Apex Engineered Track Attack Spring/Shock Discussion

[baby_Carlton]

Hi HybridZ, its been a while. Took a long sabbatical from working on my S30 to finish college and get a job. For the last 6 or so months its been full steam ahead, the project is currently being rust repaired at a local body shop and I've been collecting parts as budget allows.

 

The first piece major piece of hardware to arrived is the Viking Performance Shocks from the Apex Engineered Track Attack Front/Rear Suspension kit. I noticed that Apex’s website lacks details on shock and spring selection, so I’m documenting my findings here for others and to start a discussion on their choices.

 

What's Included:

Box as it arrives from Viking Performance

 

Serial Numbers of each of the shocks (PN: C203)

 

Viking Performance Shocks Link

 

Part Numbers of Springs (600# & 700#)

 

Initial Impressions:

The car will be caged and used primarily/almost exclusively on track, so a stiffer setup is expected. However the spring rate selection still raises some concerns:

• The S30 chassis doesn’t benefit significantly from extremely high spring rates, even with a roll cage.

• The rear suspension uses inboard cantilevered shocks, which traditionally increase effective spring rate via the lever arm.

• This spring selection guide from Viking Performance indicates that the spring rate for a car with IRS and axle weights of ~1200-1400# is a lot lower than the supplied springs.

 

I'm hypothesizing that the high rates were chosen to prevent the shocks, which are short to fit the Z’s narrow frame and tight packaging within the front wheel wells, from bottoming out.

 

I’ve reached out to Apex Engineered to clarify the wheel rates for this setup and will update this thread when I hear back. Let me know if any of you have run this kit or high wheel rates.

 

 

Edited July 7 by baby_Carlton
Inclusion of spring selection guide from Viking Performance

[jhm]

Welcome back, Carlton...and congrats on the major life changes/accomplishments! 

 

Following, as I'm super interested to hear how about the installation and how you like it.  Thanks for documenting the process!  👍

[Ben280]

Good post. I was frustrated for a long time with companies not sharing spring rates on these parts. FWIW, Viking is legit, lots of fast SCCA guys run those things with good results. 

 

IF those spring rates were chosen to prevent bottoming out of the shocks, that's pretty poor design. My guess is that the motion ratio of the bellcrank will be the limiting/bottoming out feature here, and that the conversion to pushrods has resulted in some high force multipliers. My guess would be Viking starting point is mounting in a "muscle car" front end, where the motion ratio is fairly low. 

 

I'll be interested to hear what the APEX guys say!

[baby_Carlton]

On 7/7/2025 at 7:16 AM, jhm said:

Welcome back, Carlton...and congrats on the major life changes/accomplishments! 

 

Following, as I'm super interested to hear how about the installation and how you like it.  Thanks for documenting the process!  👍

Thanks for the welcome back, this car has certainly had a rollercoaster of a fate over the last 10 or so years of ownership. Excited to build it into the best version of itself (for me).

 

On 7/7/2025 at 2:15 PM, Ben280 said:

Good post. I was frustrated for a long time with companies not sharing spring rates on these parts. FWIW, Viking is legit, lots of fast SCCA guys run those things with good results. 

Thanks for the info, seems like Viking is a non-hype brand that offers shocks that do shock things, which I can appreciate. AE is slow on CS communications but that's understandable given the size of their operation. That said, for a ~$9K suspension kit, a bit more transparency and technical detail on their website would go a long way. If I can find a shock with more travel for the same dimensions or when I blow these out I'll swap. JRi's builder series and some of their GM line looks like it would bolt right in, only 0.3" longer extended length which seems negligible in terms of fitment (PN: 100-511-300). 

 

On 7/7/2025 at 2:15 PM, Ben280 said:

IF those spring rates were chosen to prevent bottoming out of the shocks, that's pretty poor design. My guess is that the motion ratio of the bellcrank will be the limiting/bottoming out feature here, and that the conversion to pushrods has resulted in some high force multipliers. My guess would be Viking starting point is mounting in a "muscle car" front end, where the motion ratio is fairly low. 

I agree, it seems incredibly unwise if that were the case but it wouldn't be the first time I'd seen it. I've seen similar suspension choices in GTAC (cars riding on bump stops) but that's usually done purposefully to keep the aero platform working optimally and not appropriate for a package like this. Considering the shock travel is a mere 3.6", its safe to assume this is an extremely low motion ratio design. It feels like a missed opportunity to fully leverage the bell crank inboard design (traditionally speaking) but perhaps packaging constraints of the S30 chassis left little room for alternatives.

 

I'm hoping the bottoming out feature will be at the upper A-arm which would allow me to mount a 3D printed polyurethane bump stop on top of it.  Going to email AE for an update on the wheel rates and now information motion ratios, thanks for the idea.

Edited July 9 by baby_Carlton
Grammar

[Ben280]

I'd definitely talk with Viking as well. Back when I worked at a performance race shop, they were pretty helpful. Once you get parts in hand from Apex, or just generally more information, I'd call Viking up and see what's what.

