I installed some Hotchkis lowing springs about a week ago. The drop looks great but it seems like the car is more unstable at higher speeds.

When I get to higher speeds around 60+ I notice that the car seems to react to any imperfections in the road and cause the car to move a bit/change angle. The car also seems to have more oversteer at these higher speeds than with the old springs. With the old spring the steering wheel felt heavier and less jumpy at higher speeds.

I have an 05 Z so I know that the stock spring rate was 314/427 and the Hotckis springs are 340/330 which is quite a difference. Would this cause a noticable difference in steering feel?

I have not yet got an alignment for my car, but would'nt think that would contribute too much to the problem. I have done springs on a few other cars and the handling was not that much different before/after analignment after installing the springs.

Another reason why I do not want to yet get an alignment is because I want to be sure I will keep these springs. If the springs are the cause for the handling issue I would rather buy a different set.

Thanks for any help!

 

I don't know what to say for sure but I do know that the stock spring rates are 342 in the rear not 427. When I installed mine I also installed the sways at the same time for they both work so well together and I have to agree.

In straight line driving I couldn't tell much of a difference but in cornering it was a good tight feeling with an almost neutral feeling when it comes to body roll. I also would agree that alignment should not play a big role in your situation for the Hotchkis doesn't throw it off much if any. I'd check your install again and have your alignment checked and also ask them to look over it too, since your there.

 

Thanks for the reply

The 03-04 Z' have spring rates of 314/342 and in 04.5+ the spring rates changed to 314/427

I was thinking that I could get some front/rear sway bars and that might help tighten up the supsension a bit

I would get an alignment with these springs to see if it helps any, but I would rather not spend the money for an alignment and end up getting new springs if it doesn't help

 

To put it simply, your spring installation isn't complete untill you get an alignement.

Wheels don't just move up and down. You could have any amount of toe and camber all over the car...

Get an alignement...

Make sure the springs have settled properly too.

 

In reguards to the spring rates, I guess Hotchkis needs to update there info. I also have an 05. Good luck with everything. Let know if you find out anything later?

 

Sounds like an alignment problem, my guess is toe is the culprit. If you read up on the affects of toe on handling, you'll see why it can cause issues without an alignment. Installing springs involves loosening the toe bolts which may have been shifted during the install. Get in install ASAP and post the results so we can better diagnose your problem

 

Thanks for the replies. I will go ahead and get an alignment and see if it helps. Been about a week since I installed them so they should be pretty settled in.

 

I just noticed you're in Austin ... where are you planning on going for alignment? I recommend soulspeed (www.soulspeed.com). Talk to Bill Kim - he does great work and might be able to help you diagnose your problem. His prices are a bit higher but for my Z it's worth it.

 

the alignment could very well be very far out of whack....at a minimum you need to get the car on a rack run by people who know what they are doing and figure out what the current settings are.

 

Thanks for the recommendation. I have been thinking that a specialty shop would be able to do better work on the Z than a place like NTB.

 

No answer on the results?

 

Check your tire pressure as well a front tire that is lower than the other can cause issues on the road with pulling.

 

I took it in for an alignment and that helped things qute a bit. It still feels a bit twitchy at speeds around 70+, but it does feel a lot better than it did. Once I get my new rims on with wider front tires it should make the car feel much better.

 

The Hotchkis springs are pretty much the mildest springs you can get for the Z. The only difference I feel is when taking turns...there is less body roll up front and the rear (being softer) squats comfortably to keep traction. Very well designed IMO.

As the springs settle things might improve. They had no impact on my driving feel or higher speed stability. I have 245 and 275 tires and many k miles on them though.

 

Do some research concerning the necessity to match spring stiffness ratios with wheel base then shock rebound rates to tune the pitch rate to a particular speed.

The seams in road or the undulations caused by asphalt machine wheel base create minute periodic REPEATING bumps and troughs.

Oem tends to optimise 55-65 mph stiffening springs raises the tuned speed.

At 88 feet per second, a 106" wheelbase means a bump from front to rear takes 1/10th of a second and generates a vibration. The phase differences between the front and rear add and reinforce

You must tune the springs to match then the release rate [rebound control] of the shocks.

http://www.optimumg.com/ tyhen look under tech tips, then springs and dampers multiple pdf's.