Rail (625Wh) Chainline

[Peaky Rider]

Anyone know the chainline offset on a 2021, Trek Rail 7?
I have just bought a new e-thirteen chainring which gives you a choice of 53 or 55 mm but It doesn't look like either.

 

[Stihldog]

It may depend on the bike size and model but here’s what I did.

I installed a new 34t ethirteen chainring on my medium Rail 9.7 2020 to replace the original one. (chainsuck). The alignment didn’t seem right, the guard was rubbing the chain and the gap between the teeth and chainstay seemed wider.

I noticed that the ethirteen chainring had a built in “O” ring which pushed the chaining out further. I removed a brass “O” ring but left the thin plastic “O” ring. The alignment and clearance was much better once I did this. Water proof grease is your friend here.

There’s a bit more to this process but that’s just what I found. Eventually I installed a new bearing seal kit on both sides of the CX Gen4 motor.
Hope this makes sense.

 

[Peaky Rider]

I understand what you did Stilldog but the new e-thirteen chainring I have is clearly different to yours.
A bigger question I have is, why is it so tricky replacing a stock high wear item on a popular bike? You don't have this problem with the rest of the drive train. My fingers are raw with googling.

 

[Stihldog]

Hmmm, interesting .

Here’s a pic of the ethirteen chainring I used and the bearing seal kit.




Maybe there are slight differences between the different years? I’ve had good results with mine so far.

 

[Roy D]

My medium 21 9.8 had a 52mm replaced with a new 55mm for my transmission install. Truthfully I ran it with a raceface 52mm chain ring for a while and it was fine. Hope this helps

 

[Mikerb]

Standard chainline for a boost rear end is 52mm ( ie 3mm offset on the chainring). Some bikes mess with that to allow wider tyres within the chainstays but that is mostly fat bikes.
So if the chainring is direct mount the optimum offset is 3mm. If the chainring is mounted on a spider, that might provide the offset, and the only way to find out I reckon is either to buy an identical replacement to the original or see if the chainring is marked with any offset info.

 

[Peaky Rider]

My medium 21 9.8 had a 52mm replaced with a new 55mm for my transmission install. Truthfully I ran it with a raceface 52mm chain ring for a while and it was fine. Hope this helps

Not quite clear on what you are saying Roy. You ran it originally on a 52 and replaced it with a 55. Where does the Raceface 52 come into it?

 

[Peaky Rider]

Hmmm, interesting .

Here’s a pic of the ethirteen chainring I used and the bearing seal kit.
View attachment 130319

View attachment 130320

Maybe there are slight differences between the different years? I’ve had good results with mine so far.

I used the same bearing seal kit as you Stilldog but I went with steel for the chainring, not aluminium as you did.

 

[Stihldog]

I used the same bearing seal kit as you Stilldog but I went with steel for the chainring, not aluminium as you did.

Funny, I just spoke with a guy about steel vs alloy chainring. His original is steel also and needs changing.

So far the alloy chaining has held up reasonably well (ethirteen) but I bet the steel one lasts longer.

I’ve ordered 2 bearing seal kits. Motors are overdue and it’s a fairly cheap maintenance procedure. Once you do it once …it’s easy.

 

[Roy D]

Not quite clear on what you are saying Roy. You ran it originally on a 52 and replaced it with a 55. Where does the Raceface 52 come into it?

Sorry to be clear I ran the stock chain ring from e13 which has a 52mm chain line (standard boost) then I got a plus 3mm for a 55mm chain line as sram calls for 55

 

[Roy D]

Sorry to be clear I ran the stock chain ring from e13 which has a 52mm chain line (standard boost) then I got a plus 3mm for a 55mm chain line as sram calls for 55

Raceface.

 

[Peaky Rider]

I gave up with the e-thirteen chainring as it wouldn't slide onto the axle splines. I didn't want to force it and damage it in case I needed to send it back. It's now on its way back to Tredz.
I have now visited my LBS who sold me a Raceface one with the correct chainline and it fits perfectly.
I need to stop being lazy, get off the internet and use my LBS more.
Parts may cost a few quid more but at least you stand a better chance of getting the correct one.

 

[vman]

Anyone know the chainline offset on a 2021, Trek Rail 7?
I have just bought a new e-thirteen chainring which gives you a choice of 53 or 55 mm but It doesn't look like either.

