r/c info: nitro v. electric, 4wd v. 2wd, on-road v. off-road, failsafe, radio, NMT, hop-ups

your vote is appreciated

last update: 05.16.02

Before I discuss the specifics of HPI's nitro MT, I would like to comment on the basic questions one would have to ask before committing to the excitement of radio control nitro vehicles.

Nitro v. Electric

Nitro vehicles spew fuel and oil residue out of their exhausts, require time and patience to maintain the vehicle in proper running condition, depending on the pipe make loads of noise. Electric vehicles are cleaner, easier to maintain, quieter, and make better options for beginners. A beginner, however, should not be discouraged from owning a nitro. With diligence and practice a beginner could learn the fundamentals of r/c and have an enjoyable time doing so. Tuning, set-up, proper maintenance and care, and driving skills will all come in time. Electric is ok and fun to a point, but nitro is much more exciting.

First, I will discuss the speed. Although it may be comparable (electric motors have a linear power band that is constant whereas nitro engines have a power curve) when racing between these two in tight conditions, on big tracks the nitro will smoke an electric. Nitro engines have to rev up to get their power. Once the engine gets spinning, though, it's thrills all the way. Nitro is amazing because of the achievable top speed. Add a two speed transmission and you fly like a land rocket with ballooning tires just barely skimming the surface.

My second point regards run time and power source. Nitro vehicles use nitro-methane as fuel for the engine and also a battery pack to run the on-board electronics (servo's, receiver, fail-safe, voltmeter). A nitro owner could get away with a cheap overnight wall charger. Electric vehicles use Nicd or Nimh batteries for all of their power. Electric owners should invest in a nice peak charger to properly charge their batteries. Once a battery loses some power, its output decreases and it "dumps" making for boring runs after half of the battery is gone. An electric may run for somewhere between 7 and 12 minutes. Nitro runs for somewhere between 9 and 14 minutes. Nitro vehicles can run full power for the entire tank.

Third, the time between runs is also a notable difference between electric and nitro. With electric, not only do you have to let the motor cool, but you need to have fully charged and cooled battery packs ready. The few moments it takes to refuel and let the aluminum nitro engines cool down pales in comparison to the wait between runs on electric. Even when you have many packs you really ought to let electric motors cool for efficiency reasons. The aluminum used in nitro engines makes for fast cooling. I would recommend that electric owners invest in heat sinks to help cool the motors. Trinity makes a heat sink spacer as well as clip on cooling fins.

Not to downgrade the value of electric vehicles entirely, they make fantastic vehicles to learn on. Basic electronics, soldering, and everything about the vehicle mentioned above can be learned without the additional hassles of nitro. But a beginner should not fear a nitro vehicle, the additional maintenance and longer "learning curve" should not pose a problem to the determined r/c owner.

On-road v. Off-road

I chose an off-road vehicle and modified it to suit my on-road purposes. Off-road vehicles are much more durable and have greater flexibility when it comes to the running surface. Since I am surrounded by asphalt and concrete, on-road is the most available surface to run on. Even after my modifications, my NMT does not handle like an on-road touring car; but then again, on-road touring cars simply cannot go everywhere I can go with my stadium tuck. A rally car is a great hybrid between the on-road handling of a touring car and the off-road durability of a stadium truck. Either way, I still choose the truck for its stability and versatility. The NMT, with 4 wheel drive, is nimble both on and off road so do not be afraid of getting a truck.

2 wheel drive v. 4 wheel drive

The NMT is a 4 wheel drive truck and offers greater control and handling because all of the tires are putting power to the ground. Other trucks that offer 2 wheel drive handle much differently. Technically, a 2 wheel drive should have better acceleration than 4 wheel drive because the engine in a four wheel drive vehicle has to work harder to rotate all the tires and this is obviously more demanding than just rotating two tires. There is more friction involved in a 4 wheel drive vehicle, but this makes the handling of four wheel drive superior because of the driving tires' contact with the ground. It's a little give and take and once has to choose between acceleration and handling. With a nice performance engine, the Novarossi manufactured Evo II, I have loads of acceleration with my NMT, and I enjoy increased handling. You can always gear for acceleration. The NMT is also shaft driven. Although this is a often contested issue, the shaft drive is more durable and more efficient than a belt and pulley drivetrain. There is no contest between shaft and belts when gauging durability, the shaft is far more reliable and consistent. The belt system will strectch over time and it is also liable to get jammed with rocks or twigs and get cuts. Authority demonstrates the greater efficiency of a shaft drive over a belt drive, and most should agree that the belts produce greater friction as they pass through the pulleys.

