Going Faster With Upgraded Brakes | Project Triple Threat MX-5

Andy
Update by Andy Hollis to the Mazda ND MX-5 project car
Apr 14, 2021

Photography Credit: Ann Hollis

Mazda really got it right in offering the Brembo brake package on the 2016 MX-5 Club. For track use, it’s perfect. 

This setup can handle the heat of hard track lapping without fading, yet it’s docile enough to run every day on the street. Give some credit, though, to a high-performance Ferodo pad that’s more than twice the size of the standard piece.

After pushing the original pads more than 6500 miles–a large percentage of them racked up around a road course–the wear on the friction surface was quite even. That suggests optimal use of the available friction surface beneath those big four-piston fixed calipers.

 

More Stop

When it came time to replace the pads, we looked for additional performance. As we got faster in the car, and especially once we fitted stickier tires, we found that it took every bit of leg effort we could muster to generate braking forces hard enough to engage the antilock brake system. This was mostly an issue on the track, but it also showed up on autocross courses, where we’d have to bleed off 20 to 30 mph within a very short braking zone. Given that effort level, consistency often suffered. Can we do better? You betcha.

Pagid is a well-known name in Europe’s racing and high-performance circles. Recently they’ve been making inroads into North America at both the professional and amateur levels. Mazda even partnered with Pagid when developing brake pads for the latest Global MX-5 Cup cars, so using the brand’s brake products seemed a natural path for our own project. Further, we’ve had very positive experiences running Pagid pads on our McLaren 12C in the Tire Rack One Lap of America.

At big tracks with long straights, the heavier and faster the car, the more energy the brake pads must dissipate. A larger pad can absorb more heat from that dissipation than a smaller one, but ultimately the compound used must be able to tolerate that heat without fading. Such high-temperature friction materials typically have a more narrow operating range, and they don’t work well at the lower temps encountered during street use. Racing pads that do work at street temps often do so at the expense of rotor life.

Fortunately, our MX-5 is very light and the engine is not that powerful. Plus, the car handles so well that its corner-entry speeds are frequently higher than those of most other cars. As a result, the extra-large brakes can easily dissipate the typical braking zone energy using something short of a full-on racing pad. But the dizzying array of available compounds can be a challenge to navigate. So we asked for help.

Our MX-5 Club came standard with big Brembo brakes up front. Swapping to Pagid pads all around brought them to their full potential. Photography Credits: Andy Hollis

Pagid suggested that we use a split combination: their RSL29 on the front and the RS44 on the rear. The former is a track-day favorite for a variety of cars, as it features a strong initial bite, a wide operating temperature range and good modulation. It’s also easy on the rotors. 

Pagid has found that MX-5 rear pads operate about 100 degrees cooler than the fronts, so the higher friction ramp-up of the RS44 balances it well with the RSL29 fronts. This was the setup used on the front-running Freedom Autosport MX-5s campaigned in the Continental Tire SportsCar Challenge in 2016.

Installation was straightforward and took only an hour. At the front, two pins plus a sprung retaining clip secure the pads. A punch and a piston clamp tool make this job easy.

The rear caliper is a standard MX-5 single-piston floating design–painted red to match the front Brembos–that is held together by two bolts. The only tricky part involves making room for the thick new pad: A caliper retraction socket is used to wind the self-adjusting piston back into the caliper. These sockets are commonly available at auto parts stores and fit a wide variety of applications.

Pagid’s website details a fairly involved bedding-in process for their pads. However, it’s mostly for their high-end, professional race products. which take quite a bit of temperature to bed. We were advised to simply do two or three laps at the track, steadily increasing the pressure applied during braking events. The final few braking zones should be at full race pace, they said. 

We felt the pads come in fairly quickly, as pad material was transferred to our rotors. Then we experienced a slight pad fade after a few laps due to final outgassing. Cooling to ambient temps completed the process.

Results? We love these pads. 

While our lap times did not drop appreciably–tire grip is our limiting factor–they have become much more consistent. Braking effort is now reduced substantially, so modulation over the bumpy surface of our usual haunt, Harris Hill Raceway, is easier. Specifically, we are now better able to trail-brake after long straights and carry speed through the early parts of those turns.

