Review: HKS Hipermax IV SP for 370Z

MaysEffect

Right, in this case HKS made the factors dependent on spring length (which is the correct way of doing this). As noted in the photo's but not by description. The front spring looks to be longer than the rear (which isn't the norm). It also looks to have a longer max stroke length as well. Because of this, it still has a higher total load rating than the rear. Making it in line with the oem weight balance and capacity.

Making a guesstimate on sizes...

Front spring is probably a 8 inch spring , with a maximum of 5 inches of stroke. And the rear looks to be about an inch shorter.
So..
14kg/mm x 122mm(4.8") =1708kg front
16kg/mm x 101mm (4.0") = 1616kg rear
(max load capacity per spring based on max spring stroke)
Exact rates here - Swift Springs USA

This still matches the oem weight balance and also matches the motion ratios as well. At 2 inches of compression, the front will need about 1568ibs, the rear will need about 1792ibs.

Apologies in advance for getting technical. I think HKS did a good job matching the rates appropriately.

Spooler

Hmm, So my Aragosta's have a 10 in. 12kg/mm spring on the front. My rears are 7 in 10kg/mm. I am using Swift springs. How does this calculate? Do I need more info? I do not have the stroke info handy.

MaysEffect

The info is listed on the swift spring link. Look for the length (need to select the right spring i.d) and then it shows the specification for each spring rate in mm & inch.

It shows the maximum and usable stroke of the spring, the maximum is when the spring is over 95% full compression, useable is between 25-75% compression.

Based off your information though, it doesn't match the balance of the oem design. It does however match or exceed the oem GVWR capacity. I think Aragosta tried to match the oem specification with a shorter spring. Is the rear spring a linear of progressive spring? On their site it shows 2 different types.

No thread jacking here......

Jhill

This thread is getting pretty interesting and I always thought it odd how much stiffer front to rear the aftermarket change vs the oem rates for most of the aftermarket. Also I know the increase in rear rate doesn't have as much effect as the front in terms of overall stiffness increase so Im curious with the motion ratio calculated in how much stiffer % the front vs the rear is going from the oem 7.5/8.1 setup to something like my 12/11 and also the hks 14/16 (I think that's what he said it had). Be curious if the powertrix is like a 40%/25% which would re confirm my balance I feel now and is the hks something like a 50%/50% keeping the balance also wonder where something like the fortune end up in stock form as they spec an 11/8 setup and dont think going stiffer in the rear is good as it doesn't let the car articulate (when I spoke to them in the past) which I thought that balance would be really understeer biased. As it is I'm glad I went with the swift upgrade for the 12/11 setup vs the 12/10 setup stock for powertrix. I don't really want to increase or decrease my rates as I like the ride now but wonder if I can make the % difference up in bar setting.

Spooler

Linear springs. I am using SPL midlinks.

MaysEffect

The numbers in themselves have a lot attached to it. The first being the maximum stroke length in relation to the total capacity. This is what needs to be matched first before anything else. In most cases these different rated springs don't share the same length or the dampers don't share the same extension length. The HKS is not that extreme when you consider its free length is short compared to some other springs and the fact it uses a secondary spring to take up the remainder of droop. I think a properly matched tender spring would make the droop sensation feel even better, but this could add another 300+ dollars in cost. In most cases that can be the difference of someone going with a different brand.

Jhill

I'm not sure I follow you in this. The stroke will always be a ratio of droop vs travel. Now thinking about this vs other things like the offroad world I can see why they would require a helper/tender spring with very stiff springs. For example if you had a 5inch stroke shock (which appears to be the norm for the z) and you have say 30% sag with a 11k spring and zero preload (I choose 30% as that's a norm for my world). Now let's say with that 11k spring and zero preload you still feel too much roll and not enough support. Well with air suspension you can do some tweaks like reducing air volume (making it pregressve), firming the low speed damping to gain support at cost of sensitivity or boosting gas charge in damper to increase ramp up and more support. If doing it by spring rate as common in a car now you gain support at cost of traction. Given same example is 30% sag with 11k spring and zero preload what do you think your sag / - travel will be at 16k rates? Obviously less and there goes your traction over humps and inside tire lift which is where the helper / tender spring comes in to gain - / droop travel back.

ShinyaPGH

I have the Carbonsignal CS lipkit that includes the front lip, side skirts, rear diffusers & spats, and the wing add-on.

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MaysEffect

Note - You can't have sag without preload...unless you are talking about something else...

