I'm installing some Z06 springs on my Z51 and I want to keep the suspension geometry correct. Do I need to raise the ride height bolt from the measurements I took off the Z51 springs? The Z springs are stiffer so to keep the car at correct geometry(IC RC COG etc) on stiffer springs, I need to raise the bolts correct? Can the suspension geometry benefit from being a little lower because of the stiffer spring and less body roll? Is there a difference between ride height of a Z06 and a Z51?

 

You want to have the trim height set correctly.




D heigth:



Z height:

 

Thanks! Thats perfect! I'm assuming "D" is the front and "Z" is rear. Are those measurements bottom of ball joint or a-arm? It looks like ball joint from the picture. I think Ill set to the bottom of those tolerances because of the stiffer springs. Is there a manual for the preferred Z06 heights while were at it?

 

The front ride height measurement is the "Z Height", and the rear measurement is the "D Height".

The measurements of those distances is from the bottom of the lowest part of the ball joint to the center of the mounting bolt on the front side of the lower control arm. Below are the specs from my 2010 manual, which are actually about 2mm higher in the front, and 7mm lower in the rear than my 2006 manual - so they've reduced the rake a bit over the years.

The Z height specs are:
Base and F55: 48 mm (tolerance: +/- 6.4 mm)
Z51: 47 mm (tolerance: +/- 6.4 mm)
Z06 and ZR1: 43 mm (tolerance: +/- 6.4 mm)

The D height specs are:
Base and F55: 115 mm (tolerance: +/- 6.4 mm)
Z51: 114 mm (tolerance: +/- 6.4 mm)
Z06 and ZR1: 102 mm (tolerance: +/- 6.4 mm)

The tech setting the height is supposed to bounce the suspension up and down a couple times and take the measurement - do that several times and take the average to see if it's within the spec.

As I mentioned above, the specs have changed quite a bit over he years and there's a 1/4 inch tolerance, so the actual trim height is not something to get real worried about. I say just set it to what looks good to you and works with the speed bumps, driveway dips, and general road conditions you have to deal with.

Many race cars are lowered quite a bit to get the CG low and the owners are more concerned about corner weighting the car correctly than rake - they'll use aero components to get the stability they want.

Here's info from my 2006 Service Manual and you can compare it to the specs from the 2010 SM in my previous post:

The Z height specs are:

Base and F55: 46 mm (tolerance: 39.6-52.4 mm)
Z51: 45 mm (tolerance: 38.6-51.4 mm)
Z06: 41 mm (tolerance: 35.6-47.4 mm)

The D height specs are:

Base and F55: 122 mm (tolerance: 115.6-128.4 mm)
Z51: 121 mm (tolerance: 114.6-127.4 mm)
Z06: 109 mm (tolerance: 102.6-115.4 mm)

BTW, the SM says that one turn of the height adjusting bolts is equal to 2mm (.079 inches) of trim height, so 3 turns equals just under 1/4 inch.


Bob

 

Thanks! Are the spring retainer bolts TTY? I just took them out and I needed an impact all the way out but they had a crap load of locktite on them.
ps. To the moderators I think there should be a suspension section in the tech section.
Thanks again guys!

 

whats the best way to get those D and Z measurements?

 

I'm gonna try a drive on lift with a level and tape measure.

 

Save yourself all this grief and just get coilovers.

 

You need to get the car up in the air, dead level on an alignment rack.

Some people say you can use a yardstick, ruler, and a level. I think that would work for the rear suspension, but the front control arms have a curve in them that looks like it would block the yardstick.

The official way is to get the GM J42854 Trim Height measurement tool for only about $250. I bought a used one on fleabay for $25.

It takes two people to hold everything in the correct place while taking measurements.

After raising mine slightly, it took over 200 miles of driving before the suspension settled out to its final position.

As mentioned, the specs have changed over the years. Also, I have reason to believe that the 2005-2010 specs are for "settled" cars out in the field, but the 2012 specs are for an "unsettled" car on the production line.

FWIW, our 2009 has been adjusted so the rear is slightly below spec, and the front is even more below spec. But we still have the highest riding C6 I've been able to find.

The best technique is to measure the height to wheel well arches several times over several days in a level garage. Adjust, drive 200+ miles, remeasure. When you are happy and have 200+ miles on your adjustments, get an alignment. The GM method is a real PITA, and takes a lot of care to get accurate results.

 

Trust me the thought crossed my mind. but the $2000 vs $300 is real hard to swallow, especially without a blower!

 

I know what you mean. My car is in the shop right now because I decided to bite the bullet & do coilovers. The Pfadt are a little less than $2000 installed. Big difference from $300 indeed! Good luck with your mod!

 

I have a set of Pfadt coilovers for sale for 1400 shipped, they have about 5k miles on them, just took them off and upgraded to there featherlights.


PM Me

-Carl

 

Jim, don't know if you remember our discussion from the ride height thread you started, but it's been probably 500+ miles since I've adjusted mines and it's still slowly dropping. I had an alignment a while back and it's probably now off. I didn't notice the ride height change except that I started scraping every time going in and out of my garage, whereas before it would only do so if I went fast or took a bad angle.

Man, that alignment was $180 too. Will have to raise it some and probably redo it.

 

I never understood the way the service manual says to measure the ride height. If you have a flat and level surface, why not just measure the distance from the floor to the A-arm pivot?

 

Thanks for the info.
I plan to re-measure mine next Spring and compare.

 

Or measure to certain points on the frame.

Either one will be affected by tire diameter (tread wear), but that can be accounted for.