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Words & Photos by Stephen Bess

Building A 17.5-Class Maestro

So Associated released the B5M mid-motor car approximately, er, mid year 2014 (appropriately?), and along with its rear-motor B5 brother, both have made a huge splash in the 1/10-scale 2wd electric buggy market.  With indoor season upon us, I decided to build a B5M and race it in the highly competitive 17.5-turn “spec” class.  Having already tested the rear-motor B5 (AE B5 Rear Motor Test), I knew the B5M would offer an advantage on high traction tracks, both indoor and outdoor.  But how much of an advantage?  Here are my thoughts on the car, as it has been tested with a short but significant list of options and upgrades.

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B5M on left; B5 rear motor on right.

 

Out of the box, the B5M performs like a champ.  It needs nothing extra, especially if you race modified.  But as we know, the 17.5-turn class is one of the most competitive classes on the planet, and every teeny tiny little advantage makes a difference in lap times.  I didn’t go hog wild building my B5M stock racer using every titanium, aluminum and unobtanium expensive part on the planet—I mean, I only recently added titanium turnbuckles, after my test car’s photo shoot.   Knowing that the journey to the “perfect” upgraded and lightened B5M is an endless one down a deep, dark and expensive path, I practiced restraint and added the parts that seemed to make the most difference in lap times. Sure, there’s plenty of items on this list, but many of them are items you’ll need regardless of the class you plan to race.

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Parts List

Lunsford Punisher Titanium Turnbuckles –  Reduces weight, increases durability, added after photos were shot of this car. #2006

MIP Pucks Set – Lighter weight, rebuildable, reduces rotating mass and increases acceleration. #MIP14230
Schelle Ceramic Gearbox Bearing Set – Shocking reduction in transmission’s rotating drag. #SCH2301
MIP Lightened Top Shaft – Reduces rotating weight, improves acceleration. #MIP14195
AE Factory Team Aluminum Screw Set – Reduces weight. #91544
AE Factory Team Motor Plate – Reduces weight and improves cooling.  #91546
AE Rear Aluminum Ballstud Mount – Durability piece. #91520
AE Single Disk Slipper – Drastically reduces rotating mass (some stock racers run no slipper at all!)
AE XP 1015 Digital Servo – Fast, durable, digital.  #29167
AE Flat B5 Front Arms – Makes car less aggressive, which is helpful for my driving skills. #91398
AE B5 Front Shock Tower – To match the flat front arms. #91373
Reedy 4000mah Shorty 60C LiPo #302
Reedy Sonic 17.5-turn Motor – Plenty of RPM and torque to run silly gearing if needed. #232
LRP Flow ESC – Smooth, easy “blinky” set up, great throttle feel. #80970
KO Propo EX10 Helios Radio – A longtime favorite for oversize hands.
AKA Impact Super Soft rear tires – Used at Hot Rods when watered and high traction.  Have since installed AKA Chain Links for indoor clay track. #1310VR & #13124CR
AKA 3-Rib Super Soft front tires – Used when watered at Hot Rods.  Have since installed Evo Pinstripe tires for indoor racing.  #13201V & 13221CR

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I swapped the gullwing front arms for the flat B5 arms (with corresponding front tower) to calm the steering response.

 

PERFORMANCE

So how does the B5M perform on the track?  In stock form, it feels great but a little heavy and sluggish during acceleration when compared to a rear-motor B5 with similar gearing and running equipment.  I attribute this to the friction and driveline loss in the M’s 4-gear transmission—an unavoidable penalty for the mid-motor layout and the transmission design required to make the vehicle move forward. The B5M’s performance differs from the rear motor B5 in its ability to dive into corners, rotate through the center of the car (rather than from the rear end), and its readiness to leap out of corners.  While the rear motor car offers a traction advantage on dusty or lower traction outdoor tracks, the B5M offers a considerable advantage on high traction tracks.  The mid-motor layout creates a reactive, athletic chassis that feels nimble and, occasionally, a bit nervous.  For racers like me with “expert” level skills but not “pro” skills, the rear motor B5 offers a safety buffer when pushed too hard around the track.

