Question: I have a [2009 Kona Dew](http://www.konabikeworld.com/09_dew_en.cfm) and I'm just wondering how to figure out what front and rear derailleurs are compatible with my bike.

Do I just have to find a matching Shimano part that fits 8-speed gearsets? It seems like most of the [front derailleurs at Jenson USA](http://www.jensonusa.com/store/sub/132-Derailleurs+Front-Mountain.aspx?s=2922&mfg=0&closeoutHotdeal=&use=&sort=Default&show=25&pricemin=0&pricemax=900) seem to support 9-speed only, same goes with the [rear](http://www.jensonusa.com/store/sub/1565-Derailleurs+Rear-Mountain.aspx?s=2919&mfg=0&closeoutHotdeal=&use=&sort=Default&show=25&pricemin=0&pricemax=700)s too.

Answer: 
There is one other aspect that has not yet been addressed: shifters.

Shimano and SRAM use different technologies for the rear derailleur. Most SRAM has a 1:1 actuation ratio, which means that the length of cable moved by the shifters is identical to the horizontal movement of the derailleur. However, all Shimano uses a **2:1** actuation ratio, which means that twice as much cable has to be moved as horizontal movement of the derailleur.

If you have Shimano shifters, you **must** get a Shimano rear derailleur.

But if you have SRAM shifters that are X-series (X-4, X-5, X-7, X-9, X-0), you **must** get a SRAM rear derailleur.

This is a concern *only for the rear derailleur* and not for the front derailleur.
<http://en.m.wikibooks.org/wiki/Bicycles/Maintenance_and_Repair/Gear-changing_Dimensions> Shimano pulls roughly half the cable per shift compaired to SRAM.