As per my last thread, I have an M785 crankset on my bike just now. In advance of swapping to 1×10 I’ve been out (to the garage/work stand) to see how smooth it is in the big ring and the big sprocket. It didn’t seem great to me, the chain looked like it wanted to come off the sprocket, and it definitely sounded a little more scrapy than it did on the other smaller sprockets.

I therefore wonder if, rather than bolt the NW ring straight onto the inside of the crank – where the 38t ring sits now – it might be better to get longer chainring bolts and spacers, to move it in a few mm, so it’s as close as possible to being in line with the middle of the cassette? But by how much? I’m not sure what the gap between chainrings is, looks maybe around 8mm. Should I go for as much as a 4-5mm spacer and corresponding bolt? And who can I get longer bolts plus spacers from? (CRC/Wiggle etc. it’s the spacers Imnot seeing easily).

The Shimano tech doc parts list says the outer bolts on M785 are M8x7.

I’m guilty sometimes of being a bit too much of a perfectionist so apologies if that’s the case here 🙂

Spacers = washers using standard double chainring bolts

I doubt you can get bolts longer but I do not know for certain

It has to be in the same place as the one it replaced which did not break so not really sure what your issue is beyond it could look nicer

I suppose my concern is that a single ring in the outer position of the 2×10 crank will result in too much of a twist, if that’s what you’d call it, in the chain when using the biggest sprocket. At the moment, with 2×10, I wouldn’t ever have the big ring/big sprocket together, so I’ve got no basis on which to assume that that twist won’t be too much.

Too tired to visualise if it helps mine lines up with 6 th gear and the ideal has to be it being somewhere around 5/6 in a straight line as this minimises twist.

How much it can tolerate [ without dropping or excess wear] I have no idea

Thanks, guess I’ll probably just need to try it.

I moved my BB spacers accordingly to bring the NW on my 2x crank roughly in line with sprocket 6. Works very well. Would depend on your chainring/chain stay clearance of course. My other bike has a triple crank with NW ring, but I used washers to space it out as the bolts on a triple are too long for a single ring. Again, I used the BB spacers to align the ring with centre of cassette.

Same here, moved 1 BB Spacer to bring the crank in a little. Fixed the line.

That’s what I did too. So long as the crank arm has ok clearance at the chain stay you’ll never notice the change in its overall position.

Ok thanks, I have one DS spacer so that gives me 2.5mm. In addition, a set of steel 8.5mm bolts (ones on there now are ~7mm) and 2mm washers is a matter of a few quid, so that would give me 4.5mm to play with. Chainstay looks ok for that, and that should be enough scope to get it in the same place as the middle ring on a triple would be (M780 is 50mm chainIine).

I’ll just put it together and squint at it 🙂

If you’re a perfectionist, avoid the washers, it looks a bit of a bodge. Also, I had to grind one edge of each washer so it didn’t foul the chain on a 32t chainring.

I’ll send the washers away to get anodized…

Moving the BB spacer only would put the single ring at 48.8mm, further in than the middle ring of the triple, so I’ll try that first.

UK Bike store do proper chaining spacers in different widths these would look better than a stack of washers.

On my tablet which doesn’t want to do a link so just Google it.

SRAM standard mtb 1x chainline is 49mm
For cx1 it’s 45.5mm

And of course adjusting spacers on drive side cups doesn’t affect sram chainline at all, as crank floats in driveside cup and is held in position by the non driveside cup.

Thanks – it was the wheels manufacturing ones I’d spotted somewhere else, but there’s more choice on ukbikestore.

So if the SRAM chainline is 49mm, I can pretty much get that just moving the BB spacer across.

Bought some steel spring washers (99p) from ebay as I thought spacers made for bikes were just too expensive. Couldn’t move my bottom bracket spacer as I’m using a bb chainguide and have 73mm shell. They happened to be a perfect width, now my chain is right in the middle of the guide.

What crankset did you start with mudmonster?

The 2.5mm spacing offset that moving the BB spacer will give you gets it workable using a double crankset, but IMHO the best option is to space again another 2mm – I think 1x chain lines are all too far outboard as the chain line is far worse on the big sprocket top and bottom due to the shorter distance to the cassette/mech making the angle more acute.

Thanks Ben. So a combined 4.5mm shift inwards should have it working nicely on a Zero 1, to pick a bike entirely at random 🙂

Xt double

Cheers, same as mine

Just checked mine, its a slx double, chainline is straight in 5th gear. The chain is quiet on both the 42 and 11 cog, which it wasn’t until I moved the crank inboard.

Ok cheers. Where I said washers before I meant the specific spacers.

The problem you have is that Shimano changed the chainline for their 2×10 chainsets. The triple was ideal for 1×10 because the middle ring sits right in the middle of the block and can span the entire cassette without causing too much chain bend. For 2×10 Shimano in there infinite wisdom offset the 2 chainrings by a couple of mm either side of center.

the result of this is that the chainline of the bigger ring is optimized for the smaller cassette sprockets and the smaller chainring is optimized for the bigger sprockets. This works for 2×10 as you dont really want to be crossing the chain if you have 2 chain rings to choose from.

The down side is you no longer have a chainring that can comfortably cover the whole block.

bottom line – run either a triple or a single chainset for 1×10 if you dont want to bodge your chainline.

^ that figures, although I suppose it makes sense for them to do it when designing a 2×10 system.

I was out last night and today just to check that the hills I ride up regularly will be doable with the chainring I’ve bought. 24/28 is almost equal to 32/36 – 0.86 vs 0.88 – and I got up everything no bother using the 24/28 gear or bigger, so that’s all good.

I also had a look at how well the smaller ring works at both ends of the cassette. Very well as it happens, which indicates that the suggestion above to go in 2.5mm with the BB spacer and a further 2mm with a chainring spacer will put it in just the right place (assuming a 5mm gap between chainrings).

I believe the spacing on the rings of a triple is 7.5mm.

Chain line of a outer double is only 2.5mm outboard of a middle triple, so switching one bb spacer over is enough. Or spacers under the ring, which help the chain clear the tabs if you are using a 32t.

If it’s 7.5mm then that’s close to what I crudely measured it as the other day. I think I got 5mm from the Sheldon Brown website, but I may have got the wrong end of the stick somewhere in reading the article.

If you’re running a narrow wide ring is still worth adding the extra 2mm spacer to compensate for the more obtuse chain angle and increased tooth engagement when using the bigger sprockets.

I’ve got some 2mm spacers coming ben, so was planning to do what you suggested further up there and use them and move the BB spacer.