Bosch cranks and chainring question

[AssegaiRear]

Hi, everyone. I'm new here, thanks very much for having me, and looking forward to any insights anyone can provide with this problem I'm confronting. I own this bike:

Rail 9.9 XTR - Trek Bikes

www.trekbikes.com

Or rather that frame, with a Bosch Gen 4 motor. The components were/are much lower spec. I have about 5000 miles on it, and I'm really tired of snapping chains and so on. Right now, it has a full SRAM X01 mechanical drivetrain on it, and I'd really rather keep it that way to maintain compatibility of my wheels across my fleet of bikes.



Just yesterday, I snapped a new XX1 chain, loosened, and damaged my brand new Hope e-bike chainring. I had concerns about using an alloy chainring due to the nature of e-bikes, and this kind of confirmed the problem. So here is what I want to do, and I'd love all of your thoughts on whether its feasible or not:

• If I upgrade to an absolute black super steel chainring, can I keep using my Hope e-bike cranks? Everything I've seen indicates I should be able to, and indeed that any Bosch compatible crank arms should work on any Bosch compatible chainring.
• If I upgrade to a Shimano HG+ chainring, can I run an XTR chain on my otherwise SRAM 'train? XTR chains are, according to Zero Friction Cycling, the only decent e-bike rated mechanical chains. I have unfortunately also snapped at least two KMC E12 chains.
• If I upgrade to an absolute black ring, could I squeeze a 38t on there? My understanding is that larger chainrings place less mechanical/motor stress on the rest of the drivetrain. The Trek site says max chainring is 34, but I'm pretty sure I could slap a 36 on there without trouble. A 38 is much iffier.

Any insights would be very much appreciated. Thanks again.

 

[Arethustra]

What chainline are you running? I think it’s a 52mm for mechanical SRAM…the chainring should be fine but I don’t know what the offset is for the Hope cranks but I assume you have the correct ‘line if not, I’d addressed that first as it can contribute to breaks - do you know what gear you’re in when the breaks happen? Not sure about your chainring size question (I wouldn't go over 34T personally but that's a chainline thing for me - I like to stay more in the middle of the cassette than at the extremes to reduce chainwear/chain drama) but the fact that your snapping so many chains has me wondering what's outta whack on your drivetrain. Have you serviced it lately?

 

[AssegaiRear]

What chainline are you running? I think it’s a 52mm for mechanical SRAM…the chainring should be fine but I don’t know what the offset is for the Hope cranks but I assume you have the correct ‘line if not, I’d addressed that first as it can contribute to breaks - do you know what gear you’re in when the breaks happen? Not sure about your chainring size question (I wouldn't go over 34T personally but that's a chainline thing for me - I like to stay more in the middle of the cassette than at the extremes to reduce chainwear/chain drama) but the fact that your snapping so many chains has me wondering what's outta whack on your drivetrain. Have you serviced it lately?

Thanks. The drivetrain is incredibly regularly serviced. I raced the bike this year, so I had it overhauled around the start of the season. There was a golden period of about two weeks last month when it shifted perfectly for the first time since I got it, but then I naturally I crashed, lol.

I have a great relationship with my local Trek, and as of about two months ago, when I put the Hope ring on there, it had a completely new drivetrain. New X01 derailleur, new X01 shifter, new GX cassette, new chainring, new cranks, new pedals even.

I'm not totally sure about chainline. I ordered the chainring from a bike shop on Pinkbike, and they ordered it as new production from the Hope factory. According to Hope's page on the ring, it's generally a 52mm chainline, but the Hope Bosch eeb rings 2024 are said to have a 55mm chainline. I've seen indications that a 55mm chainline is fine.

The breaks do almost always happen when I'm in a higher gear. I think I was in the second or third at the time, and I was going up a slight rise from a near stop (I know). It seems the ring may have been a bit loose to begin with, which was probably the biggest contributor to the problem.

 

[irie]

... It seems the ring may have been a bit loose to begin with, which was probably the biggest contributor to the problem.

Figures

 

[Arethustra]

I believe SRAM spec's a chainline of 55mm but 52-55mm will work - that said, extremes on the cassette are a problem when you're on a 52mm chainline but are spec'ed for a 55mm. The advice I got was go up or down a few teeth in front based on where you are spending the most time riding as you want to spend the bulk of it in the mid-range of the cassette so that you're not constantly in the extreme high/low where the angles are a potentially going to cause you problems.

Most vendors seem to only have the Hope 52mm chainline (assuming you used the direct mount) so my bet is that is what you are running (see below from Hope website) - if you go AbsoluteBlack you have the spider to contend with but can also use spacers to adjust your chainline since the chainring is 0 offset. Only thing is AB rings only work on AB spiders so you're not on a standard 104 BCD ring and will have to get a whole new setup if decide you want to use anything other than another AB chainering.

// Designed to give 52mm chainline to suit 148 Boost frames​

// *New for 2024 55mm chainline Bosch (Gen 4 Direct Mount) ebike chainring*​

 

[Mikerb]

Firstly, the cause of your problem was more than likely the chainring coming loose, potentially meaning it was not correctly fitted.
I personally believe a steel chain ring is a better bet on an EMTB. A SRAM chainring is an option. You need a "boost" direct mount chainring ( 52mm chainline).
Lastly all SRAM Eagle components are compatible so you can use any Eagle chain............Im a bit confused on what chain you are using, you said you have a full X01 drivetrain but then mentioned you snapped a XX1 chain. Lots of people rate the X01 chain for lower wear than the GX chain and I have seen no reports of chain breaks with that..or indeed the GX which is halve the price....not sure why you would use an XX1 on an EMTB however. You also said you had a full X01 drivetrain but then said your cassette is GX!! Not that is matters since all the Eagle range is intercompatible.
As long as the Hope Cranks are the correct ones for a Bosch motor ( Q factor) they will fit regardless what brand chainring you get. EMTB Cranks are only concerned with spindle fitting...in this case ISIS.......and Q factor so that there is clearance to the chainstay.
i dont know what size chainring you could fit but the limiting factor is chainstay clearance........maybe other Trek users can comment on that.