Gear the engine to just touch the limiter
The above link is a gearing chart based on information provided by the community. It is maintained and edited by the community to help new racers get dialed in quicker and have more fun! Please use all the information provided, and please provide information if you have knowledge.
600cc Mciro Sprint 1000cc Mini Sprint 750cc Mini Sprint
Yamaha '06-'17 R6 Yamaha '04-'13 R1
Yamaha '99-'05 R6
Kawasaki '13-'16 ZX-6R
Kawasaki '07-'13 ZX-6R Kawasaki '05-'06 ZX-10R
Kawasaki '05-'06 ZX-6R
Kawasaki '03-'04 ZX-6R
Suzuki '06-'17 GSX-R600 Suzuki '09-'13 GSX-R1000 Suzuki '06-'13 GSX-R750
Suzuki '04-'05 GSX-R600 Suzuki '05-'08 GSX-R1000 Suzuki '04-'05 GSX-R750
Suzuki '01-'03 GSX-R600 Suzuki '01-'04 GSX-R1000 Suzuki '01-'03 GSX-R750
Honda '07-'17 CBR600RR
Honda '03-'06 CBR600RR
Honda F2-F3 600
Other Gearing Charts
Honda '89-'01CR250 Suzuki '89-'95 RM250
Honda '96-'99 CR125 Suzuki '97 RM250
Honda '85 CR125 Yamaha '79 YZ250F Air Cooled
Kawasaki '79-'82 KX250 Yamaha YZF250 4stroke
Kawasaki '88 KX250
Front and Rear Sprockets
How to Use a Gearing Chart
Use the information in the gearing charts above to determine front and rear sprocket combinations. The numbers in the charts represent the final drive ratio. This gearing ratio or final drive ratio, is the number of times the crankshaft turns to every one turn of the rear axle. The formula for calculating this is very straight forward, it is simply final drive ratio= primary x secondary x tertiary ratio
Primary ratio = crankshaft to main transmission shaft ratio, # of teeth on the trans shaft divided by # of teeth on crank shaft
Secondary ratio = the ratio between the gears in the transmission, these of course will be different for each gear that you have in the transmission.
Tertiary ratio = the rear rear sprocket # of teeth divided by the front sprocket # of teeth so a 13 - 51 sprocket combination = a 3.923 ratio.
For example, if you are running in third gear and you need to add a tooth but don’t have the sprockets to do it you may be able to use second gear. or a different combination with a different front tooth sprocket. Just find the same ratio you want in another combination, and the chart will tell you which sprockets use. It also can be used to find a ratio between two teeth, look in different areas of the chart to find different ratios that might fall in between two sprockets.
"Does it matter which gear I run in and does it matter which size front sprocket I use?"
It does not matter which gear you use or what size front sprocket, the final drive ratio is all that matters. If a smaller front sprocket made you come off the corners better, we would all be running 6 tooth front sprockets. "but my car comes off the turn a lot better in 2nd gear than third" I'll say it again, the final drive is all that matters, I have won a lot of races using 6th gear on a small track, now it takes some funky sprockets to make that work, like maybe an 11-60, but it works the same as running in 2nd gear with a say a 16-47. The engine and rear axle only know how many times the crankshaft turns relative to how many times the rear axle turns.
Now, let me make another statement here, there may be some slight advantage to running larger front sprockets because the chain does not have to wrap as tight and may be more efficient, but on the dyno it does not show an advantage. Also a bigger sprocket, front and back adds some rotating weight. Again, these effects seem to be so small it does not matter.
