Why do most aftermarket springs have a lower spring rate in the rear compared with OEM.

04.5+
314/427

The majority of linear springs or popular springs for that matter will have a lower spring rate in the rear compared with OEM. Why is that? I know that earlier Zs have less spring in the rear, so in that regard aftermarket springs would be stiffer than OEM. Is this the only reason though, because R&D took place before the upgraded OEM suspension was introduced.

Would anything be sacrificed from switching to a lower spring rate in the rear? Or is it more than just spring rate.

BTW, I have an '06 Z and am planning on aftermarket springs while maintaining my stock shocks for the time being.

 

Lower rear spring rate prevents the mid corner bounce effect that annoyed me so much with the stockers, I have the Hotchkis and Tokico combination and it's ironed that particular problem out

 

Your correct that that majority of the springs on the market were R&D during the period where the oem spring rates were 314/342. However, they also had the oem shocks to deal with as well. Some found that the rear 03/04 shock was not "comformatable" (in very simple terms) with higher rear spring rates. 03/04 oem shocks have more compression dampning and less rebound control. Having been on several different spring rates, where I played with front to rear rate balance don't worry about springs that are softer in the rear then 427lbs. Worry about if your choosen spring rate the front rate increase your after, how do you feel about progressive vs linear, does that given spring offer the drop height I'm after, is it from a brand name I won't have any worries about as far as sagging 6 months or latter down the line?

Here's a comment from Hotchkis that is relavent to the conversation.

09-01-2004 06:34 AM

VandyZ
Human Consult-2
Nashville, TN
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Here is an email I got from John Whatley of Hotchkis:
quote:


There is no error on the spring ratings. The rear spring is in fact softer than the stock. The reasoning behind this is that: during testing we found that the rear end likes to bounce under hard cornering. By reducing the spring rate in the rear we were able to get more MPH in slalom testing and stopped the bouncing that occurred. These springs in conjunction with our swaybars will be matched with each other to provide a neutral feel under hard cornering.

 

The published spring rate MUST be corrected for mounting angle and offset distance from the hub [wheel/tire centerline] to create the real world wheel spring rate...............which is the important number.

Front and rear has different mounting parameters so you cannot just use published numbers..........................all one can say is a spring is stiffer or weaker than oem....................the percentage published must be divided by 2-3.

The real wheel spring rate might 200 lbs front and 170 lbs rear.

Also one must be aware of suspension changes which might affect the mount angle and offset.

 

DITTO: except i have D-specs and SPRINT Linear rates. The real suspension winner was the HOTCHKIS sways.

SWAYS FTW!!!

 

Would the 04.5+ OEM shock with more rebound control be able to handle more spring rate in the rear?

Also, I know the Hotchkis sways and springs are matched together, but that was for the older suspension. Would they still considered to be a match with different OEM shocks and possibly different OEM sway bars.

Oh and I never really thought about it, but what do they mean by sways and springs that are "matched." Wouldn't the springs be able to match with any other adjustable sway bar?

 

Did you have the same problem with mid-corner bounce on your '06 as you did with your '04?

 

Problem is, if your still on oem 03/04 shocks, you'll still have bounce from the front shocks even with the lower rear rates. Springs were never the source of the problem, but it was the choosen baidaid of several spring manufactuers. Best solution is better dampning, kiilling off the problem at it's source.

 

06 car's have different shocks then 03/04 cars AND 04.5-05 cars. A few owners here with 06 car's have complained about bounce.

 

Unquestionably yes, 04.5-05 rear shocks are able to handle more spring rate in the rear. HOWEVER, that does not mean they have a reserve capacity to deal with much more then the oem 04.5+ 427lbs rear rate. I ran them with 448lbs for a couple weeks without issue.

Yes, they TVS kit is still a match even with 04.5+ oem shocks. Your not dealing with rear shocks that will be overdampned because they are dealing with 330lbs vs 427lbs, the rear shocks are simply not that stiff. Nothing would stop you from keeping your rear 427lbs rear springs and cutting down your oem upper spring seat and running the Hotchkis front springs, you'd end up with a exact same drop, .6"/.8". That can alway's be your plan b, if what whatever reason you don't care for the 330lbs Hotchkis rear rates.

I can't speak for them, but IMO that they mean by "matched" is that they tested the springs and sway's in R&D together. Yes, you can use the sway's with any spring and being adjustable, you have choices reguarding stiffness levels.

 

One more question. Do the stock shocks wear faster due to springs being lower or because they're much stiffer? Or a combination of both?

I currently have about 40K miles on the car. If I do get springs, should I expect to need some shocks such as tokico or koni soon thereafter? Do you know how long shocks normally last with aftermarket springs.

Thanks in advance.

 

Most all aftermarket lowering springs don't have suffecient stiffness level's to really get concerned about wear and tear, nor have I seen a trend among owners having issues either. However, aftermarket shocks like Koni's or Tokico's are much better then all oem shocks. I'm not just talking performance, but the kind of differance that doen'st take a long drive or a keen sense to pickup on. It's the sort of thing that let's you clearly know why you just spend $500-$700, much superior valving vs oem.