Can I put a bigger chainring on it? Does it fit?

[SimonG]

I am running a 38t chainring on trek rail with spider and 1mm spacers, can you put a 36t or 38t on the Amflow. Also, I read the Amflow knows what gear is in, If I change the ring does it screw that up?

 

[zshift]

I am also looking to change my chainring. I hear there is a need to order a steel one rather than alu due to the torque. Wondering if anyone tried yet.

 

[SimonG]

You don’t need a steel one. An aluminium ring is good for about 400nm. I have a x sync on my trek rail with no issues.

 

[tehviking]

I’m running 36T, I can’t remember where I saw but IIRc that’s the largest supported chainring size. You actually tell the bike in settings your chainring size and cassette model and it adjusts the gear calculations for you.

 

[zshift]

I’m running 36T, I can’t remember where I saw but IIRc that’s the largest supported chainring size. You actually tell the bike in settings your chainring size and cassette model and it adjusts the gear calculations for you.

36 was the biggest i can fit. I bought a 38 but the shop said it will eat away the rear frame under compression

 

[SimonG]

36 was the biggest i can fit. I bought a 38 but the shop said it will eat away the rear frame under compression

That is correct 36t is the biggest without scratching the rear frame. You use a miranda spider with chainring bolts and 1mm spaces to increase the chainline. It moves the ring 1-2mm further from the frame allowing you to fit 38t.

 

[Pentti]

Plus 38T is supported in the software

 

[nowayfra]

I’m running 36T, I can’t remember where I saw but IIRc that’s the largest supported chainring size. You actually tell the bike in settings your chainring size and cassette model and it adjusts the gear calculations for you.

What for is the gear calculation neccessary? Suppose i put a hub with xdr freehub and a 10-33T road cassette on it, would the bike let me ride it? As the base model comes with analog drive train the software shouldn't know anything about the gear i am in.

 

[Pentti]

What for is the gear calculation neccessary? Suppose i put a hub with xdr freehub and a 10-33T road cassette on it, would the bike let me ride it? As the base model comes with analog drive train the software shouldn't know anything about the gear i am in.

The bike software displays what gear you are in on the display, it calculates this using the wheel size, chainring size and gear sizes, which is why you have to tell it (otherwise it can't know). The bike knows your cadence and wheel speed. 38T is supported in the software even though it will probably foul on the bike if you fit one (without some method of spacing).
You can fit any combination you want mechanically, but the gear indicator will be wrong, plus the assistace algorithms will be corrupted.

 

[AF1]

Plus 38T is supported in the software

How big a chainwheel does the Bosch Gen4 software go?

 

[nowayfra]

Got me a 38T chainring although I read somewhere here in the forum that it would "chew the frame under compression" but apparently it doesn't since the chainstay moves away from the chainring under compression.
There are roughly 2mm left between nearest tooth and the frame.
For the SRAM steel chainring you will need to remove the spider to assemble it.

 

[steve_sordy]

With clearances that tight, would frame flex become an issue?

 

[nowayfra]

Maybe if you exert really huge force to the rear wheel. The point where the teeth pass the frame are roughly a sixth of the chainstay length so you would probably need to laterally shift your rear hub by almost an inch or so to make the frame hit the chainring. I would report back if this happened but I guess my riding style is fairly tame

 

[AF1]

Re-posted from another similar thread: "Other posts on here said that the chainring size can be changed in the Diagnostic software by LBS. However my LBS tried to do this but failed because, in its infinite wisdom, Bosch no longer include this option on their latest software update. We have been told by Bosch to contact the bike manufacturer for support on this!"

 

[curufinwe_wins]

Honestly that side on clearance looks good enough that I wouldn't worry about it. I've done much much tighter than that and not had issues except one time my derailleur got stuck and then the bike drive train yanked it sideways.

It will be pretty obvious if there are issues for early rides and then you can just swap back with minimal paint damage.

 

[nowayfra]

There is a new bash guard out from eThirteen which by the looks of it could be used to put on even larger chainrings if you dont mind the slightly shifted chainline - just swap the bashring with a chainring.

 

[Rideit]

Running a 38tooth Race Face ring, no issues at all.

 

[Pentti]

Running a 38tooth Race Face ring, no issues at all.

On Amflow?

 

[Rideit]

On Amflow?

