oh boys. i have an amazing link for you. something i put a bit of time into. in fact, lemme just post the pic here. easier anyways. this is basically a spreadsheet depicting a bunch of information about sprockets' gearing ratios and wear/tear factors. on alot of our bikes, stock is the 16/43 which presents the corresponding 2.68 gear ratio and 344 wear factor. the thing to keep in mind is that you want Wear factor high as possible, unless u wanna replace sprockets and chains alot. also, notice, the most common 15/45 change leads to a nearly 11.6% change in gear ratio - increasing torque low end and decreasing top end speed. the 15/45 however greatly reduces the wear factor!! there are several sprocket combinations that lead to a higher low end torque, i used to have a 14/43 combo that yielded a 14% change (better than 15/45) and still maintained a high wear factor. i currently run a 15/43 setup and have a 6.66% change in torque and maintain a relatively good wear factor.
now, almost Anyone you talk to is always going on n on about a -1/+2 setup to a 15/45... i know it runs great, but for someone looking to get a lil more longevity out of their chain/sprockets, just do a lil homework. i've done plenty and trying to display it for us all ;)
here's some background info on the numbers displayed above, explaining the meanings:
'Same tooth - same link' chain rotations
Besides obvious factors for chain wear like not enough maintenance (i.e. greasing it) and misalignment of sprockets and chain, the chain will simply wear out more when it is used more ..... Especially if the same tooth hits the same link all the time the chain wears out faster then when that tooth hits another link instead. Whether or not this will happen depends on the combination of teeth and chain links. Three type of combinations are possible:
1) Worst: every chain rotation, the sprockets (front or rear or both) are at the same position
2) Better: it takes more then one chain rotation for it to hit the same tooth with the same link
3) Optimal: it takes the maximum number of chain rotations for it to hit the same tooth with the same link
Table "Same tooth - Same Link" shows what type of combinations you have or are about to get. This by showing the actual number of chain rotations and marking them red when 'Worst', green for 'Optimal' and not for 'Better'.
Number of contacts
Another factor that influences the chain wear is of course the number of contacts a tooth has with links and the other way around for the chain, the number of contacts a link has with teeth. The more hits, the faster the wear ! So obviously, the more you use your bike, the more the final drive will wear out. But changing the final drive does not make you use your bike more or less, it just changes the use of the final drive when driving the same distance as before.
That is also why changing the rear sprocket, say bigger, wears out the front more when driving the same distance .....
Therefore the table "Tooth-Links contacts & Link-Teeth contacts" shows the number of contacts between teeth and links, for every driven mile or kilometer.
Info from: http://gearingcommander.com/
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