mighty muscle sleds

RX-1
Grins:
Intoxicating power performance.
Groans: Suspensions are stiff and tough to tune.

What's New?
There isn't a lot that isn't new on the RX-1. The delta box chassis is constructed with stamped, extruded and high-vacuum die cast aluminum pieces. Yamaha's new vacuum die casting system allows the pieces to be much thinner than ever before, while still retaining their strength. The two nose pieces, and the front and rear tunnel pieces are built of the new material. With the engine mounted deeply in the chassis, the whole sled shows a tremendous amount of strength and rigidity.

The front suspension on the RX-1 is the first foray into A-arms on contemporary Yamahas (see Sled Tech sidebar). The setup makes use of larger, 40mm aluminum gas shocks. The new absorbers offer a greater range of valving adjustments as well as increased resistance to fade, due to their larger volume. The front suspension is rated at nine inches of travel.

Yamaha redesigned its plastic ski for the RX-1. The new ski has thinner walls for lighter weight and a deeper, narrower keel for improved handling performance in multiple snow conditions with less actual drag.

The rear suspension is the same skid as found on last year's SXViper. It has Yamaha's Full Rate Adjuster system on it to quickly change the shock and spring rates on the rear arm by relocating the forward mounting position into one of three slots. The ProAction SXV also features adjustable transfer control rods. The control rods are actually a vastly underrated tuning agent for the rear suspension. By letting out a lot of the coupling, the ride gets softer. The payment for that is increased ski lift on acceleration out of the corners. Also, the spring preload can be tuned using the spanner wrenches included in the tool kit.

The RX-1 engine represents a big step forward in the high performance snowmobile market (see Sled Tech sidebar). The inline four Genesis Extreme four stroke mill is said to crank out between 140 and 150 horsepower at its 10,000 rpm peak speed. Yamaha keeps its clutches alive by using a gear reduction system to connect the crankshaft to the primary.

The digital gauge pod is very similar to the one used on last year's Viper. In addition to speed and engine rpm, the gauge displays fuel level and warmer intensities plus the warning lights are integrated as well. Yamaha finally moved the warmer switches up to the handlebars. The hand warmers are operated from the toggle switch on left side, while the thumb warmer is adjusted on the right. A note of caution: the RX-1 was designed to have the heaters automatically default to medium hot when you start the sled. If you forget that, you could be scorched on warm days!

The RX-1 doesn't have an official dry weight as yet. Yamaha announced that it set a goal of no more than five percent over the SRX, which by our calculations is 548 factory pounds or 645 pounds based on our Shoot-Out data, with three gallons of fuel and 192 studs.

Ride Impressions
There is no getting around the fact that the RX-1 can put a smile on anyone's face. Get that sled out on a smooth lake surface, let it rip and you can't help but be intoxicated by the silky smooth acceleration. But our crew also felt it deserved some credit as a trail machine. It's not a mogul-busting ditch banger like the other new bodied performance machines, but it is good on the trail nonetheless. "All I had to do was start the engine and drive the RX down the trail far enough to squeeze the throttle to know this was a sure winner for Yamaha," said Test Rider Doug Erickson.

The RX-1 hides its weight fairly well as long as it stays behind the groomer. It can handle the bumps as well as most sleds in this class, but the hefty sled will take the wind out of all but the heartiest riders on a long run through the moguls.

The RX-1 didn't win the Ride and Comfort category based on its suspension ride; it took the class by storm with its quiet operation and smooth power delivery. "Not only is the RX-1's sound velvety and quiet, but the rear-exiting pipes leave the sound behind you when you're riding," said Test Rider Wade West. "You can still hear it running, but it doesn't penetrate your helmet with tinny twang. This is a sound for others to strive for."

The RX-1 took top honors in the Performance Feeling category, too. Our riders gave high marks for the sled's engine and clutch response as well as its throttle response. "I think the motor's the best part of this sled," said Test Rider Steve Ingram. "It is just amazing! You have to ride it to really appreciate it."

SLED TECH 2003 YAMAHA RX-1

ENGINE
This engine's pretty trick. While it is, indeed, based on the R1 bike engine, the RX-1's Genesis Extreme engine was designed specifically for snowmobile applications. It hits its peak torque at roughly 8300-8400 rpm and top horsepower at 10,000 rpm. To ensure the primary clutch's survival, the engine features a gear reduction box intermediary between crankshaft and clutch axle. The 31/37 ratio reduction unit is mounted on a rubber isolation unit, which also diminishes the amount of vibration transferred from the engine to the rest of the drive train.

Since the drive train uses a gear reduction system, the engine itself spins in the opposite direction of the clutches. The result is that the engine can be spun around, with the intake on the nose side of the sled and the exhaust exiting through individual straight pipes toward the driver. This is step one in maximizing airflow. Fuel and air are introduced through rack-mounted 37mm Mikuni constant velocity carbs. The spent gases are released through dual exhaust pipes out behind the seat. What you won't see is that under the seat itself, the two pipes cross the streams in an "X" intersection and dump into a muffler under the seat bun.

The engine uses a double overhead cam design with three intake and two exhaust valves per cylinder head. The five-valve design is where the real airflow efficiency takes place. Better airflow means better fuel economy and improved performance for the engine.
No firm data has been released on fuel mileage, although we've heard it will come in right around 16-18 miles per gallon depending on how you ride.

FRONT SUSPENSION
Yamaha brought its version of A-arm front suspension to market this season as well. The RX-1 front end features unequal-length arms and a progressive linkage stabilizer system. The unequal geometry maintains the spindle's 23-degree caster through the entire nine-inch travel stroke. Additionally, Yamaha reports that the skis maintain their ski-to-ski alignment from full extension through full compression.

A pair of 40mm high-pressure gas shocks controls the rate of travel. The added diameter increases the volume of oil the shocks hold. The more oil, the more fade resistant they are.

The progressive stabilizer features a hinged linkage arm from the lower A-arm to the sway bar. This allows each side to be quick-moving in the smaller chop, but still able to deliver a more solid response to the deeper, nasty bumps and holes of a rough trail.