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Old 04-15-2011, 01:07 PM   #1
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Motorcycle Sprockets/Chains: Explained

Just thought I'd put this together since the common questions arise often and some of the math can be daunting. I've included links for charts and a great calculator.

Sprockets
By changing front and rear sprockets (or pulleys for belt drive; ring and pinion gears for shaft) you can alter your bike's final drive ratio, which in part determines wheel speed for a given rpm. Gearing ratio refers to the ratio of rear to front sprockets. For example, a stock Honda CBR600F4 has a 16 tooth front sprocket, and a 45 tooth rear, for a ratio of 45/16, or 2.81. Substituting a larger front or smaller rear sprocket lowers the ratio (sometimes called "taller" gearing), resulting in more speed for a given engine rpm. Likewise, a smaller front or larger rear sprocket gives less speed for a given rpm ("shorter" gearing).

Gearing Chart:
http://srs6.com/gearratiochart.html

This begs some obvious questions: "Why can't I put a 20 tooth sprocket on the front and go 200mph," or "With a 13 tooth front sprocket will my 600 do eight-second quarters?" Performance numbers can be enhanced by sprocket selection to a certain extent, but the overriding factor is your engine's power and its characteristics. Choosing the correct gearing optimizes your powerband usage, maximizing power delivered to your rear wheel for the given conditions.

Speed = (rpm X rear tire circumference X front sprocket) / (primary gear ratio X sixth gear ratio X rear sprocket X 1056)

Now for the fun stuff. Notice on the chart how 15/44 is virtually identical to 16/47 gearing...or is it? One obvious difference is that with larger sprockets, 16/47 gearing will give a shorter wheelbase than with 15/44, giving your bike a slightly more rearward weight bias. Or, maybe it's enough of a change that you could add a link to the chain and lengthen the wheelbase. Given sprocket sizes and chain length, comparative wheelbase numbers can be calculated and added to the chart, eliminating any guesswork.

A front sprocket with fewer teeth works the chain harder and robs power, as the chain has to curl more to match the smaller diameter. In general, a 14 tooth front sprocket is the smallest advisable, with 13 being used in extreme cases.

One thing to watch is clearance between the swingarm and chain. Smaller sprockets can result in the chain laying on the swingarm, and actually working the suspension when power is applied. One notable example is the early Kawasaki ZX-7R, on which many racers had to have the swingarm relieved for chain clearance. With high-horsepower machines, chain pull and its effect can be altered using sprocket selection. Anti-squat torque-which extends the rear suspension under power-is determined by swingarm angle and the distance between the swingarm pivot and top chain run. Even if the chain doesn't touch the swingarm, running it close to the pivot will enhance the anti-squat torque, much in the same way raising the swingarm pivot does.

CHAINS
When choosing a new chain and sprockets for your scoot, there are a number of things to take into consideration. A popular modification for racers is to replace a stock machine's 530 chain with a thinner and lighter 520 series chain and matching sprockets. Generally, roller chain is denoted as follows: the first digit specifies the chain's pitch, in 1_8 inch increments. The remaining digits correspond to the width of the chain in 1_80 of an inch. A 530 chain, then, has a pitch of 5_8 inch, and a width of 30_80 inch, or 3_8 inch. A 520 chain is 1_4 inch wide, correspondingly lighter, but also somewhat weaker than a 530 chain. There are some exceptions to this; For instance, 125GP machines utilize a 428 chain, which is a 425-sized chain with slightly thicker sideplates. Front sprockets are usually steel, but rear sprockets are available in either steel-which is somewhat heavy but lasts a long time-or aluminum (lighter, but less wear resistant).

Most stock bikes are equipped with an O-ring chain, and are endless-there is no link to split the chain for removal, and it has to be "broken." Replacement chains generally utilize either a rivet-type link, which must have the pin ends peened for assembly, or a clip-type link. A rivet link is generally stronger and less likely to come apart on its own, whereas a clip link is easier to assemble/disassemble but may come undone. If you use a clip link, safety wire around the sideplate and clip to hold it on, or use a dab of silicone sealant on the clip.

An O-ring chain employs tiny rubber seals between each plate and roller to keep the chain permanently lubricated. While it does add weight, this style of chain lasts longer and requires less maintenance than a non O-ring chain. The small seals may seem to add friction also, but once in use the grease thins out due to the induced heat, and an O-ring chain may spin as freely as a non O-ring unit.

Both styles, however, need periodic lubrication. The non O-ring variety more so-the O-ring type only displaces water and stops the outer surfaces from rusting. Use the appropriate type of lube-some spray-on types may damage the rubber O-rings-and oil your chain immediately following a ride. This will give the maximum amount of time for the oil to soak in. Always apply the lubricant from the inside of the chain, because centrifugal force will help the oil penetrate, rather than fling it on your tire.

If I Change My Sprockets
What is it going to do to my top end?
What are my RPMs going to look like in a certain gear?
How many links does my chain need to be if I choose a different from stock setup?
Here is a handy website with alot of bike specific info to compare different sprocket setups:

gearingcommander.com


Credits:
Trevitt, Andrew "Sportbike Rider Magazine"
Gearingcommander.com
SRS6.com
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Old 01-31-2012, 06:29 PM   #2
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bump for the noobs.
Search function is wonderful.
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Old 01-31-2012, 06:42 PM   #3
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MODs please sticky this thread

thanks senator..great write up...
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Old 01-31-2012, 07:15 PM   #4
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Quote:
Originally Posted by BaoPee View Post
MODs please sticky this thread

thanks senator..great write up...
Thanks man. It would be the first one in this section.
I guess not many people know about what they're modifying....
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Old 01-31-2012, 07:20 PM   #5
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some people bought the 520 conversion kit, just because it says quicker acceleration on the package...just like you have mentioned in earlier post "most people do not know what they are modifying.
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Old 02-02-2012, 03:19 PM   #6
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Old 06-10-2012, 10:16 AM   #7
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There has been lots of chain questions lately thought I'd help everyone out

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Old 06-10-2012, 11:15 AM   #8
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good article for all
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