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How to Install a Big Wheel Kit

Regain horsepower with a do-it-yourself install
Rotating mass, combined with friction and tension, robs precious horsepower. Sometimes, when tension is coupled with a fast rotating rear axle wheel, slowing this rotation may return some lost horsepower. There is a limit, however.

Big wheel rear axle kits are popular for those who understand rotating mass and free rotating tracks.

An ultimate ratio between the front track drivers and the rear axle would be 1-to-1. However, having rear axle wheels the same circumference size as the front drivers will pose a problem- track tightening and stretching.

In a matter of definition, as the suspension collapses under the tunnel, the track tightens- sometimes immensely. If the track has to rotate and flex around an overly large wheel, this problem is compounded as the suspension collapses. This is one reason why a track must run fairly loose.

Think about it, if you as a driver are whipping moguls and driving through every compaction, the track tightens and strips your sled of horsepower; your sled's potential is not realized. On this basis, you need exists to claim, as close as possible, that 1-to-1 ratio while not pulling the track too tight.

Big wheel kits try to close that gap- delicately. Basically, by reducing the effort- and radius- a track turns around the rear axle wheels, a higher and quicker track speed is obtained.

Two kits American Snowmobiler learned about were Tri-City Polaris and Fett Brother's big wheel kits. TCP's kit mates to a Polaris. Fett Brothers produces kits for all brands. Installation for the two appear to be very similar. If choosing these kits, or others like them, consult the builder, designer or manufacturer as to what diameter wheel kit will work best for your sled's application as relates to its drivers and track.

Installing kits such as these are not a huge time commitment, nor a technical undertaking. Expect to plunk down about 200 bucks and, if more than adequate with tools, an hour's worth of time.

On American Snowmobiler's Polaris 800 RMK 151, we installed TCP's kit. As mentioned, we discussed this matter at length with Bill Fett, who provided us information about how to install his kit.

TCP replaces the Polaris stock axle and 6 1/4-inch diameter wheels with new 7 1/8-inch diameter wheels. The kit consists of four new 7 1/8-inch wheels with bearings, four CNC-machined offset aluminum axle blocks, spacers and an axle.

We at American Snowmobiler, void of a high-lift table/jack, rolled our RMK on its side and went to work. Here in step-by-step instruction, is the sequence needed to place a big-wheel kit on your trail or powder rocket.

1. If rolling the sled on its side, turn off the fuel to the sled's motor.
2. Loosen the rear axle's center bolt.
3. Loosen the rear axle's track alignment bolts to give the track its greatest flexibility.
4. Loosen or disconnect the rear suspension's load/torque springs, if required for your specific brand.
5. Lay down a carpet on either side of the sled to protect the snowmobile's belly pan and hood.
6. Roll the snowmobile on its side, or raise the rear up on a lift or jackstand.
7. Loosen and remove rear suspension mounting bolts and brackets.
8. Slide suspension out, or drop from under tunnel.
9. With rear axle center bolt loosened, remove center bolt and remove axle.
10. Assemble big wheel kit.

Note: Some big wheel kits contain
three or four axle wheels. Some will have a center offset axle to allow the axle to sit in-center as the original OEM axle.

1. Install kit and slip rear axle mounting bolt through the axle center.
2. Slide suspension back up into tunnel and insert mounting bolts through mounting brackets.
3. Reconnect or replace the rear suspension's load/torque springs, if required for your specific brand.

Once the snowmobile's big wheel kit is installed, take the time to properly adjust and align the track to a proper setting. Here is the sequence.

1. Measure the distance between the track clip and the hyfax. Take this measurement approximately six inches in front of the idler. Repeat for the other side.
2. Ensure the axle idler wheel axle mounting bolts are loose, if not loosen.
3. If one side has a wider measurement, loosen the opposite side idler tension bolt. (The converse holds true for the narrower measurement, tighten the opposite idler adjustment bolt).

4. Return the motor's fuel supply valve to its flow through position.
5. Start the snowmobile, throttle up the engine to spin the track.
6. Retake the measurements and repeat steps 1 through 3 and 5 as necessary.
7. Once the measurements are equal, check track tension by lag at mid-point from the bottom of the hyfax to the track. If greater than one-half inch, the track is too loose. If less than one-half inch, it's to tight.
8. Turn the idler tension bolts in or out, according to need. The bolts must be turned in or out equally, one turn for one turn. If not, alignment is sacrificed.
9. Look through the track window to ensure the rails are evenly spaced to the hyfax clips on each side.
10. Repeat steps 6 through 9 until tension matches manufacturer's recommendations, as recorded in the operator's manual.
11. Tighten the axle bolts.
12. Tighten adjustment bolts and nuts.
13. Place the snowmobile on the ground.

For current pricing and model availability of Tri-City Polaris' big wheel kit call 801/298-8081 or log on to You can call Fett Brothers Performance at 218/334-FETT (3388) or log on to
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