Review: HKS Hipermax IV SP for 370Z
 

My apologies on this review has been long overdue. But the opportunity to take my car to the track has been challenging this year and has delayed this review. But enough with the excuses, and onto the good stuff.
This is a review for HKS Hipermax IV SP for 370Z. SP model has been released this year for 370Z finally. Until this year, only Hipermax IV GT was available for 370Z from HKS. On my 2013 370Z Nismo, I was running the GT model through last year. I was running the GT coils in conjunction with Eibach sway bars. GT coils are aimed to be for street focused application. Even at the stiffest settings on the sway bars as well as the coilovers, the set up was too soft for the track driving. It rode very smoothly but the 10k/8k spring rate just wasn’t strong enough for the track driving in my opinion.

Current suspension setup:
• HKS Hipermax IV SP
• Eibach swaybars
• SPL front control arms
• SPL rear camber arms
• SPL toe bolts
• SPL endlinks (front/rear)
Current tire setup:
Street: Bridgestone Potenza S-04 Pole Position 265/35-19, 305/30-19
Track: Toyo Proxes R888 265/35-19, 295/30-19

When I received the Hipermax IV SP coilovers and read the spec, I was shocked to find out how stiff the spring rates were. Front came in at 14k, while the rear springs are whopping 16k! Moving from 10k springs to 14k springs is a good upgrade considering how soft the car was running on 10k. But I was curious how stiff the car would ride in the rear, going from 8k to 16k, basically doubling the spring rate.
Wanting the coilovers to perform at is full capacity, I read the instructions HKS has sent me carefully, and settled on a lowest recommended ride height to start. Also, I did not add any preloads to the springs. As these coilovers come with 1-way adjustment, I initially set both the front and the rear at 10clicks from the stiffest. (30clicks total available). Upon my first drive, I immediately noticed how loose the car was, especially on the rear end. I assumed it’s due to the stiff springs, and I started lowering the compression on the coils. The front end also would understeer on turn in. And I started taking out the compression in the front also.
What I first noticed, was how smooth the ride was even though the springs were very stiff. The car felt stiff, but very well dampened. As low as my car rides, often, my front end will scrape on highways when I hit dips. But with the SP coilovers, I was not scraping anywhere as much as I was with the GT coils.

My first opportunity to drive on the track was supposed to be in April at National Corvette Museum in Bowling Green, KY. However, due to the forecast calling for 100% rain, I cancelled the track day, as it would have not been a good test at all to go out in the wet as the first test.
Instead, my first chance to drive aggressively came at Zdayz 2017, at the tail of the dragon and other twisty roads. This is when I fell in love with these coilovers. Not only these coilovers handle the rather heavy weight of 370Z way better than previous set of coils I had, these rode more plus than stock NISMO. Best of both world!
However, I was starting to feel the car wiggle more as the trip went on. I suspected that the alignment may be off in the rear. I took a wild guess, and ordered the SPL lockout bolts for the rear. Upon taking the car to the alignment shop, we discovered that the rear was not holding the alignment, and we went ahead and installed the lockout bolts.
Two weeks later, I had an opportunity to go back down to Tail of the Dragon, and even through the abuse I could throw at down there, the rear alignment didn’t budge. Problem fixed!

Finally, the first week of June, I could get on the track at Mid-Ohio on my new setup. But this again is where my luck worked against me. My first session, I took it easy but was cranking out time that were a few seconds under my last year’s time. I felt a slight understeer at mid-turn, and decided to take out a couple of clicks of compression out from the front coilovers to fight that. I went out for the second session, and only 4-5 laps in, the organizer decided to exercise the “emergency red flag” as a drill, and our session was cut short. My cell phone/Harry’s laptimer crashed also during this session, and I was not able to capture my laptime. But the setup was allowing me to drive more aggressively, and felt close to be “dialed in” even though I had not taken a lot of laps yet. After a lunch session, I was getting all geared up and ready to go. But the nature decided to not let me have any more fun. The sky opened up, and the track day was completely ruined. There were running water all over the track, and it was not worth my time for me to even check out the wet condition with the R888.

