v7 sub

Chain (or belt) & Sprocket wear influences: Number of contacts between chain & sprocket

When you change one or both sprockets, you probably won't drive your bike less or more miles to compensate....
When you mount a smaller front sprocket and keep your rear sprocket, the front has to rotate more for every mile you drive. The more it rotates, the more the individual teeth have contact with a link and the more it wears out.

Let say you have a 15 teeth front, a 36 teeth rear and 94 links on a 190/50/17 rear tire. Now for every mile you drive, the rear wheel has to rotate about 824 times. This means your rear sprocket rotates 824 times. This causes 824 * 36 = 29664 links to be transported to the front sprocket. So the front sprocket will have to rotate about 29664 / 15 = 1977 times for every mile you drive !

Now you change to a 14 teeth front sprocket and keep the rear and the chain but switched to a 180/55/17 tire.
For every mile the rear now has to rotate 813 times (tire is less wide but has a bigger circumference), transporting  813 * 36 = 29268 links to the front. Now this time it has to rotate even more: 29268 / 14 = 2092 times for every mile! That is 114 (rounded) contact per mile extra, in percent that is 5.78%. (Not so odd because that is the percentage the ratio changed as well !)


So what the 'tooth - link contacts' table shows, is the number of contacts per mile or per kilometer between:

  • a Front sprocket tooth comes in contact with a chain link
  • a Rear sprocket tooth comes in contact with a chain link
  • a chain link comes in contact with a sprocket tooth (both front and rear).

This is shown for all 3 setups (hence relative) and does not indicated the absolute amount of wear.
I admit it is kind of hard to grasp....

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