              O-ring Verses Non O-ring.Measuring Chain Wear:How do you determine when your chain is beyond the manufacturer's wear limit? First of all let's correct the myth that chains stretch. Chains don't stretch. The outside measurement of an individual link plate does not get longer with wear. Your bike is not "so powerful" that is stretches chain. Chains are constructed of essentially link plates, pins, bushings and rollers. In order for a chain to roll around a sprocket the pins must have clearance through the bushing holes, allowing them to pivot. That clearance begins at about .0005", or 1/6 of a human hair. The pins and bushings are subjected to continual pivoting, and as they pass a sprocket, steel against steel wear occurs. This causes the pins and their mating holes to wear in an eccentric manner as the diagram below shows. In abrasive dirt conditions and especially mud, grains of sand are introduced between these mating surfaces and wear is accelerated many times over. A sealed chain (O-ring, X-ring, Z-ring ...) acts to prevent abrasives from entering this pivoting joint. For all full sized dirt bike, the standard chain pitch is 5/8". Chain code numbers indicate the pitch. a 4xx chain has a 4/8 or 1/2" pitch. A 5XX chain has a 5/8" pitch. Sorry to those fond of metric units. Like pipe sizes the world around, chain is measured by the "kings thumb". 5/8" is the center-to center distance between pins. Most chain manufacturers limit chain wear to approximately .006" per link. So if you take that number and multiply it by 100 links, the accumulated clearance that some refer to as "stretch", is close to a full pitch or 5/8". So if 99 spaces fit in the distance that 100 spaces were suppose to measure, your chain is shot. So here are two ways to inspect your chain for wear:
O-ring or sealed chains verses non-sealed chains:What is the difference in weight between the two?A Regina 520-RX3, non-sealed premium racing chain, weighs 4.05 pounds. A Regina 520-ORN weighs 4.24 pounds. The difference is 3 ounces. That's the equivalent of three first-class letters, 1-1/4" of Coke in the bottom of a soda can, or one pair of "tighty-whitey" underwear. Insignificant! What about rotating inertia? A single knob on a rear tire has a larger rotating inertia (polar moment) than 3-ounces of chain weight. Contrast that with the 3-pound difference between various brands of equal-sized rear tires. Insignificant! Anyone who claims that they can feel the difference between the two chains while riding, needs to loose their underwear.
How much additional horsepower does an O-ring chain consume?Well, you can take all the anecdotal remarks about how "I can feel the power difference", or " you should never use an O-ring chain on small bike", or we can measure this objectively. Let's look at the science.
Here is my method of measurement:
Data:
The load was determined by hanging weights on a rope wrapped around the rear tire. Small weights were added until the tire would remain rotating but not accelerate. The idea was to measure rolling friction as opposed to static or break-away friction. Calculations: HP=T x RPM/1,008,000 (T in oz-inches) HP=T x RPM/5252 (T in pound-feet) 19" Rear tire diameter = 25" actual diameter Tire RPM at 20mph = 265 RPM Tire RPM at 40mph = 530 RPM Tire RPM at 60mph = 795 RPM
Summary: What can we conclude from the calculations above? Considering that the average speed around a stadium motocross track is about 30 MPH, we can say that the average horsepower loss between a sealed and unsealed chain is approximately 1/50 of one horsepower. Considering that modern 250F motorcycles being raced, generates about 42 horsepower at sea level. One-fiftieth of a horsepower equals one-two-thousandth or a 0.05% change. To put that in perspective, engines loose about 3.2% of their power for every 1000-feet of altitude gain. A change of 0.05% would occur with an altitude change of 15-feet. Here is another comparison. Horsepower is lost at a rate of approximately 0.4% for each degree of temperature (F) rise. Therefore a 0.05% power change would result from a temperature rise of one-tenth of one degree Fahrenheit. My opinion is that no one is capable of differentiating the power difference with a 15-foot altitude change or a one-tenth degree temperature change. Likewise no one is capable of feeling the power change between a sealed and an unsealed chain.
Which Chain should be on your bike?Based upon the evidence above, that the weight and claimed power losses are of no consequence, you need to make your chain choice solely upon economics, since performance is not at issue. Two factors determine how much you will spend per year on chain: One - riding conditions. Two- hours of riding per year. If you ride primarily on the street, a sealed chain will not last much longer than an unsealed. For a 450cc bike, we are talking in the range of 5000-15000 miles. If you ride in wet muddy conditions off road, a non sealed chain has a life of about 4 hours versus 40 hours on a sealed chain. In dry dusty conditions, I would estimate, based on our experience, the life of an unsealed chain to be from 10 to 30 hours versus 100-200 hours on a sealed chain. Cost: A high quality unsealed chain retails for about $70 and a high quality sealed chain can be bought for about $90. Summary: If you ride on the road, stay with an unsealed chain. If you ride motocross or off-road for more than 4 hours per year, the $20 additional investment will save you the cost of a new chain in one day of a muddy ride, and if you did not know which chain was installed, you would never have known the difference in performance. I might add that one huge advantage of sealed chains is the rare need to make chain adjustments. It is not uncommon for experienced motocrossers with unsealed chains, to make chain adjustments after every moto. That alone is a testament to chain (and sprocket) wear (not stretch).
Author: Greg Burns, Mechanical Engineer, Dirt Tricks Inc. Last edited: June 12, 2010 If you have questions, feel free to email us at: sales@dirttricks.com
|
