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

[NissanGuy]

Originally Posted by 7thgear

SAI is SAI (steering axis inclination), it is the angle between the true vertical and the pivot points of the wheel assembly looking from the front in 2D, be it wishbones or macstrut

Caster is Caster

it is the angle relative to vertical of the same assembly looking from the side

it is important to have a balanced relationship between the roll center AND center of gravity

so you want a low center of gravity and the roll center a bit below it, this is what leans the car left when you turn right,

you could build a car that does the opposite, but that would be weird

you could also build a car that does not roll, but that creates more problems than it solves.

Ahhhh. I thought I had something wrong there! Lol I'm a mechanic, I should really know...

I still have no clue why roll center actually matters, the same way I have no clue how a rotary engine works. You can read and read and read, but sometimes it's all still witchcraft. Whatever, at least I understand auto transmissions

I read exactly once that the Citroen DS (for those unaware: super futuristic 1956 French sedan with trick hydraulic suspension) would, in a long corner, bank inwards rather than roll outwards. I've still no pictures of it happening, but that would be incredible. I'm certain the alignment wouldn't work, but whatever haha.

[7thgear]

Originally Posted by NissanGuy

I still have no clue why roll center actually matters, the same way I have no clue how a rotary engine works. You can read and read and read, but sometimes it's all still witchcraft. Whatever, at least I understand auto transmissions .

grab a pencil and hold it vertically between your index finger and thumb, gently, don't squeeze it.


first hold it in the middle, with the top and bottom portion of equal sizes


now move it side to side quickly, notice how it remains vertical. This is because its roll center (the place where you hold it) is in the same location as its center of gravity.


now hold the pencil higher, 2/3 below your fingers and 1/3 above, now move it side to side. Notice that it swings about the point where your holding it.


this is because the center of gravity is now BELOW the roll center.


now flip this the other way around and you get a standard production vehicle, where the center of gravity is above the roll center, so that you lean left when you turn right and vise versa

Originally Posted by NissanGuy

I read exactly once that the Citroen DS (for those unaware: super futuristic 1956 French sedan with trick hydraulic suspension) would, in a long corner, bank inwards rather than roll outwards. I've still no pictures of it happening, but that would be incredible. I'm certain the alignment wouldn't work, but whatever haha.

this is not magic, designing this would be somewhat simple, especially on some of the newer electric cars that have their center of gravity nearly at ground level.

[NissanGuy]

Originally Posted by 7thgear

grab a pencil and hold it vertically between your index finger and thumb, gently, don't squeeze it.


first hold it in the middle, with the top and bottom portion of equal sizes


now move it side to side quickly, notice how it remains vertical. This is because it's roll center (the place where you hold it) is in the same location as its center of gravity.


now hold the pencil higher, 2/3 below your fingers and 1/3 above, now move it side to side. Notice that it swings about the point where your holding it.


this is because the center of gravity is now BELOW the roll center.


now flip this the other way around and you get a standard production vehicle, where the center of gravity is above the roll center, so that you lean left when you turn right and vise versa

I like that explanation. The main thing I struggle with is that it just doesn't intuitively make sense to me, why the roll center is where it is. I can look up how to plot it out, it's just that the methods seem arbitrary to me. Not saying people are wrong, just that I don't comprehend. I'm sure it'll eventually click with me. Probably after midnight, on a weekday.

this is not magic, designing this would be somewhat simple, especially on some of the newer electric cars that have their center of gravity nearly at ground level.

Anything's possible. But just think about how that would feel from inside the car. So smooth!

[7thgear]

Originally Posted by NissanGuy

The main thing I struggle with is that it just doesn't intuitively make sense to me, why the roll center is where it is.

it is where it is because the chassis is suspended in the air by sticks connected to a tire....ie.. all those control arms....


where they connect to the wheel and where they connect to the chassis determines the location of the roll center in time and space.


a vehicle "roll" is simply the representation of the chassis changing direction and following Newton's laws.


if you get the schematics of your car, all you have to do is use a ruler and a pencil to draw some lines and presto, you figure out it where it is.


for a macpherson strut the basic measurements are


1. take the top of your strut, and draw a perpendicular line from it out into space
2. take the angle of the control arm, and just extend it out into space (until it connects to the previously drawn line)
3. from the point where the two previous lines intersect, draw a line towards the center of the tire on the ground


where that 3rd line intersects the vehicle centerline... is your roll center

that's it!

[finch1750]

Originally Posted by solidONE

Let's try something more constructive and useful... lol

With camber specs on this car your generally want the fronts to have a tad more negative camber than the rear. Since you've already lowered the car you probably have something close to -2 in the rear and maybe -1.8 out front with your camber bolts. So you'd either want to add a bit more camber out front or reduce the amount that's in the rear, or both. Something like -2.5f -2.0r or -2.0f -1.6r, with the latter being less aggressive.

