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.