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

[CSG Mike]

Originally Posted by ZDan

Regarding toe...

I tried running a lot of rear toe on my '01, and it sucked, bad, for everything. Worse tire wear, worse straight-line stability in dicey conditions, worse turn-in, worse everything.

In my experience with the AP1, minimal toe is FAR preferable to maximal toe. 0.15 degrees total was totally predictable and driveable for me, while on the high side at 0.64 degrees wear was outrageous and the car's handling was atrocious over bumps and in wet/inundated conditions.

More toe doesn't necessarily give more "stability", though that was preached for a long time at s2ki...

Anyway, I can't speak for the 86, but I would definitely first try to optimize the car around minimal, near-zero toe all around. Having the tires grind away working against each other is IMO a poor utilization of the most valuable traction-generating assets we have!

my 5/32" is 0.3624431633361682 degrees... although I've been known to run less at times :p

I agree. That's where we started, and that's where we're staying.

[Dimman]

When you are getting dampers revalved, how specific can you get and what do the companies do? Can you graph out a target curve and have them try to match it, or just tell them general info like, for example, the springs will be x lbs/in stronger and you also want more low speed rebound?

[CSG Mike]

Originally Posted by Dimman

When you are getting dampers revalved, how specific can you get and what do the companies do? Can you graph out a target curve and have them try to match it, or just tell them general info like, for example, the springs will be x lbs/in stronger and you also want more low speed rebound?

It all depends on your budget, and the talent of your builder. Given enough of a budget, anything can be done; you just need to be able to convey what exactly you want to your builder.

For example, we have absolutely no problem releasing shock dynos for our (prototype) CSG-spec SRCs, because it's extremely unlikely that anyone can emulate/replicate the damping curves and still spend less money than what the CSG-spec SRCs cost. In other words, anyone with that talent charges enough for their time that it likely won't be copied.

Also, when you're looking at that type of spring rate and damping, you want adjustability for different conditions, and vehicle changes.

Lastly, the graphs only show part of the story.

[Calum]

[Wepeel]

Originally Posted by CSG Mike

Lastly, the graphs only show part of the story.

Elaborate?

[Dimman]

Originally Posted by Wepeel

Elaborate?

I'm assuming it's to say the curve doesn't solely indicate the quality of the shock. Rebound separator valves, shim and seal durability, mid valves to reduce shock 'lag', how it manages temperature/cavitation, body and shaft stiffness, etc... All factor in to the quality (and price, sigh...).

[midnight23]

Just got back from my first auto cross, first run was 50 sec, then 44 sec then 41 sec, then consistent 39s and ended with 38, I had an issue with traction control where it would take the power from the car, so I tried turning it off and my times got slower because the rear just would not stay down, any suggestions to increasing rear grip to pass the 38 sec mark with tc on? I'm using tein flex and cusco LCA rpf1 17x9 with hankook v12 245/40/17, 2.1 camber all around.

[solidONE]

Originally Posted by Dimman

I'm assuming it's to say the curve doesn't solely indicate the quality of the shock. Rebound separator valves, shim and seal durability, mid valves to reduce shock 'lag', how it manages temperature/cavitation, body and shaft stiffness, etc... All factor in to the quality (and price, sigh...).

An unaveraged shock dyno will give you a better idea on the quality of the damper than the averaged dyno that typically gets published. Even then you don't get the whole story.

From my experience with motorcycle suspension having gone through various different shocks and fork valves and various different set ups and combos, I learned that those pricy suspension components are honestly worth every penny that they cost. That is why I don't plan on going through the same thing with my 86 by getting "middle of the line" dampers just to regret the purchase down the road. I just don't want to waste the time and money experimenting with less than top notch stuff. But man.... Cars have 4 of these suckers rather than just 1 like a motorcycle.....
'Spensive dampers, Y U No Cheaper?!?

[mike156]

Originally Posted by Wepeel

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

Originally Posted by Wepeel

....

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.

Don't take this the wrong way as I'm only looking to add to the discussion on the analytical side. I can tell you from firsthand experience, your simplified diagram makes several poor assumptions. The small angles matter. Also, realize the strut sits at about a 15 degree angle and since the length varies with suspension travel, this angle changes, which means the hub centerline rotates (positive camber gain).

I will say, I've seen 0.90 to 1.0 being quoted all over the internet on motion ratios for struts. I spent a good deal of time building a solid model of the EVO front suspension though and to my surprise, the average motion ratio was over 1. Hub spacers do mater, but only slightly because of the small angle changes.

That said, even after you square it, you are talking about a ~10% error. Seems like most springs have about that much variance in rate anyway. While your analysis is analytically incorrect, assuming a 1:1 motion ratio gets you "close enough for the girls (you) go with." If that’s not good enough, then measuring it is the way to go. “HOW” you measure is also another issue though since technically, you would be interested in the center of pressure, and not the center of the actual tire.

[Dimman]

Originally Posted by mike156

[COLOR=black][FONT=Verdana]
Don't take this the wrong way as I'm only looking to add to the discussion on the analytical side. I can tell you from firsthand experience, your simplified diagram makes several poor assumptions. The small angles matter. Also, realize the strut sits at about a 15 degree angle and since the length varies with suspension travel, this angle changes, which means the hub centerline rotates (positive camber gain).

