Apocolipse

Curious in regards to more coil over guys.

Been trying to think of a ride height I'm going to set my stuff at. Not worried about the stupid plastic part under the bumper getting scraped but how much clearance from the rockers to the ground before u scrape the actual nose on entering parking lots, and hit the bottom of the car going over a speed bump...

Hit the rockers? Bottom out and teeter totter on a big hump?
V
I'm debating between 3 to 4" ride height.

Solofast

The sweet spot for suspension geometry is lowered one inch from stock. Any lower and the geometry falls off of the camber curve. That is, the camber gain is positive and the geometry works down to that height. If you lower it more than that, it goes all to hell.

That's why real racers don't lower the car as much as you are talking about lowing it.

It's not as fast and for that reason we don't go there.

If you want poor handling as well grinding all the time over speed bumps and driveways, go for it...

Apocolipse

Yes I completely agree in respect to the geometry. Reason I am asking is because I am modifying the frame rails on mine to give the body a lower drop while maintaining the proper suspension travel and geometry. Yes I know that drop spindles would do the same thing but I am not going that route. Don't ask lol

I read somewhere that racers typically drop a stock car ~1" to get into a better damping area...not sure how that would affect things tho or how that works.

I have been using suspension analyzer and it seems that the lower you drop the suspension the more antisquat you get as well as a lower instant center. Now I am not sure if the front and rear increase/decrease the same proportionally with the same drop or not...which can lead to issues when it comes to the angle of the rotation axis front to rear. With that comes an increased camber curve.

Solofast

If you are willing to correct the geometry then as a practical matter you really shouldn't go much lower than about 4". The reason is that at that point you start grinding the bottom of the car on a driveways and speed bumps. These cars have a pretty long wheelbase and because of that they bottom easily. If the wheelbase was shorter they wouldn't bottom so much, but such is life.

Apocolipse

OK 4" it is. Should I keep it stock geometry at 4 or lower the bolts a bit as well?

Solofast

Four inches is beyond where the geometry is correct, and handling and bump steer will suffer. If you aren't looking for super handling and you have coilovers so that you aren't bottoming out you could live with that on the street.

You will still, at that height, find it difficult to get into some driveways and can easily damage the bottom of the car and break open the fiberglass and get water into the balsa floor at that height, but if you are careful you can live with it. If you damage the bottom of the floors you need to make sure you repair it before you get water into the balsa or it will rot.

When I first lowered my car it was at 4" in the front jacking point and 4.25 at the rear jacking point and there were a lot of places where I scraped the bottom of the car. It wasn't horrible, but I always made sure I didn't go straight into any driveways or it would seriously scrape. Side rail protectors and front frame protectors are a good idea if you are that low.

Apocolipse

I'll have rail protection for sure. As I said initially it's not the actual suspension thats lowering. I'm cutting the frame rails, trans tunnel, etc and lowering the car while keeping stock geometry then welding back up.

It's a project car so it's stripped right now which is how I'm able to do this.

duegatti

If I could get involved, I'm about to have Pfadt single adjustables installed, and I've been agonizing over ride height. I wanted to compare some of what I understand from Pfadt with the considerations discussed here, at an extremely non-technical level.

Pfadt's "starting point", if you will, for ride height involves lowering by one inch from stock. From what you're all saying in this thread, it sounds like stock is 5" to the ground at the rockers, and the 4" number that is being talked about so much here would match the Pfadt one inch drop. Would you say that is correct?

I'm very concerned about the ride height because I pretty much take my car everywhere, and while I'm careful, I don't want to get into an unrealistic ride height.

From this thread, it sounds like I probably don't want to go down an inch. I wonder if I should try a half inch, be careful, and see how it goes. Or, should I just stay stock?

Any thoughts would be appreciated. Particularly if you can confirm that the 4" height you're talking about equals Pfadt's one inch drop, because then I can relate what's being said here to what will happen to me.

Many thanks.

