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2005 Mazda RX-8 - Geting A Grip On Grip - Project RX-8

Moton Club Sport dampers solve the 8’s rear grip problem.

David Pratte
Nov 10, 2011
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Modp 1111 01+2005 mazda rx 8+cover Photo 1/9   |   2005 Mazda RX-8 - Geting A Grip On Grip - Project RX-8

Hey, an actual tech story about Project RX-8! That’s right, boys and girls, the 8 is officially back in action now that the lame owner (that’s me) has finally regained enough Achilles’ tendon function to abuse it on the street and around the racetrack. First on my to-do list was to find a cure for the unpredictable rear grip I’d been fighting with at the track.

On the street, the 8’s handling and overall ride quality was excellent with BC Racing’s entry-level BR coilover system, but at the track the short rear dampers were running out of travel, which meant the rear suspension was spending too much time on the bumpstops. This resulted in an unpredictably tail-happy Mazda. After trying to work around the problem with stiffer spring rates and alignment settings (and disconnecting the rear antisway bar), ultimately we knew the only real solution was to get some dampers with more travel.

For this we turned to Moton, a company with a long and storied history in the world of motorsports (with wins at Le Mans and Daytona), opting for the more affordable but still highly sophisticated Club Sport line of two-way adjustable dampers. These bad boys have separate rebound and compression controls, where each of the seven adjustment levels result in significant changes in damping behavior. We also like the fact that Motons are capable of handling a wide range of spring rates, so you can run as mild or as aggressive a spring setup as you want without having to re-valve them or worry about them prematurely wearing out.

Modp 1111 02+2005 mazda rx 8+club sport Photo 2/9   |   2005 Mazda RX-8 - Geting A Grip On Grip - Project RX-8

As for spring rates, we opted for a middle-of-the-road approach of 700 in-lb front and 350 in-lb rear Hypercoil springs (sourced from Paragon Competition), a setup that’s stiffer than most RX-8 autocrossers use, but softer than what you would typically find on a World Challenge or Grand Am RX-8. For a STX street tire setup, these spring rates are probably a little too firm for optimal tire performance (and ride quality on the street is a bit harsher than our previous setup), but should work very well with the stickier race rubber we’re planning to use now that we’re targeting SM class for SCCA Solo 2 action and Modified/Limited class for time attack.

As some of you know, Moton was recently acquired by AST (a high-quality damper/coilover kit manufacturer from the Netherlands), but you’ll be happy to know that the Moton line, including the Club Sport, will continue to be produced under the new ownership. As Brian Hanchey from AST USA told us, “The Club Sport name is going to continue as the two-way solution for Moton. It will be made with Motorsport parts, but we felt that it had such a strong name that the brand needed to continue. We also have some exciting new changes that we will announce later this year, based on lessons we’ve learned in Grand Am and via customer requests.”

Modp 1111 03+2005 mazda rx 8+full view Photo 3/9   |   2005 Mazda RX-8 - Geting A Grip On Grip - Project RX-8

Speaking of customer requests, one thing we’d like to see is easier installation of the RX-8 Club Sport kit, since we had to do a fair bit of customizing to make it fit. Sasha from SG-Motorsport, who handled the install for us, half-jokingly suggested that Moton (under its old ownership) purposefully makes its dampers a bit tricky to install as a way of scaring away the non-hardcore. Regardless of the reason, we had to machine some height off the inner lip of the coilover collars so they wouldn’t make contact with the Hypercoil tender spring centering rings (this won’t be an issue for anyone opting to forego the tender springs and just run a single main spring). We also had to enlarge the inner diameter of the metal bushing that centers the rear dampers within the OE upper mount/shock tower to accommodate the Moton’s larger shaft diameter. Oh, and the thicker-than-OE front lower shock mounts used by Moton mean the OE bolt that fastens the damper to the lower control arm is too short, so we had to source a couple automotive-grade bolts with an additional 10mm of length.

Modp 1111 04+2005 mazda rx 8+front view Photo 4/9   |   The combination of Moton Club Sport shocks and stiffer Hypercoil springs means Project RX-8 is now cornering flatter than ever and with total composure.

It was finally time to do some track testing at the same circuit (Toronto Motorsports Park) that we’ve been evaluating Project RX-8 at throughout its upgrade process. The Moton Club Sport and Hypercoil spring combo lowered the RX-8’s best lap time by a full second, and as you can see from the data overlay from our Vbox Driftbox data acquisition system, the lateral acceleration in just about every corner showed significant improvement. The Motons were doing a particularly good job soaking up the bumps in turns 1 and 2, the fastest and also the bumpiest corners on this circuit, and the longer travel rear dampers meant the twitchy rear end was completely cured. After a few initial adjustments to damper settings to dial out a touch of understeer, the 8 was remarkably neutral and corners could be attacked with total confidence.

Modp 1111 05+2005 mazda rx 8+installed Photo 5/9   |   We routed the rear remote reservoirs through the vent in the trunk/rear fender area, which meant removing the rear bumper during installation.

All in all, we’re extremely pleased with the composed and planted feeling the RX-8 now has, thanks to the highly sophisticated damping of the Moton Club Sport kit. But we’re not done quite yet — next up, we’ll test an adjustable front sway bar along with some sticky 275/40ZR17 DOT race rubber so that we can start dialing in the 8 for some serious time attacking and cone dodging.

Modp 1111 06+2005 mazda rx 8+coilover Photo 6/9   |   The lower lip on the white nylon spring “hat” on the rear assembly needed to be trimmed by about half-inch so that it wouldn’t rub on the shock body under compression.

Sourcebox

Moton/AST USA
Club Sport Dampers
motonsuspension.com & ast-usa.com
972-424-3700
Paragon Competition
Hypercoil Springs
paragoncompetition.com
905-760-9996
SG-Motorsport
Suspension Installation & Race Alignment
sg-motorsport.com
905-463-1483

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Sources

Moton Suspension Technology Inc.
Cumming, GA 30040
770-886-8777
http://www.motonsuspension.com
SG-Motorsport
905-463-1483
http://www.sg-motorsport.com
Paragon Competition
http://www.paragoncompetition.com
By David Pratte
216 Articles

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