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

[Calum]

Originally Posted by CSG Mike

If altering the mounts only increases damper stroke, then your springs will still be more compressed; you'll likely want slightly stiffer springs... exactly what you said. Keep the springs balanced relatively the same as stock, and the dynamic feel will be roughly the same.

You might want to look into roll-center correction as well, to compensate for the sluggishness you introduce into response by dropping the car without correcting it.

Disclaimer: The CSG BRZ doesn't have roll-center correction (yet). Our spring rates are high enough that the sluggishness is more than offset, but we do plan on eventually adding adjustble RCAs to maximize the effectiveness of our suspension.

How much of a difference would RCA's make with RCE yellows?

What is your opinion on the rates and drop RCE picked for those springs when they are paired with stock dampers? Is there anything that should be done as supporting mods at such a moderate drop?

[Calum]

Originally Posted by Figo

@Racecomp Engineering, I am still waiting for a good quality Camber Top Mount. Last time I asked you about the issue of Whiteline mount, and u told me that its not fixed. So I did not placed an order.
I have a Cusco strut bar so its seems like all mounts like HVT and Ground control will touch that bar.
So would u plz tell me when those Whiteline mount will be avaliable for sell?

There is a thread about the whiteline mounts, I really think you should be asking that there. Or even better you should ask whiteline directly. RCE is only a vendor for these, they don't have anymore input into what WL does then you or I.

Presently, WL is testing their latest revision. I don't know the details but the idea is to put the load on the bearing race, not the dust cover as it seems that has been the cause of the issue. So far from what we've heard, the testing is going well. But they appear to be taking there time on ths one. This platform has a lot of money potential for WL, they do seem honestly embarrassed by the way this has turned out.

[CSG Mike]

Originally Posted by Calum

How much of a difference would RCA's make with RCE yellows?

What is your opinion on the rates and drop RCE picked for those springs when they are paired with stock dampers? Is there anything that should be done as supporting mods at such a moderate drop?

For the price of springs, IMO, it's not worth doing the supporting mods (they'll cost you more than the springs!)

The RCAs will be most noticeable with turn-in response; the car will settle faster.

[RehabJeff86]

I have been tracking FRS x 8 events now bone stock now finally upgrade to Enkei RPF1 17x8 with 225/40/17 Rivals due to OEM tries were heat cycling out. My question is to what point will I need to add front and rear strut bars and upgrade to thicker front and rear sway bars?? TIA much!!

[Calum]

Originally Posted by CSG Mike

For the price of springs, IMO, it's not worth doing the supporting mods (they'll cost you more than the springs!)

The RCAs will be most noticeable with turn-in response; the car will settle faster.

If price weren't an option? I'm not going to spend mega bucks, but I didn't go with springs because of the price. Well, not the price alone. I don't need height adjustment and don't trust any shop local to me to adjust a set of coilovers properly. In my opinion, which is rather uneducated I understand, the springs suit my use. Now I want to make sure I optimize the rest of the system.

[Dimman]

Originally Posted by Dimman

I've been using this:

Originally Posted by solidONE

So making the contact patch of the tires sit further outboard does not change the amount of leverage it has on the spring? Im just talking about how this effect the springs and the amount of force it puts against the spring, nothing else. I think an actual formula for calculating wheel rate would help me better wrap my mind around that.

I'm picturing a longer lever on the spring as a result of positive offset vs. negative offset, therefore requiring less force (but longer distance of travel) to compress the spring which stays in the same position relative to the inner pivot.

Edit: I'm just going to leave this link here for @Dimman , @Wepeel and @ZDan. According to this guy that created the PDF file linked, motion ratio on a mac stut system is dependent on the centerline location of the wheel, thus wheel offset. [backs away slowly]

I will defer to ZDan and Wepeel for the (surely math intensive) technical explanation.

However back to the book definition, you see that the guys in your link are treating it like a swing axle according to the book, not a Mac Strut. The main difference is that the lower arm on the strut pivots at the hub while the swing axle doesn't.

I think it took me actually drawing, measuring and making paper cut outs and moving them and measuring to understand it (well 'not be as confused' is maybe better...). The wheel of the strut doesn't stay perpendicular to the arm like it would on the arc of a swing axle. It moves along the line of the strut. As the arm swings its arc the strut and hub pivot slightly, but together, to account for the length change. (This is what cause Mac Struts' less than ideal camber changes.)