Apocolipse

Stock ride height at the rockers is 6" front approx 6.25" rear (iirc). So lowering to 4" is way lower than one inch.

duegatti

I just double checked the Pfadt instructions, and it appears you are absolutely correct; my memory had shifted the numbers by an inch.

So now, the 4" threshold being discussed here is an inch below Pfadt's recommendation of 5". Does the collective experience suggest I would be ok at 5"? As I drive the car everywhere today, I almost never scrape. If I hit my driveway straight on at high speed, I will touch, but with just a little care I clear it easily, routinely. I don't have clearance trouble anywhere else that looks reasonable as I approach it. I routinely go ever speed bumps, carefully, without incident. Will I be ok at 5"?

travisnd

What do you consider 1" from stock on a C5? I've read the OEM height is 6.0" frame rail to ground at the front jacking point and 6.22" at the rear.

I recently installed LG G2 coilovers and am at 4.125" front and rear. I only have about 1.5" of droop travel so I don't see how I could raise it much more.

RX-Ben

Let's unpack this a little more. What is so "sweet" about what geometrical point(s) with a 1" drop?

Solofast

There is a good discussion on Dennis Grant's "Far North Racing" site. If you want to learn a good bit about setup, you can spend a lot of time reading what he wrote on setup.

Basically you want to be in a good area of camber curve so that you have camber gain (and not loss) as your roll increases. If you lower it too much you will lose additional camber as the car rolls and this is a very bad thing.

Here is what Dennis said about the C5 suspension...

The bold is my addition, but it makes the point perfectly, that the camber curve is more important than the CG height (within reason), and lowering the car a bit more to lower the CG isn't generally as important as getting the geometry right.

It's also noted in the video that came with the C5 that the suspension is optimized for track setup if it is lowered about an inch... So Dennis is right, GM knew exactly what they were doing.

Apocolipse

OK so if static height is 6", put in lowering bolts to go down to 5", cut the frame rails and move them up 1" front and rear, which gives me 4" at the rockers with a 1" suspension drop.

RX-Ben

The camber curves for a car going straight don't look terrible with a 2" drop.
Both have roll centers that drop below ground level but the 1" drop has an RC that is above group except towards the extreme of the 2" dive.
Below are points along the toe, camber and roll center curves - I can't figure out how to post a pdf, but the camber range is about a degree more with a 2" drop. You can keep the RC mostly above group and still maintain the same camber curve as is shown in the 2" drop by moving the upper control arm inboard mounting points down by .75".
The camber changes at the extremes (+/- 2" dive) of the 2" drop about about .5deg camber gain and loss.
It doesn't seem like this marginal gain/loss at camber is enough to cause noticeably "bad" handling, but maybe I am missing something. It seems like the main issue with the 2" drop is possibly the roll center migration, spending a decent amount of time underground when it matters (during turning), which would maybe require an overstiff suspension to handle the "pro-roll" loads encountered with underground RCs, so the transition from an above ground to under ground RC might be more pronounced/commonly experienced. But I'm not sure how much difference this transition is in real life. I think I've been driving with something like this "bad" drop (or more, as my HF floor jack didn't have much clearance and it requires 3 3/8") for a couple years on the tracks and things seemed ok.
Any thoughts? I should run though these calculations with some wheel angle as maybe that paints and uglier picture with the larger drop.

