Anyone Using Spacers to Fit a 36T Chainring

[dixie600mhz]

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 thinking of using spacers on the crank to try and fit the steel E13 36T chainring. From reading forums and complaints, it looks like some folks could benefit from installing spacers just for their 34T stock rings that rub the chain stay.

Can I go as far out of whack as 3mm on the chain line without problems? Not sure if there might be chainrings with custom offset to achieve the same goal?

 

[Mikerb]

Increasing or decreasing the size of the chain ring has no effect on chainline but using a chain ring with a different offset to the original will, of course.

Chainrings are available with various offsets but the original set up on the bike, as dictated by the bike brand, has to take account of the effective width of the bottom bracket...which in this case is of course a motor rather than a BB shell, and the effective centre of the cassette..........which varies dependant on the width of the hub ( e.g boost/non boost) and how the hub fits between the chainstays. A chain ring with appropriate offset is then chosen/specified.
Even so on a 1x system there is no perfect chainline. The priority has to be that every gear can be selected and that the chain avoids hitting the chainstay and tyre in every gear, but that does mean extra chain noise and wear is likely at the extremes of the cassette when the chain is at its most acute angle to the chain ring.

So........changing the manufacturer's selected chainline can lead to problems. From what I have read on here it does suggest Trek may not have selected the ideal chainline to avoid hitting the chainstay, so a chain ring with a greater offset away from the bike centre line than the original would help in that respect..........but could cause problems in other areas! Fitting a larger than standard chain ring often means there is even less ( or no) chain stay clearance if the same offset is used.

The offset on any chainring is the distance between the centre line of the chain ring and the teeth........offset towards the BB or away from the BB.

Putting spacers behind the chain ring will reduce the already minimal number of threads available to properly secure the lockring, so I would not do that.

 

[Philly G]

As @Mikerb pointed out, its probably not going to work putting spacers behind the chainring. But you might get away with using an offset chainring. Only way to know really is to take a punt and try it out. The Rail would certainly benefit from a 36T. Maybe we'll see that on next year's bikes, if anyone can actually get hold of one!

 

[dixie600mhz]

Yeah spacers won't work due to the lock ring thread length. I might cut a 36T into two parts and TIG it back together using a central ring, or take it to a friend at a machine shop for advice. If somebody made these with an offset that works on the rail I bet there would be a market for them.

 

[neiloxford]

I suggest you investigate a bosch gen4 spider, with spacers to attach the chain ring ?

For example...

Spider 1x Bosch GEN4 engine bcd 104mm offset 53mm for boost frames FS

- Forged in AL6061 - 104mm - 53mm offset - Weight 66.5gr E-bike Drivetrain, Spider E-bike, Price 28.4EUR FSA Code 421589628 4710243882573

www.ridewill.it

You might find a chainring with a built in offset ?

Oneup come with a 2mm shim...

Understanding Chainline for Optimal 1X Conversions (Boost and Non-Boos

Have you converted your bike to 1X in the past 5 years? If so, your chainline could be causing premature drivetrain wear. Find out how to optimize your setup and save money. What is chainline? Chainline is the distance between the centerline of your frame and the average centerline of your...

www.oneupcomponents.com

 

[JMD]

Get a Bosch gen4 104bcd spider to fit motor & you can play around with std 104bcd chainrings/spacers.
Miranda spiders available on eBay

 

[JMD]

I suggest you investigate a bosch gen4 spider, with spacers to attach the chain ring ?

Beat me to it?

 

[Mikerb]

I suggest you investigate a bosch gen4 spider, with spacers to attach the chain ring ?

For example...

Spider 1x Bosch GEN4 engine bcd 104mm offset 53mm for boost frames FS

- Forged in AL6061 - 104mm - 53mm offset - Weight 66.5gr E-bike Drivetrain, Spider E-bike, Price 28.4EUR FSA Code 421589628 4710243882573

www.ridewill.it

You might find a chainring with a built in offset ?

Oneup come with a 2mm shim...

