Rail (750Wh) 36 tooth chainring (AXS T-Type) on 2023 Trek Rail 9.8?

[JC-1]

I've ordered a 2023 Rail 9.8 GX AXS Gen 4 and plan to upgrade to the GX AXS Transmission. The GX T-Type groupset (Bosch variant) I bought has a 36 tooth chainring. I've just noticed that the Trek website states a 34 tooth chainring is the maximum. Is that correct?

Thanks!

 

[Stihldog]

On my Rail I have a 34t ethirteen chain ring …and that is definitely the maximum. Outherwise the teeth on the chain ring could slice or scratch the chain-stay. It’s very close as it is. I’d imagine a 36t chain ring would need shim to help with any clearance issues. But then there could be an alignment issue, albeit minor.

 

[JC-1]

Damn. The Bosch groupsets for GX Transmission all come with 36 or 38 tooth chainrings, so that was the smallest I could get. I guess I’ll have to find a seperate chainring. Thanks.

 

[JC-1]

Hmmmm, even separately, the Bosch chainrings only seem to be available in 36t or 38t.

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[BuzzinHornets]

The 34 tooth limit is due to chainstay interference with the stock chain line. The Transmission chainrings are available in 34 tooth, I have one. But I am currently running the 36 tooth with no issue on my 2022 9.8 thanks to the 55mm chain line.

 

[JC-1]

The 34 tooth limit is due to chainstay interference with the stock chain line. The Transmission chainrings are available in 34 tooth, I have one. But I am currently running the 36 tooth with no issue on my 2022 9.8 thanks to the 55mm chain line.

Thanks for the reply! That's great to hear. Much appreciated

 

[JC-1]

The 34 tooth limit is due to chainstay interference with the stock chain line. The Transmission chainrings are available in 34 tooth, I have one. But I am currently running the 36 tooth with no issue on my 2022 9.8 thanks to the 55mm chain line.

While I have you for advice... is the stock chain guide adjustable for the new chainline and additional chainring size? If not, can I just use any ISCG '05 guide or is there something specific for the Bosch motor?

 

[BuzzinHornets]

While I have you for advice... is the stock chain guide adjustable for the new chainline and additional chainring size? If not, can I just use any ISCG '05 guide or is there something specific for the Bosch motor?

I could not get the stock chain guide spaced out enough for the XX chain ring. One up makes a guide for Bosch that I used, it includes spacers for a 55mm chain line.

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[JC-1]

thanks!

 

[JC-1]

Is the Bosch mounting points different to ISCG? I’m just wondering what makes an ebike specific chain guide

 

[Link]

i've been running a 36T on my Rail for over a year, no issues at all

Anyone Using Spacers to Fit a 36T Chainring

I love my rail 9.8XT but the one design flaw that pisses me off is how close the chain stay is to the stock 34T chainring. I know that the chain line is important but how much out of line can you go before it becomes a big deal? My bike is simply geared too low for the fast a flowly trails. I'm...

www.emtbforums.com

 

[JC-1]

Thanks for the info and link. A lot of customisation and tweaking. I definitely want to avoid all that as it’s a brand new bike and the Trek dealer is doing the T-Type group set installation.

Do you think the T-Type 55mm chain line would be enough to give the 36T chainring the clearance it needs?

 

[JC-1]

Is the Bosch mounting points different to ISCG? I’m just wondering what makes an ebike specific chain guide

The Bosch chain guide mounts do seem to be ISCG so not getting what makes a Bosch-specific guide since lots of guides are adjustable for height and chain line.

 

[JC-1]

The Bosch chain guide mounts do seem to be ISCG so not getting what makes a Bosch-specific guide since lots of guides are adjustable for height and chain line.

Answering my own question. It seems the only difference is the shape of the chain guide between the bolts (which are positioned the same). It’s slightly different for clearance of the protruding motor casing, but if you’re using spacers behind the chain guide, it doesn’t seem to matter. I used a non-ebike ISCG guide I had laying around and it worked perfectly.

 

[fasterjason]

Thanks for the info and link. A lot of customisation and tweaking. I definitely want to avoid all that as it’s a brand new bike and the Trek dealer is doing the T-Type group set installation.

Do you think the T-Type 55mm chain line would be enough to give the 36T chainring the clearance it needs?

I have been running a 36t chainring on my Rail 7 for the last three years and on my Rail 9.8 for the last six months. I upgrade all my Rail bikes with XT 11sp and install the Bosch 1mm countershaft spacer behind the chainring for clearance on the chainstay. To solve the chainguide issue I add (to the existing spacers) the spacers installed on the front brake caliper after I install a Fox 38 (because Rock Shox are garbage). The spacers are installed on the caliper from the factory to make the Rockshox fork work with the shimano brakes with 203mm rotor (because Sram brakes are garbage).