Royal Enfield Super Meteor / Shotgun 650 belt drive
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Zero maintenance belt drives have been readily available on production motorcycles since 1981. Quiet, smooth, no more adjustment issues, no more oily mess, no carrying chain lube on a trip, lighter, and lower long term cost due to extended belt and pulley life when compared to a chain drive.
The most common rider comment is on the smoother ride, and effortless gear shifting. This is most noticeable in on/off throttle moments, with the lack of chain snatch in transition from being fully loaded to no load. Consequently, it has less effect on the frame attitude when entering corners.
THE BELT MATTERS - A Lot:
There are a couple of Gates Poly Chain belts traditionally used in motorcycle drive applications, and RSTech uses a standard Gates 14mm pitch, high torque, Poly Chain Carbon GT belt, that is readily available from Gates Dealers worldwide. As the name suggests, this belt uses carbon fibre cords, for high tensile strength, that for all practical purposes, do not stretch.
We choose not to use the 11mm pitch, medium torque, Poly Chain belt, as this is an OEM only product, and cannot be bought from a Gates Dealer. Worldwide belt availability is important, and the rider should not be tied into buying a special belt available only from the drive manufacturer.
WEIGHT MATTERS – Perhaps most of all:
“Simplify and add lightness” is often attributed to Colin Chapman of Lotus fame, and adding weight is the last thing you want in motorcycle design - more so when that weight is un-sprung, and a heavy rotating mass on the wheel, negatively affecting both performance and handling.
RSTech values the importance of a properly engineered rear pulley that “adds lightness” and is not only less than half the weight of a cast steel pulley, but results in a final drive system that is lighter than the chain set it replaces, thereby improving the handling and performance of your bike.
Yes adding lightness costs more than a cheap iron casting, and the lightweight rear pulley is a work of art that you will be proud to have on your bike. Fully CNC machined from a solid billet of 6061-T6 aluminium, and then Type III hard anodized black. Not just a simple cosmetic coating, this results in a durable wear surface with a hardness in the mid-50s Rockwell C - the same range as high tensile steel.
No heavy, cheap iron casting on the front pulley either. The front pulley is engineered to be lightweight, and fully CNC machined from a billet of high tensile steel, and then post machining heat treated for durability on the spline drive. Rather than a cosmetic paint finish, we use a low phosphorus black zinc plating for corrosion resistance, and a hardness of 58-62 Rockwell C for additional wear resistance over that provided by the hardened high tensile steel substrate.
You have a choice of gearing when buying a RSTech belt drive kit. Most riders prefer the higher ratio, as there is little noticable sacrifice in acceleration, with the benefit of lower engine rpm at cruising speeds.
Gearing is a bit confusing with a larger number being "lower" geared – IE the SM 650 stock sprocket ratio at 2.66:1 is lower than the "16T front sprocket mod" at 2.5:1
A lower gear ratio will accelerate quicker, but top speed will be lower. At highway speeds the engine will be spinning at a higher speed, and depending how fast you are riding, you may not want to work the engine that hard for very long.
A higher gear ratio will accelerate slower, but (theoretical) top speed will be higher IF you have the HP to pull the gearing. Practically you will not notice the loss of acceleration unless really thrashing the bike, and after all this is not a drag racer. Top speed on a SM/Shotgun is usually not a consideration, and most riders, prefer lower engine speed on the highway, and a cruising rpm in the meat of the torque band.
The Enfield 650 engine has modest torque and horsepower, so gearing becomes a compromise between acceptable performance, and the ability to pull a higher gear, with ones tolerance for wringing its neck to keep up with motorway speeds in some countries.
So how does this math translate into seat of the pants riding:
km/h (mph) rpm Ratio "16T" Ratio
100 (62) 4330 4060
110 (68) 4760 4460
119 (74) 5150 TQ peak
120 (74.5) 5180 4870
127 (80) TQ peak 5150
130 (81) 5610 5270
140 (87) 6050 5670
While the “16T” gearing affect is modest, it is of benefit in lowering engine speed, and related wear. We are currently testing an even higher gear ratio for those that do a lot of higher speed highway riding, live in the prairies or desert with long flat roads, or have the extra torque of an 865 kit to pull the higher gearing.
