Longer chain needed?

[Sbaumann14]

So….I have a shimano 8 speed 11-34 with the SRAM x4 med cage with a Luna 42 tooth up front powered by my BBSHD. The chain keeps jumping like the derailleur is trying to shift. Adjusted the derailleur to no help, so I’m pretty sure it’s the chain or cassette. My bud has an 8 speed cassette he’ll give me, but the gearing is 11-45. I know I’ll need a long cage derailleur (pretty cheap), but am I gonna need a longer chain as well? I think I’ve got a 116 on there now.
Any help would be great! Thanks!

 

[Annieolnie]

This is just a thought, but you might want to flip the bike over and check that your cable is not snagging anywhere and also how well any ferrule caps on them are sitting. I had trouble with shifting on my Kona with a bbs02 when the cable was slightly off the guide that ran between the motor and the frame.

 

[major masingil]

I used this formula when I changed my rear cassette to a 11-42 a few months ago. I have a 42t front chainring and BBSHD. So far no problems...seems a little tight but it's shifting fine


L=2C+(4F+4R+1)
Where:

L is the chain length in inches (rounded to the nearest inch).
C is the chain stay length in inches.
F is the number of teeth on the largest front chainring.
R is the number of teeth on the largest rear cog

 

[Chuy]

Sounds like an alignment issue to me. Check that the hanger is straight. If using SRAM derailleur, do you also have SRAM shifters?

 

[Rawly Old]

So….I have a shimano 8 speed 11-34 with the SRAM x4 med cage with a Luna 42 tooth up front powered by my BBSHD. The chain keeps jumping like the derailleur is trying to shift. Adjusted the derailleur to no help, so I’m pretty sure it’s the chain or cassette. My bud has an 8 speed cassette he’ll give me, but the gearing is 11-45. I know I’ll need a long cage derailleur (pretty cheap), but am I gonna need a longer chain as well? I think I’ve got a 116 on there now.
Any help would be great! Thanks!

Could just need the index adjusted. I'm old school; anything with more than 7 spds. is too many, before ever putting
on the chain i make sure the derailleur moves sideways to exact limits hi & lo. Then with chain on I carefully adjust
the index up or down to keep it from jumping multiple gears at once.

 

[Lovetoride]

Could just need the index adjusted. I'm old school; anything with more than 7 spds. is too many, before ever putting
on the chain i make sure the derailleur moves sideways to exact limits hi & lo. Then with chain on I carefully adjust
the index up or down to keep it from jumping multiple gears at once.

before ever putting on the chain i make sure the derailleur moves sideways to exact limits hi & lo.
Good advice, thank you !