Supercharged111

I've seen a jillion threads about people doing it for asthetics, and even searched it in here, but all I found was that it can be done, not whether or not it's better for handling. I understand I'll need to re-align it when it's done and that there's a certain rake I must maintain, I just wonder what changes in handling might I see? Will lowering on stock bolts put me beyond the sweet spot in the suspension's geometry? I'm currently on NT05s (295 square setup) and eventually will graduate to stickier tires, but not this year. Remember, this question ONLY revolves around changes in handling, not how much more difficult it'll be to get in and out of my driveway/trailer.

Solofast

Lowering too much has been proven time and time again to be slower. We tested and found for autocross that lowering more than 3/4" to one inch was slower. That was also with shorter than stock shocks. Since the car being tested was a stock class C5 Z on Hoosiers and V710's this applies to sticky tires.

Lowering too much kills the camber gain and yes you are beyond the sweet spot.

Top performance setup shops like Phoenix Performance don't lower these cars more than that either, so that tells you a lot.

If you have stock shocks you will run out of travel anywhere near the limits of stock bolts in the back. On a road course you need more travel than autocross and you will be into the bump stops all the time if you lower it all the way in the back and start pulling some heavy G's, and the snap oversteer that creates is nasty on the track.

That's pretty much the story, and if you do a search on this subject in this part of the forum that's pretty much that you will find.

Supercharged111

Is finding the ideal ride height going to be trial and error, or is there a more scientific method to finding it? I've considered removing the stock spring and pinning a camber gauge to the wheel and moving it up and down while on stands to see where the camber curve starts to go positive. From there it's a matter of determining how far the car is rolling on track. I don't know that my driving is consistent enough for it to show in lap times, but I do think I'm getting fast enough to start feeling changes made to the car's setup.

froggy47

IMO lowering is slower if that is all you do, on a stock car.

Mine is lowered, however, the springs, shocks, bars, bushings and more are all set up so that it's a pretty stiff package.

When your suspension travel is in a very small range none of the problems associated with lowering an otherwise stock car ever happen.

Fully developed race cars are lower for a reason, yes, it's faster.

The lower you get your CG and keep all the rest (of the suspension) optimized the faster it will accelerate, brake , and corner.

But you have to be willing to develop the complete suspension as a "system" with all parts working together.

Supercharged111

I understand that, the goal here is to lower and stock bolts and keep it optimized. The big question I have though is, on stock suspension, what's the lowest you can go before you're no longer optimized, i.e. out of the sweet spot.

The research I have done has netted some vague results, I didn't see any where someone did it and actually reported back on whether it was better or worse. Then again, their level of qualification on the subject may have been questionable.

I have an event next weekend, are there any tricks I can use to see how much travel I'm using as the car sits right now?

sleeperstyle

I have seen Drag racers put a zip tie on the shock/ metal piston, where the shock ends/ rod begins.. and it will slide up as far as the shock pushes it. Then you know where you are at.. My bilsteins have covers that would have to be removed to do this, which could be an issue.

Supercharged111

Same with the stock shocks, I'm thinking of wrapping big ones around the body itself so the cover can push it down. A gopro on the side of the car would be nice to see what my fender clearance is. I really think the smart thing to do is yank both springs and observe the camber curve through the suspension's travel. My goal isn't stance, I just have to wonder if there isn't a little left in the stock suspension as it is a street car after all. I'd like to be scientific about it if possible.

froggy47

The zip tie trick is pretty good. to measure if you are bottoming shocks. But that's just shocks. The stock c5z springs are fairly soft so you will be going thru suspension travel geometries more than I do.

I like to keep 1/4 inch rake.

I don't see how you could go too wrong going 1/2 to 3/4 inch lower front and then set the back for rake.

If that amount of lowering was going to ruin the car's handling I don't think the adjusters would be there.

On the c4 we would trim the little rubber/metal sandwich that was on the ends of the front spring to lower a bit.

Alignment required after.



Remember, even with the z06 GM is building the ride height so Grand Pa won't bi$%h to the dealer that it scrapes going out his driveway. It can be improved but the whole "system" has to work.

mesospeedy

Definitely be careful with the rake. I asked an instructor at VIR to give me some tips when I first got my GS. He had a C6Z. He mentioned that if I wanted to lower my car any to be sure to keep the rake angle close to stock, otherwise it could really f up the feel and handling under certain circumstances

Supercharged111

And this is why I raised the question.