Understanding Chainline for Optimal 1X Conversions (Boost and Non-Boos

Have you converted your bike to 1X in the past 5 years? If so, your chainline could be causing premature drivetrain wear. Find out how to optimize your setup and save money. What is chainline? Chainline is the distance between the centerline of your frame and the average centerline of your...

www.oneupcomponents.com

That seems a very sensible suggestion to me. The chain ring he pictured above already had what looked like a pretty large positive offset as far as I could tell from the photo and I am not sure he could find a direct mount chain ring with more than that, and spacers will not work, so changing the set up to a spider plus BCD 104 chain ring is worth a try.
The only issue might be that by using a spider and an offset BCD 104 chain ring, the chain line becomes compromised especially on a wide ranging cassette.

 

[dixie600mhz]

Thanks guys! I just ordered one of the direct mount Miranda 104BCD spiders from ebay. The adventure continues : )

 

[dixie600mhz]

36T Chainring rocks!! I used the Miranda Bosch Gen4 spider and Praxis steel 104BCD.

eRING STEEL MTN 1X 104BCD - Praxis Works

Praxis high-grade cold forged 4130 steel 104BCD eRings for eBikes

praxiscycles.com

Install wasn't quite straightforward. The Miranda is designed for the chainring on the inside of the spider to get the 53mm chain line but as we know a 36T won't fit. I mounted it on the outside of the spider. It's about 4mm further out or about one gear off center relative to the cassette.

The praxis chainring comes pre chainring bolt threaded and has directional teeth. The problem is that its designed to mount on the inside so you can't flip it and simply mount it reversed. I had to drill out the threads on the chainring to 10mm and use regular 8.5mm long chainring nuts/bolts to mount it to the spider. I will mention that a standard HSS drill bit wouldn't even scratch the ring. I had to order a cobalt bit then drilling was no problem. It made me glad I went with this chain ring seeing how tough it was to drill.

It's been torrential rain here in Austin, TX for two weeks so trails are all closed. I did give it a spin round the neighborhood and it shifts like butter. I won't know the improvement until I hit my usual trials in a few days.

My chain guide is ready to go back on. I just had to find a longer mount bolt and washers to line it up with the new chain line.

original 34T

34T rub (disgrace)

new goodies

new chainline

 

[dixie600mhz]

Just a quick update. Although the new chain line is about 5mm further out from the frame, the bike shifts flawless into and out of all gears. I also replaced the worn 10T and 12T cassette sprockets and the bike feels like new. No skipping. Wish it came with 36T from the factory. The 104 BCD will let me swap out to any cheap front chainring now. Very pleased with the mod.

 

[Link]

Interesting thread, I have just had to order a new cassette as it was skipping in one of the smallest sprocket gears, had a hell of a job even fishing a cassette, had to buy one from Germany !, The rail badly needs a 36T chain ring, I spend a disproportionate amount of time at the bottom of the cassette in general. A 36 would shift all that usage into the middle off the cassette and help stop the wear on the smallest cogs.

Hopefully a solution can be found, I did order a replacement 36T SRAM replacement ring, then remembered about the space issue so cancelled it.

 

[Link]

after another ride and paying more attention to the gear i am in it is clear that around 80rpm cadence in 10th gear is 15.5mph hence its the gear i have worn out. The 34T ring has to go, so i have ordered the Miranda spider and now sourcing a chainring, thankfully @dixie600mhz did the hard work and worked out a plan - thanks !. From what i can tell the praxis ring is just a normal flat ring with no offset ,?, hence any ring mounted on the outside of the spider should be ok ?. I am thinking the SRAM one which is not threaded should be a good option (all be it a bit more expensive). Did you use just some normal chainring bolts ?

 

[dixie600mhz]

after another ride and paying more attention to the gear i am in it is clear that around 80rpm cadence in 10th gear is 15.5mph hence its the gear i have worn out. The 34T ring has to go, so i have ordered the Miranda spider and now sourcing a chainring, thankfully @dixie600mhz did the hard work and worked out a plan - thanks !. From what i can tell the praxis ring is just a normal flat ring with no offset ,?, hence any ring mounted on the outside of the spider should be ok ?. I am thinking the SRAM one which is not threaded should be a good option (all be it a bit more expensive). Did you use just some normal chainring bolts ?

