rumatt

I'm trying to run a 42/26 tooth 2x setup using a Shimano XT M785 crank. I have it working except my 42T chainring was designed to run as the outer chainring so it dosn't have recessed holes for the bolts. THus the bolts stick out too far and the chain hits them when it's on the small chainring.

I see Blackspire makes one, but the reviews align with my experiences - they look cool but the shift quality is low.

Are there any other options out there?

Iride01 

You confused me at "middle" chainring in your title and 2x in your post. What is middle for a 2x?

rumatt

I mean that it's designed to be mounted with the outside of the chainring up against the spyder's inside surface, rather than the other way around.

The 42T chainring I have now is designed to mount on the *outside* of the spider. The chainring's holes are not countersunk on the inner side, so when I put in the bolt sleves they stick out too far and the chain hits them when it's in the smaller gear.

Chainrings meant to be mounted inside a spider have a larger bore and the bolt sleeve gets pulled inside it so it sits flush.

shelbyfv

I'm not surprised it's hard to find! The 42 middle would have been fairly common on 130 BCD road triples, though. Maybe get one of those, swap the small 30T for a 26T and make a bash guard of the big ring.

Iride01 

Part of the reason the mfr doesn't offer you every combination under the sun for your choosing is because they've found that there aren't that many combinations that offer the excellent shifting they are marketing to the public.

Things like where the tooth will be that the chain is moving to. Many ring combos, the tooth to snag may not get in the proper position soon enough and you'll just have poor shifting and maybe even more wear on your chain rings resulting in shorter life.

So you might just look for combos that you see generally offered by shimano on cranksets and just change up your cassette to give you more of what you are wanting with a particular chain ring pair that meets specs...... if you are worried about the poor shifting others complained about in the reviews.

If not, just try it and see. You might have a good experience with it or not need the standard of performance they wanted.

Eggman84

You might want to look at Vuelta chainrings. They make a 42T 104 BCD versions without ramps and pins (SE Flat) and ones with ramps and pins (SE Plus). The 42T version is listed for both middle and outer position. I can not tell from their website whether this means the holes are countersunk on both sides. Seems like the ring would e pretty thin at this point.

Eggman84

Lets step back for a minute. The Shimano FC-M785 crankset only comes as a double (either 40-28, 38-26, 38-24 matched rings) so there is no "middle" position. The larger chainring fits on the outer face of the spider. The smaller chainring fits on the opposite (inner) face of the spider. Are you trying to put both chainrings on the same side of the spider?

rumatt

Yeah, the M785 has both chainrings on the same side of the spider. See the pictures here

https://www.amazon.com/SHIMANO-CR440.../dp/B008Z9CUQU

Eggman84

You are correct, my mistake. In that case, good luck finding a 104BCD 4 arm 42T middle ring; in the MTB world that number of teeth was designed primarily for the outer position of a triple crankset. Did any 10 speed doubles go that big? Its funny how in the name of achieving perfect shifting performance, Shimano has really limited your choice of chainrings, and because they seem to tweak the design every few years no one else has any interest in making replacement rings.

fietsbob

Sell that crank that is limiting your choices, & get something that will take a 42t as a 'middle' or inner..

110 or 130 - 74

hermanchauw

How often do you plan to shift? If not often, how about singlespeed chainring?

Eggman84

Just wondering, what 42T chainring are you using now (manufacturer and model #?


Looking at the archived Shimano Compatibility Chart from 2014/2015 (file:///C:/Users/eggma/Downloads/201...ty_v010_en.pdf, see page 5), I see that the FC-M985 came as a 10 speed double with a 42T large chainring (paired with a 30T small ring). This crankset is the XTR version and was manufactured in the same time period as your XT M785. If you could locate that 42T chainring it might work. But I see now that the 985 has a 88BCD. Thanks Shimano. As I said in an earlier post, good luck.