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I notice that except for small commuter bikes and older bikes (before the 80s), hardly any of the larger and/or sportier bikes have covers to protect their chains: Honda Cub. Hero Honda Passion

They seem quite practical, and conducive to chain life- by protecting the chain from the elements and requiring less frequent lubrication. Then why don't larger bikes have them? Is it purely for aesthetic reasons? Or is there a safety aspect as well? Are there other reasons? What would happen if the chain broke in a bike with a chain cover?

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Chains for Scooters and Small Bikes

One of the primary reasons revolves around the type of rider that purchases these bikes and their mentality toward riding.

In the 1970's many riders were starting off on these vehicles and consequently were not wearing the standard safety gear that a more seasoned rider would wear. As a result scarves, pant legs, etc. were getting pulled into the chain and sprocket and injuring riders.

As a result, many of the manufacturers began putting fully enclosed chain guards on these types of vehicles. Later, when shaft drive came about, these obviously went away, mostly on scooters.

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Those bikes are small engine, low torque and consequently have smaller/narrower chains. They are designed for use commuting to/from work with little or no protective clothing over your normal clothes. Consequently the chain needs to stop spatter getting on your clothes and as a result has a chain guard.

The chain - due to its smaller weight and less torque of the engine will likely stretch less than a bigger bikes and should in theory need tensioned less often.

Larger bikes have much heavier gauge chains that have a lot more mass with them. The larger bikes also have much more torque applied through the chain. In the event of a chain failure the guard would have to be much thicker than on those bikes. Additionally the chains on larger bikes need to be adjusted more regularly (in my experience) and are less tolerant to slack/tightness so you need ready access to them.

That being said, larger bikes tend to have a nominal chain guard to stop laces/clothing etc from the pillion passenger being taken up by the chain.

Also the chain covers don't look very nice compared to a gold x-ring chain and anodised sprockets.

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1. Agree. With the cub, Honda marketed the bike as an appliance needing less care and attention from the user. Regarding para 2.& 3. Chain covers do provide access (via pluggable holes) for checking chain slack and lubrication. They do make it harder to verify the chain condition at a glance though Agree with para 5. I am beginning to think that this was the real reason they were killed off.. – nedR Feb 12 '14 at 20:11
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I would also add that the bikes above are marketed in countries where they are used as family vehicles. Kids legs and wives dresses are often hanging over the side near the chain, so its a real safety thing. – MeltingDog Feb 20 '14 at 5:04
    
very Good answer. +1. – Shobin P Aug 25 '15 at 9:38

Many sport bikes have a partial chain cover. The front sprocket is covered and the upper portion of the chain is covered along the swingarm area.

This is done purely for aesthetics and to prevent chain lubricant from getting all over the bike and rider. They actually contribute to chain wear, because they trap road grime and prevent proper cleaning of the chain. The front sprocket cover in particular is almost always filled completely with lubricant and road grime.

Riders looking to get the longest lifetime from their drivetrain components simply purchase a shaft-driven motorcycle. As a result, there is no incentive for manufacturers to creative a better system for protecting the chain.

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