38t chainring on Amflow
- Thread starter SimonG
- Start date
Had a little project the last few weeks to get some more tooth on my front chainring since the max allowed 38T weren't enough for my taste. Even if in low power eco settings the chain almost always lingers around the smallest 3 cogs (its rather flatlandish in my vicinity) and too often on the smallest one. So 40T or if possible 42T would be nice which apparently only would work with a custom spider. Although i considered to put some washers between the default spider and the motor interface get some room for larger chainrings i decided to make my own since the avinox thing looks rather bland.
Working out the CAD fortunately wasn't a problem since i do this stuff all the day. However the devil is in the details - as it turned out after scrutinising every iteration of my attempted spider . For the first drawing the chainring bolts most likely would have hit the motor block, the second one was probably a bit to thin partially and had the potential to crumble under full load. The third one finally passed the the checklist. The final layout shifts the chainline 2.5 mm to the right side. On the color side i was a bit undecided between some decent silver or some less lowkey red. I went for red.
Next hurdle: get someone to make it. I first searched the web for some companies doing small batch sizes but no one of them even bothered to answer my mails. Next one was checking some sort of "graigslist.com" only for germany (kleinanzeigen.de). Turned out there were some offering carving shapes out of metal but none of them in an acceptable price range for T6 or T7 aluminium with anodized finish. So I ended on aliexpress where i found a company with a nice and capable lady which convinced me to use some T6 alloy. Out of curiosity I also asked for T7 or titanium which she was very unwilling to offer primarily because it would have much more impact in degrading their tools. Titanium would had cost me 5 times the price compared to aluminium T6-6061. It took then roughly 2 weeks on their side until shipping. Cost: 185€ for production including shipping plus 25€ import duty.
Conclusion: works as expected, the 40T fits with around 2 mm distance to the lower chainstay. With default sag its around 3 mm. The chainline looks a bit more ugly now if on the largest cassette cog but all works fine still without making any additional noise. As a nice side effect i now could swap chainrings without disassembling cranks and spider first. 42T probably also would work if using a washer of around 1mm between spider and chainring.
Gauss Guzzler
Member
Wow, nice work! I'm just going to buy the SRAM 38 when it comes out in July and bend it. 
How does 40T get along with the computer? I'd expect it to throw some errors, but maybe Avinox isn't as uptight as Bosch, whose tamper detection algorithms will immediately disable the motor if you fart too strongly.
Also, that's an amazing price (and delivery time) for a custom part with time-consuming broached splines!
How does 40T get along with the computer? I'd expect it to throw some errors, but maybe Avinox isn't as uptight as Bosch, whose tamper detection algorithms will immediately disable the motor if you fart too strongly.
Also, that's an amazing price (and delivery time) for a custom part with time-consuming broached splines!
ericm
New Member
Wow, nice work! I'm just going to buy the SRAM 38 when it comes out in July and bend it.
I just bolted an Sram 38t to the existing carrier. It clears the frame with no issue.
Part # 11.6218.057.002
No problems so far at least no errors, but the 40T and the road cassette makes the gear display now completely messed up ^^
Pentti
New Member
Hope (alloy) R22 38T fits OKWow, nice work! I'm just going to buy the SRAM 38 when it comes out in July and bend it.
Pentti
New Member
38T and 7-speed XX DH Cassette (+ derailleur) play ball with the software and Smoothshift
Gauss Guzzler
Member
Curious why OP milled out a couple millimeters then? Is it only the Eagle 38T that doesn't fit, while the T-Type does?
Thats probably contributed to his personal feelings about "safe space", from a technical point its not necessary. In 29" mode (flipchip) the clearance is about 2mm. In 27.5" its a bit less, which I rode with a 38T for more than 3000 km with not a single scratch in my chainstay. Besides as soon as you sit on your bike the clearance is ~1mm more.
Pentti
New Member
OP found that his steel Sram 38T fouled.
Alloy Hope R22 38T fits and is suitable for Eagle & T-Type (with bigger rollers)
ericm
New Member
Interesting that mine did not. 29er mode, PL Carbon with shock from a regular PL. I'm pretty sure they are the same length.
petro1head
Member
I have the SRAM x sync 36t and would like to go 38t. Some have said the sram 38t fouls but some have said the hope works. What the difference between the two
ericm
New Member
The Sram is steel. The 38t part number I posted earlier in this thread fit my PL Carbon just fine. It's the 38t version of what came on the bike.
petro1head
Member
Cheers
Got my sram 38t sprocket today, it fits
Got my sram 38t sprocket today, it fits
petro1head
Member
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