46 RCCar Action.com
Geared for Speed
All 4-Tec models roll out of the box geared for all-around action, and get an extra
gear ratio in the accessory bag just for goin’ fast. The difference in ratios between
the brushed and brushless cars, and between the stock and “speed” gears, is
pretty interesting. Check it out:
The 4-Tec VXL gets Traxxas Stability
Management, which comes in very handy
when you’re shooting for 70mph. TSM
can be dialed up or down or switched off
completely right from the radio.
The Traxxas Link app connects instantly for tap-and-slide
adjustability of all the radio’s tuning functions, model memory,
telemetry, and more.
The Bluetooth module plugs into the back
of the TQi. It’s the best $30 you’ll spend
on a 4-Tec (or any other TQi-equipped
The 4-Tec 2.0 comes with either a standard TQ radio or the Bluetooth-ready
TQi transmitter, depending on which model you get. The 4-Tec VXL chassis
and Ford GT RTR get the TQi, the brushed-power chassis and Mustang GT RTR
get the plain TQ. Set aside an extra $30 for the Traxxas Link Bluetooth module,
which installs in ten seconds to make your phone or tablet a high-res display and
interface for the TQi via the free Traxxas Link app , available for iOS and Android
devices. You can choose what to assign to the radio’s Multi-Function knob, set
sub-trims and endpoints, adjust “sensitivity” (aka exponential), and set
steering and throttle rates. Plus, you can manage model memory,
operate the Traxxas Drag Timing System, display telemetry
data on a virtual dashboard… it’s a powerful system.
When the pinion is nearly as big as the spur
gear, you know some serious velocity is
about to go down. This is the VXL’s “speed
gearing,” a 35T pinion and 55T spur gear.
The VXL model gets the same motor plate and 70 T spur gear as the Titan-powered cars,
but the pinion is a 29T—that’s an 8-tooth jump up from the brushed 4-Tec.
The VXL’s “speed ratio” is twice as tall as the brushed car’s stock ratio—that’s a
big gear. If we factor in the 4-Tec’s 2.85:1 drivetrain ratio and 68mm tire diameter
(I’ll spare you the math), we get a “rollout” of 48mm. That means for every
revolution of the Velineon 3500 motor, the 4-Tec VXL (with
speed gearing) covers a tick less than two inches. At the
motor’s peak speed of 50,000rpm, that works out
to 1.5 miles per minute, or 90mph! That doesn’t
account for drivetrain friction, rolling resistance,
and aerodynamic drag, however—that’s how
20-ish mph gets scraped off for a final top
speed of 70+mph.
4-Tec Brushed 4-Tec VXL
Stock gearing (pinion/spur) 21 / 70 ( 3.33:1) 29 / 70 ( 2.41:1)
Speed gear (pinion/spur) 25 / 70 ( 2.8:1) 35 / 55 (1.57:1)