Tech talk: Know your sprockets
FB: What is a sprocket?
MF: Technically, a sprocket or chain wheel is a profiled wheel with teeth that mesh with a chain to turn the rear wheel. The name ‘sprocket’ applies generally to any wheel upon which radial projections engage a chain passing over it, driving the machine.
FB: What are they made of?
MF: Renthal rear sprockets are made from 7075 T6 aluminium alloy which is then surface coated with a hard anodising for increased wear resistance, whereas Renthal front sprockets are made from 655M13 nickel chromium steel that is then case hardened for maximum durability. Given what they do, they need to be strong!
FB: How long do they last?
MF: This is a very open ended question as sprocket life is dependant on so many things, such as riding conditions, weather conditions, maintenance regime, drive chain condition, riding style, power of the bike, chain pitch/size – these will all affect the longevity of the sprockets. As an example, a brand new front and rear steel sprocket fitted to an old 520 chain that has covered 3000 miles on a 150bhp machine ridden hard in the winter with snow, rain and road salt with virtually no cleaning or lubricating will last less than 5,000km. If we then take the same bike but this time it’s fitted with a brand new 530 pitch chain, of the correct grade, and new sprockets ridden sedately in the summer while being cleaned and lubricated thoroughly on a regular basis it will see more than 24,000km.
FB: Is there a difference between standard and aftermarket sprockets?
MF: There shouldn’t be. The shape and profile for the teeth is an internationally accepted standard design. However, the type of material used, and the heat-treating process of steel sprockets could vary between manufacturers, affecting the way sprockets wear. OEM front sprockets generally have rubber pads bonded to them just below the teeth, which slightly reduces the noise of the chain as it engages with the front sprocket but has absolutely no benefits to the life of the sprocket. One of the biggest differences between an OEM rear sprocket and a Renthal rear sprocket is the weight. Obviously, this is because the Renthal rear is made from an aluminium alloy and the OEM is made from steel. For example; a 530 pitch, 47 tooth steel rear sprocket for a 2014 Yamaha R1 weighs 1.1kg, whereas the same sprocket from Renthal is 0.44kg. There are weight savings to be made by fitting a Renthal Ultralight front sprocket, but obviously these are very small due to the size and material they are made from.
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FB: Do they need any type of maintenance?
MF: Yes. The chain and the sprockets need to be cleaned regularly using a proprietary chain cleaner, such as TechCote TC160, and a stiff nylon bristle brush. This is done to remove the road dirt that has combined with the chain lube. Once this has all been removed and allowed to dry the chain needs to be re-lubricated with a quality chain lubricant, such as TechCote TC100 or TC110.
FB: How do you know if they need changing?
MF: As a rule, it is always recommended that a new chain is fitted with new sprockets, so it will always be the chain that dictates when the sprockets should be renewed, regardless of how good the sprockets look. Most modern bikes have indicators on the swingarm that show that the chain has stretched to a point that it needs to be replaced, and on the sprocket, you can tell at the bottom of the teeth where the chain makes contact with it. Badly hooked teeth and excess wear in the bottom of the tooth area would require a sprocket change. This is more evident on off-road bikes due to the amount of whipping in the chain and dirty passing through the chain which grinds into the sprocket.
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FB: What difference does it make if you change the number of teeth?
MF: Changing a sprocket tooth size is probably one of the most popular and cost-effective performance changes you can make to a motorcycle. Taking just one tooth off the front gearbox sprocket is the equivalent to going up three teeth on the rear sprocket. This makes the bike accelerate more quickly, giving you a noticeable difference in the feel of the bike. Different sprocket sizes are crucial in racing to get the right set up gearing wise for a track or to achieve a certain wheel base length as well. Changing gearing on a road bike can give you many advantages too, whether you’re touring and want a less revving motor or are seeking that extra advantage in performance with increased acceleration.
FB: Will it alter anything else on the bike?
MF: Dependant on the motorcycle and how the speedo picks up its reading, changing the sprockets can alter a reading either by over reading slightly or under reading dependant on what you have done. Modern speedos take their speed readings electronically and some can be adjusted within the settings if the sensor reads from the gearbox.
FB: What’s the difference between 520 and 525 sprockets?
MF: It’s all down to the thickness of the sprocket. A 520 sprocket looks the same as a 525 sprocket from the side but look at it straight down the teeth and you can see the thickness difference – the thickness of a 525 sprocket is 7.25mm and a 520 pitch is 5.9mm. There are many other pitches of sprockets available from 415 up to 630 – so as an example 428 is mainly used on 125cc machines to keep costs down and as they have lower power outputs they don’t actually require a bigger sprocket and chain. The Hornet’s standard chain and sprocket set up is 525, but if you were taking that bike racing you would swap them to Renthal 520 Sprockets which offer a weight saving and a much larger range of tooth sizes.
FB: How do you know what works best for you?
MF: Mainly by what you’re using it for. If you’re riding on the road mainly leave your chain and sprockets with the standard pitch and adjust the tooth sizes to suit you. If you’re going racing, then use the lighter 520 sprockets set up!