BTW, this is also posted in the Autocross and Roadracing Forum - Hope I didn't break any rules by posting it in both places.

I have a '91 Z07 that I am doing some suspension work on and I am thinking now is a good time to lower it. In looking at the methodologies for lowering the front and rear springs it would appear to me that the front spring lowering kit wouldn't have much affect on the spring rate. Maybe a little bit due to a slight geometry change but the springs should be at about the same point in it's curvature.

On the rear, however, I could see how just simply lowering the nut on the bolt will cause the spring to be more curved, and I would think therefore less stiff. Am I thinking about this correctly?

Also, I saw a post a while back that said lowering the rear by one turn on the bolt actually removed 3 lbs of load from the rear on corner scales. This seems to be the opposite of what I would expect.

The balance on the car with the stock setup is very good and I don't want to change the balance too much, just lower the CG for more overall grip. My concern is that the lowering kit may change the balance due to the rear spring rate being effectively different after the lowering kit install.

Thanks.
--Calvin

 

Lowering does not effect spring rates. I believe the 3 lbs your referring to was translated to the other end of the car. On the other hand, what difference does 3 lbs make to a 3400 lb car that driven on the street?

You may also be thinking about preload?

My one word of caution is to remember the bump stops must be cut back to compensate for the ride height. Otherwise you'll bounce down the road like a teenage ricer.

 

As allueded too, must modify bump stops. FYI, I do not think a little lower is going to get you better handling. A C4's COG is 15 inches off the ground stock. A 90's Indy is 12 inches, today's Porsche Cayman S is around 17 inches. Go to local road course or auto-x, how many very low/lowered cars do you see? How many of those are the fast guys?

You want to go fast or look cool? Frankly, a stock Corvette is almost too low, at least where I live.

You need to have suspension travel for good handling hit the bump stops and you lose control.

A stock Z07 car will handle very well, if anything, tires are the biggest thing. The Z07 Package is a great handling package.

Tell you what give me your springs and what not, and you can have my FX3 stuff...

 

I love the guys that lower cars, have stiff springs, with crappy dampers. Bouncy, bouncy, bouncy...

 

Geez! Why own a Corvette then?

Your right about lowering to go faster. Gotta have a suspension that works and lowering is not always the best choice. Keeping all four planted and digging is the goal.

Some of the early C4's were too high. And lowering was necessary to avoid that 4x4 appearance. I love the way my 86 looks and the changes have had little effect on the handling. With the exception of dragging the front tires in the wheels wells (hard fast turns) and debris on the road. Hit a green pine cone last month and thought I shredded the under side.

 

The good news is that with the '91 Z07 you get the stiffest springs and the FX3 all in one package

So it sounds like maybe keeping it stock height is good and then just having the longer bolts in the back to provide the fine cross-weight adjustment is the way to go.

 

Very good idea!

 

Lowering/raising effects camber curves, bump steer, roll center heights, CG & roll couple.

Adjusting weight bias works diagonally & is defined as cross or diagonal weight. Example: Adjusting the LR corner up (body higher) will add weight to that corner + the RF & lighten the opposite diagonal (LF to RR) to a lesser extent.

Static front to rear bias can only be changed by moving components fore/aft or
removing/adding weight.

Spring rates are not effected unless the attachments points are relocated.

 

FWIW the only nationally competitive Vette I know is lowered.

For comparison, I am not lowered, and am not nationally competitive.

Sounds like scientific proof to me...

 

Back to the ops original question. The center of the rear spring is connected to the body, the ends are connected to the suspension. Lowering the bolts at the end just drops the body down on the suspension.

 

Ahhh, of course. Now I have the visual and my question was kind of dumb

 

Nationally competitive in what? Autocross or Road Racing? It seems like the consensus over on the other forum is that it definitely helps in autocross but due to things like curbing and sometimes a little rougher surface on road courses it may not be advisable there. Still collecting opinions, though

 

Yes, Autocross. Good question, obviously set ups are different for different purposes, with Autocross you can take a lot more spring usually too.

That said, I know several C4s that RR are lowered but definitely not slammed. However competition wise I'm not sure how they stack up so I wouldn't make a judgement from that.

I'm lowering mine now, but I've made a couple of replacement shims so I can adjust total drop. As mentioned previously some of the early cars were jacked, combine this with dropping weight off the front and lowering the car isn't as big of a drop as it seems. Lots to consider. Good luck.