CSG and RCE tag-team suspension Q&A thread! Ask us anything!

[new2subaru]

Originally Posted by Racecomp Engineering

Any time there's more than just 1 axis of movement/rotation, a solid poly bushing makes me nervous due to binding or increased wear/fatigue elsewhere. The whiteline alk is designed to pivot or flex some which is nice, but it's still going to be different than a spherical bearing.

- Andrew

Thanks for the response, Andrew. I had a feeling that was the case and I believe I had seen you write that before but wanted to confirm. It makes complete sense.

[TylerLieberman]

Did some searching and couldn't really find any concise answer, so here it goes.



^^With LCAs like these (SPL) and others with multiple mounting points for the shock, moving more inboard and outboard, would you effectively be able to alter the motion ratio of the rear by bolting the shock bottom to different locations on the arm?

Meaning, if I bolt the shock to the most inward position, the value decreases, and moving outward causes the value to increase? If so, what kind of effects would one expect in terms of handling if everything else remained the same on the vehicle? And how much of a change would there actually be in the effective spring rate between those slots? Would it be changing the spring rate by like .5kg/mm each, or more like .05kg/mm each lol

[solidONE]

Originally Posted by TylerLieberman

Did some searching and couldn't really find any concise answer, so here it goes.



^^With LCAs like these (SPL) and others with multiple mounting points for the shock, moving more inboard and outboard, would you effectively be able to alter the motion ratio of the rear by bolting the shock bottom to different locations on the arm?

Meaning, if I bolt the shock to the most inward position, the value decreases, and moving outward causes the value to increase? If so, what kind of effects would one expect in terms of handling if everything else remained the same on the vehicle? And how much of a change would there actually be in the effective spring rate between those slots? Would it be changing the spring rate by like .5kg/mm each, or more like .05kg/mm each lol

Bust out your measuring tape. Thats the surest way to get accurate numbers.

[TylerLieberman]

Originally Posted by solidONE

Bust out your measuring tape. Thats the surest way to get accurate numbers.

Yikes. Such math lol I did some calcuating.

I did MR = A/B though.

A- Overall LCA length (450mm)

If stock MR is ~0.75, then factory shock mount is at 337.5mm from the center point. If the holes are ~25mm apart, that gives a range of 312.5mm to 362.5mm.

So 312.5/450 = .694
And 362.5/450 = .805
That means that (rough estimation) the outer most hole would yield an MR of ~80% and the inner most hole would yield an MR of ~69%.

So a 6k spring can effectively be a 4.8k, 4.5k, and 4.14k with those numbers. Of course, that's all estimated.

But those numbers can also vary with alignment changes, as the LCA with change in overall length to decrease or increase rear camber. However, the differences between each hole should remain the same, meaning roughly .3k/mm or roughly 17lbs/in in effective spring rate between each one.

Cool. That answers one part of my question then haha. Now I'm curious how that would impact the handling of the vehicle by changing from one spot to the next.

[solidONE]

Originally Posted by TylerLieberman

Yikes. Such math lol I did some calcuating.

I did MR = A/B though.

A- Overall LCA length (450mm)

If stock MR is ~0.75, then factory shock mount is at 337.5mm from the center point. If the holes are ~25mm apart, that gives a range of 312.5mm to 362.5mm.

So 312.5/450 = .694
And 362.5/450 = .805
That means that (rough estimation) the outer most hole would yield an MR of ~80% and the inner most hole would yield an MR of ~69%.

So a 6k spring can effectively be a 4.8k, 4.5k, and 4.14k with those numbers. Of course, that's all estimated.

But those numbers can also vary with alignment changes, as the LCA with change in overall length to decrease or increase rear camber. However, the differences between each hole should remain the same, meaning roughly .3k/mm or roughly 17lbs/in in effective spring rate between each one.

Cool. That answers one part of my question then haha. Now I'm curious how that would impact the handling of the vehicle by changing from one spot to the next.