I think your examples further establishes my vague point. Droop is a portion of the total damper travel, where as it ISN'T relevant to the total spring length. Sag is however a factor used for springs, not dampers. Thus my point on why these two things need to be matched dependent on weight and length. Using a tender or helper spring ensures there is still some load on a spring at full droop. You are inevitably going to have some preload on the spring in order to measure sag. The differences would be where in the damper stroke the spring starts to compress.

I didn't include an example for it to make sense previously. But in a situation where you have a damper that has 8 inches of extension at full droop, but your spring is only 6 inches long, you have a situation where there is no load on the main spring when it goes passed 6 inches of droop, this would be zero preload. In reality like you said, normal road cars won't see this level of extension during driving where as a extreme off-road truck can work well passed 8 inches of droop from static ride height, but in any case you never want your spring fully extended before the damper fully extends.

Adding a tender/helper or even a secondary main spring is what needs to be done, with your example of off-road vehicles, they are going the route of a secondary rate spring> and then a helper spring if needed. In the case where a spring rate is significantly stiffer than the total load on said wheel, the spring does not need to be long or longer than the damper stroke length, but in such case the damper travel is still based off the factory length and available perch length. The complexity of tenders comes from trying to match weights when the damper is extended farther than the spring and trying to manage compression difference's. This is a completely different discussion though.

Jhill

I think we mean the same thing but using different wording. However not having sag without preload? Never heard this before, I've always heard sag referenced as where the vehicle rest at with a given spring rate and preload as pre compressing the spring with no weight on it. For example if I have a 5in stroke shock with a 8 inch long spring that has a usable stroke length of 5.4inch. Now if I have the car in the air and turn the spring perch till it just touches and lock in down that is zero preload, the spring is not loose and it is not pre compressed. Now if I put a wire tie on the shock shaft and lower the car on turn plates and then lift it back up and measure 1.5" then I now have achieved 30% sag. If I drop a spring rate I will need to add preload to it to maintain this 30% sag and if I increase my rate I will have to add a helper/tender spring to maintain this sag otherwise I'm losing sag which equals a lose of droop (negative) travel.

MaysEffect

I think i understand what you are getting at, but using sag as a nominal point of reference isn't the correct way of determining anything without factoring preload. It's relevance is to the rated amount of compression (spring rate/weight) vs how much force is actually applied. In your example, 30% spring sag may or may not be acceptable depending on the amount of preload and the total length and weight. But it's not accurate or relevant if you haven't set preload. Thus what i meant by not having sag without preload. If what you are measuring is 30% spring compression with no preload, you are measuring the static weight divided by the spring rate, while also taking into consideration the motion ratio and angle correction). There is no point to making hypothetical changes. If you match your springs to have 50% bump travel with little to no preload and still fall within a safe limit of stroke before fouling anywhere, you've already accounted for sag. Whether or not the spring continues to sag overtime is a different discussion.

In any case not setting any preload means there is a point within the damper travel where a spring isn't engaged. Simply tightening it down to the lowest point of engagement is still adding preload, regardless if it's a significant amount of force or not. Spring sag can only then be determined once the spring is loaded, without preload you are measuring the percentage of load capacity used. This is not the same as sag.

I'm not sure spring sag is even a good reference for cars anyways. We are dealing with weights far greater than with motorcycles where the rider weight is a significant factor on overall load. Unlike with a car, where driver weight is only a small percentage and usually less than the standard amount of preload that should be applied.

With cars, the manufacturers usually account for driver weight by counter weighting the car and setting preload. With bikes the sag is generally countered with 1/2 - 1.25 inches of preload.

We'll need to start a new thread for this topic lol

littlejuanito

OP, Any follow up reviews on these coilovers??? How are the holding up so far?

ShinyaPGH

it hasn't seen any other track days unfortunately. But more I drive on them, more I fall in love with. A track coil overs, that are impressively comfortable on the streets. As some of the guys were mentioning, the dampers are quite good and the car doesn't feel too stiff, even though they are such high spring rates.

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ShinyaPGH

Any specifics questions you would like me to ask to HKS? I have access to the engineers in Japan who should be able to answer any technical questions for us.

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2013 NISMO. Motordyne Longtube Headers/Catback exhausts, Carbon Signal CS lip kit etc.

littlejuanito

I've read that the Hipermax GT were cornered balanced for other car applications but would like to know if these are corner balanced for the 370z. Supposedly the HKS are pretty much ready to go outta the box, without the need to adjust height.

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