I will say, I've seen 0.90 to 1.0 being quoted all over the internet on motion ratios for struts. I spent a good deal of time building a solid model of the EVO front suspension though and to my surprise, the average motion ratio was over 1. Hub spacers do mater, but only slightly because of the small angle changes.

That said, even after you square it, you are talking about a ~10% error. Seems like most springs have about that much variance in rate anyway. While your analysis is analytically incorrect, assuming a 1:1 motion ratio gets you "close enough for the girls (you) go with." If that’s not good enough, then measuring it is the way to go. “HOW” you measure is also another issue though since technically, you would be interested in the center of pressure, and not the center of the actual tire.

How do the small angles matter if the strut and hub are locked together? They just move up and down relative to each other. The leverage looks constant, while the fitted rate changes with angle, but the spring angle change affects almost all suspension geometry, plus changes through its travel.

Are you talking about materials deflecting under load?

[ZDan]

Originally Posted by Dimman

How do the small angles matter if the strut and hub are locked together? They just move up and down relative to each other.

Unless the strut is infinitely long, it is rotating as the suspension compresses. This smallish rotation is why you will get a slightly different motion ratio, the further out the wheel is, the more this rotation moves it vertically. In the simple strut model I made, a 50mm increase in offset only resulted in a change in motion ratio from 0.95 to 0.93, so it's not a huge effect. 2% change in motion ratio => 4% change in wheel rate, though, so it is definitely worth taking into account.

[Dimman]

Originally Posted by ZDan

Unless the strut is infinitely long, it is rotating as the suspension compresses. This smallish rotation is why you will get a slightly different motion ratio, the further out the wheel is, the more this rotation moves it vertically. In the simple strut model I made, a 50mm increase in offset only resulted in a change in motion ratio from 0.95 to 0.93, so it's not a huge effect. 2% change in motion ratio => 4% change in wheel rate, though, so it is definitely worth taking into account.

Goddamn it... I'm not understanding it. Let me find my geometry set and graph paper to show you how I see it, and hopefully you can point out what my error is. Be back in a while...

Edit:
@ZDan

This is how it works?



Edit 2:

When a strut starts to lose camber the motion ratio starts to increase too?

(These were done with a shitty dollar store geometry set, so all measurements are approximate...)

[whataboutbob]

Originally Posted by midnight23

Just got back from my first auto cross, first run was 50 sec, then 44 sec then 41 sec, then consistent 39s and ended with 38, I had an issue with traction control where it would take the power from the car, so I tried turning it off and my times got slower because the rear just would not stay down, any suggestions to increasing rear grip to pass the 38 sec mark with tc on? I'm using tein flex and cusco LCA rpf1 17x9 with hankook v12 245/40/17, 2.1 camber all around.

Throttle and steering inputs. Imagine a string tied between the gas pedal and the side of the steering wheel. You should never be on full throttle when the wheel is turned. Leave the TC off.

I drove the 1st 6 months of autocross in VSC sport. I was told over and over that it was slowing me down. I finally decided that I'd learn to drive with it off one day. Did 8 runs total that day. the 5th run I decided to try turning the TC back on to see how my times compared. I was over 1 sec slower.

Hope this helps. Keep at it and have fun.

[Wepeel]

Originally Posted by mike156

[COLOR=black][FONT=Verdana]
Don't take this the wrong way as I'm only looking to add to the discussion on the analytical side. I can tell you from firsthand experience, your simplified diagram makes several poor assumptions. The small angles matter. Also, realize the strut sits at about a 15 degree angle and since the length varies with suspension travel, this angle changes, which means the hub centerline rotates (positive camber gain).

I will say, I've seen 0.90 to 1.0 being quoted all over the internet on motion ratios for struts. I spent a good deal of time building a solid model of the EVO front suspension though and to my surprise, the average motion ratio was over 1. Hub spacers do mater, but only slightly because of the small angle changes.

That said, even after you square it, you are talking about a ~10% error. Seems like most springs have about that much variance in rate anyway. While your analysis is analytically incorrect, assuming a 1:1 motion ratio gets you "close enough for the girls (you) go with." If that’s not good enough, then measuring it is the way to go. “HOW” you measure is also another issue though since technically, you would be interested in the center of pressure, and not the center of the actual tire.

Discussion is good .

I don't think we disagree - keep in mind, that illustration and post was specifically addressing whether or not wheel offset has any "leverage" affect on compressing the spring in a strut suspension. It was not intended to be a complete guide to motion ratio for a strut.

Yes, angles will make a difference... most obvious is the SAI (not sure if you read the whole thread but that was discussed and accounted for), and as the strut swings out, a component of that should raise the wheel vertically (and that is not attributable to spring movement). But the point of that post was illustrating that wheel movement due to compression of the strut/spring will always be a 1:1 with the movement of the spring (or whatever the cosine relationship is due to SAI), regardless of offset (and forcewise exerts no leverage).

But yeah, even if the reasons are wrong, most sources arrive at some value around 0.9ish or close to 1. And like you said, it's not a lot of error. Add to that the fact the most springs are only available in increments of 1k or 50 lb to begin with, so even if you are targeting some super-specific frequency (for whatever reason), the solution is already limited in resolution.