The internet seems a bit thin on useful information regarding the effects of rear suspension on derailleur capacity. Particularly with my bike (Norco Aurum A1) so I thought would share here and hopefully the search engines pick it up. I can’t be the only person to buy a used downhill bike thinking they could add some gears and pretend it’s an enduro.
TLDR: Budget 8-10 chain links for suspension movement.
Details:
The bike came from factory with 3 of 10 gears on the cassette removed and replaced with a spacer either because:
A) Its cool
B) It saves weight
C) Because the derailleur didn’t have enough chain wrap to support them.
It’s C, definitely C. If you put any climbing gears on the back you are goin to bottom out on the chain before you hit the bump stop.
So I got the biggest capacity 10 speed derailleur I could find that still mounted with a b link (11-48), under sized the cassette 11-40 and hoped my suspension only used 8 links. I got lucky and It worked. 11-40 is the most it could fit, maybe 11-42 but that would be the absolute limit.
I am pretty sure most bikes have less travel and less chain growth than the Aurum so if your doing a big travel enduro build or modifying a DH bike you are probably safe budgeting for around 8-10 links of chain wrap for your suspension.
Maybe someone can confirm this translates to trail bikes? By my logic a trail bike with 100mm of rear travel would need 4-5 links of chain wrap capacity on average.
Keywords: Chain Growth, Aurum, Enduro, Bike Setup, Norco