How fast can custom-built coil-overs at off-the-shelf prices actually be?

Andy
Update by Andy Hollis to the Mazda ND MX-5 project car
Sep 11, 2023 | Koni, Shocks, Coil-overs, RedShift Competition

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Back in the day, lowered sports car life was so much easier: Install Koni Sport dampers with lowering springs and become one of the cool kids. A lower center of gravity reduced weight transfer, and the stiffer springs helped reduced body roll while keeping off the bump stops. 

Need a little more spring? A set of Ground Control coil-over sleeves with Eibach racing springs was the answer. Need to damp those stiffer springs properly? A Koni revalve was available for that purpose.

Fast-forward to today, and coil-over options are wide open. Trickle-down from professional motorsports has pushed the high end skyward, with a plethora of choices as to capability and prices to match. Penske, Moton, Öhlins, JRZ, MCS and Multimatic can all be found on the world’s fastest race cars.

Over the past few years, however, a mid-point category has emerged. It takes its cues from the pros but uses high-volume, modular components. Cost savings in scale are passed on to consumers like us. 

The off-the-shelf versions of these overseas-produced products are typically designed for street use rather than motorsports, but there is another option: Don’t buy coil-overs. Hire a shock builder instead.

Fortunately, there are shock builders who are adept at reconfiguring these inexpensive, generic units to provide valving and range of travel more suitable for quick lap times. Their versions often have larger shafts for more fluid movement, different seals for less stiction, and non-standard body lengths to better fit a lowered application.

One such builder is RedShift Competition. Originally a Honda-oriented supplier of custom motorsports suspension products, the business expanded its offerings to include most popular vehicles. 

Critically important is the long history of direct participation and championship success in our specific disciplines–autocross and track. That’s where the know-how comes from for valving and dimensions that work right the first time. And if you still want something different after first use, revalves are also on offer. 

We first worked with RedShift owner Chris Shenefield on our One Lap CRX, replacing a set of custom high-end, triple-adjustable, remote-reservoir dampers with his single-adjust product. That change yielded better curb-hopping compliance while losing nothing elsewhere in overall pace. It also resulted in a pair of SCCA Time Trials Nationals victories. 

More recently, we decided to move our Triple Threat Miata project to a modern coil-over. While this moves us up a category in SCCA Time Trial from Sport to Tuner, our real motivation was more consistency in our tire testing program since this car serves as one of our primary test mules. 

Our home tire test track, Harris Hill Raceway, has been developing some bumps that make it more challenging to drive at the limit. This exposed a key limitation of the previous Koni-plus-lowering spring combo: compression travel. 

Since the Koni is a full-length damper designed to be run at stock ride heights–and to work for a wide range of customers–it ends up on the bump stops a lot when used with lowering springs. Flyin’ Miata cured some of that with the supplied shortened rear stops that came with the springs, but it’s really just a Band-Aid.

Keeping in mind the Triple Threat nature of the project, we wanted to retain streetability at the expense of outright max pace. So a plan was hatched to initially install RedShift dampers with valving similar to the Konis but with much more range of travel at our lowered ride height. 

 At less than $1100, our RedShift Standard street single-adjust coil-overs cost less than most other options while delivering impressive lap times. 

For springs, we first approximated the rates of the Flyin’ Miata lowering springs. We then progressively stepped up the rates until the street ride became annoying, all while maintaining the same ride height offered by the Koni/Flyin’ Miata setup. We recorded our lap times to track objective performance improvements, and we took subjective notes as to balance, clearance and ride quality with each combination. 

To evaluate fitment, we used two popular tire sets from our recent testing program: the 235/40R17 Falken Azenis RT660 and 245/40R17 Nankang Sportnex CR-S, all mounted on 17x9-inch Kogeki wheels from Flyin’ Miata. 

Our test regime included a 45-minute highway drive to the track, two or three sessions to find the performance limits, and a return trip over country back roads.