This may not be a super technical explanation but it's what I saw with my kindergarten-level experiment, but it is pretty well supported by published experts. The other thing to note is which geometries end up with the center of the tire's contact patch as a point to measure.

Still want to read @ZDan and/or @Wepeel 's explanations.

[Wepeel]

Ah, just saw the edit to solid's post. I looked at the pdf, yes that is incorrect. I'll put together some sketches tomorrow morning that show why (it will be way easier than words), but time for bed now.

And lol at the Chuck Norris pic, that was blocked when i was viewing it earlier.

[solidONE]

Originally Posted by Dimman

This may not be a super technical explanation but it's what I saw with my kindergarten-level experiment, but it is pretty well supported by published experts. The other thing to note is which geometries end up with the center of the tire's contact patch as a point to measure.

Still want to read @ZDan and/or @Wepeel 's explanations.

Originally Posted by Wepeel

Ah, just saw the edit to solid's post. I looked at the pdf, yes that is incorrect. I'll put together some sketches tomorrow morning that show why (it will be way easier than words), but time for bed now.

And lol at the Chuck Norris pic, that was blocked when i was viewing it earlier.

Yeah man.. please dumb it down for me. lol If they had explained to me in school that this math will help me go faster in a car, I would have studied much much harder. I regard engineers and suspension nerds (no offense intended) very highly.

I'm starting to see what you mean also after having made some drawings of my own. Although, even understanding that the strut/spring, knuckle, and wheel as a singular pivot-less unit, it's still a little difficult to believe that a more outboard sitting wheel has no effect on the amount of leverage it has on the spring at all since it is still attached to the lower outboard pivot.

[CSG Mike]

Originally Posted by Calum

If price weren't an option? I'm not going to spend mega bucks, but I didn't go with springs because of the price. Well, not the price alone. I don't need height adjustment and don't trust any shop local to me to adjust a set of coilovers properly. In my opinion, which is rather uneducated I understand, the springs suit my use. Now I want to make sure I optimize the rest of the system.

Ah, let me clarify. If you're doing springs, it's not worth doing RCAs in addition; the RCA's benefit is not worth the cost at this level of modification, IMO.

[CSG Mike]

Originally Posted by RehabJeff86

I have been tracking FRS x 8 events now bone stock now finally upgrade to Enkei RPF1 17x8 with 225/40/17 Rivals due to OEM tries were heat cycling out. My question is to what point will I need to add front and rear strut bars and upgrade to thicker front and rear sway bars?? TIA much!!

You'll never NEED to. Generally, my advice is to add a mod when you feel that the car is limiting your driving, rather than you limiting the car.

Given your seat time with a stock car, I'd say you'd be a fairly good judge of when you're truly being limited by the car, rather than just blindly throwing money at mods.

[CSG Mike]

Originally Posted by solidONE

Yeah man.. please dumb it down for me. lol If they had explained to me in school that this math will help me go faster in a car, I would have studied much much harder. I regard engineers and suspension nerds (no offense intended) very highly.

If had told me in high school that calculus and physics were the two classes that I'd be applying the most, I would have laugh in their faces.

They'd be getting the last laugh now...

[RehabJeff86]

Originally Posted by CSG Mike

You'll never NEED to. Generally, my advice is to add a mod when you feel that the car is limiting your driving, rather than you limiting the car.

Given your seat time with a stock car, I'd say you'd be a fairly good judge of when you're truly being limited by the car, rather than just blindly throwing money at mods.

Totally agreed, so far I have not feel the need of struts or sway bars at all, the car is amazing as is.

After I got the CSG Spec SRC, I gave David deposit already, how would you be helping me dialing in correctly base on how I track? :happy0180:

[FR-S Matt]

So I have my Tarmac 0's on, absolutely love them. I got one small alignment with the stock LCA's, but now I have SPC LCA's to help with the camber in the back and I was also worried about the toe. Should I go with some SPC camber bolts up front and do those let me go a little negative? I know the stock ones let you adjust back to 0, but nothing negative camber.

Also, do I need to worry about UCA bushings on the rear or am I okay with only using the SPC LCA's? I know they are a pain to install, but I definitely don't want to put heavy strain on a part and have it go out on me later.

