Installation of 47-Tooth Rear Sprocket


Having been pleased with the responsive feel and performance enhancement provided with the 15-tooth front sprocket I decided to go even further and install a 47-tooth rear sprocket in addition. This is larger by three teeth over the stock 44-tooth rear sprocket.

47 teeth is the largest size that can be installed with the smaller front sprocket and still maintain the use of the stock 116 link chain. The stock chain can be used with a two-tooth net increase. I went down one in the front and up three in the rear for the two-tooth change.

With the combination of the smaller 15-tooth front sprocket and the larger 47-tooth rear sprocket the final drive gear ratio is increased from the stock value of 4.348 to 4.954. This has the effect of increasing the engine rpm at all speeds in all gears.

primary reduction ratio = 68 / 43 = 1.581 (internal transmission gears)

secondary reduction ratio = 44 / 16 = 2.750 (44 = teeth on rear sprocket, 16 = teeth on front sprocket)

Stock final drive ratio = primary reduction ratio x secondary reduction ratio = 1.581 x 2.750 = 4.348

Modified final drive ratio = 1.581 x (47 / 15) = 1.581 x 3.133 = 4.954 (47 = teeth on larger rear sprocket, 15 = teeth on smaller front sprocket)

Approximate Engine RPM in Gears (Stock / 15-47 Sprocket Combination)
Speed (mph) 1st Gear 2nd Gear 3rd Gear 4th Gear 5th Gear 6th Gear
203000 / 34002200 / 25001800 / 21001600 / 1800------ / 1700------
304500 / 51003300 / 38002700 / 31002400 / 27002200 / 25002000 / 2300
406000 / 68004400 / 50003600 / 41003200 / 36002900 / 33002700 / 3000
507500 / 85005500 / 63004500 / 51004000 / 45003600 / 41003400 / 3800
609000 / 102006600 / 75005400 / 61004800 / 54004300 / 49004000 / 4600
7010500 / ------7700 / 88006300 / 71005600 / 63005000 / 57004700 / 5300
80------8800 / 100007200 / 82006400 / 72005700 / 65005300 / 6100
90------9900 / 113008000 / 92007200 / 81006400 / 73006000 / 6800
100------11000 / ------8900 / 102007900 / 90007100 / 81006600 / 7500

At all road speeds, the engine operates at even higher rpm's where even more power is available for even better acceleration. Also, because of the torque multiplication effects of transmission gearing, the modified gear ratio has the effect of increasing the effective rear wheel torque even more by a computable amount:

Rear Wheel Torque with 15-47 Sprocket Combination = Rear Wheel Torque with Stock Sprocket x (16 / 15) x (47 / 44), or, a 13.94% increase.

Note that this does not theoretically increase the power at the rear wheel. At each engine rpm the shorter gearing increases multiplied torque at the wheel but also decreases the wheel rpm in the exact proportion to maintain the identical power value. This is also not a reference to the 'Rear Wheel Torque Curve' which is a measure of the engine's ability to deliver torque to the rear wheel independent of the torque multiplication effects of the transmission.

Fuel economy will be reduced by about 10-11%

A Theoretical Performance Comparison Table is shown here. The striking thing is the roll-on times, faster than an R1 and nearly as quick as a GSX-R1000.

The larger sprocket costs about $60 and is available from Sprocket Specialists, Part #336-47 for the 530 chain. I ordered the optional hard anodizing (Titan Tough) for an additional $10.

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Due to the way that the speed sensor is used to compute road speed, by measuring the countershaft rotational velocity and using the known stock secondary reduction ratio and rear wheel size to convert that to miles per hour, a speedometer error due to the two-sprocket combination reading high by about 14% is introduced. This is in addition to any existing stock speedometer error. This is corrected by using the Yellow Box.

The larger rear sprocket more than cancels out the 5mm wheelbase increase of having the smaller front sprocket alone. The wheelbase is now actually 8mm less than when stock.


Place bike on centerstand

Remove Rear Wheel

Remove Stock Sprocket from Wheel

  • Remove self-locking nuts in a criss-cross pattern with 14mm socket
  • Pull off stock sprocket
  • Clean the rear wheel hub with a clean cloth especially the surfaces that contact the sprocket

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Install New Sprocket

Reinstall Rear Wheel

  • Lubricate wheel axle, wheel bearings, oil seal lips using a lithium based grease

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  • Insert wheel in wheel well and install drive chain around new sprocket

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  • Swivel brake caliper back around brake disc, verify pads are on either side of brake disc

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  • Reinstall rear axle through brake caliper axle bracket, wheel hub and bearings, and slider blocks (watch their orientation), leave wheel axle nut loose
  • Wheel must be lifted to do this and it's a little tricky to do

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Next, adjust the drive chain slack. You don't have to do the first part of that, the bolts and nuts are already loose. Wheel axle nut and brake torque bolt should be tightened to spec after this procedure.

Clean and Lube Chain. I understand there are many different approaches to chain maintenance and I offer the following only as a matter of personal preference.

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Replace Hugger or chain guard, verify wheel clearance sufficient and does not rub or contact hugger

1600 x 1200

Recalibrate Yellow Box, see Addendum II

Check Your Work

  • Verify Rear Brake Operation Prior to Riding Bike
  • Take Bike for a Careful Test Ride
  • Recheck All Bolts Properly Tightened
  • Take Bike for a Performance Test Ride

Subjective Riding Impressions:

  • Not overkill at all, another nice improvement for sport riding
  • Gains best felt in upper gears, even more responsive on highway
  • Lower gears were already very quick, be even more careful now in 1st & 2nd


Some owners have reported that use of a Vortex 47-tooth rear sprocket cannot be done because the stock chain is too short.

Daniel Hereford, an owner installing the 15-tooth front and 47-tooth rear sprockets from Vortex reports:

"Got the Vortex 15/47 sprockets installed this weekend and I will say as an authority that you DO NOT have to replace the stock 116 link chain. I can see why people might think this because to get the chain on the sprockets I had to seat the chain on the rear sprocket BEFORE putting the axle through the wheel. The axle does come right up to the front of the swingarm, but I actually had to adjust out a few turns for proper tension."

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Last Updated: 08-08-2005

Copyright © 2001-03, Patrick Glenn, All Rights Reserved.
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The information presented here reflects solely my personal experience with my motorcycle and is presented for entertainment purposes only. No information presented here is to be relied upon for issues of rider safety nor to replace the services of a qualified service technician. Any attempts to follow or duplicate any of these procedures are done so completely at your own risk. By reading the information on this site, you agree to assume complete responsibility for any and all actual or consequential damages that may arise from any information presented herein.