Suggest you reach out to Trek Customer support if you want to know 100%. Trek confirmed for my 2021 Rail 9.7 that 53 mm to 55 mm was the accepted range. If you are running Shimano with the TSB ring there were some issues with a 1 mm spacer to place between the motor and the chainring making the chain line 53 mm - EThirteen TSB #162.https://support.ethirteen.com/hc/en-us/sections/4408352455067-Technical-Service-Bulletins-TSB-

V

 

[Peaky Rider]

Suggest you reach out to Trek Customer support if you want to know 100%. Trek confirmed for my 2021 Rail 9.7 that 53 mm to 55 mm was the accepted range. If you are running Shimano with the TSB ring there were some issues with a 1 mm spacer to place between the motor and the chainring making the chain line 53 mm - EThirteen TSB #162.https://support.ethirteen.com/hc/en-us/sections/4408352455067-Technical-Service-Bulletins-TSB-

V

Thanks vman but I ended up reaching out to my LBS and they have sorted it out for me,

 

[steve_sordy]

I am setting myself up for a lot of finger-pointing here, but here is what I always thought was the chain line:

The position of the chainring is adjusted so that it is in line with the middle of the cassette. In other words, the top strand of chain is straight and without any deviation when viewed from above.
The dimensions given by Shimano, Sram and sundry bike makers are for convenience. But what is important is that the chain is straight, or equally out of line when on an even numbered gear cassette (when on gears 6 & 7 on a 12-speed for example).

If there comes a point where I can't get the mid-point and it's an either/or choice, then I favour lining up with the larger gear (no 7 in the 12-speed example above)

Because I have always "known" this and it seems so logical, I have never questioned it, never ever looked it up on some website or other. I can't even recall where I got to "learn" this. Have I made it up and been wrong all these years? I don't seem to have suffered any transmission mishaps.

PS: On a triple front chainring, line up with the middle gear. I accept that when I fitted my first 2x chain set, it caused me some head scratching, but I muddled through and it went OK.

 

[Mikerb]

Well I think you are right and bike manufactures aim to achieve that since it delivers equal amounts of chain angle across the cassette cogs up and down from the centre............even more important on a 12 speed where the chain angle is pretty acute on cogs 1 and 12. (which is why I never use either gear 12 or gear 1!)

The normal position of the chainring from the centre of the bike/centre of what would be a BB on an analogue bike is 49mm and that will deliver a central cassette position for the chain on a 142mm ( non boost) rear hub. Most ( if not all) of our bikes use boost rear hubs at 148mm........ie 6mm wider. The cassette is therefore 3mm ( half of the 6mm) further out on the drive side of the bike. A chainwheel that has 3mm offset ( or a chainline of 52mm) keeps the chain straight on the central cog of the cassette therefore.
On mountain bikes, manufacturers also have to use a chainline that enables the chain to avoid hitting the chainstay ( typically on the upper cogs of the cassette) whilst also allowing enough clearance between chainstays for tyres up to 2.6....or on a fat bike 2.8 or 3!!. There are various ways they can achieve that and moving the freehub/cassette position slightly further out on the hub is one and using starting position at the BB of more than 49mm is another.
In most cases if the rear hub is boost the chainline is 52mm.
I think from reading some of the posts on Eagle "T" the required chainline is 53mm?? ( not interested so not sure!! ) presumably because the "T" cassette sits further out on the hub.

 

[vman]

Anyone know the chainline offset on a 2021, Trek Rail 7?
I have just bought a new e-thirteen chainring which gives you a choice of 53 or 55 mm but It doesn't look like either.

Well I think you are right and bike manufactures aim to achieve that since it delivers equal amounts of chain angle across the cassette cogs up and down from the centre............even more important on a 12 speed where the chain angle is pretty acute on cogs 1 and 12. (which is why I never use either gear 12 or gear 1!)

The normal position of the chainring from the centre of the bike/centre of what would be a BB on an analogue bike is 49mm and that will deliver a central cassette position for the chain on a 142mm ( non boost) rear hub. Most ( if not all) of our bikes use boost rear hubs at 148mm........ie 6mm wider. The cassette is therefore 3mm ( half of the 6mm) further out on the drive side of the bike. A chainwheel that has 3mm offset ( or a chainline of 52mm) keeps the chain straight on the central cog of the cassette therefore.
On mountain bikes, manufacturers also have to use a chainline that enables the chain to avoid hitting the chainstay ( typically on the upper cogs of the cassette) whilst also allowing enough clearance between chainstays for tyres up to 2.6....or on a fat bike 2.8 or 3!!. There are various ways they can achieve that and moving the freehub/cassette position slightly further out on the hub is one and using starting position at the BB of more than 49mm is another.
In most cases if the rear hub is boost the chainline is 52mm.
I think from reading some of the posts on Eagle "T" the required chainline is 53mm?? ( not interested so not sure!! ) presumably because the "T" cassette sits further out on the hub.

Agreed....to note - Trek allows you to push out from 53 mm to 55 mm because you don't have frame clearance issues going wider. Note - unless you change the front chain ring to less than 34T you cannot get any closer in ie less than 53 mm without risking hitting the chain stay under peak load. Shifting would be optimal with no offset but in practice the modern systems work fine even with some offset to deal with frame clearance. Note - in practice going back and forth between a 53 to 55 chain line is not a big deal - a much bigger deal is making sure you have a chain and cassette in good repair and are running a compatible front chainring --- Shimano 12 does not play well with SRAM. Jury is still out on proprietary chainrings pattens that supposedly work well with both Shimano 12 and SRAM