Sprocket

One of the simplest and cheapest modifications you can do, swapping the front sprocket shifts the RPMs higher or lower (higher if you go down in size, lower if you go up in size) at a certain speed in a certain gear.

For reference - 80mph indicated in top gear is ~6000RPM. Stock gearing is 16/39. Going down a tooth in the front is equal to going up 3 in the rear.

Stock Gearing / RPM / Speed Indicated
4th @ 4,000 = 60km/h (37mph)
5th @ 4,000 = 70km/h (43mph)
6th @ 4,000 = 80km/h (50mph)
6th @ 5,000 = 100km/h (62mph)
6th @ 6,000 = 120km/h (74mph)

The Gearing Calculator can be used to calculate engine speed vs. motorcycle speed for other sprocket combinations.

Front Sprocket

1988 to 1993 = No flange on Sprocket (Part# JTF 565)
1994 to 2007 = Flange on Sprocket (Part# JTF 516)

Rear Sprocket

1988 to 2007 = All GS500's use the same model rear sprocket(Part# JTR 823)

Down

Going down in size, and therefore shifting the RPMs higher, allows quicker acceleration and a possible higher speed due to the GS's power limited top speed.

15 tooth front sprocket

Going to a 15 tooth front sprocket is a very common mod, allowing the GS to have quicker acceleration without sacrificing high speed cruising rideability.

The math works out like this: 16/15 = 1.066667. This means that there is a 6.667% change in RPMs at a given speed in a given gear. At 80mph in top gear, the RPMs would rise 6.667% to 6400 RPM.

The lower gearing applies to first gear as well, giving it a bit more pull off the line.

14 tooth front sprocket

A bit more radical than the 15 tooth swap, the 14 tooth swap essentially removes the stock 6th gear and adds an even lower 1st gear. This can cause the bike to wheelie far easier than with the stock gearing. See Hahahahahahahahahahahaha - aka Impressions of a 14T sprocket for more information on this mod.

Math: 16/14 = 1.142857. This means there is a 14.29% increase in RPMs. Top gear at 80mph will have the RPMs sitting around 6857 RPM(pretty much 7000 on the tach).

49 tooth rear sprocket

Going up in the back, does the same as going down in the front.
If you want to do wheelies on your GS500, consider buying a larger rear sprocket. The are available in 41T, 45T and 49T. See: JT-Sprockets
Haven't tried it on public roads, so I don't know what it does for the topspeed. But it wheelies very nice on the parking lot!

Up

17 tooth front sprocket

Quite the opposite from above, going up a tooth on the front sprocket will lower your RPMs, thus allowing lower cruising RPMs and possibly better fuel mileage. See Adding a Tooth -- Going Up to a 17T Front Sprocket for more information on this mod.

Math: 16/17 = 0.941176. This means that the RPMs will drop 5.88% in a given gear at a given speed. Top gear at 80mph will change to 5647 RPM, a drop of 352 RPM.

18 tooth front sprocket

While they do exist, no information has been found about them.

Calculating Required Chain Length

Stock sprocket sizes are 16T front, 39T rear. The OEM chain is 110 links. When different size sprockets are installed, it is possible that a different chain length will be required. The required chain length can be calculated as follows:

  1. Open the chain length calculator provided by Tsubaki at: http://tsubaki.com.au/tsscs/chain_length.htm
  2. Enter the number of teeth on the new front and rear sprockets
  3. Enter the chain pitch of 0.625" (The pitch represents the length of a link. The pitch is 5/8" for any "5" series chain: 510, 520, etc.)
  4. Enter a center-to-center distance of 25.5" (This is an approximate value only; the chain calculator will provide the ideal value in the outputs)

Example (stock setup)

Inputs

Teeth On First Sprocket16
Teeth On Second Sprocket39
Chain Pitch In Inches0.625
Centre Distance (inches)25.5

Outputs
Your required chain length is 110 pitches. (i.e. 110 link chain)
Your ideal centre distance is 25.679 inches.

Links

JT Sprockets - these will fit all years of GS500.
AFAM Sprockets - ranging from 13T to 18T, these will fit all year models.
Motorcycle-Superstore offers many different brands of sprockets.