1" drop:

Suspension Analyzer v2.4 Performance Trends
Std Conds:
Right:
Left:
Camber:
78.3
78.3
Caster:
10.10
10.10
Toe In:
10.1
10.1
Track: Roll Center:
Ht: 1.47
Right: .00
Dive ToeIn ToeIn Camber Camber RC Lt/Rt,inRC Lt/Rt,inRC Ht,in RC Ht,in
deg deg Lt Rt Lt Rt Lt Rt
Lt Rt
2.000 -.702 -.702 -1.302 -1.302 .000 .000 -.620 -.620
1.500 -.531 -.531 -.890 -.890 .000 .000 -.121 -.121
1.000 -.358 -.358 -.537 -.537 .000 .000 .396 .396
.500 -.182 -.182 -.241 -.241 .000 .000 .928 .928
.000 .000 .000 .000 .000 .000 .000 1.471 1.471
-.500 .189 .189 .185 .185 .000 .000 2.021 2.021
-1.000 .388 .388 .315 .315 .000 .000 2.574 2.574
-1.500 .597 .597 .387 .387 .000 .000 3.126 3.126
-2.000 .819 .819 .399 .399 .000 .000 3.674 3.674
Report Conditions:
Hold Roll = .000
Hold Steer = .000

2" drop:
Suspension Analyzer v2.4 Performance Trends
Std Conds:
Right:
Left:
Camber:
78.3
78.3
Caster:
11.18
11.18
Toe In:
11.18
11.18
Track: Roll Center:
Ht: .07
Right: .00
Dive ToeIn ToeIn Camber Camber RC Lt/Rt,inRC Lt/Rt,inRC Ht,in RC Ht,in
deg deg Lt Rt Lt Rt Lt Rt
Lt Rt
2.000 -.676 -.676 -1.943 -1.943 .000 .000 -1.802 -1.802
1.500 -.500 -.500 -1.359 -1.359 .000 .000 -1.376 -1.376
1.000 -.331 -.331 -.844 -.844 .000 .000 -.918 -.918
.500 -.165 -.165 -.392 -.392 .000 .000 -.433 -.433
.000 .000 .000 .000 .000 .000 .000 .073 .073
-.500 .167 .167 .334 .334 .000 .000 .596 .596
-1.000 .339 .339 .612 .612 .000 .000 1.131 1.131
-1.500 .517 .517 .835 .835 .000 .000 1.676 1.676
-2.000 .703 .703 1.003 1.003 .000 .000 2.227 2.227
Report Conditions:
Hold Roll = .000
Hold Steer = .000

Crepitus

Are these all C5 values?

Apocolipse

Yes, when u install suspension analyzer it has a demo version of a 2001 c5 stock.

I knew that when u lowered all the values got better for anti squat but I believe the roll center being too low may cause jacking? Also, at a ride height under 4" did you bottom the middle of the car on speed bumps? I'd like to have the rockers lower than 4 but I drive on the street too...

Solofast

If the roll center is too high it will cause jacking...

Having a roll center too low doesn't cause jacking, just the opposite, it causes additional body roll.

It's just the same thing as reducing roll stiffness. There are two components to roll stiffness. One is the springs and bars, and the other is that resulting from the suspension geometry. If you lower the roll center you reduce the roll stiffness caused by the geometry, and that can be substantial. So you end up with more body roll.

If you are going to all the trouble to put in negative camber you don't want to lose some of it due to additional body roll.

Apocolipse

Ah yes had it backwards. However body roll is proportionate to the distance from the height of the cg vs roll center height is it not?

If lowering causes the roll center and cg to be further apart then it would increase roll but if they get closer together would that not reduce it?

The distance between the two creates a torque arm which is what makes it roll.

Solofast

Yes, the total roll moment that is reacted by the springs and sway bars is equal to the distance between the CG and the center of mass, so your total roll angle is based on the lateral G, the roll resistance and the distance between the CG and roll center. Lowering the car an additional inch lowers the roll center even more, since the roll center goes below ground. So even though you have lowered it two inches if the roll center moves down three inches (or more) you end up with more body roll and not less.

There will be less total weight transfer due to the lower CG, but the stock CG is at 16 inches, the 1" lower CG is at 15 and lowering it two inches gives you a 14 inch CG. So you gained only about 7% less weight transfer from the ideal 1" lower setup, but you increased body roll and lost negative camber from that move. For that reason the gain in CG wasn't worth much and you increased body at the same time which hurt the handling...