V20 Build Question

[unc99]

Got a frameset and am just about finished with the build. One issue though that I wanted to ask the group about. I just installed the chain and the chainline is off. When the chain is in the lowest sprocket on the cassette (11T) and the lowest chainring (34T), the chain rubs the inside of the big chainring. Any thoughts on what is causing this? Perhaps the answer is just not to do small/small.

Here is what I am running below. Thought I had everything matching perfectly. Bottom bracket and crank arm were torqued with a torque wrench to spec.

SRAM Apex 10 Speed 50/34T Crankset
SRAM Team GPX Bottom Bracket (68 mm) (not using any spacers)
SRAM PG1070 11-36T Cassette
SRAM 1071 10 speed Chain

 

[castlerobber]

The same thing happens with the 50/34 crankset and 12T small cog on my Silvio. One of the guys explained why it does that, but I can't find the thread. I try not to cross-chain if I can help it; so for me, hearing that rub is a useful, audible "shift the front already" indicator.

 

[unc99]

Thanks Castlerobber. After checking further, I am actually getting the rub on the bottom three sprockets, so I think something must be amiss.

 

[ratz]

On a 50/34T you will get rub on the inside of the 50 when you run little x little if you are on a medium and under 6ft tall in your setup.. That's normal.

If you arent getting rub in other sprockets the likely causes are:

1) You have SRAM Cassette 11sp on 11spd hub; or 10sp on 10spd hub; and you used the the Shimano spacer included with the wheel behind the cassette. With a Sram cassette that spacer should not be used and it will push the cassette too far to the right; but you'll still be able to screw it on to the wheel.

2) You have a disc brake wheel with 132.5 or 135mm spacing; and you didn't use the MTB spacer 2mm spacer with your bottom bracket to correct the chain line this will result in the crankset being too far to the left relative to the rear wheels width costing you 1-2 gears of clean running.

3) You don't have your B-screw tightened down enough; you can tell if that is true if you have a very loose chain when in little x little; a derailleur ships from the factory with the bscrew positioned for a 39T or 43T small chain ring; for a 34T you will have to tighten it at least 4 complete turns.


4) You derailleur hanger isn't mount correctly and it's not sitting in the Notch correctly causing it to be kattywompus .

Check those items and if non of that applies get use a close up photo of the rear derailleur setup to look at.

 

[super slim]

On a 50/34T you will get rub on the inside of the 50 when you run little x little if you are on a medium and under 6ft tall in your setup.. That's normal.

If you arent getting rub in other sprockets the likely causes are:

1) You have SRAM Cassette 11sp on 11spd hub; or 10sp on 10spd hub; and you used the the Shimano spacer included with the wheel behind the cassette. With a Sram cassette that spacer should not be used and it will push the cassette too far to the right; but you'll still be able to screw it on to the wheel.

2) You have a disc brake wheel with 132.5 or 135mm spacing; and you didn't use the MTB spacer 2mm spacer with your bottom bracket to correct the chain line this will result in the crankset being too far to the left relative to the rear wheels width costing you 1-2 gears of clean running.

3) You don't have your B-screw tightened down enough; you can tell if that is true if you have a very loose chain when in little x little; a derailleur ships from the factory with the bscrew positioned for a 39T or 43T small chain ring; for a 34T you will have to tighten it at least 4 complete turns.


4) You derailleur hanger isn't mount correctly and it's not sitting in the Notch correctly causing it to be kattywompus .

Check those items and if non of that applies get use a close up photo of the rear derailleur setup to look at.

kattywompus means knocked askew!

I would not have thought about note 2, Very good!

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