Originally Posted by
Jipe
I agree with you, several Shimano rear derailleur accept bigger biggest cog that what Shimano specify. I know the the RD-R8000-GS medium cage that according to Shimano is limited to 34t can work with 36t.
But I have an Ultegra RD-R8000-GS medium cage on my Birdy and its not too close to the ground, its even slightly higher than the R&M factory mounted RD-T610-SGS, so I see no reason to take the risk of using a short cage instead.
For the chainrings, the difference between brands is as Glye says for more sophisticated chainrings like narrow-wide and even more for double chainrings that have grooves and pins to help and speed up the chin going from the small to the big chainring. Each brand has its own patented tricks.
Yea, we have a saying about Shimano in our local community, "Shimano is way more conservative than an old granny." My mechanic told me the GRX810 RD on my new Gravel bike can easily go up to 40T even pairing with a double chainring setup.🤣
I was worrying about the GS cage length so decided to go with the SS cage. Works ok but the limitation is so real. I had to keep monitoring the shifting. It's quite annoying TBH.