Yeah the Praxxis chainring has no offset. Any straight 104BCD chainring will fit on the outside if it's designed for standard 10mm diameter chainring nuts/bolts.

The Praxxis is super strong steel but turned out not to be ideal since it comes pre-threaded for standard chainring bolts. However, since it's directional and has a collar around the threads to lock into the spider, the collars are on the wrong side when you try to mount it on the outside of the spider. Probably too much detail, but that's why I had to drill out the chainring to 10mm and use standard chainring nuts/bolts. It let me keep the directional praxxis rotating the correct way after drilling out the alignment collars in the chainring.

I used 8.5mm long chainring bolts to get the length just right. Any 104BCD chainring should work with the miranda spider.

 

[Link]

great, thanks. I have ordered a SRAM ring and the Miranda spider. Out of interest could you not have just bolted the ring from the back, i.e. go through the spider from the back into the thread on the ring ?, save you drilling it out ?. Anyway I have ordered a could of sets of chainring bolts to hopefully get something which fits .

thx

 

[dixie600mhz]

Yeah you could bolt it from the back but the spider holes are 10mm and the threaded chainring holes were 8mm. The raised collar on one side of the chainring fits into the 10mm holes for alignment. If the collar is on the wrong side there's nothing to align the 8 to 10mm holes. You want the chainring either keyed to the spider or tight fitting chainring nuts/bolts.

With the sram you'll be fine.

 

[RickBullotta]

after another ride and paying more attention to the gear i am in it is clear that around 80rpm cadence in 10th gear is 15.5mph hence its the gear i have worn out. The 34T ring has to go, so i have ordered the Miranda spider and now sourcing a chainring, thankfully @dixie600mhz did the hard work and worked out a plan - thanks !. From what i can tell the praxis ring is just a normal flat ring with no offset ,?, hence any ring mounted on the outside of the spider should be ok ?. I am thinking the SRAM one which is not threaded should be a good option (all be it a bit more expensive). Did you use just some normal chainring bolts ?

That really doesn't make sense though. 34T chainring + 10T small cog + 2.6" 29er tires should yield about 26 MPH at 80 RPM if my calcs are correct.

Each rev of the cranks should result in 3.4 revs of the wheel.

Wheel circumference is about 100 inches or so.

So at 80 RPM you would cover 3.4 * 100 *80 or roughly 275,000 inches per minute.

In an hour, you'd cover roughly 1,632,000 inches, or 25.76 miles.

 

[Link]

not looking to verify your calcs , but as i mentioned i am not in the smallest cog (10), I am 3 up, 9th gear, not sure of the tooth count but can be sure in that gear (not smallest cog) at 80rpm it is 15.5 and its worn and skips

my smallest cog 10 Teeth is fine, not skipping, I don't use that often

 

[Link]

36T Chainring rocks!! I used the Miranda Bosch Gen4 spider and Praxis steel 104BCD.

eRING STEEL MTN 1X 104BCD - Praxis Works

Praxis high-grade cold forged 4130 steel 104BCD eRings for eBikes

praxiscycles.com

Install wasn't quite straightforward. The Miranda is designed for the chainring on the inside of the spider to get the 53mm chain line but as we know a 36T won't fit. I mounted it on the outside of the spider. It's about 4mm further out or about one gear off center relative to the cassette.

The praxis chainring comes pre chainring bolt threaded and has directional teeth. The problem is that its designed to mount on the inside so you can't flip it and simply mount it reversed. I had to drill out the threads on the chainring to 10mm and use regular 8.5mm long chainring nuts/bolts to mount it to the spider. I will mention that a standard HSS drill bit wouldn't even scratch the ring. I had to order a cobalt bit then drilling was no problem. It made me glad I went with this chain ring seeing how tough it was to drill.

It's been torrential rain here in Austin, TX for two weeks so trails are all closed. I did give it a spin round the neighborhood and it shifts like butter. I won't know the improvement until I hit my usual trials in a few days.

