Review: HKS Hipermax IV SP for 370Z

MaysEffect

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.




Excellent review OP.

Spooler

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.

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.