Even with these limited testing, I must say these Hipermax SP coilovers are HUGE improvement for a driver like myself. I do not daily my Z, and only drive about 3000-4000 miles a year. I trailer my car from time to time, so the driving comfort isn’t huge on my priorities. But I have taken a trip down from Ohio to the Dragon comfortably on this set up. I’m amazed how well damped these dampers are, considering how high the spring rates are. They must have some amazing valves on these. I still have ways to go before these are 100% dialed-in, but I’m confident to say these are probably one of the best, if not the best coilovers you can buy for under $2000.

If you have any questions, please feel free to contact me. Here are some photos:

https://uniim1.shutterfly.com/ng/ser...085027/enhance
https://uniim1.shutterfly.com/ng/ser...085028/enhance
https://uniim1.shutterfly.com/ng/ser...085027/enhance
https://uniim1.shutterfly.com/ng/ser...085028/enhance
https://uniim1.shutterfly.com/ng/ser...085026/enhance
https://uniim1.shutterfly.com/ng/ser...085026/enhance
https://uniim1.shutterfly.com/ng/ser...085026/enhance
https://uniim1.shutterfly.com/ng/ser...085026/enhance

Awesome review bud. Do you recommend these for the street or are they strictly track oriented. I like to get a stiffer spring rate as my 12k/11k swifts feel really soft.

By the way, any reason why the spring rate is higher in the rear?

If you have 12k/11k swifts on OEM shocks, these SP coils will actually ride better on the streets. I know many people love KW v3's, but they still come with progressive 8-9k springs in the rear, and these HKS coils will probably outperform them on the track. KW v3 probably will ride a tad smoother on the streets though. (that's the nature of the progressive springs anyway.) But just comparing to all the coils out there under $2000, I'd rank these HKS Hipermax IV SP at the very top imho.

On the spring rate, it does seem unusual. But just from watching so many of the HotVersion and Best Motoring videos on Youtube, Japanese race drivers who test for these JDM tuners typically HATE understeer. And having such high spring rate in the rear ensures the car will not understeer on corner exits. Higher spring rate with better damping seem to work better for our heavy Z34 cars. The car has more tendencies to oversteer on mid turn and exits now, and I've been able to dial them out with adjusting compression and sway bars.

Another thing I noticed from this setup change, is that Toyo Proxes R888 are better match to these SP coils than S-04. S-04 has a hard time gripping with such stiff suspension. S-04 felt better on the GT coils with softer springs. I didn't realize tires can feel so different with different coilovers.

This review is perfect! We sell these and we havent had any complaints at all.

The one thing that people are pleasantly surprised about is how well (Comfortable) they ride for how high the spring rates are. HKS is knows for have an AMAZING shock. Everyone over at Swift also says HKS has one of the best shocks on the market. They are valve perfectly. So when that happens you can get a higher spring rate but the harshness is lessened.

So if you plan on autox or track days and also daily your Z. Do not be afraid to step up into the HKS Hipermax SPs.

Again, great review man. We stand by HKS products 100%!!

Those look great!

The helper springs help with the harshness. Guess that is why they can get away with the high spring rates on the rear. Normal thinking with what track guys have used says your car should over steer pretty bad. They are doing some trickery with the helper springs. I need to up my springs rates on my Aragosta coilover myself to 13k front and 11k rear.

See this is why I think a lot is all preference. Littlejuanito is running powertrix 12/11 as am I and I wouldn't want it any stiffer (mine is daily) car right now is firm but comfortable but I did notice more understeer vs oem with just stillen bars. It went like this for me: bone stock I feel the car has a lot of understeer and wants to roll over on the front, especially on any down swooping freeway on ramps. OEM + stillen bars set mid/mid the roll was helped a lot (at least didn't feel like my bumper was going to scrap at any minute) and car balance was perfect or near perfect, the rear would get slightly loose before the front indicating to me I was pushing it. Now the roll is greatly reduced and car is planted (for a dual duty car) but now I have a slight flat pushing understeer when getting nearer the limit. So next track day is aug 30th and I'll be trying a softer front setting or a firmer rear setting I think and see if I like the balance difference. But going from stock 7.5k/8.1k and then adding stiffer bars with a greater increase in rear really helped bring the car more neutral to me, now with the stiffer rates but a firmer front bias I feel some of the understeer is back. That said on really tight stuff like autocross the oem with stiff bars was a bit of a handful on the rear end and is now easier but high speed swooping turns the other felt better and now pushes. So these rates as a more track oriented kit makes sense to me.

