Hi :) I just bought a 2015 Specialized Diverge A1 with almost completely stock components. With some adjustments everything seems to work well except for the disc brakes.
This bike has a Shimano Claris 2x8 groupset and the mechanical disc brakes are Promax Render R.
I've ridden other road and gravel bikes before with mechanical disc brakes, and never felt unsure about stopping power, whether from the hoods or drops, until now. That's just to say I know what a brake should feel like, and I have decent hand strength. With this particular bike and brakes, I can hardly squeeze the levers if I'm riding on the hoods, and even if I get maximum leverage riding in the drops and can squeeze all the way, the stopping power is terrible. There's no hope of locking the wheels even just going 5mph. It's a very slow, weak rolling stop.
I've tried checking and adjusting just about everything I could think of or google, to no avail. I'll go through what I've tried:
adjusting the internal pad to rotor distance (don't know if there's a better term for that) both closer to the rotor, to see if less travel and squeezing as hard as I can would help, and farther from the rotor, to see if more travel made it easier to squeeze the lever from the hood. Closer to the rotor was slightly better.
inspecting and replacing pads. They didn't look very worn or warped (definitely at least 3mm of material left on each pad) but i replaced them anyway
rotors do not look warped/bent either
cable tension. Can't find a happy medium where there's enough tension for the pads to clamp hard on the rotor and there's enough slack that i can move the lever effectively from the hoods.
cable/housing condition. Looks very clean. If I release all tension from the cables, the levers move freely. I don't feel any friction.
these levers don't have the built in reach adjustment, so I put in shims to bring them a bit closer to my fingers to make it easier to squeeze. Not enough help.
In summary, I can't get enough stopping power with my disc brakes, and I'm also finding it practically impossible to squeeze the levers effectively from the hoods. They feel so stiff.
In terms of my inability to squeeze from the hoods, do my hands just hate this Claris lever/hood geometry? Are they weaker than I think? For the lack of braking power, is there some adjustment I missed? Is something else going on?
I'm doing all I can to fix this myself even though I'm a total novice, so any help is greatly appreciated :)