Alright guys, I have been rolling on HKS Hypermax RS and want to change the rear suspension a bit. The main reason is because I just think the rear springs are too soft and whenever someone is in the back seat, the car bottoms out on rear left. Also when under hard acceleration the weight of the car shifts a tad to much to the rear and might be hurting traction. One thing that did help was to increase the dampening (maxed) and raise the spring almost all the way. As of right now the left side is a heck of a lot more pre-loaded than the right.

I talked to an HKS representative not too long ago and they recommended to go no more than 2kg over the standard setting which is:

F / R
288 230 (5Kg/4Kg)

While looking at other coilover sets I noticed that all of them tend to be stiffer in the back. Ex. Progress 257/360 (4Kg/6Kg), KW v2 and Tanabe 6Kg/8Kg.

So with that in mind, per HKS they would only recommend 5Kg/6Kg. But all the coilover sets have a 2Kg difference from front to back. I do love the way it feels right now, confi as heck and still handle everything I throw at them. Probably more of a shock/strut function than anything else.

So should I go two up 5Kg/6Kg or three 5Kg/7Kg? For those running specs close to them, how's traction and comfort. I bought them mainly for comfort and adjustability, but I wouldn't mind some straight line traction as well.

It's my DD and I don't auto-x, just 1/4 mile once in a blue moon.

Thanks

 

wow, really? This many views and no bite :-)

 

I'm not entirely certain, but the reason why other brands that you mentioned, Progress and KW, has a much higher spring rating in the rear is because of the amount of the shock travel or the size of the strut. The smaller the strut or the less travel it has, the higher the spring rates.

But you since you are having an issue with your rear bottoming out, i would suggest you to get higher spring rates. However since this is your daily driven car and its for comfort, it will stiffen up your ride and making it a bit more bumpy.

 

if you don't do auto x then just move up to the progress set. The stiffer the springs, the less forgiving, and the less comfortable the ride will be.

 

I'll prolly do the 7Kg in the back then. No need for progress, all I need is different springs. I mean, 7Kg is still a heck of a lot softer than Tein 10Kg that most ride around here and r ok with it. Eventually I might stiffen up the front if I decide to do some auto x'ing, the spring set is only about $200-$250.

 

that is good.

 

I'm on Tein coilovers, the rear is actually quite soft and stable. Don't be too concern about stiffening the rear, because most of the forces, harshness, bumpyness comes from the front.

 

^ true that. I've noticed that even when the rear dampening was all the way stiffened up, it was still very good. The front I have to keep it at a happy medium, too soft (confy) it feels like a wild horse when I get on it. Too hard (stability/harsher) and I get too much wheel spin when I get on it.

Well I decided to give a couple of places a call today and pretty much everyone wasn't soo sure it it was the springs. One of them being Tony over at Jotech recommended double checking the coils, so I decided to take them all apart. Well I found out that the rear/left measured 7 7/16 in and the right 7 13/16 in decompresed. With my weight left was 6 10/16 in and right 6 15/16 in.
The shocks were perfectly fine, pretty hard to get them to absorb and normal coming out of the shocks. This leads me to believe that the problem is with the springs being too soft and me cranking the ____ out of that left side.

Will be making a call tomorrow and ordering some 7Kg. Heck, I talked to Brian over at Ptuning he might have some some input on something higher than that. Now to find the dang part number for the springs, tried calling HKS and the technical line is going to be temporarily out :-(

Thanks guys!

 

With the front spring rate at 5kg, I'd go with 9-10 kg springs in the rear.
The current spring rate setup you got is all wrong and generally produces more under-steer. I have no idea why HKS would choose these spring rates. 7 kg is slightly too soft... go at least 8kg, you won't regret it.

 

Go figure, the r like the only one's running such a weird setup. What r u running?

 

Currently, I'm running Koni Yellows with Ground-Control coilover sleeve conversion paired with some GC Eibach ERS springs in the Front with some Hypercoil springs in the Rear.

6 kg/mm (340 lbs/in) FRONT
9 kg/mm (500 lbs/in) REAR

However, I still feel the REAR need to be at about 10-11 kg/mm (~600 lbs/in).

If you're looking for new springs, depending on the type of spring that comes with the HKS coils, you may be able to use different manufacturer springs that are better and probably cheaper or equal to what HKS is charging you for their springs. You would just need to know what length, diameter (typically 2.5"), and spring rate your looking for. Swift, Hypercoils, Vogtland, Ground-Control Eibach ERS Springs are a few companies you can look at for racing springs.

Also, you may want to look into what the HKS rear strut valves can handle in terms of spring rate.