Author Topic: Gr048 with Tansmission?  (Read 278 times)

landboard

Gr048 with Tansmission?
« on: May 27, 2024, 02:11:48 AM »
Hello

I am looking to build an endurance gravel bike with 1x/transmission. I am eying the GR048 frame. They currently only offer the M size with UDH, but with 179/83 that should fit okay.

http://www.tantancycling.com/index.php?_m=mod_product&_a=view&p_id=1094

Would love if you can help with 2 questions:
1. Geo seems nice slack ST/HT with 74/71. Anything i am missing on fit for a touring gravel?
2. Has anyone tried this frame with SRAM transmission? Chainline?

Thanks for your help!




carbonazza

Re: Gr048 with Tansmission?
« Reply #1 on: May 27, 2024, 04:10:48 AM »
I've built a few gravel bikes with the Transmission system with the CFR-505 from Carbonda.
All the riders are extremely happy!
I'm a bit jealous now, still riding the old Eagle AXS on my gravel  ::)

The chainline of the SRAM gravel/road crankset (wide) is 47.5mm, which may cause chain rub on a couple of small sprockets if your chainstay length is on the short side (420-430mm).

I contacted SRAM to see if I could safely widen the chainline a bit. A colleague of the person who responded to me had the same issue with a mullet setup. I mentioned that the chain rub would cause some noise and lateral chain wear, but they said he was managing it fine...

I escalated the issue and eventually got someone who, after some back and forth, confirmed that SRAM has 47.5mm max only.
If I remember well, they didn't say it directly, but implied that it would be okay to use a wider chainline if found, as MTB setups allow for much more.
I added a 1mm shim on the right side, which solved the rub issue.

In addition, the app from SRAM to know the chain length, and the position of A/B setup key is not reliable.
It stops at around 38T, so add one link per additional teeth.
And it puts the setup key to A while it should generally tell B. Test both options and see which one works better.

Now, I'm about to build another one, and this time I'll try with XX1-Quarq/104BCD crankset with a 49mm chainline

landboard

Re: Gr048 with Tansmission?
« Reply #2 on: May 27, 2024, 07:23:18 AM »
Thanks a lot for your comprehensive and insightful reply.

Its a good point on the spacers - given that the wide and non-wide BBs are the same and only differ in the included spacers, there should be a good bit of flexibility. I will check the spacer recommendations from SRAM. Aftermarket chain ring with 6mm offset might be an alternative here.

RE frame: Carbonda, especially the 707 might be the better option. The GR048 in M might just be a tad small, when looking at it in bike-stats. The 707 in M also has a 435mm chainstay and a generally longer wheelbase.  :)