My chain guide is ready to go back on. I just had to find a longer mount bolt and washers to line it up with the new chain line.

original 34T
View attachment 62475

34T rub (disgrace)
View attachment 62476
new goodies
View attachment 62477

View attachment 62478

View attachment 62479

new chainline
View attachment 62480

View attachment 62481

My parts have arrived, all looks good before trial fitting, i have a boost and none boost spider to try the offset, BTW the chainring is meant to go on the outside of the spider as you have it, not the inside. The stepped lugs on the outside are for location of the ring. Just waiting for the bolts to arrive and i am do a trial fit.

 

[Link]

36 fitted, looks good so far, the chain is outward about 4mm like mentioned but that's no problem, it's just changed slightly the chain angle from one side of the cassette to the other, my other bikes running double chainrings run much more of an angle so it won't be an issue. Need to fit a new longer chain, also I am changing to a 10-50 cassette instead of the 52, so can run a tighter 'b' gap on the smaller cassette cogs. So far I would say this is the perfect solution. I'm also using a SRAM syn2 chainring so the chance of the chain jumping off is pretty much zero. Going to design and 3d print a new chain catcher for the new location too. Will finish off this weekend and take it for a ride ??. Should stop all that wear on the small gears and save me a fortune in cassettes ?

 

[Philly G]

@Link top mod, looks great ! I'm very tempted to follow suit??

 

[Link]

I am going for a ride tomorrow so will report if anything is amiss, quick spin up the road and it seems peachy. In the end took the opportunity to ditch the chain catcher too as I am running xsync 2 ring which never drop ??

 

[Link]

Long ride today,.and it was faultess, my use of the gears has moved up the block by 1 or 2 gears which was the goal. Zero problems with the chain line or shifting. Great success ??. I was even able to use the same chain from the 34T as Trek make it overlong by default so there is plenty of slack. Will run this 52 tooth cassette until the existing chain measures some wear then then switch out to my new 50 and new chain. Thankfully now I can avoid the worn slipping gear due to the bigger chainring ??

 

[Cummins0867]

Try this website for calculating gears (link below). Plug in what chainring, cassette and wheel size that you had and what you changed to and compare the two. Or if you what to upgrade like I did on my M2S Kush MD 750 from an 8speed cassette to a 12 speed. It didn't give me what I was looking for...it actually gave me 4 lower gears and I was looking for 2 higher and 2 lower.....then I found this website....I ended up changing my chainring from a 36 to a 44....man what a difference. I don't have that bike anymore....I sold it and now I have a Rail 5....also thinking about doing this mod.

http://gears.mtbcrosscountry.com/#26I1I1

 

[SydB]

Looks like a good upgrade to make, did you go with the boost or non-boost spider?

 

[Link]

Boost

 

[dixie600mhz]

I went with the Miranda 53mm spider. With the 36T mounted on the outside it is a good 4 to 5mm outside the 53mm chain line. 36T is too big to mount on the inside since it would have the same chainline as the original 34T.

I'm going to order the 50mm FSA W0134 Bosch Gen 4 Spider to compare to the Miranda. The Miranda is great but I want to try to get my final chain line as close to 53mm with the bigger 36T.

 

[aviserated]

Dixie600mhz,
Did you ever try out the Bosch Gen 4 spider? Are the Sram Sync2 ring gears hard to find, like everything else?

 

[dixie600mhz]

Aviserated, I've tried three spiders so far and the best one for the 36T is the FSA 1X Spider Boost 104mm BCD for Bosch Drive Unit Gen4 - W0138. With the FSA W0138, I added two thin washers and now the chain line is as close to stock as I can make it. The 36T is almost rubbing like the 34T was. The washers are thin enough that the chain ring still rests in the spider alignment grooves.

My trick to finding parts is get the part number and spend a while googling. It usually works but I've been looking for a smith mainline helmet in stock now for over 8 months! I feel your pain.

 

[aviserated]

Yes I ordered that Bosch Spyder. Thanks for the quick response.