How much for these single-adjustable coil-overs custom-valved for our specific application? How about $1095 complete? That’s less expensive than the other setup and about a quarter of what you’d spend for high-end motorsports dampers. Can we go faster while spending less? Let’s find out. 

 

Round 1: Setting a Baseline

  • spring rates: 6K/4K
  • best lap: 1:26.66

The RedShift setup features adjustable damping, but we started with them at the recommended baseline setting–again, remember that comment about working with a shock builder. 

The first time on track with the new setup was eye-opening. For sure, we’d achieved the primary goal of getting the car off the bump stops. At the limit, bump/dip-induced breakaway was much more progressive, making the car more consistent–although we did have to relearn how to drive the car at the limit. 

Previously, on the Koni/Flyin’ Miata setup, we’d mildly toss the car into turns to combat the bump-stop-induced understeer. Once settled, we’d go to throttle early and hard to help rotate the car off the turn. Our fastest lap with this setup–and that’s after dialing in the fastest damper settings–was 1:26.68.

On the RedShift dampers, both compression and rebound are adjusted together with a single knob, whereas our Konis feature only adjustable rebound. Backing off compression can help soften the street ride. Photography Credit: Andy Hollis

Driving the RedShifts that way had us losing the tail either on entry or exit. With the balance shifted now to mild oversteer, we found ourselves braking a little easier and earlier, carving into the turn, carrying more speed mid-corner, and more smoothly applying throttle just a touch later on exit. It was just as fast, but it took some experimenting to get there. 

With the shock settings softened, the ride quality driving to and from the track was excellent despite the typical harshness of the 200tw Falkens.

Some spreadsheet analysis explained the balance: The 6K/4k setup delivers ride frequencies that are 16% stiffer in the rear relative to the front. This is typical for a street setup to deliver a comfortable “flat ride” over bumps, but it’s not ideal for motorsports. As a temporary fix, we disconnected our 14mm Fiat 124 rear anti-roll bar and found more neutral handling while lowering our best lap with the RedShifts from 1:26.73 to 1:26.66.

 

Round 2: Going Stiffer

  • spring rates: 8K/4K
  • best lap: 1:26.35

Looking for a more permanent balance solution, we upped the front spring rate to 8K, evening out the ride frequencies front to rear. Ride height and shock settings remained the same as before.  

The results weren’t exactly what we were expecting, as the car continued to be a little loose. The front end, however, also felt more responsive–our stiffer rate had gained us some front grip. More roll resistance was keeping the front tires a bit flatter in the turns. The car was equally quick with and without the rear bar, but easier to drive without. Most importantly, our lap times had improved by a couple of tenths.

The damper body has graduations on the threads to keep track of perch and body length adjustments more easily. We had to adjust the latter to keep static ride heights the same when fitting stiffer springs. Photography Credit: Andy Hollis

On the street, ride quality was noticeably stiffer but still quite comfortable. In fact, adjusting the damper stiffness had a greater impact than the spring rate.

 

Round 3: Even Faster?

  • spring rates: 10K/4K
  • best lap: 1:26.11

This combination delivered magic on track. Another couple of tenths were shaved off our lap times, and the balance felt perfect. At this point, we had only stiffened the front springs, and on track we still ran the initial, recommended shock settings. We did try it with the rear bar disconnected, but understeer then reared its ugly head.

The bad news came on the ride home: The ride quality had begun to veer down the race car path. It was especially noticeable in the pit of our stomach in the compression of a dip. Thump! 

The lightweight alloy bodies of our coil-overs deliver an unsprung weight savings of 2.5 pounds per corner. Photography Credits: Andy Hollis

Although even more spring rate could have possibly made the car quicker on track, we still wanted to keep it streetable. This result was not surprising–check the sidebar on ride frequencies for more details here. 

Luckily, we have a set of 300tw Continental Extreme Contact Sport tires on OE BBS wheels that provide more sidewall flex to soften things for longer-term street usage.

