Corvette Z06 Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
37 Posts
Discussion Starter #1
I know I've done the search and found some good info. Most people recommend lowering as much as stock bolts will allow...

I have an 02 Z and I was thinking about getting the 04 shocks. My car is lowered a little more than the stock bolts(i have new ones) and the front is also cut a little.

I do a lot of trackdays and like the way the car feels generally, I don't notice any shock bottoming, but am always looking to make it slightly better.

Can everyone chime in about what is recommended for the lowest ride height with stock 02/04 shocks. I've heard that 26.5 F 27.5 R works well.(using measurements from the fender to the ground at the center of each wheel)
 

·
Registered
Joined
·
5,491 Posts
The OEM shocks are marginal if you ONLY lower using the OEM hardware.

If you lower more than the factory recommendations using aftermarket rear bolts and cutting most of the OEM bushings off or replacing the front spring perch bolts, such as Hardbar's SS bolts with Delrin bushings, then a shorter shaft shock needs to be used. I recommend Penskes Double Adjustable with Remote Reservoirs.
 

·
Registered
Joined
·
37 Posts
Discussion Starter #3
Ya,
I was thinking about possibly raising it a bit,, thats why I was wondering about the recommended ride height.
 

·
Registered
Joined
·
131 Posts
Has anyone ever quantified the change in geometry realized when lowering past the factory range, without changing any hard parts?

I know the factory shocks become susceptible to bottoming even at the lower end of the factory adjustment, but I've been hearing more and more of T1 cars setting ride heights higher than in the past because of geometry issues with maximum lowering.
 

·
Registered
Joined
·
5,491 Posts
T1 cars can not lower past factory recommendations to be in compliance with SCCA rules. T1 is basically a stock class in which you can not use aftermarket parts for lowering.

There is an allowance on the T1 Corvette Spec Line for the T1 suspension kit. This was basically engineered to make a C5 suitable for the track and is made to work at stock ride heights. In fact the T1 springs and T1 Sachs shocks will actually raise the car. To use these parts correctly the car needs suspension travel and stock geometry.

However, if you lower the car beyond factory recommendations it will handle better by virtue of having a lower CG and lower Roll Center. NOTICE, almost all unlimited suspension classes such as the WC, GT1, ASP/SM2 and the C5R's & C6R's run max. lowered. A maximally lowered car will net a mininimum of 2-3 seconds a lap faster than a T1 car, all other things being equal. The caveat is that geometries will change and you need to correct some things.
- Lowering raises the scrub radius. The scrub radius needs to be brought back to Zero. This is easily accomplished by widening the track. That is why I recommend using an SCCA allowable +0.25" offset on all wheels and widening the track at least 1/2" + wider tires.
- More Negative camber is needed with race tires and lowering helps this.
- Bump steer is induced by lowering and is aggravated by speed and amount of turn. This can be corrected by using adjustable pin height Heim jointed Spherical Bearing Steering and Toe rod kits which allow the rods to be brought back into proper parallel alignment.
- Longer A-Arms are available custom for lowered cars (C5R)
- Custom Spindel uprights/hub carriers are available for lowered cars (WC)
- Shorter shaft/body shocks need to be used
- Stiffer transverse springs with a lower recurve is available from VB&P which allow a lower ride heiight with less deflexion
- T1 bars are necessary to reduce Roll to a minimum on a lowered car.
- Ultimately for lowest ride height and corner weight, coil over springs should be used on dedicated track cars.
 

·
Registered
Joined
·
654 Posts
So DJWorm I lowered mine on the stock bolts. Left about a thread on the front and set the rake. Should I replace the shocks ?

I was planning to anyway but should I put the 04 shocks on and everything will work fine ?
 

·
Registered
Joined
·
37 Posts
Discussion Starter #7
Would it be recommended for me to raise my car a bit and put 04's on or leave it low and put on some bilstein sports?
How much lower can you run with the bilsteins?
 

·
Registered
Joined
·
131 Posts
DJ, thanks for the comprehensive post above...it confirms my suspicion that lowering past the factory reccomended 15mm +/- without changing out hard parts is not a good idea. I'm beginning to think there are a good number of "slammed" Z06's out there that have handling characteristics far inferior to a car lowered within what the factory parts will support!

If I were in a class which allowed bump steer kits, lca swaps etc. I do understand the benefit of a lowering cg further...
 

·
Registered
Joined
·
412 Posts
As usual, thanks for sharing DJ! :cheers:
 

·
Registered
Joined
·
350 Posts
tigerdrvr said:
DJ, thanks for the comprehensive post above...it confirms my suspicion that lowering past the factory reccomended 15mm +/- without changing out hard parts is not a good idea. I'm beginning to think there are a good number of "slammed" Z06's out there that have handling characteristics far inferior to a car lowered within what the factory parts will support!

If I were in a class which allowed bump steer kits, lca swaps etc. I do understand the benefit of a lowering cg further...
Exactly correct. Most people (me included) lowered the car because a lower CG is generally better. But what I (and most) don't know is that you do screw up the suspension geometry and bottom out the shocks. I've posted this information before, but don't screw with the ride height on these cars. Take it to the pros (Phoenix Performance did mine) and have them set the right height and corner balance it for you. Their suspension work alone dropped my lap times 2 full seconds. The Kumho V710 and the Kodiak wheels got me another full second...and the car is now a joy to drive instead of ultra twitchy!!!!

Learn to drive the car as it is. Improve the driver first and then begin to make small mods to the car. But trust me, save yourself a lot of time and money and go to the pros - you'll spend far less $$$$ and go much faster, safer!
 

·
Registered
Joined
·
5,491 Posts
The Bilsteins are only marginally shorter than the OEM's.

The Sachs OEM '04's are the same length as the other OEM Sachs shocks so there is nothing to be gained there length wise. The '04's are better by virtue of their mid range rebound valving.

For a street driven only and factory lowered car I suggest only the '04's

If you are bound by T1 rules then:
- T1 kit
- Corner weight
- Competition alignment
- 315/35x17 on 10x17 Front
- 315/35x17 on 11x17 rear

If you track the car and want better handling and are not bound by T1 then you should start with a minimum set up first and then correct any deficiencies. For a minimum lowered set up I recommend:
- Maximally Lowering
- Hardbar Titanium Rear lowering bolts
- Hardbar SS Front lowering bolts with Delrin Bushings
- VB&P Poly Graphite Bushings
- VB&P Front Extreme Spring
- T1 Sway bars and Heim jointed end links
- Shortened Penske DA shocks with Remote Reservoirs
- Corner Weighing and Corner Weighting
- Competition alignment
- 305/30x18 on 10.5x18 Front with +0.25" offset
- 315/35x17 on 11x17 rear with +0.25" offset

You can add coil-overs, Custom Spindel uprights, Bump Steer and add Tracker Rod end links at a later date, if necessary.
 

·
Registered
Joined
·
5,491 Posts
The delrin bushings are shorter and harder and allow the lowering yet still have a competent bushing. When you cut 2/3'ds off the OEMs there is not much "cushioning" effect left and they tend to deteriorate.
 
1 - 14 of 14 Posts
Top