GP Hyper Knuckle - Roll center adjusters

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To start off I wanted to increase the handling performance of my car. I did everything from adjustable arms, roll center adjusters in the rear (moonface), custom coilover settings, etc. I still was getting a bit of roll in the front accompanied by a feel of uneasy handling near the limit. Speaking with my bro who a mechanical engineer major, suggested I look into roll center adjusters. Doing a bit of reading, roll resistance could be tuned in by: increasing spring rate, increasing sway bar diameter, or heightening roll center. For the s14 chassis, everything but the latter is much more obtainable; but at a cost.

Increasing front spring rate increases road harshness. Also, If the spring rate is TOO high this could lead to loss of road traction during bumpy road encounters. A front sway bar on the other hand only works during lateral load transfer, which is good, but if you excessively lower the car and ultimately lower the roll center a thicker sway bar might not be enough.

So that leaves us with roll center adjusts. Increasing the roll center on the 240sx chassis has a few options. One of the ways is to change the inner height of the pickup point of the front lower control arm. D-Sport magazine (April issue I believe), illustrated an s15 with roll center adjustment, although they defined it as being more of a bump steer concern. The main drawback is that the tension rod now moves in a different arc and will cause binding. The s15 in the D-sport magazine alleviated that problem by mounting the tension rod below the LCA in conjunction with a set of custom FLCA (can't remember the name). I wouldn't recommend this method though as it is very easy to damage the suspension geometry of the car.

The 2nd option is to space the distance from the spindle to the lower control arm pick up points. This is where GP Sports Hyper knuckle comes in. The unit is a fully casted for strength and the dimensions of the unit are a bit bigger than the OEM stock. The GP Sports knuckle allows drivers to increase, or decrease the heights of roll center and bumpsteer respectively. Without spacers (+10mm or +20mm), the Hyper knuckle adds 20mm of height adjustment. The unit also allows for more steering angle which is a plus for drifters (my car is built for grip). Depending on how much you lower the vehicle, having the ability to adjust roll center is a big plus when fine tuning the balance of the car.

As for driving impressions I could not be happier. There is less body roll, more cornering power (seat of the pants feel), and much more stability during low/high speed transitions. I'd rate installing a 4/10 assuming you have the right tools (wrench, mallet... i think that's it). You will also need to realign the car as well.

Now the unit is not cheap. I purchased the unit with spacers which came out to be approx $1400 through JDM Option (Thanks Inada for delivering the unit yourself!!!). But there's an upside. There is an equivalent unit GP Sports provides called the Super Knuckle which adds 20mm of adjustment at the fraction of the price (approx $800ish). Both units are fully cast and VERY strong. There isn't welds to break or snap. The unit not only adjusts roll center and also allows for more steering angle and bump steer correction. These adjustments alone could run over $500 dollars ($200 for roll center adjustment and $300+ for spindle modification.

And for pictures...

Picture of actual unit...





Notice inner pickup point to the center of pillowball are parallel to the ground.



The topic of suspension geometry is very complex, and this thread only scratches the surface. For more reading do a search on "roll center + center of gravity" to get an understanding of it.