On the street, even in cooler temps, the pads work similar to an OE setup but deliver higher grip. While they’re not overly grabby, we have had to alter how hard we pressed the brake pedal so as not to stop short at traffic lights. We have not yet tried the pads around cones, but we’re confident that they will meet those needs as well. Our triple-threat MX-5 just got a whole lot more threatening.

 

More Go

Our SCCA Street class rules don’t allow much room for adding massive power, but they do contain one opportunity for increasing speed: a provision that allows the wheel diameter to go up or down by 1 inch.

The postscript to that statement is the fact that our MX-5’s short gearing required some shifting back and forth between second and third gears on many autocross courses. So, we wondered, would a shorter or taller tire allow us to shift into third and leave it there? 

Our preliminary conclusion–detailed last issue–found that running the short 205/45R16 tire on super-light wheels was indeed effective in that regard, but only with the right course design. Further, shifting proficiency was a key ingredient in that mix.

Last month’s issue also contained a teaser. In the test of the new Continental ExtremeContact Sport, we used the Bridgestone Potenza RE-71R as a control tire during our autocross laps–in two sizes. 

We again tested that tire in 225/45R17 and 205/45R16 sizes in order to get more data. This test, we reasoned, would be even more focused and controlled than our original shootout. 

We did this second short-versus-tall comparison in two phases. The first was simply to see if the taller, 225mm tire provided any more pure grip than the shorter, 205mm tire when both were mounted on a 7-inch-wide rim, the max the rules allow. 

The MX-5 Club also comes standard with 17-inch wheels but on the right course, shorter 16s can be an advantage. Photography Credit: Ann Hollis

For this test, we timed each combination around the skidpad–the same way we typically test for optimal inflation pressures. We also did sweeps on pressures to see if perhaps some speed was hiding somewhere. Would lower pressures help the 16’s short sidewalls? Did the taller 17-inch tires need more air? 

What we found was that the 16s had a nice sweet spot right at 28 psi that was a touch faster than anything the 17s could muster. And while we could somewhat alter the feel of the 17s with more air, it made little difference in lap times.

For the second phase, we set out to dodge some cones using our standard test course: a five-cone slalom down one side and three offsets down the other, connected at each end by a pair of on/off-camber sweepers. The speeds on this layout are low enough to stay entirely within second gear on both setups. And since acceleration runs are few on this course, we’d be testing pure handling and responsiveness. Results would be measured in lap times, but we’d also collect subjective performance impressions.

A second driver–multi-time SCCA Solo National Champ David Whitener–took turns behind the wheel to add veracity to our data. Up until this test, David had little time behind the wheel of an ND-chassis MX-5 around pylons. As usual, though, he quickly adapted. As expected, his run times show a little more improvement throughout the course, so think of him as a guest driver who was there to confirm the easy time gains and differences in feel.

Our test format again used a pair of laps to total one run. It’s an easy way to quickly duplicate the typical 60-second autocross run using our limited space and easily driven course. Pressures were reset after each run. 

Since we were piggybacking on our Michelin versus Continental test, there were actually five cycles driven in an A-B-C-D-A pattern, only three of which matter for this particular story. Given the extra time in between the back-to-back A-B and the final bracketing retest of A, some improvement simply due to driver learning and surface cleanup is to be expected.

The SCCA Street-class autocross rules allow a one-inch increase or decrease in wheel diameter. Since tire sizes are wide open, the change in overall diameter can be significant.

 

Conclusions

So what did we find? Both drivers reported similar subjective impressions. The taller, 17-inch combination was vague in feedback and less precise. The shorter 16s were much more willing to quickly change directions through the slaloms and could run at smaller slip angles. As a result, both pilots drove their best laps on the shorter tires. The time deltas were not huge, but they were consistent. Adding these new results to last month’s, we now know the following: 

1) On a 7-inch rim, the 205/45R16 tire delivers slightly more grip than the 225/45R17.

2) When no shifting is involved, the short-sidewall combination is slightly quicker on a balanced handling course.

3) On courses featuring significant acceleration runs, the shorter combination is significantly quicker.

4) All of the above can be negated through too much sloppy shifting.

Bottom line: We’ll be carrying two sets of wheels and tires with us for competition events. Why? Two reasons: to build up our gear-changing proficiency and to improve our ability to predict course speeds and optimal shifting patterns. Stay tuned as we continue to squeeze more and more performance from our triple-threat MX-5.

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