Discussing the differences between the M and rear-motor B5 often results in heated, though (usually) good natured arguments in the pits.  Some racers swear that the B5M is not only the best B5 version, but they go so far as to proclaim that “you simply can’t win without the mid-motor car nowadays.”  I’m not sure I agree with that.  As many other racers point out, the rear-motor B5 is consistent, it’s more predictable, and it handles low traction surfaces better without getting too sketchy.  The B5/B5M debate popped up at least 37 times over the summer, while the debate over traction additives, dinner at Rattlers and just what the hell a “cookie experience” is rages on.

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LRP’s Flow ESC provides buttery smooth throttle response, and includes a “blinky” setting for 17.5 no-boost/timing racing. Note the blue FT alum. screws and XP servo. 

But back to the cars.  Drive clean lines in the groove, and the M is faster if you can handle it.  Fly too hot into a corner and get off the racing line, however, and the B5M will bite back with snap oversteer.  The M is less forgiving than the B5, but it’s also faster in capable hands on the right track. And on my local indoor clay track, SCVRC in Santa Clarita, CA, having the correct tire that’s properly broken-in, bagged and sauced for weeks on end to become sticky as flypaper will mean the difference between putting around the track and actually racing around the track, on the pace…no matter what buggy you drive. So put some thought into your tire selection before getting too lathered-up over the B5M’s handling characteristics.

So how did the upgrades work?  Very well indeed; the acceleration difference between the out-of-the-box B5M and my lightened, reduced rotating mass B5M 17.5 racer is drastic to the point of shocking.  The buggy accelerates hard with no hesitation, and maintains corner speed that outpaces the heavier box stock car.  As Colin Chapman of Lotus is famous for saying, “Adding power makes you faster on the straights; subtracting weight makes you faster everywhere.”  In following Chapman’s insistence to “add lightness,” the B5M’s transmission and driveline benefits in incredible ways from reduced rotating mass.  If I had to list the most important, most effective upgrades, I would list the MIP Pucks, AE aluminum top shaft, Schelle ceramic transmission bearings and the AE single-disk slipper as most vital.  Should I decide to get really jiggy wid’it, I may also install the Schelle slipper lockout to provide maximum acceleration and with maximum pucker factor for my transmission’s well being.

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Reedy Sonic 17.5 + AKA tires + FT motor plate + MIP Pucks (and lightweight MIP topshaft, hidden inside the transmission) makes for rapid acceleration.

 

I didn’t go so far as to chop up the plastic upper deck/battery holder area like many racers have done, nor did I remove the battery strap in favor of industrial strength Velcro.  I want the car to remain durable and somewhat close to stock, should I decide to convert it to modified use.  Suspension bind is a performance killer, and out of the box, AE’s new rod-ends are durable…but I’ve yet to find one (out of a B5 and B5M kit) that wasn’t bound up on the ball-stud.  AE’s Jake Mayo suggested chucking the ball studs into a drill and polishing the surface with a mild polish (I used 1200-grit sandpaper).  Once polished, the rod ends move smoothly on the ball stud; if they still bind and don’t fall under their own weight, use pliers to firmly crush the ball-end while it’s mounted to the ball stud.  This seems to do the trick every time.

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WHAT’S NEXT
At some point, I’ll install a mod and compete in the ultra fast modified class.  If you’ve made it this far into the article, I’ll also point out that my test car’s “Team Moo” paintjob is an homage to AE president Cliff Lett — he often rocked this paintjob during his racing career, so it seemed appropriate to tip our cap to him with this scheme.  As it is now, the 17.5-turn class is by far the most competitive class in my area with multiple heats and mere seconds separating the top 10.  High bite tracks tend to accentuate any set-up or design flaws, and the B5M performs its best on high bite.  This tells me that the car is solid, the design is right, and ultimately whether I finish well or not is entirely in my hands.  I’d love to blame the rare lackluster finishes on the car, but I can’t; the B5M is a refined and solid platform.  It’s up to you to get it across the line in first place.

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