LOSI PROMOTO-MX 1/4-SCALE R/C BIKE

BEHIND THE WHEEL: A TWO-WHEELED OFF-ROAD TESLA

LOSI PROMOTO-MX R/C BIKE

Q: WHAT’S A LOSI PROMOTO-MX RTR?

A: Losi is one of America’s premiere radio-controlled car and truck manufacturers, and now Losi revolutionizes the radio-controlled motorcycle with the introduction of the Promoto-MX RTR 1/4-scale with MS6X technology. MS6X stabilizes the two-wheeler with a 22,000 rpm gyro mimicking a motocross bike’s flywheel inertia, and the gyro is placed exactly where an MX bike’s flywheel goes. Losi partnered with Spektrum for the SPMXMXA1 Firma 2700Kv gyro and SPMXSM3200 Firma 3800Kv electric motor, which rides above the gyro, and they’re connected to the Spektrum DX3PM transmitter and SR6300PM receiver. The transmission drives a 10-tooth countershaft sprocket and a 36-tooth rear sprocket via a 70-link drive chain. Spektrum’s Smart Charger communicates with and charges a Smart G2 5000mAh Li-Po battery, and the DX3PM transmitter changes frequencies when there are other Promoto-MXs nearby. All this makes the R/C ultra-controllable at low and high speeds over rough terrain.

There are three versions of the Promoto-MX – a #1 Pro Circuit Kawasaki with a Mitch Payton rider, a #6 FXR/Club MX Yamaha with a Jeremy Martin rider, and a #23 Honda with an HRC Chase Sexton rider. Only the Pro Circuit bike is truly RTR with an included Smart charger and battery. Each Promoto-MX comes with a works stand, a launch gate, chain-adjustment blocks, spacers and some spare parts, and tools for tearing down and tuning the forks and rear shock. The blue and red versions come with everything except a charger and battery. MSRP’s are $600 for the Pro Circuit and $549 for the other two.

 

Q: HOW DOES THE LOSI PROMOTO-MX RUN?

A: It is unbelievably fast! Pull the trigger, and the bike digs a trench with its branded Dunlop Geomax MX53 rear knobby on a spoked wheel. It’ll flip over on its back if you apply too much throttle too quickly with hero dirt, and you have to be careful even in slick conditions. The Promoto-MX has three drive modes – dirt, street, and wheelie – that are chosen by an up-down toggle on the transmitter. Dirt is an unrestricted full-power mode, while street detunes power to keep the ride level. Wheelie mode uses sensors to modulate power for riding extended wheelies. It sounds cool, but both wheelie and street modes cut power up hills and jump faces, which messes up your momentum and lap times. Use dirt mode.

LOSI PROMOTO-MX R/C BIKE

Q: HOW DOES THE PROMOTO-MX HANDLE?

A: Beautifully. Other firsts for this innovative R/C bike are direct steering and a servo-controlled cable front disc brake, which backs up the electronic rear-wheel engine braking. Past R/Cs actually moved the front tire off-line to lean the bike into turns, and it’s up to the driver to power around the turn and maintain balance. The Losi has triple clamps, but they’re reversed with the headset ahead of the fork tubes, and the servo has a built-in servo saver to insulate impacts from the servo. It also has damping in the headset to prevent crash damage from collisions and endoes. Steering is actually reversed; turning the steering wheel right turns the forks left and visa versa – it’s called “counter-steering.” Under power and braking alike, the bike slides around turns with the flywheel maintaining balance.

Adjustable outriggers with wheels help a downed bike stand up via an 180 or 360, and the transmitter has a switch for more experienced drivers to make it steer like a full-sized bike. There are also front-brake trim and throw adjusters on the radio, and the aluminum front brake rotor floats on the wheel. The plastic caliper has a plastic piston inside, and the inner bore is threaded so the piston applies pressure on the brake pads when the cable is pulled.

Losi recommends doing figure 8s on level ground to get the hang of turning, braking, and accelerating. Once you get the hang of flicking the wheel to create leans for turns and then standing the bike up with throttle, hit the track! We found that keeping a quarter throttle on downhills works best, and then letting the suspension take a set with half throttle on exits before pinning the trigger to full throttle creates the best lap times. Full throttle, full brake, and turn in with half throttle. Repeat. For jumps, brake as you approach, then hit the throttle up the face. Yes, you can even drop the front end in the air by hitting the brakes. Sometimes, too much throttle on turn exits will set up a tank-slapper wheelie.

LOSI PROMOTO-MX R/C BIKE

Q: HOW IS THE SUSPENSION?

A: It’s really good right out of the box, and the rear shock has a rising-rate linkage like most MX bikes. After a few batteries, we dialed in a turn of preload on the shock spring as the spring settled a bit. Yes, the shock and forks have internal damping and steel springs, and the excellent manual has optional fork- and shock-spring kits for tuning. There are different viscosities of shock oil, and the shock comes stock with 45-weight. There are also spacers for adjusting fork ride height and travel, and there are optional Pro Line Supermoto tires and wheels, so the Promoto-MX can be road raced or dirt tracked with shortened suspension. Overall balance between the forks and shock is good, but it’ll endo if you don’t set up for jumps properly (brake then gas up the ramp). It’s by far the best R/C bike suspension ever.