Is there a definitive source for what the factory rake is supposed to be?

phipp85

Factory ride height specifications will be in your model year service manual. I'm sure someone on here has a C5 service manual and will chime in with the factory specs. If you plan to track your car a lot then you should just buy one anyway. It will surely come in handy when you have to replace broken/worn out items due to heavy track use.

Solofast

Actually the ride height procedure in the factory manual involves measuring with special tools from the lower ball joint to the suspension pivot points. You can make your own tools, but it is not as simple as measuring from the ground or rack to the frame.

There was, very early in the C5 life, a ride height spec as measured to the jacking points, but remember that different tire sizes can significantly effect that relationship, and that is likely why they chose to use a measuring method that relates to the actual geometry and not from the ground.

If you do a search on "J" and "K" dimensions in this section of the forum you should be able to find the thread where this is all explained.

Also note that in the C5 "how to" video tape that came with the car it mentions that lowering of the car will help performance but they only recommend lowering it by about 1 inch for "best performance".

95jersey

3/4" inch per Solofast is good on stock suspension. That is a significant lowering. Mine was lowered 2 centimeters which is 0.78" and I have lots of trophies. Want to buy one?

skyavonee

Are you guys getting these numbers with stock bolts? I lowered my front bolts to the max, then backed them out 1/8 turn, and I only got about a 1/2" drop.

The rears are capable of more than that, but the way I see it, you can max out the front stock bolts, then just lower the rear until you get the stock rake again, and you're good to go. At least that's what I did... am I missing anything? I don't see how it's possible to over-lower a C5 on its stock bolts, as long as the rake is maintained.

Supercharged111

I keep forgetting to search the j and k dimensions when I'm at home and able to log in. I went square (tires) and wonder if that's altered the ride height. My gut tells me it's lifted the front end a bit, which is probably undesirable.

ltborg

That's how mine is although the front ends up closer to a 3/4" drop. The rear has a ton more adjustment range than the front.

For the OP, if you haven't found it yet, you might like Dennis Grant's Autocross to Win series. From the suspension section:
He recommends measuring the car to know exactly what is happening and that is how he came up with the "sweet spot" he refers to in the above post. I'm hoping to do that over the winter once the race season ends and will be able to confirm if that's true at that point.

As mentioned before, watch how much the dampers get into the bump stops. I've noticed if I get snap oversteer over bumps in autocross, a little more ride height in the rear seems to fix things. I am not sure yet whether this is due to less bump stop engagement, a geometry change, or both.

Be careful with the zip tie measuring method. I've pushed shaft seals into the shock body when the damper bottomed out using zip ties. On the Konis I currently run, the bump stops are accessible so I just slide them into contact with the shock body, make a run, then see how close they are to the bottom of the shaft (they are mounted shaft down) at the end of the run to determine how much travel I am using.

Hope that helps.

froggy47

Yes,stock ride height is with a taller rear tire, so if you go square (no matter the size) you have nosed the car up.

davidfarmer

My opinion is lowering on stock bolts (no cutting, trimming, replacing) is great. You need to be symmetric and lower only the amount with the LEAST all around. In other words, don't drop one corner 5 turns, another corner 3 turns, another corner 1 turn! Best case, come to someone like me that has scales!

It is hard to claim an exact sweet spot, but lowered this way is close. I know that lowering much more than this makes things bad really quickly, unless you can afford drop spindles!

froggy47

Supercharged111

So I lowered the car, 4 turns per corner. Screwed up the back though and ended up with a huge rake! Car was within 20# on the corner weights at stock height and 5/8 tank of fuel, so I should be close now that I unfudged the *** end but can easily verify on the NASA scales and hone in on near perfection. Even with the bigger tires up front, I still had what I eyeballed to be 1/4" rake, expecially when extrapolated to the far ends of the car. There was less than 1/4" difference in OD between the stock front and the current front, so divide that by half and that's how much the rake changed. Negligible. I was shocked to see how little the toe changed, that must be a trademark of a well engineered suspension. Once I get the rear settled again, I'll borrow the camber/caster gauge to make sure that's properly set and I should be good. When I drove it yesterday, it felt a little funny, but I had the *** end cranked so hard it's no wonder. I'll have to drive it more to make sure I didn't lose too much travel, but it's not slammed by any means. I had marker marks on the bolts and my tools as well so I could count the number of turns I was putting to them.