Hello
I have a bike with a 42/12 cassette and single crank. I am having trouble with the derailer. The bike came with a SRAM x4. I think this derailer is too short and will not support 42t. I am thinking I can not extend this derailer because it doesn’t support 42t. Can soneone help me. This is an e-bike I built. Thanks

Welcome to bike forums.

Can you first tell us what derailleur you are using?

Barry

a SRAM x4... TLS needs a Wolf Tooth or a different derailleur.

The SRAM X4 rear derailleur has the following specifications:
mackadamfactors.co.uk
+4

Speed: 9/8/7s
Cable pull ratio: 1:1
Cage: Long
Maximum tooth capacity: 34
Pulley bearings material: Steel
Cage material: Aluminium
Weight: 280 g
Color: Black
Compatible with SRAM 1:1 actuation ratio shifters (triggers and twisters).

i advised the mods to move this thread to the Bike Mechanics sub-forum..

a wolf tooth would not work? This derailer does not have the tooth capacity?

sorry I must have posted in the wrong folder.

Wolf Tooth Roadlink is what you want.

I moved this thread to bike mechanics from General Cycling. TLS, it isn't a problem, but you might get more help here

oops
Im a Shimanoguy, didn’t know that’s then name of a derailleur.

Barry

Click your link and look up the specs. I doubt the Wolf Tooth is going to cut it.

Not only does the jockey pulley have to clear the 42t big cog. To be effective, it has to get close enough to the small cogs (11t) on the other end of the cassette. The X4 is designed to work with a 23t spread, not 31.

Your derailleur maxes out at 34T the way it is. Wolf Tooth at 20 USD or its ChiCom Knock Of on Amazon for 7 USD are workable. And thats with modified wheel position and B screw adjustments. You should be able to get up to a 36 teeth, maybe, but not more using the extender. I would go to another derailleur if I wanted to get to 42 teeth.

Could you recommend a derailer for my situation.. This is an e-bike I will use on my farm that has steep hills. It doesn’t have to be anything fancy just reliable. Thanks for your help.

my bike has a 12-42 cassette and a 28t lekki bling ring. It is an 8 speed.

Whoa.. I dont know much about ebikes of any type. You are looking foe a heavy duty long cage derailleur for 42 Teeth. Most max out at 42T so you may still need a Wolf Tooth. This is a tougher call then expected. Maybe a Shimano GRX Long Cage would work...

the Long Cage version will work, if a wolf tooth is added... the X4 has wrap capacity for a 3x front crankset, and a 34-11 rear cassette.
SRAM's spec sheets leave a lot to desire.

as to the distance from the 11t to the upper pulley... meh... it's a seldom used cog anyway.. small cog shift crispness would suffer, but not enough to matter.
as long as the chain is kept fresh, the shift speed would be acceptable.

all of this is dependent on the der. being the more recent x4 long cage offerings, and not a hammered-on old timer unit.

i'm an ALL Shimano owner/operator/installer, btw. I avoid SRAM parts, when possible.
my co-op has over two hundred bins of parts... one bin of SRAM ders, one of Campy ders... i have 4 bins of old suntour, and over ten bins of shimano ders, as a comparison.
i mostly toss out old SRAM ders as "worn out" or "broken".
.