Can you please help my Haibike Trekking 4 has now covered 1800 miles I am now having some problems gear changing and also chain jumping when using the 2 smallest cogs on the cassette . I suspect a new chain and cassette are needed my problem is do I change them on a like for like basis or change manufacturer and is it possible to change ratios I never use the largest gear on the cassette. Currently fitted is a Shimano hg500 11-42 teeth 10 speed cassette.