Jhill, you should run a softer front and a stiffer rear rebound on the Powertrix so you can dial in that understeer. (Are you still going airborne? lol)That's what I did cause I ended up running a 40mm stagger difference 255/295 and the understeer was huge. I'm switching to a 285/295 tire combo.

As far as the springs go, the swifts on these Powertrix are actually soft and I do wish the spring rates were higher but the coilovers do ride really well tho.

Lol only on one hump on 101 to 85 merger but there is even a warning sign now so I guess I wasn't the only one. Yea I can try tweaking the damping too but that's more a fine adjustment and I think I'm going to want a bit more but we will see. The rates for me are perfect, firm enough to track with street tires (I stuck with oem size as well) yet smooth enough that passengers still fall asleep and myself almost once (that's not good) so even though they are firm they are still a smooth ride.

Nice review and great contribution to forum members and visitors.

What type of front spoiler lip does OP have on his nismo? I want it for my car.

Great review and it I am amazed that the car understeered with higher spring rate at back.



I agree that rear stiff spring make the car oversteers, maybe the tires make the difference, as I have 12k front and rear OEM style, whiteline swaybars, with PSS the car oversteered in mid turns. Removed the rear swaybar and changed them to Re71r and it made a big difference.

Sorry to be a source of annoyance again. But the helper springs are not for controlling or helping compression during normal conditions, as arse backwards as that sounds. They're fully compressed and only aid in seating the main spring under full droop conditions. most helper springs if not all are less than 2kg in rate, usually less than 1kg (10-55ib/in)

The rate of those main springs are actually properly matched for the weight of the car, the caveat is the overall length. You'd only really need to use the helpers if the spring itself is shorter than the perch to perch distance or to reduce adding additional preload during droop.

Tender springs need to be used when trying to add dual rate functions and can range from 1kg-20kg.

:tiphat:


Excellent review OP.

HKS and Bilstein most notably setup there rates to match the oem Frequency balance. Considering the rear spring design and motion ratios, the harder rear spring is not unusual.

Do you notice the car rotate quickly when turning abruptly into corners? OR does it load up and start to drift with a bit of latency?

Also have you tried setting the front dampers a bit stiffer than the rear? What do you notice?

NP, I don't know much about helper springs. The only issue with the spring rates is it is the exact opposite of what other folks use that track and autocross. Got me puzzled a bit.

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.

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.

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......:tup:

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.

Linear springs. I am using SPL midlinks.

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.

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.

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

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.:stirthepot:

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.

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 :rolleyes:

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

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.

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.

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.

How do they feel about true type coilovers vs oem type for the z34? Also do they offer any true type coilovers for the z34?
Thanks:tiphat:

Isn't that nearly impossible? Difference in driver's weight can upset the corner balance. 150lbs driver versus a 250lbs driver can make quite a bit of difference. The right and the left coilovers did not come set up in different heights, so I doubt that they are corner balanced.

If you're talking about Front/Rear weight distribution, out of the box, the coils were set up with 689mm front, 690mm rear. But again, since the driver is no located in the dead center of the car, driver weight can change the front/rear distribution also.
FYI, I'm running F:669mm R:657mm, so I would've shifted the weight toward the rear with my current set up from the out-of-box setup.

This example doesn't take into consideration driver weight or asb endlink alignment. Either factor can change the cross weight by 2-5% easily.

But for an out of the box cross weight of around 50% this is a decent range but not untypical, certainly if its a true coilover kit and preload is preset. This is much harder to do with a divorced spring in the rear unless the perch was preset evenly.

I stand corrected, sir! I spoke with the HKS engineer in Japan, and he said they make the best effort to send out the unit with the settings that's close to being balanced for the front/rear distribution of the weight. Obviously, those concerns I had applies, and the car will not truly be balanced, but it would be a good starting point.

The out-of-the-box setting was rear being 1mm taller as far the ride height goes. I'm running about 4mm shorter in the rear instead. So, I may have a little more weight in the rear than their "balanced" set up. But I'm not exactly the smallest guy either at 195lbs, so by accident, I may be close. :-)

Thanks for inquiring with the engineer and good to know that these come so well setup from the factory.