Review: HKS Hipermax IV SP for 370Z

ShinyaPGH

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.

Jhill

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.

littlejuanito

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.

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Fast Intentions Non-Resonated Carbon Fiber CBE | Berk Non-Resonated HFC | Powertrix Coilovers | RJM Clutch Pedal | LatheWerks Shift Knob | Stillen Sway Bars, |SPL Parts | Enkei RS05RR | Fujimura Diffuser | Ecutek Tuned by Seb | 308whp

Jhill

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.

MaysEffect

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?