Oops, totally incorrect, that’s a 36.

 

[Pentti]

Thanks for the confirmation @Rideit I was hoping for a second opinion on 38T @nowayfra managed to fit one, but it must be very tight. Amflow say 36T max but include 38T in the software options.
Is it you that obscured the decals (rather than removing) to avoid warranty problems? because it seems you've swapped most of the components on the bike there, which would void warranty anyway?

 

[preedy62]

I've fitted a 38T with no issues ~500 miles done. Changed the software option to reflect 38T.

 

[Rideit]

Nah, just making it more stealth, lol. Changing components doesn’t void the warranty, unless you exceed the parameters of the shock and fork, and *possibly* the seatpost length. (which I have not).
I think the only original parts on my entire bike are the headset and seatpost collar clamp!
(which I need to swap for a QR, I simply can’t get the post low enough for my 33” inseam).
I normally run a 210.

 

[Pentti]

How's it going with the 38T Chainring @nowayfra and @preedy62 on amflow, any problems?
Also what did you do with the chain guide to make it fit? Thanks

 

[preedy62]

How's it going with the 38T Chainring @nowayfra and @preedy62 on amflow, any problems?
Also what did you do with the chain guide to make it fit? Thanks

I’ve had no issues. The chain guide needs to be adjusted which was a bit fiddly but not too difficult to do.

 

[Pentti]

Confirm 38T chainring fits Amflow @SimonG @zshift with 1-2 mm clearance which only gets bigger as the suspension loads and it's selectable in the software. No spacers or modifications required, the chain guide bracket can be adjusted by tapping lightly around it's mounting to accommodate the larger ring also.

 

[dreys]

Confirm 38T chainring fits Amflow @SimonG @zshift with 1-2 mm clearance which only gets bigger as the suspension loads and it's selectable in the software. No spacers or modifications required, the chain guide bracket can be adjusted by tapping lightly around it's mounting to accommodate the larger ring also.

Chainstays are designed to flex so slightly (1-2mm) under load. With less than 2mm clearance you will scratch your chainstay. While 38t physically fit, it is not recommended to use it.

 

[Pentti]

Fair enough, that's why I checked how others got on first. It's close to the chainstay pivot point, you would need to move your wheel hub 10mm laterally to take up the 2mm, I think spokes would flex first. There will be no flex when it's unloaded, when it's loaded the clearance grows. There's more chance of the chainring or spider bending/flexing, although 104 BCD is pretty big compared to the dia of the ring and the spider is steel.

 

[dreys]

Fair enough, that's why I checked how others got on first. It's close to the chainstay pivot point, you would need to move your wheel hub 10mm laterally to take up the 2mm, I think spokes would flex first. There will be no flex when it's unloaded, when it's loaded the clearance grows. There's more chance of the chainring or spider bending/flexing, although 104 BCD is pretty big compared to the dia of the ring and the spider is steel.

Huh?

Spokes flex has nothing to do with chainring clearance. Chainring doesn't flex more than 0.1mm, otherwise your shifting would be junk if chainring would be flexy. And no, you cannot move hub by 10mm.

Chainstay does flex. You can easily see the flex by removing the rear wheel and squeezing chainstays together with both of you hands.

My advice - don't be a keyboard engineer. When it's clear that 38t will scratch your frame, don 't use it. But at the end of the day it is your bike, you do what you want.

 

[nowayfra]

Spokes flex has nothing to do with chainring clearance

Should be obvious that there is a "chain of bend" which goes from the tire to the rims then to the spokes and through some fairly rigid hubs into the chainstay. And this all inversely exponential. The distance from the lower chainstay axis to the nearest point to the chainring is roughly 1/9 of the total chainstay length so if you manage to flex your chainstay so that it touches the chainring you most likely have much more expensive worries than a scratch in your coat.

 

[SimonG]

Confirm 38T chainring fits Amflow @SimonG @zshift with 1-2 mm clearance which only gets bigger as the suspension loads and it's selectable in the software. No spacers or modifications required, the chain guide bracket can be adjusted by tapping lightly around it's mounting to accommodate the larger ring also.

View attachment 170094

I bought a 2nd amflow spider. I’m popping down to a local engineering shop and getting 1.7 mm of material removed from the spider arms to increase the distance from the suspension arm.