Will the Ultegra FC-R8000 50/34 175mm work on the Trek Checkpoint SL-5?
With longer chain and - what front derailleur from Shimano?
Other suggestions welcome; I understand gear ratios but little else about "the best" drivetrain component combinations for my riding.
OEM on the Trek Checkpoint SL-5 is 2x 46/30 chainrings.
But I want something like 50/34.
Trek told me "The Shimano cranks use a 110 bcd for the mounting pattern, so as long as the 50/36 uses that as well, we are good."
However the dealer checked QBP etc. and could not find 50 & 36 rings listed for use with the OEM crankset Told me to go back to Trek.
Another dealer told me, nope, not with the RX600, but it looked like the Ultegra FC-R8000 11-speed would work with the OEM cassette and rear derailleur, although OEM front derailleur might need to be replaced.
I also looked at the SL-6 AXS with SRAM 10-44 in back and 46T in front, also listed as 50/37 or 50/36 max, but even more question marks trying to customize that one from 1x to 2x. Still interested, though.
There's no standard 50/36, just a 50/34. You can buy a 36 and swap it out though. They're 20 bucks on Amazon. Your dealer was right that there's no GRX chainrings in that size.
Shimano will say a GRX front derailleur won't work with a non-GRX crank. They're only 2.5mm off but that's probably enough to make shifting bad.
Oops, my mistake. I edited the post. The "max" smaller chain ring mentioned by Trek is 36 but I wanted the 34. Not the 36. That works out OK because the OEM on the Ultegra is 50/34.
Volsung wrote:
Shimano will say a GRX front derailleur won't work with a non-GRX crank. They're only 2.5mm off but that's probably enough to make shifting bad
OK so then yes, change the front derailleur too for something compatible with the Ultegra 11-speed.
My LBS and Moots customer service say match the Ultegra crank with Ultegra front derailleur and GRX crank with GRX front derailleur if you have GRX rear or clutch Ultegra rear and Ultegra or GRX brifters. This assumes compatible bottom bracket and staying within the rules (directions) for chain length.
The OP might be wanting bigger gearing, in my case the interest is in deeper gearing (going to GRX crank). I'm well aware of 3rd party ring options and not everyone swaps the front derailleurs but the LBS and Moots staff seemed very familiar with making the changes and people wanting the shifting quality to remain great. Both had same point on you want the derailleurs to match different diameters of the cranks.
