Optimum ride height for 1LE w/ OE 20" wheels

[cdb95z28]

What IS the optimum ride height? Not for looks but for maximum grip suspension geometry. I understand excessive dropping will lower the roll center, which is no good. Also no good because of diminishing (negative) camber gains.

I remember Justice Pete stating a ride height of no less than 660mm (measured from lower wheel lip to fender lip). For which on my 1LE the OE ride heights were front 668/ rear 685. I want to keep the OE rake which is 17mm difference from front to rear. So that would put me at:
F: 660
R: 677

I have seen others state 1/2" drop is acceptable without any adverse issues. That would take the ride heights to:
F: 656mm
R: 673mm

Thanks!
Chad

[Mikamaro]

Ok, excellent statement. Is there anything else you need to know?

[cdb95z28]

Originally Posted by Mikamaro

Ok, excellent statement. Is there anything else you need to know?

I guess I never phrased it in a question

Any thought's on this, what do you run?

[X25]

You can get more camber if you can drop 1", while still not much negatively impacting the geometry, which might let you increase overall handling, not to mention the reduced air drag and CoG. That said, you'll now have compromised the tune of your excellent 1LE shocks/struts.

In my opinion:

• If sticking to 1LE shocks, don't change height.
• If using coilovers, do at least 1", at most 1.25".
• You might as well switch to Z/28 units, which also drop about 1".

[cdb95z28]

Actually, X25, your pictures of your front Trofeos is one of the reasons I started thinking more about this.

I'm focusing more on the front suspension. So going to 1" won't adversely affect the roll centers and the dynamic camber gain? Yes, the drop helps the CG, but the roll center drops faster than the CG. Resulting in a negative change to the roll couple. Which causes the car to roll more which just abuses the outer tires even more. Though drop springs are stiffer so that's should be a wash on the roll control.

Getting adequate static negative camber is not a problem, (for me), at some point, dropping MacPherson strut suspensions will reduce the dynamic camber gain, not good. So we end up throwing all kinds of static negative camber to it and while that helps the outer tire in a turn, it doesn't help the grip of the inner tire. And we probably are not adding enough caster which helps the inner tire add grip.

-IF sticking with 1LE shocks and no drop springs, nothing gained unless you add camber plates and more caster
-If using coilovers we can gain improved CG, possibly at the expense of dynamic camber and lower RC, which hurts the roll couple, which creates more roll (unless the spring upgrade/anti-roll bar upgrade counteracts it). If 1" is the max w/o causing the above trouble,
-While I agree the Z/28 components are bitchin', they might be a bit stiff (ride is subjective) and buying just the Z/28 springs/struts alone isn't possible without getting the entire kit which offers some duplication to some of the 1LE arms and bits.

Making a change will affect other things, what are our limits?

[Nor Cal ZL1]

All very valid points. The ideal solution would be drop spindles, but I think Justice Pete did not produce them due to cost. That would have been the best solution to keep the roll center in check, along with other issues such as bump steer etc. Once the lower control arm changes position the camber gain curve is also changed, which on some designs can be a real mess in geometry. Another solution wold be a redesigned LC arm that allows the LCA to stay clocked in the stock position while placing the spindle up higher with lowering springs. Either case would be expensive and it would have to be certified by load testing to be sold.

There are very few cars designed that can be lowered without some sort of negative impact. I suggest wherever you end up to log the tire temps inner/middle/outer at the track to arrive at the best compromise.

[cdb95z28]

Dropspeed (Matt) checked the ride heights of his Z/28 setup and they came out to (from his post) 10/15mm (.393"/.590") at the front, 20mm (.787")at the rear, his pics of it show a slight rake, looks good.

[Mikamaro]

I'm in the same boat. Especially since I've put 275×35r20...I want to drop it by 1/2in too. The Only solutions right now are ZL1 or Z/28 springs and those brings their own load of questions and concerns.

[X25]

I ended up installing camber plates from PegasusCNC. They're very similar to Pfadt's design, and do not increase ride height or require drilling. I'm thinking about (hoping to) hitting -3 degrees camber and 7 degrees caster with them. My favorite alignment technician has been sick all this week, but should get this done next week.

