On my gravel bike I would like to switch the equipped 1x11 GRX cranks for a 105 crank with a 1x Wolftooth chainring. The reason is that the 105 has a smaller q-factor (yes, I can really feel the few mm difference).
The Chainlines according to Shimano:
105: 43.7mm (measured in between the rings) => 46.2mm outer ring
How much will the difference affecet drivetrain efficiency? Is there a noticeable shifting difference? From my general thinking, I guess that higher gears will run less smooth, lower gears run smoother (because of less chain crossing).
Another, potential option may be pedals with a lower Q factor or moving your cleats inboard. Thought that highly depends on the exact setup you have today. And moving the cleats too fast relative to the shoe center may cause other problems.
To answer your question, I have a Cervélo Aspero GRX 2x11. It’s all GRX except for the crank, which came with an Easton EA90 2x crank with a chainline of 45 mm instead of the GRX 2x crank with a chainline of 46.9 mm. Chainline on a 2x crank is measured between the two chainrings, so the inner ring on the Easton crank is probably sitting around 42 mm and the GRX 2x inner ring is probably about 44 mm chainline.
The rear shifting works fine in either gear. It’s the front shifting that’s compromised, which is because the GRX front derailleur is really designed for the wider chainline of the GRX crank. I have bought a GRX crank to swap in but haven’t gotten to it quite yet.
So long story short, the shifting will be OK, probably perfect. Since you already checked tire clearance, you should be good.
A great thing about Shimano is they truly design a whole system. They created a pedal to specifically address the Q factor issue. It actually gives you 1 mm better Q factor than the 105 crank will
From an interview with Shimano engineering team.
Will the increased +2.5mm chainline have an effect on pedaling Q-factor?
Dave: Our traditional road cranks have a Q-factor of 146mm, so the GRX line up will increase to 2.5mm on each side, bringing Q-factor to 151mm. However, we make a new XTR pedal that features a -3mm spindle on each side, so you could narrow the gap back to your road setup.
Note from JOM: Shimano’s part code for the XTR 9000 Race series short-axle pedal is IPDM9100S1.
Nick: This is an excellent pedal for people who are more road-focused and occasionally ride on gravel or a mountain bike.
Hi I’m still confused about this Q factor and chain line. Does it really depend on frameset/bb choice? I want a full gxp di2 but sram compact crank. Maybe this is not possible? Is 50t much loss of top speed going to 48/31? Also the pedal solution seems good but what if I’m running power tap pedals already? What power meter choice do I have with gravel bike? Future wilier Jena owner hopefully. Thank you if there’s any advice!
I have a Giant Revolt on order with GRX Di2 but the crank is a Praxis one with a chain line of 44.5mm which I would like to switch out for a GRX 800 crank (chain line 46.9mm). Will this be a simple swap chain line wise or will I have to adjust the limit screws?