Moving from autocross to time trials | Project Triple Threat MX-5

Andy
Update by Andy Hollis to the Mazda ND MX-5 project car
Oct 21, 2021

Photography Credit: Chris Tropea

Put a car on track? Yes, please. But first, our suspension and safety equipment needed some proper preparation.

We initially took our Mazda MX-5 autocrossing but soon expanded to track days. How much faster could the car go on track, we wondered, if we pushed it beyond those cone-dodging rules? And could it compete nationally? 

Within SCCA’s Time Trials program, the most streetable preparation category is Sport. It allows simple, off-the-shelf modifications that maximize track performance and safety without compromising road use. That’s where we were headed. 

 

Better Suspension

Photography Credit: Andy Hollis

Our first step was to install Flyin’ Miata lowering springs, which were developed specifically to match the damping capabilities of the Koni shocks we had previously installed. They drop the car about 1 inch and double the stock spring rate, and both changes help reduce weight transfer and the associated camber-robbing body roll. 

As a bonus, the lower static ride height moves the suspension geometry further into camber-gain territory, enabling up to 3 degrees of negative camber all around. This improves both grip and tire wear characteristics. Win-win. The combination netted a solid seven-tenths lap time improvement at Harris Hill Raceway, our test track for this project. 

 

Better Wheels and Tires

Photography Credit: Andy Hollis

Next up, we maximized the wheel-and-tire combo within the unmodified fender wells, as the Sport rules allow.

949 Racing was the first firm to develop lightweight, track-oriented wheels for this application, offering its 6UL model in a 17x9-inch ET45 size at a weight of just 15.4 pounds. When wrapped in 245/40R17 Bridgestone Potenza RE-71R tires, the combination offers maximum grip while just barely grazing the plastic fender liners occasionally. Key to this setup is dialing in about 5 degrees of caster in front, which centers the wheel in the wheel well. 

Result? Another seven-tenths improvement on track. Plus, it made the car look simply amazing.

 

Better Wheel Studs

Photography Credit: Andy Hollis

Since we often use our Miata as a tire testing mule–you saw it at work in the last issue–the OE wheel studs and nuts had taken a beating. Even with a careful cleaning and install technique, we’d broken a couple of studs and chewed up a fair number of nuts. 

The typical solution is to install ARP studs, which are stressed for racing and coated for easy nut threading. However, for this application, ARP lists only an extended-length stud designed to allow for the use of thick spacers. 

Perusing the dimensional data in the ARP catalog revealed a shorter option (part No. 100-7726) designed for GM cars which turned out to work perfectly. This stud measures 5mm longer than stock, providing full thread engagement, and has a bullet nose for easy starting. We paired these with a 50-count box of Gorilla-brand M12x1.5 nuts purchased through Amazon, so we now simply throw away nuts that start to get cranky.

 

Better Anti-Roll Bar

Photography Credits: Andy Hollis

Our final suspension move was mostly for rules compliance. To mitigate cost concerns, the SCCA Sport category limits anti-roll bar replacements to stock-style units. As a result, the splined Karcepts bar in our car had to go. 

We replaced it with a Progress front bar sourced from Good-Win Racing, along with a Megan Racing rear bar purchased on eBay Motors. These provide similar roll control and adequate adjustability–we typically run both ends full stiff–with zero maintenance.

 

Better Brake Pads

Photography Credit: Andy Hollis

As cornering speeds increased, we looked to fine-tune our braking setup. Having had good luck with pads from Pagid Racing in our earlier setups, we explored other options in that line.  

In particular, we looked for more front bias than provided by the RSL29/RS44 combo we had been using. Swapping the fronts to the Global MX-5 Cup-spec RST3 provided a much more stable corner entry phase when trail-braking. In addition, these pads are available at great prices from Mazda Motorsports. The downside of this combo was some nasty squeaking on the street; plus, the RS44s didn’t last long on the rear. 

Moving to Pagid’s endurance line cured both ills, so we’re now running RSL1 fronts and RSL29 rears. On the track, the car became much easier to drive hard into certain tricky corners, allowing for consistent dips into the high-1:25 range. Our developed ND2-chassis MX-5 now lapped the track nearly 10 seconds faster than our stock ND1, with 1.6 seconds of that achieved by stepping beyond the autocross rules.

 

Better Safety

Photography Credit: Andy Hollis

We’ve always been comfortable pushing the limits at Harris Hill Raceway. The facility boasts ample runoff, and we’ve run thousands of laps there. We also typically run sessions with very few other cars on track, most of them familiar. 

Competing around the country in a time trials format, however, introduces a lot more variability regarding tracks and traffic. The Miata’s OE rollover hoops seemed woefully inadequate for high-speed risk mitigation, as they were basically a pair of unsupported, butt-welded loops covered in plastic. 

First to market with an effective roll bar for the ND was Blackbird Fabworx with its RZ design, which maximizes main hoop height while still fitting under the stock folding soft top. The brand also offers a GT3 design for even more protection in an open-air race car configuration.

Installation of the Blackbird Fabworx bar requires removal of some plastic trim, which can be refitted with minor modification to provide a more finished look. We chose to leave off the plastic bits–as allowed by the rules–for both the weight reduction and the eventual return to stock when we sell the car. 

Sport rules also allow for race seats, which would move the driver’s helmet farther below the roll hoop, but this conflicted with our street comfort requirements. Fortunately, we ordered our ND2 Miata with the Recaro seat option, providing similar levels of support but with ample cushioning. We then installed a lowering bracket from Aurora Auto Design, which dropped the height by an inch while still providing adjustability. 

 

Better Results

Photography Credit: Chris Tropea

Our competition results speak for themselves, as the car has been undefeated in SCCA Time Trials competition for three years. That includes a win in Sport 5 at the 2019 Nationals and a still-standing track record for the class at NCM Motorsports Park. 

The car also continues to deliver some amazing drives on twisty roads, all with a low cost of consumables. And while it’s no longer configured to win national autocrosses, strong regional results are attainable in the STR class.

 

Triple-Threat Project Lap Time Recap

The project started with an early ND-chassis Mazda MX-5, but when Mazda added more power to the model for 2019, we switched horses. Concentrating on suspension plus that power boost helped us shave nearly 10 seconds from our Harris Hill Raceway lap times. 

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Comments
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jerel77494
jerel77494 New Reader
10/20/21 3:56 p.m.

Any reason why you didn't go with the sway bars FM designed?

Andy Hollis
Andy Hollis
10/22/21 7:11 a.m.
jerel77494 said:

Any reason why you didn't go with the sway bars FM designed?

Progress makes the stiffest front bar available in the OE style (per the rules).  Very similar range, albeit less granularity in adjustment, as the Karcepts bar we had been running for autocross.

The rear FM bar is too stiff for our liking.  The Megan bar is about halfway between the stock bar and the FM.

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