I think you, sir, are the best equipped to finding the answer these questions right now. lol Find out for us and let us know! haha

[TylerLieberman]

Originally Posted by solidONE

I think you, sir, are the best equipped to finding the answer these questions right now. lol Find out for us and let us know! haha

Lol nah. I can do a little bit of calculating. But I trust the suspension experts more than myself doing some quick math on the interwebz for estimation purposes.

[solidONE]

Originally Posted by TylerLieberman

Lol nah. I can do a little bit of calculating. But I trust the suspension experts more than myself doing some quick math on the interwebz for estimation purposes.

I figured you had these LCA "in-stock" already in your garage or on the car. lol

Changing the mounting point would change the dynamic response, but it shouldn't behave too different from reducing or increasing spring rates at the same mounting points considering how little the change is. That's all speculation tho. I've experimented with different pick-ups from damper and hubcarriers using various different brands of LCA's, but not enough to answer your question. I made fairly large changes, not small ones.

[Racecomp Engineering]

Multiply spring rate by the square of the motion ratio, not just the motion ratio.

https://www.instagram.com/p/B3cDzqOD..._web_copy_link

You're almost there with the math. Changing the rear shock mounting point to change the motion ratio will change your wheel rate. Compare it to a swaybar change but remember it also affects ride, not just roll.

- Andrew

[TylerLieberman]

Originally Posted by Racecomp Engineering

Multiply spring rate by the square of the motion ratio, not just the motion ratio.

https://www.instagram.com/p/B3cDzqOD..._web_copy_link

You're almost there with the math. Changing the rear shock mounting point to change the motion ratio will change your wheel rate. Compare it to a swaybar change but remember it also affects ride, not just roll.

- Andrew

Gotcha. That would mean a 6k rate with a .80 MR (furthest mounted hole) would have an effective wheel rate of 3.375. That’s pretty wild. That means the stock FRS rear springs have an effective WR of like 1.8kg/mm lol.

Very interesting. Thanks a bunch for the help! I LOVE learning these little nuances of suspension workings and stuff. I don’t know why but I find it to be one of the most interesting things regarding vehicles and modifying them/setting them up.

[solidONE]

Another thing to consider with the different pickups is changes to the amount of wheel travel and ride height change. This is the main reason why i tried out the different pickups. the further inboard you mount the less damper stroke required for a given amount of wheel travel aside from the change to the motion ratio.

[Spacemane969]

I've been running TRD springs for a while now and I want to upgrade to BC coilovers. I want moderately more stiffness but I'm so hesitant to make drastic changes in the overall engineering so I'm thinking 5k front and 8k for the rear to simulate the OEM FR-S 2.3k and 3.8k rates. Anything wrong with this idea of matching the spring rates F/R? Thanks

[Takumi788]

Hi guys. (track car only) How important is it that caster is the same on both sides? I understand caster and what it does but I got my car back from being aligned and noticed it different on both sides. I do not currently have adjustable caster. I have OEM front control arms with Whiteline anti-dive and caster bushings.

[churchx]

I never cared much about caster evenness. Imho it allows even greater disparity then camber, before "detectable by average butt dyno". I usually care more about getting camber even, and to even much greater extent - toe.
Of course, CSG/RCE guys will now better, as what i wrote is from my subjective feel, with me having rather imprecise calibrated butt dyno [tm] . But for me it was so, that toe amount and unevenness by +/- 0.05dg was relatively easy to feel in handling, i guess camber changes like 0.5deg will start to be noticeable in right vs left turns, and i always left caster as is, whichever values it had.

[Racecomp Engineering]

Originally Posted by Takumi788

Hi guys. (track car only) How important is it that caster is the same on both sides? I understand caster and what it does but I got my car back from being aligned and noticed it different on both sides. I do not currently have adjustable caster. I have OEM front control arms with Whiteline anti-dive and caster bushings.

A little bit of unevenness happens stock, but it could also be either bent front control arms or the install on the Whiteline bushings wasn't perfect. A full degree is a little more than usual.

- Andrew