[Dropspeed]

Originally Posted by cdb95z28

Dropspeed (Matt) checked the ride heights of his Z/28 setup and they came out to (from his post) 10/15mm (.393"/.590") at the front, 20mm (.787")at the rear, his pics of it show a slight rake, looks good.

Thanks. Here is a rolling shot that shows the slight rate with the Z/28 Susp and the stock 20"s

Matt.

[Camaro Dude]

^^^^^^Liking that Z28 suspension set-up more and more! ^^^^^^

[White_SS/RS]

What I’ve discovered about 1” lowering springs:

· Center of gravity would lower 1”.
· Roll center would lower approx. 3”.
· The Roll Moment, the difference between the CoG and the Roll Center increases by 2”. (With my assumptions noted below it’s an increased effect of approx. 6000lbs split between front and rear damper assemblies)
· Static camber gain can increase about -.50*
· Typical lowering springs are about 50% firmer (portion may be offset by increased Roll Moment)
· Some reduction in sway bar effect (new Roll Moment)
· Aero improvement (car closer to ground)

Some measurements were done by eyeballing or rounding to the nearest half inch when I couldn’t get an exact measurement, I also estimated on weight figures such as the roll force. To get quality data it would require extensive work; taking apart the suspension and fabricating parts to simulate dampers for quality weight properties. Even with some assumptions I have been able to come up with approximate effects of lowering a car by the use of lowering springs and what it does to the geometry of the suspension.

Things I assumed:

Center of gravity is at the camshaft. It’s quite common for most cars have a center of gravity very close to where the camshaft is (except overhead cam). Of course that is left to right CoG not front to rear.

I didn’t go into a lot of effort finding the reduction in dynamic camber gain but looking through other people’s work and various different MacPherson strut designs I’ve found that a 1” spring lowering will net a loss of about .10*@1", .20@1.5", and .30@2".

I also assumed that the stock Roll Force would be about 3000lbs. I based this assumption off of excluding the weight of suspension components and a little that would have a small effect being that it’s directly under the center of gravity. Of course this is a very dynamic weight because it would change as the car body continued its roll. In fact, CoG, Instant Centers, Roll Center, and Roll Moment are all dynamic when the car is in motion.

My thoughts:

My initial thoughts are that there is a lot of negative effects to the suspension geometry. Two particular ones having the most dramatic effect being the loss in dynamic camber gain and the increase in Roll Moment. Remember some of my figures are calculated off of estimates, so it may not be as dramatic as it seems. Nevertheless it’s a good model of what’s going on. The positive effects are a significant increase in spring rate, lower CoG, possibility of higher static camber and aero benefits. I don’t feel that the increase in spring rate is entirely consumed by the increase in Roll Moment. Where the Roll Moment is a simple geometric calculation, the CoG is not, and acts more ‘fluid’. I think there is more going on with CoG than it simply being 1” lower, my assumption is that it’s even lower and therefore reducing Roll Moment. Like I mentioned all parameters are dynamic and without extensive measurements it’s hard to say. I would expect that a large part of the Roll Moment can be mitigated with bigger sway bars. Rather than go with 25/28mm sways, even with the increased spring rate a better choice may be 27/32mm. Also realize that these effects are already taking place. 1” dynamic compression on a stock suspension would look similar to a 1” lower ride height. Were just starting the process sooner with lowering springs. Overall I believe there to be a performance benefit and that the positive effects out weight the negative ones. Coil overs share the same fate as well. The key element is keeping the lower control arm at its current angle or adding to the Steering axis Inclination SAI (leaning the strut in at the top as seen from the front). Any change here will have a direct effect in the Roll Moment. SAI is probably the best place to correct this since it’s also beneficial in increasing Static camber gain, dynamic caster gain and subsequently dynamic camber gain.

[Nor Cal ZL1]

Nice write up.

When the RC is far away from CG (lower RC), when the car corners the CG has more leverage on the RC, so the car will roll more. This is what happens when the LCA is re-clocked into a more parallel position as with the installation of lowering springs. The typical fix for controlling this is stiffer springs which also aid to limit suspension compression.

When the RC is closer to CG (higher RC), when the car corners the CG has less leverage on the RC, so the car will roll less. This is the LCA clocked in the stock position, or the ball joint end is lower than the body pivot pick up point.

I'm surprised is no one has designed better LCA's for the purpose of properly lowering the car.