Q: WHAT DID WE HATE?

A: The hate list:

(1) Cheesy thin decals. The rear fender sticker was toast halfway through the very first battery. Endoes wipe out the rear and front fender decals quickly. I tried protecting them with Upgrade clear vinyl, but it was no use.

(2) The rider. Like a doll, the rider has a head and arms that plug into the rubber torso with foam inside, and a dowel holds the torso and lower body on the seat. Three of my friends have Promotos, and two have completely lost their heads. Endoes create tears in the back of the neck, and the head will eventually break off. Shoe Goo it on when it cracks. Also, dowels on the foot pegs hold the rider on, and the rider rides on arches, not the balls of his feet. Dragging in turns will wear holes in the toes of the boots. Drill out the boots so the rider is on the balls of his feet.

(3) Weight. The Promoto-MX weighs 7.7 pounds in RTR form, and adding billet bling makes it even heavier. The tandem electric motor stacked over the flywheel with the rubber rider on top gives it a top-heavy feel.

(4) Front brake. Dust gets past the foam donut on the brake actuating piston and causes the front brake to stick on, trashing handling. Take the piston out and sand down the casting edges in the grooves and around the piston. Grease very lightly and reassemble, turning the piston so brakes drag slightly, then back off a hair and tighten the hex bolt.

(5) Rear fender. Losi designed a two-piece rear fender that flips up during wheelies and endoes, so it skids on a wheelie bar under the fender. The front piece is too thin, and so is the rear piece. These need to be thicker for durability. Todd strengthened his by placing Jammer (1/10th-scale truck) shock pistons on the mounting screws; the  pistons even have holes like factory bike washers.

(6) The RTR charger. As great as the cover line “Mitch Payton rides again” sounds, the RTR charger that comes with the green bike takes 6-8 hours to charge one battery, and the optional S155 Smart charger ($60-$70) only takes an hour at most. There are also three battery options – 30C, 50C, and 100C – and we couldn’t tell the performance difference between the $45 30C and $55 100C.

(7) Durability. Two of our four Promoto-MXs have lost the right footpeg in crashes; the mounting screw ripped out of the case, and we replaced them with washers and Shoe Goo strengthening the case. Two have blown the chain-side swingarm pivot bearing in less than 100 batteries.

Losi Promoto MX

(8) The linkage arm bolt (left). On two of four Losi Promotos in our crew, the stepped linkage-arm bolt snapped (center), and we had to drill out the threaded portion and brass insert to fix it with an 8-32 screw (right).

LOSI PROMOTO-MX R/C BIKE

Q: WHAT DID WE LIKE?

A: The like list:

(1) Branded Dunlop MX53 tires. As you can see in the photos, the awesome MX53 tires are slightly out of scale, but they provide great traction, even worn down to nubs. This thing digs trenches.

(2) Power. This thing is a two-wheeled Tesla. Power is plentiful and it spools up quickly, so you really have to apply the throttle smoothly to set the suspension for full throttle.

(3) Life-like handling. I wasn’t going to buy one until I saw what Todd, a pro-level R/C car racer, could get it out of it. Power-slide out, brake-slide in; the Promoto-MX makes you a better rider.

(4) Tunability. The manual lists four gearing options for the transmission primary gear, plus you can tune the forks and shock with different springs and shock oil. Racers can lower suspension for Supermoto and road racing, and there are optional Pro Line MX and Supermoto tires. Losi also has a carbon-fiber inner chassis.

(5) Customization. Losi has billet-aluminum upgrades for a full works-bike treatment with color co-ordinated plastics, hubs, triple clamps, fork lugs, calipers, and foot pegs. They also have billet aluminum swing arms, linkages, and chain-adjuster inserts and titanium suspension pins. Losi lists Hot Racing billet aluminum options as well. The aftermarket is all over the Promoto-MX, and FXR will customize rider gear with your favorite rider’s name and number. James has a full-on Jett Lawrence replica, and he feels the extra weight of billet helps handling and tracking.

LOSI PROMOTO-MX R/C BIKE

Q: WHAT DO WE REALLY THINK?

A: Where past R/C bikes were only good for Supercross stadium parking lots, Losi has created a true scaled-down motocross bike that can shred in the dirt and on Supercross-style MX tracks. It rips, blows up berms, and jumps like the real thing, because it is the real deal. It takes a few batteries to get the hang of it, but once you do, it’s a total blast. As I write this, I’m too banged up to ride my YZ400F or KLX450R, so a couple of good motos with my J-Mart FXR/Club-MX Promoto-MX will peg the fun meter. It’s the best R/C dirt bike ever made, and I’m working on making it better yet. Stay tuned; see www.horizonhobby.com.

 

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