 

Final Comparison: Custom vs. Off-the-Shelf

We had one last question: How much further had we really come during this development work? Since this type of test program takes a lot of calendar time, many variables can creep into the results, especially weather and track evolution. 

For our final comparison–the custom dampers versus the off-the-shelf ones–we needed to run back-to-back tests on both setups during a very narrow window. 

A move to a different tire for this part of the test also necessitated the revised baseline, as we fit the new Nankangs that performed so well in last issue’s tire test. Our CR-S tires now sported about 3/32 inch of tread and were quicker than ever. 

On the RedShift setup with the 10K/4K springs and the Nankang tires, we quickly found ourselves in the 1:24 range–new territory for this car–with a fast lap of 1:24.61. The street drive also felt a bit more comfortable than before, as the Nankangs aren’t quite as harsh over road irregularities.

Once on the Koni setup, we were only able to come within a half-second of the RedShifts with a best lap of 1:25.13. That result matched the earlier long-term improvements when running on the Falkens. 

To properly clock the rubber suspension bushings during coil-over installation, it’s critical to tighten all connections with weight on the wheels. We simulate this by jacking up each lower control arm with the anti-roll bar disconnected before torquing it all down. Photography Credit: Andy Hollis

Looking at the data confirmed that the time delta mostly came during high-speed corner entry as well as a quick left-left-right sequence that delivers periods of long lateral loading with undulations challenging roadholding. The car made more peak grip on the RedShifts and kept it more consistently.

By contrast, the Koni setup was a bit better at putting down power onto the back straight exiting the very tight Turn 7. A new dip had recently emerged right at that turn’s throttle-up point, with the more tossable Koni setup allowing an earlier exit at power-up because it counters throttle-induced oversteer with bump-stop-induced understeer.

Looking for the best of both worlds, we reinstalled the RedShifts and returned to the track with a new plan: We’d finally make a damper adjustment aimed at a dynamic handling fix. 

There is slop in the front-upper control arm mounting bolts that will affect the camber settings. Using a pry bar on the front bolt while tightening will add an extra ¼ degree of negative camber. Photography Credit: Andy Hollis

That approach smoothed out the bump enough that we consistently nailed a series of our quickest laps ever, with a best of 1:24.22. Data analysis confirmed that we’d picked up the lost time accelerating down the back straight. 

Closing out this phase of suspension development, we were now setting times a full second quicker than the original setup while delivering more consistent laps–all while still sparking joy on the street. We’ll call that a win. 

Plus, we’ve yet to take advantage of the corner-weighting capability of our coil-overs, so there’s still more unlocked potential.

 

Other Options

We’ve worked with several shock builders that can provide low-cost solutions with high-performance results. In addition to their budget in-house products, most also build and service many brands of high-end shocks. They’re a great resource for explaining the differences and what the extra expense delivers.

RedShift Competition
Chris Shenefield
budget brands: Standard and RedShift Competition
redshiftmotorsports.com

Shaftworks USA 
Jonathan Lugod
budget brand: Bilanx
shaftworksusa.com

Inertia Lab
Chris Hagen
budget brand: Nitron 
inertialaboratory.com

Whitener Racing Shocks
David Whitener
low-cost bespoke Bilstein-based coil-overs; now also a RedShift dealer
whitener-racing.com

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Comments
jerel77494
jerel77494 New Reader
9/12/23 7:53 a.m.

What about FlyinMiata Vmaxx XXtreme coilovers? Or the Dekker Package from FlyinMiata (Read "Miatagasm" in Road and Track.)? Also never heard of your shock tuner, but Fat Cat Motorsports is all over the Miata forums even though their work isn't limited to Miatas.

ericwang
ericwang GRM+ Memberand New Reader
5/19/24 12:20 a.m.

Just upgrade to RedShift 8k/4k. Wondering what front sway bar are you running with these tests, and what do you recommend, stock or Karcept? 

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