Ha! My first “bike tech” question…my local LBS told me that when I switch out my rear gears that I need a new chain because each chain “wears itself” into the grooves. New gears, new chain.
Is this true or just BS to make more money selling me a chain?
i hope not, cuz that means i should be changing my cassette out every 2000 miles along with my chain. sorry, not going to happen. that would get way expensive. eventually, if you don’t keep your drivetrain clean, or live in a sandy area, you may see a chain wear a cassette bad, but with regular maintenance (ie. every few rides run your chain through a rag, and relube) you should get a good 7000 out of a cassette.
Ha! My first “bike tech” question…my local LBS told me that when I switch out my rear gears that I need a new chain because each chain “wears itself” into the grooves. New gears, new chain.
Is this true or just BS to make more money selling me a chain?
It is true IF you don’t change your chain often enough and the danger of not replacing the cogset in that case is the likelihood of the chain slipping…which isn’t fun.
How often is “often enough”? Well, if 24 links of the chain (under tension) measures longer than 12.125" from “pin to pin” (i.e. >1% elongation), you left it too long. I typically replace my chains when they measure less than half that just to be safe.
Here’s an easy way to check. Put the chain on the big ring and in the middle of the cogset so that the bottom span of the chain is under moderate tension. Place one edge of a 12" metal ruler up against the edge of a pin. If, on the opposite edge of the ruler you see half of the pin “peaking” out from behind the ruler, it’s time to change the chain. This works because chain pins are typically 0.125" in diameter.
Or…an even easier method is to do what I do on bikes of mine that see common use. Just replace the chain every 6 months. Using this technique, I have 4 cogsets for 2 bikes and I’m able to interchange them at any time with no danger of skipping. At least one of these cogsets is almost 5 years old…and I ride at least one of those cogsets almost every day.
Chains are cheap…cogsets and chainrings aren’t.
Hope that helps.
Ok - here’s what I’m gathering from this…if I get a new rear cassette, I SHOULD get a new chain. Not because it won’t “match” the old cassette, but because it’s just about time to get a new chain for preventive maintenance purposes? I don’t want to make this too complicated - being off by 0.125" vs. just telling me “change your chain every 1000 miles” or whatever is a lot easier.