My car is a daily driver, occasionally drive spirited here and there. Looking for some great advice on what kind of camber I should aim for without ruining my tires. I've got a square setup, and roughly a 1.3-1.4" drop for a flush look on 18X9.5's, 245/35.

[Wepeel]

Okay, let's see how this image turns out. Please excuse the low-tech sketch.

The top image is a highly simplified representation of the McStrut setup. The lower link (AB) is the control arm, the vertical link (BC) is the strut/spindle assembly. It is evidently not to scale . You can see I added a silly long lateral extension for the wheel force application. For simplicity I put the spring at perfectly vertical and the control arm orthogonal to it (so we're not puking sin/cos terms everywhere). And I think we've already covered the angle correction factor and there doesn't seem to be confusion there. The lower image diagram is a more detailed diagram of the BC link.



For those that haven't looked at these kinds diagrams before, in the top diagram, the A and C joints indicate that the mounting can not support any moments (they are free to pivot), they only resist linear loads, and that's how they're mounted to the chassis. The B joint is free to pivot.

For the lower diagram, the B joint just shows that that end is not constrained vertically but it is laterally (representing the force imparted by the AB link). And still, there is no moment supported by that interface.

Looking at the lower diagram, if we apply a force (Fa) at a given distance along the extension, you get a resultant equal/opposite vertical force (FRy) at C, and resulting lateral forces at C (FRxc) and B (FRxb) due to the introduced moment (equal opposite to each other). The reason the moment is there is because Fa is laterally offset to B/C. This is where wheel offset matters - it will impact these lateral forces. But, these forces are not contributing to compressing the spring. So the way these things work is the forces and moments all need to balance out:

Sum of vertical forces: Fa + FRy = 0; Fa = FRy
Sum of lateral forces: FRxc + FRxb = 0; FRxc = FRxb
Sum of moments about C: Fa*l1 + FRxb*l2 = 0; Fa*l1 = FRxb*l2
Sum of moments about B: Fa*l1 +FRxc*l2 = 0; Fa*l1 = FRxc*l2

The thing to note here: there is no "l" term in the vertical forces, which is what the spring sees. Meaning l1 (offset) can be 0 (what you'd get with 0 scrub radius), 2 cm, 10 feet, 1.21 gigawatts, a furlong, on the other side of the strut... it won't matter. The only thing it will affect is the lateral forces since that's the axis it has leverage on. However, more force will be going through the control arm, laterally the strut top (the "strut tower bar" force), and there will be more bending experienced by the struts.

(For fun), going back to the first diagram, IF joint B was not free to pivot/rotate, and was rigidly fixed, now l1 will directly affect the force going through the spring, since the entire assembly would rotate around A. If you summed moments about A, the resultant vertical force at c (call it FRcy), times the length of AB (call it lAB) would have to equal the product of the applied force and the total length of AB+l1, so

FRcy*lAB = Fa*(lAB+l1)

Now we've introduced leverage on the strut. This seems to be the scenario that confuses people, because looking at the drawing, it looks like there is leverage there. But the fact that the lower link only acts in tension/compression, and the balljoint is free to rotate, changes how the forces are transmitted.

Yes the diagram is simple, but even if you introduce a curve along BC (like there is with the actual hub), and even if B was not directly under C, that still wouldn't change things as far as "leverage" on the spring.

I *think* this is correct . I dunno, researching motion ratios on the internet there is a lot of contradicting information (which is why I'm trying work through it). I've seen contradicting info on if the angle correction factor is squared or not (I've seen 2 Eibach spring catalogs where one had is squared and the other didn't; and I think Hyperco's online calculator does not square it), but if you work through the math... my numbers indicate it should be squared. And of course there's some reputable sources saying the offset/scrub radius should affect the MR and some say it shouldn't - for some suspensions it does, but for most it doesn't (it shouldn't matter on our rear suspensions either).

I think the best definition of motion ratio I've seen is in RCVD (Milliken), basically stating it's the travel of the spring relative to the travel of the wheel. We can ballpark it analytically like we're doing, but the best way is just to measure it - lift the car, remove the spring, install the damper, jack the wheel up to ride height, and compare the change in the distance between the spring perches to the amount the wheel has traveled vertically - focus on the range of articulation you plan to be in... something like ride height +/- 2 inches, depending on spring rates and travel. And this will not be linear - since the spring angle changes with wheel travel (since it travels along an arc), it will vary somewhat.