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Rear Spring Rate Suggestions

Looking for suggestions for rear spring rate with the following mods:

475lb front springs
Stock front sway bar
Strano 3-way adjustable rear sway bar
Square tire setup (Continental's)

I have not run my car with these mods yet so I cannot offer any info on how it currently handles. I'm thinking 275lb rear would be a good starting point with the ability to fine tune with the rear bar. Thoughts?

Thanks for any suggestions.
 
My CorteX/JRi coil overs have 450/250 so your 275's should be in the ballpark. I'd check with the supplier of your coil overs and ask them for their recommendation.
 

Grant 302

basic and well known psychic
I think the spring will work, but wouldn't be surprised if you end up wanting to go stiffer on the front bar.

Is this for a rear coilover or on the axles?
 
I haven't purchased the rear shocks yet, but will likely go with a true coilover.

Is there a difference in how the springs perform on the axel vs a coilover in the rear?
 

Grant 302

basic and well known psychic
They both have their functional pros and cons IMO. My view is probably biased as I chose coilovers. Coilovers will be closer to a 1:1 wheel ratio and my thinking was that it would be more consistent in tuning for roll vs. bump travel. With the same spring rate, I think the bump/dip (both sides at the same time) feel should be similar, but roll resistance should be better with the outboard spring location. Single side bumps/dips might disturb the coilover more. I wish I was able to directly compare.
 

Grant 302

basic and well known psychic
Not to throw a monkey wrench in everything we just discussed...but considering your other thread on the 305 GT-I/R7 tires, I wouldn't be surprised if the spring rates all around are a little light for the level of grip from those tires.

Even with the 550/350 and Pirelli 305 scrubs, I'm thinking I could have gone stiffer for a full weight car. Hopefully that will change when or as I lighten the car.
 

JScheier

Too Hot for the Boss!
I'm gonna side with Grant on this one. When running the Continentals on my car (and the Pirelli's), it screamed for more spring rate. I was looking into 700# in the front with a 300-350# spring in the rear (OEM location) with my AST4200RRs. I didn't get far enough to install / test as another car has taken up residence on the lift.
 
JScheier said:
When running the Continentals on my car (and the Pirelli's), it screamed for more spring rate.

Being that I do not have a lot of experience in this suspension stuff, can you elaborate why you thought it "screamed" for more spring rate. I currently run 305 Pzero slicks and have the stock Boss 302 struts/shocks along with P-springs. My car handles extremely well. So how do you know if one should install stiffer springs and shocks/struts? What are the signs?
 
Grant 302 said:
Not to throw a monkey wrench in everything we just discussed...but considering your other thread on the 305 GT-I/R7 tires, I wouldn't be surprised if the spring rates all around are a little light for the level of grip from those tires.

Even with the 550/350 and Pirelli 305 scrubs, I'm thinking I could have gone stiffer for a full weight car. Hopefully that will change when or as I lighten the car.

I think a higher rate would be ideal but the front set of coilovers I'm getting have 475# springs with them so I will give them a try. Not to mention, I still drive my car on the street a fair amount so I don't want to go too stiff.

I've run A6's and Conti's on the stock suspension for the past few years. Aside from nose dive and body roll the car is extremely neutral, which I like.
 

Grant 302

basic and well known psychic
KBBOSS1086 said:
I think a higher rate would be ideal but the front set of coilovers I'm getting have 475# springs with them so I will give them a try. Not to mention, I still drive my car on the street a fair amount so I don't want to go too stiff.

I've run A6's and Conti's on the stock suspension for the past few years. Aside from nose dive and body roll the car is extremely neutral, which I like.

Certainly makes sense to try what you already have. My GT is my daily driver, and I'm surprised that I'm thinking I could still tolerate a bit more rate for street driving. I am a little concerned about road trips now and if I can handle a 360 mile trip...but I'll find out in May on the way to Laguna Seca.

06mach1 said:
Being that I do not have a lot of experience in this suspension stuff, can you elaborate why you thought it "screamed" for more spring rate. I currently run 305 Pzero slicks and have the stock Boss 302 struts/shocks along with P-springs. My car handles extremely well. So how do you know if one should install stiffer springs and shocks/struts? What are the signs?

Your wallet has money in it! ;)

Just kidding, of course...But I am surprised at how much the increased rate improved grip even with my street tires.
 

JScheier

Too Hot for the Boss!
06mach1 said:
My car handles extremely well. So how do you know if one should install stiffer springs and shocks/struts? What are the signs?

You will feel it in your butt and see it in photos. Car rolls more, nose dive under braking, overall 'wallowing' type feel. The stiffer / stickier the tire, the more spring rate the vehicle can take up to a point.

My car handles extremely well too (450/250 springs)... but it could handle better. With the dampers I have on the car, the street ride should not suffer much with more spring rate.
 

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