

Most are running airstrips and fresh paved highways, coil over geometry is negligible unless it's a basher or heavy road course rig. Like liberty said, your k-value spring rates will change with angle and actual suspension travel will vary on fixed positions. Not apples to apples.

 

[Steve B in Vegas]

Here is the upside; this is all already figured out:

https://www.amazon.com/Physics-Gearheads-Introduction-Dynamics-Motorsports/dp/0837616158

s

 

[BruceRC]

 

[Steve B in Vegas]

I thought aluminum A Arms were bad.

I keep telling my partner to start fabricating RC parts from magnesium. We already machine mg in our day job, so it's really not a big step. Wonder how much we could charge....

 

[NitroK]

Here is the upside; this is all already figured out:

https://www.amazon.com/Physics-Gearheads-Introduction-Dynamics-Motorsports/dp/0837616158

s

Never imagined I would need knowledge of advanced physics for rc car setup...

 

[LibertyMKiii]

Try the shock in different spots and compare how it feels.

Do test runs and see what works best.

 

[Steve B in Vegas]

Never imagined I would need knowledge of advanced physics for rc car setup...

Ah, it appeals to our nerdy side. That book does a great job in explaining the fundamentals, and after combing through it for quite some time, I see videos like the original post, and it makes me wonder....

It's a great book, and I'm still learning much from it.

Anyhow, we are quite proud of our 50 YT subscribers.! They are willing to sit through some pretty basic and bland videos.

 

[Dan B.]

I don't know the answer to this but wanted to talk through it because there are 2 things going on.

When you move the shock outwards more, there is a difference in leverage 100% true.
The other thing that changes is that you are no longer directly moving the shock towards compression and instead it pivots more and has less compression per distance of the arm travel. What amount of difference is there in leverage vs compression change ratio?

View attachment 364084

In my MS Paint example the image on the left when the arm moves the shock compresses almost the same amount as the arm movement.
For the right side image due to the shock angle the shock compresses less per distance of the arm travel.

View attachment 364082

That is 100% correct. Since you made those points I’m now trying to talk my own way through your points. The shock does indeed have less travel per degree of upward motion of the a-arm the farther it is mounted outside on the bottom. However, it is still less easily compressed/manipulated to that point of compression, right? So if we were to introduce a variable rate spring the amount of total compression would indeed become present in the equation, even while agreed that it would be more easily compressed the further inboard the shock was mounted on the lower a-arm.
I removed the black Perfect Pass springs (even though they look awesome) because the windings were too soft and I could no longer tune with absolute coil bind as I’m able to do easily with those repurposed Redondo Beach titanium valve springs which are, BTW, freaking awesome.
Long story short, regardless of the spring weight or type (linear or progressive) the spring is more easily compressed the closer it is mounted to the pivot point of the lower a-arms. So yeah.
To simplify, whatever setup you’re running, if you mount your shock farther to the outside on the lower a-arm the harder your suspension will be. Not softer.

 

[danny1202]

Raz put his holes on the wrong side then

 

[Dan B.]

Try the shock in different spots and compare how it feels.

Do test runs and see what works best.

I’ll save everybody the trouble. The suspension is much harder to compress the farther outboard the lower shock mounting point is. Period. Mic drop, if I was that cool, but I’m not. It gets easier to compress the shock/spring the closer you go to the lower a-arm pivot point, or inboard.
As for running it to your preference, that’s up to the individual and what they’re trying to accomplish. And as they tune the suspension it will be helpful for people to know that as they move the lower shock mounting point outboard the stiffer it gets, and the farther inboard they move it the more supple it becomes, which is the exact opposite of what the expert Raz (with 177K subscribers) said. There’s a ton of people and fans of his out there who take his word for gospel and have frankly gotten spurious information from him in this instance. That said, I’ve found some of his suspension setup advice to be extremely helpful, especially his approach to setting front toe. In fact, I’ll probably never use another method. But he should acknowledge this error and inform his fan boys that they’re doing it wrong.

 

[danny1202]

Thanks for clearing that up anyway, half the time I know I’m probably wrong but like to get involved with the convo to learn something. I remember watching a video on the subject ages ago.. I just assumed someone else had done their home work

 

[Dan B.]

Ah, it appeals to our nerdy side. That book does a great job in explaining the fundamentals, and after combing through it for quite some time, I see videos like the original post, and it makes me wonder....

It's a great book, and I'm still learning much from it.

Anyhow, we are quite proud of our 50 YT subscribers.! They are willing to sit through some pretty basic and bland videos.

Jeez man, I was totally going to put that in my cart until I saw the $85.00 price tag. For something that’s still printed on (what the hell is that stuff called..oh yeah) PAPER?
I’ll prefer, as others have chosen, to remain comfortably ignorant of the physics the book would otherwise explain.

 

[NitroK]

Jeez man, I was totally going to put that in my cart until I saw the $85.00 price tag. For something that’s still printed on (what the hell is that stuff called..oh yeah) PAPER?
I’ll prefer, as others have chosen, to remain comfortably ignorant of the physics the book would otherwise explain.

600+ pages.