Hi Guys,

I bought my dahon s18 road bike one month ago, I used it around 15 miles (25KM) a day Monday to Friday, I checked the chain length after two weeks of use, it indicates the chain not even close to 0.75% worn, but I just checked it today, after 4 weeks, it is already 1.% worn with totally less than 400 mils (650km). I take it to the shop, the guys says my chain and cassette has completely worn out, I need a new chain and cassette. But the bike never skip the cogs or feel anything strange.

My question is, how is it possible that the chain worn out so quickly in less than a month? do I need to replace cassette along with the chain or I could try new chain first and replace cassette afterward if the new chain doesn't fit well.

Also another question is that, my original cassette is 9 speed 11-25T, can I use 9 speed 12-25T instead? will it cause any issues?

Many thanks guys