The low buck option without going camber plates and/or control arms for the adjustment are:

1. Another set of camber bolts on the lower holes for more negative front camber. For a total of 2 sets of camber bolts on the front struts. (what I did)

2. Slot one of the mounting holes on the strut to get more camber adjustment.

3. Camber bolts for the inner LCA mounting bolt to reduce negative camber in the rears. H&R makes some that works quite well, but has only +- .4 degree of adjustment. (I have them on my car currently)

You can do either combination of 1+3 or 2+3 to get the desired camber specs. I might be changing up my set up real soon so I might have some of these camber bolts for sale if you are interested you can PM me.

Part number for said LCA bolt?

[solidONE]

Originally Posted by finch1750

Part number for said LCA bolt?

H&R TC112

[Malt]

Originally Posted by finch1750

Part number for said LCA bolt?

I don't want to see you end up down the same path I went down. Just go ahead and buy yourself a set of LCA's and save yourself the headache. I know some people on here dislike SPC products but you can have a set of SPC LCA's for ~$200 and have LOADS more adjustability.

The H&R bolts cost ~$50 and have a tiny fraction of adjustability. If you don't get what you need out of them, then you'll have to buy LCA's anyway and then your stuck with $50 bolts that are useless AND the cost of another alignment.

Trust me... don't try and cheap out on the rear suspension as it will cost you loads more in the long run.

[finch1750]

@CSG Mike and @Racecomp Engineering what are you experiences if any with the Whiteline UCA camber kit?

I recently got one used for fairly cheap but am having second thoughts. I knew it was a PITA to install and adjust but recently was told that it is not as simple as adjusting equally but the suspension needs to basically be loosened in multiple areas for the adjustment to be done. Is this correct? Also, would these be prone to slipping requiring constant re-alignment? I DD and auto-x the car (kept saying I would head to the track, but don't think it will be happening any time soon with this car).

[Captain Snooze]

Originally Posted by 7thgear

where that 3rd line intersects the vehicle centerline... is your roll center

I would like to point out that the roll center moves around. That is, the car doesn't roll around that point at all suspension movement. The center can move up and down and side to side depending on suspension configuration. It is the roll center at that instant.

[Racecomp Engineering]

Originally Posted by finch1750

@CSG Mike and @Racecomp Engineering what are you experiences if any with the Whiteline UCA camber kit?

I recently got one used for fairly cheap but am having second thoughts. I knew it was a PITA to install and adjust but recently was told that it is not as simple as adjusting equally but the suspension needs to basically be loosened in multiple areas for the adjustment to be done. Is this correct? Also, would these be prone to slipping requiring constant re-alignment? I DD and auto-x the car (kept saying I would head to the track, but don't think it will be happening any time soon with this car).

The OEM bushing in that location is soft and squishy, so replacing it makes a big difference on it's own. It's also arguably the proper place to adjust camber. So in theory, the whiteline UCA camber kit is fantastic.

It just sucks to install and adjust. Really bad. That is the only drawback.

A good alternative is LCAs and the non-adjustable whiteline UCA bushing.

- Andy

[Malt]

Originally Posted by Racecomp Engineering

The OEM bushing in that location is soft and squishy, so replacing it makes a big difference on it's own. It's also arguably the proper place to adjust camber. So in theory, the whiteline UCA camber kit is fantastic.

It just sucks to install and adjust. Really bad. That is the only drawback.

A good alternative is LCAs and the non-adjustable whiteline UCA bushing.

- Andy

To add to this, I originally was going with these at the recommendation of RCE. I wish I could have gone this route as they clearly are the superior choice for alignments because of the reasons Andy mentioned but I wasn't comfortable installing these on my own since I don't have access to a press. I can't imagine that these would be more likely to slip than other adjustment options.

Two different shops quoted me $600 for the install alone! Then I'd was going to have to pay more per alignment because they are a pain in the ass to adjust. If you can install them on your own, can do your own alignments, or have an alignment shop that won't bend you over to do the alignments on these then by all means have at it. I decided it wasn't worth it to me for the hassle and went with adjustable LCA's.

[enivid]

I got my whiteline uca bushings installed for 70 bucks!

[Malt]

Originally Posted by enivid

I got my whiteline uca bushings installed for 70 bucks!

Then you sir got an amazing deal! I wish I was as fortunate as you as I would have loved to use the ones I had.

[finch1750]

Originally Posted by Racecomp Engineering

The OEM bushing in that location is soft and squishy, so replacing it makes a big difference on it's own. It's also arguably the proper place to adjust camber. So in theory, the whiteline UCA camber kit is fantastic.

It just sucks to install and adjust. Really bad. That is the only drawback.

A good alternative is LCAs and the non-adjustable whiteline UCA bushing.

- Andy

What needs to be done to adjust? Is it more than just adjusting the bushings evemly that makes it a pain? The whiteline instructions dont make it seem that bad but I cant really find details beyond they suck to adjust. Lol

I ended up getting them fairly cheap and part of my decision was the info I have seen from you on the benefit of those bushings being changed.