Radio Gear

Regardless of whether you choose nitro or electric, you will need the transmitter and receiver, known as radio gear. I totally recommend FM over AM. The advantages include: stronger signal, less glitching and longer range. FM radios also come with useful features as proportional dual rates and end point adjustments. Having the ability to fine tune your servo travel is also very nice. I am using a JR XR3 radio that I think is fantastic. This radio offers great "bang for the buck." With my antenna extended, I have never gone out of range and am able to drive as far as the eye can see. Once I forgot to raise my antenna and I had a runaway. You can see photos of the aftermath on my r/c pictoral page. I would also recommend a receiver cover to protect the receiver from dust and fluids. A failsafe is also good protection against runaways, it certainly would have prevented mine. What the failsafe does is put the throttle servo to a preset position, usually full brake, whenever there is glitching, radio signal loss, or power below 4 volts.


Because the risks of injury to people and damage to property are so high, some basic measures of precaution should be exercised when operating these land rockets. There are many ways for your radio control vehicle go out-of-control and there are some safety devices that can be installed to prevent some mishaps: 1) failsafe, 2) throttle return spring ("TRS"), 3) voltage meter. Risk of injury to people and property could occur when your r/c vehicle's receiver loses contact with the radio, a failsafe would prevent this from happening. Any kind of signal loss, or "glitching" could be dangerous. When the failsafe is "tripped" it will move a servo to a pre-set condition. For nitro vehicles this would likely be full brake on the throttle servo. These failsafes also monitor the voltage and they will "trip" when the voltage goes below 4 volts. However, a failsafe will not work in the event that your batteries disconnect. For this reason, it is recommended that you use a TRS to mechanically move the carb to a closed position. A TRS need be strong enough to move the carb back, but not so strong as to over-strain the throttle servo. Another handy device is a voltage device that keeps you visually informed of the power voltage. After all, you should be aware how much power your receiver batteries have b/c this affects your servo's performance, as well as the range of the receiver.

atm92484's NMT after collision with a brick mailbox (from the HPI forum)


I think this truck is fantastic and I am entirely happy with it. Its simple complexity makes for fun tinkering. I have great handling on-road when I race r/c sedan's in parking lots, I find that I can enter and leave turns faster than sedans with wide travel. There are plenty of hop-ups for the NMT, allowing the owner to customize their truck and make it truly unique and their own. Performance improvements are also readily available. Engine options include .12 race engines, small block .15's; and with a conversion kit the NMT will also accept big block .15's and even .21 engines. I am currently running a .12 Evo II and I may consider a .21 conversion sometime in the distant future.

With my current on-road setup, I thrash the asphalt and concrete parking lots around the Chicago Loop. Lowering the truck is a necessity, otherwise you risk poor handling and high risk of rollovers. A fiberglass antenna would help protect the truck's innards, especially if you drive without the body (I enjoy watching everything on the truck do its part). Street tires are also helpful for traction. Save those pinned tires for the dirt, if you try to use them on-road you will turn them into slicks in no time.

The NMT setup for street offers greater flexibility, and durability, than typical sedans.

Top hop-ups for stock NMT:
1) air filter
2) fuel filter
3) performance clutch
4) fiber brake disk (or consider a metal brake disk conversion)
5) header (t-maxx, t-maxx big tube, or CEN)

Next 5 great hop-ups:
6) 2 speed or slipper clutch
7) tuned pipe (Associated, Paris Turbo Ring, CVEC, Novarossi)
8) titanium turnbuckles and RPM heavy duty ball cups
9) aluminum upper deck (I think this is better than the graphite upper deck, although you lose removable radio tray)
10) upgraded servo (Hitec offers the greatest "bang for the buck")

Other must have's:
11) Performance Engine (this choice starts an entirely new conversation, see my Engine page)
12) anti-sway bars
13) upgraded shock towers (preferably titanium over aluminum)
14) failsafe and/or throttle return spring
15) receiver cover


If you think the above list should include other items, then feel free to e-mail Kedar.