After racing our bone-stock 2014 Suzuki GSX-R600 project bike with Moto West Grand Prix last month, we became tempted by basic modifications that could give us an edge on the competition. What quick and cheap modifications could give our bike better drives out of the corners and reduce the gaps placed on us by the fully-built, highly-tuned race machines we were going up against on the race track? The added performance shouldn’t harm our daily commute on the street either…
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An upgrade with one of the best performance per dollar ratios on the sportbike market over the last decade has not increased airflow into the engine, optimized fuel burned in the combustion chamber nor augmented the manner in which exhaust gases exit the motor. Instead, one of the better bangs for your buck is accomplished by simply adjusting the final drive ratio of the gearing between the output drive gear on the transmission and the sprocket on the rear wheel. This is most commonly acquired through a chain and sprocket kit offered by a wide range of vendors.
For this project, Motorcycle-Superstore hooked us up with a size 520 D.I.D ZVM-X Super Street X-ring chain, a size 520 Vortex 15-tooth steel front sprocket and size 520 Vortex 45-tooth steel rear sprocket. We went with the 520-sized chain and sprocket pitch because of popularity allowing for many aftermarket sprocket options in addition to slightly reducing the mass of the spinning chain as a bonus (the stock chain size is 525). Heavier duty chains such as 525 or 530 varieties are also popular sizes but these are better suited for larger bikes producing more power. These larger sizes are overkill for a 600cc sportbike in most cases (especially ours which is 100% stock) but would be more applicable for high-powered 1000cc superbikes or big dog rides approaching the 1.5 liter engine displacement mark. Additionally, O-ring or X-ring chains are ideal as these seals do an excellent job at containing lubricant and keeping dirt out of the pivot points.
Steel was our sprocket material of choice because of its increased durability over aluminum and our minimal concern for minute weight savings. Finally, and arguably most importantly, we decided to go with a 15-tooth sprocket for the front main drive and 45-tooth for the rear sprocket on the wheel. The stock gearing is a 16-tooth front sprocket and 43-tooth rear.
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This gearing adjustment is known as “one down, two up” and is a very popular modification from the stock tooth-count. This increased gearing ratio enables the motor to spin the rear wheel up to speed over a shorter amount of time and distance without changing the input power (no modifications to the engine). This results in quicker acceleration with a relatively low time and money investment, exactly what we were looking for.
We tested our newly-installed chain and sprocket kit on the very track we raced our stock GSX-R600 project bike on a couple weeks prior; The Streets of Willow Springs. The clean whine of a fresh chain rolling across brand new sprockets is always a refreshing sound but this auditory drivetrain bliss was just the beginning. Pulling down hot pit lane then accelerating hard into turn one was an eye-opening experience. This was a completely different bike.
The increased gear ratio vastly improved drive out of corners, wide-open pushes down the straights and even engine braking entering the turns. This also increased attention directed towards throttle modulation and traction as things became much twitchier with every input of the right wrist. However, only a few orientation laps were required before we were able to dial in and harness the newfound performance increase of our project bike.
Another side effect of an increased gearing ratio is a reduction of the vehicle’s top speed. This is a result of the rear wheel turning less revolutions at the same main drive shaft speed. Furthermore, the speedometer will read high (about 10% above the true rate of speed from our rough calculations) as this figure is calculated by measuring the RPM’s of the drive shaft. The top speed reduction was less of a concern on the relatively-tight Streets of Willow track and definitely a non-issue for daily commuting. We did, however, have to keep the speedometer error in mind when riding on public roads.
It was immediately apparent that we made an excellent choice going with a new chain and sprocket kit with an increased gearing ratio to quickly improve our acceleration performance. For a total just under $300 and a couple hours of wrench time in the garage, we were able to vastly improve the GSX-R’s drive out of the corners and acceleration down the straights. This relatively simple modification enabled our GSX-R600 to chip away at the gap placed on us by the full-on race bikes and reel in the competition without breaking the bank.
Next up, air/exhaust flow optimization? Next week we'll show how to install a sprocket and chain on any sport bike.
Photos by CaliPhotography and Bob Hartman at eTech Photo