[baby_Carlton]

Update

 

From Apex:
 

     Front

          • Motion ratio: 0.92 : 1 (wheel : shock)

          • Wheel rate: 0.92² × 600 lb/in ≈ 510 lb/in

          • Wheel travel with 3.5" shock stroke: ≈ 3.2"

 

     Rear

          • Rocker motion ratio: 1.00 : 1

          • Wheel rate: 700 lb/in

          • Wheel travel with 3.5" shock stroke: 3.5"

 

Some confusing design and hardware choices here. Using a bellcrank/rocker with a 1:1 motion ratio doesn't take full advantage of the system. I will end up designing and having manufactured a new billet bellcrank/rocker with a lower motion ratio to get more shock travel. Highly likely I'll source a Hyperco spring at a different rate but that'll be handled during the bellcrank redesign and is a straight forward task. 

 

The front axle is giving me some headaches. The lack of suspension travel could be fixed by adding a bellcrank/rocker, but there isn’t enough space to fit one between the top of the strut tower and the hood. Making room would require major cutting and fabrication to the strut towers.

 

Mike Maier Inc.'s solution to a similar problem was to completely replace the original shock towers with a custom design, allowing a full-length shock to mount higher and further inboard. On the Z, moving the strut tower further inboard could create enough clearance between the upper control arm to let a coilover mount to the lower control arm. But by that point, I'm only a few steps away from designing a fully bespoke 1:1 double wishbone kit, making the OTS kit a useless purchase. I've been drawing up some concept sketches on how I could possibly do a pull rod but that would render the OEM strut tower essentially useless.

 

Alternative to implementing a front axle rocker would be to modify the upper wishbone where the bottom of the coilover mounts to be further inboard which would lower the motion ratio more but I'm not keen on trying that solution. 

 

I think I need a sanity check, I'm used to working on strut-type suspensions that have decently high shock travel to the point where coil-bind is a more pressing issue at low ride heights. Is there another solution to a short shock stroke and high spring rate I'm not considering? Or is this a case where the problem is all in my head and having 3-3.5" of shock stroke isn't that big of a deal? I've spoken to Rob Fuller from ZCarGarage regarding this problem who had some great insights on Z suspension, unfortunately he wasn't able to help me much past confirming that the wheel rates are ludicrously high. I'm aiming for a front axle wheel rate in the range of 300# to 450# and even then 450# still seems extremely high for the front axle.

 

 

Edited yesterday at 09:30 AM by baby_Carlton

[baby_Carlton]

Spoke to Mike Maier today seeing as the front suspension is most similar to that of an old Mustang. I wish I could write notes faster because holy hell that man is a wealth of knowledge. Suggested the reason for high spring rates is to prevent the upper control arm from camming over (poor arm design) and that the 3.5" of travel is definitely not enough for a road racing/track car (burms). Looks like my next steps are installing an adjustable upper ball joint that can move up/down to change the coilover angle and shock pot it at ride height looking for the lowest load value. If no substantial gains can be made there it's either back to the drawing board to make a push/pull rod cantilever or cut out the shock towers entirely and try to copy MMI's own Mod 2 strut tower modifications as well as new control arm(s) to gain the ability to mount a full length shock to the lower wishbone. This is becoming more and more of a fully custom project by the day.

[tube80z]

Hi Carlton,

 

A lot of this has been hashed out over the years.  There are some helpful stickies available in the FAQs for selecting damper and spring rates that you may want to refer to.  Before you get too far into recommendations about springs, etc., would you tell us what you intend to use this car for (track only, dual purpose, autox, street, etc.) as this will help give you better recommendations.  It would also be helpful to know what you intend to use for tires, as this is one of the most important factors to know.  Low-profile radials will require softer springs than a higher sidewall racing tire (such as a slick, R-compound, or HP 200 TW).  The more grip the tires can generate, the higher the spring rate needed to be able to deal with the forces that take up suspension travel.

 

I'd agree with Mike Maier's criticisms of the Apex upper A-arm on the front suspension.  It is going to always limit the amount of available suspension travel that can be used.  With regards to how much travel you need, that will depend a lot on tires and the use of the car.  On my autoX/hillclimb 240 that weighed 1850 or 2050, depending on class, I ran Hoosier bias-ply racing slicks and some of their radial slicks.  The spring rates I typically used were 400 to 600 lbs/in on the front and 400 to 550 lbs/in on the rear.  This car was droop limited, and front suspension travel on the roughest hill was typically less than 2.75 inches in the front and 3.5 inches in the rear.  I experimented with softer and stiffer rates but found this range worked best.

 

A friend's street legal dual-purpose car running on 200 TW or R comp low-profile tires weighed 2400+ (LS and T-56).  This car was happier with 375 on 450 spring rates.  It was also droop limited and I found out how horrible this made the car ride on normal street drives.  So if you go down this path I'd recommend a quick disconnect when not needing the limited travel.

 

My personal feelings on the Apex upper a-arm are that it should be about 7 inches long to get adequate travel.  On my a-arm mock ups, the only reliable way I could see doing this was to use holes or pockets on the inner fender that allowed moving the inner pickup to the center of the frame rail.  Then it looks more like a '90s to 2000s Mustang strut to a-arm conversion.  The parts to do this are that bad if you use circle track components, and you can source used parts from eBay for trying out different ideas.  This requires you to have access to fab equipment, so if you don't, this isn't a road to go down.

 

Cary