TRA Thunder Shift Arms & Rollers

* Billet TRA arms with threaded holes

* Allows precise placement of mass

* Replaces existing TRA arms

* Can be tuned for maximum acceleration, mountain, or trail applications

* Rollers available in 1mm & 2mm Oversize

It shouldn’t take more than a brief moment for a Ski-Doo clutch tuner to instantly recognize the benefit of having adjustable TRA arms. It may take a while longer for a tuner to understand the benefit of different diameter rollers that can be fitted to the TRA. All of these new products are compatible with stock Ski-Doo components and the original Thunder Shift Kit (threaded and adjustable pins).

According to Thunder Products, the TRA primary works extremely well through the low end and midrange, but it tends to over shift on top end due to the amount of weight on the tip of the shift arm. When this “over shift” occurs, the rpm's are pulled down causing the engine to go flat on the power band. In other words, you lose acceleration and power. The new Thunder Shift Arms are designed to eliminate this problem by allowing you to relocate mass from the tip (pin and roller) and place it further down the arm.

Just like the Thunder Shift Kit flyweights, placement of the mass is a valuable tuning aid in getting your clutching set-up for your engine and riding application. The two threaded holes in the arms allow you to place weight via various mass fasteners (bolts) and washers (shims) of different materials and sizes. The number of possible combinations is endless, but the key here is the adjustability. You add more weight to reduce engine rpm, and subtract weight to increase engine rpm. The lower hole has the greatest affect on the first part of the shift curve, the middle hole most affects the midrange, and the (optional) adjustable threaded pins allow you to adjust the tip mass.

Even the planet’s best Ski-Doo clutch tuners recognize the benefit of having adjustable arms, especially when the adjustability is down to a resolution of about a half of a gram; The winning Stock 800 machine at the Haydays grass drags, driven by Guy Parquette and tuned by Glen Kafka was fitted with adjustable Thunder Shift Arms. Yes, they’re race-legal; a simple, bolt-in component that does not require any drilling, tapping or grinding.

Ski-Doo does have available some different mass arms for their TRA clutch. The stock aluminum arms weigh about 40 grams, and Ski-Doo also offers lighter magnesium arms that weigh about 27 grams. The Thunder Shift Arms are available in two base weights, 30 grams and 37 grams. The 37 grams arms are the ones that will work best for most common applications, where the lighter arm may be better suited for engines where lighter mass is desirable (higher RPM or lower power, such as higher elevations). Both of these arms have been pressure tested, and are said to be 4-5 times stronger than the stock arms due to their billet aluminum construction.

Most sleds will replace the stock solid pins with hollow pins and add mass to the arms. According to feedback from field-testing, the 700 & 800 Ski-Doo twins usually require an approximate 5-6 gram reduction at the end of the arm with 5-6 grams added to the highest threaded hole. The lower hole will usually use a 5.8 gram fastener. This has been a good starting point, with adjustments from this baseline. The exact combination for any given condition will always vary, but these products give the tuner a whole new world of tuning options they haven’t had before. By reducing the tip mass, the back shift response is usually improved along with the increase in acceleration; a tough thing to find these days.

Also new this season from Thunder Products are different diameter rollers that compliment the adjustable arms and pins quite nicely. They not only vary the entire shift curve due to their different diameter, but they also change the tip mass. The stock Ski-Doo roller is 10.0 grams; the 1mm oversize Thunder Shift Roller weighs 12.5 grams, and the 2mm oversize roller weighs 15.5 grams. These rollers are heat treated and bushed, and a set of three retails for $69.95.

Thunder Products also carries a complete line of adjustable flyweights for all other makes and models. Contact them at 320-597-2700 or visit www.thunderproducts.com