Tire Size Does Matter
There is a simple formula for figuring out how a different size tire will affect the gearing. Rear tires can be inconsistent in diameter, so you need to take in to account how it will affect your gearing when you change tire sizes in your micro/mini sprint, even from a 68" to a 69". Lets take a common example of changing from a Hoosier 69W tire to an American Racer 70" tire (which actually measures more like 71"). The formula is
Old Tire Size/New Tire Size = New Sprocket/Old Sprocket or (New Tire/Old Tire) x Old Sprocket=New Sprocket
Lets say you were running a 52 tooth rear sprocket and you are changing from a 69" to a 71" right rear tire:
So you have to go up at least one tooth maybe two teeth on the rear due to the 3" increase in right rear tire circumference. It does not appear to me that the left rear affects the gearing, at least not nearly as much as the right rear does.
Comparing Ratio of Different Engines
If you switch engine models or manufacturers or you are trying to compare what gear you are running compared to your friend who has a different type engine, there is a formula to do just that.
Due to different rev limiters, the final drive gear ratio will be differnt for each type engine. Here is the formula:
(New RPM Limit/Old RPM Limit) x Old Ratio = New Gearing Ratio
Generally we try to gear our engines so we just hit the rev limiter at the end of the straight. If you have a rev limiter that is not stock and it higher than where you actually want to rev your engine, then use the RPM of your desired max rev limit.
On 600's make sure you are using an good high tensile strength chain like the DID VX Gold O-ring Chain. Cheap chains may not even last one race. There is a very wide quality range of chains available on the market. To answer your question I am going to talk only about the chain we sell.
Also, do not use a master link on your chain, it WILL fall off. Use a Rivet Link. Yes these are harder to install, but done correctly, it will never fall off and is as strong as the other links in the chain. You know the old saying...
Generally, the chain listed above will last at least 40 races if maintained correctly and it never fell off the sprockets or got twisted or something weird like that.
How to maintain a chain:
Clean your chain after every race with parts cleaner using a brush to loosen the dirt and grime. Dry with compressed air. Dirt in the chain causes wear and it also causes an increase in friction causing losses in speed.
Lube it before every race using Silkolene Pro Chain Lube, I know it might sound like I am trying to sell you product here, but there really is no better chain lube on the market. This stuff does not fling off and make a mess of your car, yet it provides plenty of lube to keep the chain cool and prevent wearing of the chain and sprocket. Chain wax or similar "dry" lubes do not work, they create excessive heat in the chain and will cause your chain to wear and break prematurely. Other lubes fling off making a mess of your car and leaves your chain without lube. We have tried them all.
Examine your chain for tight spots or "kinks". Roll the chain around your hand freely making sure it rotates freely. Another way to evaluate your chains life is to lay your chain on a large flat surface with the link plates vertical. grab the two ends of the chain and try to bend it against the link plates keeping the chain flat on the surface. Do this when new and make a note of how far it will bend. As the chain wears, it will bend more. Generally a new chain will bend about 70 degrees and a wore out chain will bend about 130 degrees. But these numbers vary depending on the manufacture and the length of the chain.
Also you can hold two links in your hand and press them toward each other. As a chain wears, you will begin to see play between the links.
How to set chain tension on a wishbone chassis:
To properly set chain tension, the car needs to be setup (rear axle square, blocked, and turns set) and on the ground race ready. First align the rear sprocket with the front sprocket with a straight edge on the rear sprocket. You may need to adjust the panhard bar to align, or if far off, move the sprocket carrier on the rear axle by swapping spacers.
Once the sprockets are aligned, then you can put on the chain and adjust the tension. Do this by sliding the engine front until there is about 1" of free play in the chain. once the free play is set, lock the engine down by tightening the three engine bolts. Then crank and extra turn into the engine jacker bolt. This pre-loads the engine in the front position so the force of the chain under load does not pull the engine back and loosen the chain while you race.
Hyper Chassis must use the chain guide that mounts to the left rear bearing carrier. It needs to be adjusted up against the rear sprocket, no more than an 1/8" gap between the two. When you change sprockets the chain guide block needs to be moved. Make sure the chain guide is centered on the chain. Do this by changing the length of the spacers that hold the chain block out from the bearing carrier plate.