I want to go bikepacking with my old road bike. The road bike has a standard crankset (53/39, double not triple), and an 11-28 cassette. The groupset is Shimano Ultegra 6500.
Because I want to do some large climbs in the Alps, I would like a lower gear. I considered changing the crankset, but that seems a bit expensive.
I also have two old city bikes that have mountainbike derailleurs that I could remove: One is a Shimano Deore LX 9 speed, the other is a Sram s500 RD 9 speed.
Can I use one of these derailleurs to fit a 12-36 cassette to my bike, or will that exceed the total capacity of the drivetrain with the non-compact chainset?
I mention both the Shimano and the Sram derailleur because I think the Shimano is more likely to work, but in slightly worse condition than the sram - so if the Sram works too, I will try that.