To all you 29er's out there!

I do have reservations however as I think the idea is to run two chainrings so that the axle position remains constant and the disc brake pads do not need to be adjusted. So my question; do you reckon swapping between the 17t and 19t cogs (with single chainring) would cause a large enough difference to warrant adjustment each time?

I'm a bit confused here. I can see why you'd be concerned about chainline ( although this would be fine if you used a multi speed chain ) What puzzles me is how the axle position is changed by switching between the 2 cogs on the freewheel & why the brakes would need adjusting? Surely moving the brake rotor out of alignment would involve moving the hub sideways, thus putting the whole wheel off centre :-/

What am I missing here?

Because the wheel will be moving forwards or backwards depending which size cog he's using.

I thought it meant moving the axle forward/backward in the dropouts. In which case you'd need to move the calipers too.

Because the wheel will be moving forwards or backwards depending which size cog he's using.

Duh, of course :-s

Adjusting pads made me think of sideways adjustment & my brain got stuck there.

Not sure how much a calliper would need adjusting for a 2 tooth difference :-/

^ I think I'd dinglespeed it to save the hassle.

Because the wheel will be moving forwards or backwards depending which size cog he's using.

I thought it meant moving the axle forward/backward in the dropouts. In which case you'd need to move the calipers too.

^Yep, that's what I mean. Sorry, possibly not very eloquent of me! Yes, my initial reaction is that a cog difference of 2 teeth may not cause enough forward/backward movement to mean the brake pads need to be adjusted each time, however £84 is quite a lot to fork out for a cog when i'm not certain.

Just off the top of my head, wouldn't 2 extra teeth on the cog equate to 2 extra chain links? So if you added 2 links ( 1 inner & 1 outer plate ) to your chain, then you could move your wheel back in the dropouts & check if the calliper would need moving when you switched between 17t & 19t.

Or am I just very tired :-/

Distance wise its half a full link. I'm pretty sure you could place your caliper such that it functioned well in both gears. This is the only time its really advantageous to have SS threading (as opposed to threading for sprocket and lockring), as it allows for a more adjustment room. But with a standard 9/8 speed chain, chainline wont be a problem.

I'm not going to promise anything over the interwebs. I'm pretty sure you could get this to work well.

2 teeth difference on my tricross is enough to make me unhappy, they work, but I'm always worried about rubbing my tyres or have the pads jumping on top of the rim under hard breaking.
I think it also depends on the angle of the dropouts, some are more forgiving than others.

^^ Without going off to measure chainlinks ( which I'll probably go & do in a minute ), magic gear calculator is telling me it's a 6.1mm difference between the 2.

^ Yes, workable, but not sure I'd be totally happy.

Conclusion = Dinglespeed ;-)

Sorry. Are we not talking about a disc brake here.

#goestositincorner

Sorry. Are we not talking about a disc brake here.
#goestositincorner

Come out of the corner furry, it's a disc brake

2 teeth difference on my tricross is enough to make me unhappy, they work, but I'm always worried about rubbing my tyres or have the pads jumping on top of the rim under hard breaking.
I think it also depends on the angle of the dropouts, some are more forgiving than others.

^ How did I not read that bit?

I think I'd just see how well the disc brake calliper copes with 3.05mm difference either way. Probably be fine :-)

*goes for a lie down.

ah disc brakes talk, my apologies.

Cheers all. Right ok, first I think I will remove chain altogether then move axle back and forth in dropouts and see how the disc handles braking with no adjustment when just freewheeling down the hill outside.

The chainline thing wont be a problem.

If your rear caliper is mounted in the most common, top of rear triangle position. You'd need to set up dead center when inbetween the 2 axle positions. Then it will be moved 3mm in either direction. The loss of pad contact area will be minimal.

If you caliper is mounted within the rear triangle. You can only go from say 1mm from fowling the caliper body to pulling it 6mm directly out. The loss of pad contact area will be loads more.

I'm pretty sure Tester himself has mentioned you can have a variation of a couple sprocket teeth without notable braking loss.

Thanks, mine is mounted in the more common above rear triangle position. So am I right in thinking that in theory if I run the same length chain as currently running with 33x18 the axle position should only be moving +- 3mm (from the current position) when swapping between the 17t and 19t?
p.s. that second green frame looks pretty sexy.

p.s. that second green frame looks pretty sexy.

Are you sure about that?

Wow. My eyes.

What a waste of sexy paint.

Wow. My eyes.

What a waste of sexy paint.dropouts

:-)

The chainline thing...
If you caliper is mounted within the rear triangle. You can only go from say 1mm from fowling the caliper body to pulling it 6mm directly out. The loss of pad contact area will be loads more.

Sorry to but in...

...do those ^ drop outs mean that you don't have to worry about adjusting your brakes as the caliper moves as you effectively adjust the dropout/chain length?

yes

yes

^ whs

It's a great idea really. Some designs work a lot better than others though.

Quick question,
I'm converting my tricross from SSCX to a kind of lightweight singlespeed 29er lowpro (V-brakes, fatter tyres, wide flat bars).

What max size tyre would you recommend on an open pro rim? I'd like to think that I can go up to 2" but maybe it means too much side roll.