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I recently installed new brakes (Shimano SLX 675), shortened hoses for front/rear brake, done bleeding but even after that rear brake lever feels much softer than front. (I had identical issue with old brakes (M446) which acted in the same way and that is partially the reason for asking this question).

New brakes work fine, they have nice stopping power, there are no signs of oil leaking etc... It is just that rear brake lever feels much softer (and I don't think it is due to lever reach adjustment; it isn't nearly reaching handlebar).

Can the longer length of disc brake hose (rear breake) influence the 'feel' while braking (assuming brakes are correctly installed and working properly) or there is something else causing this 'problem'?

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    Certainly, the hose expands somewhat under pressure, so the longer the hose the more "spongy" it will feel. For good quality hose, however, this effect should not be significant, unless you're running 10-20 feet of hose.
    – Daniel R Hicks
    Commented Jan 4, 2017 at 19:15
  • Braided brake hoses certainly addresses hydraulic cable expansion.
    – OraNob
    Commented Jan 5, 2017 at 10:44
  • Trying not to be dismissive, but, have you considered that the two brakes have different performance requirement and that there is a possible asymmetry among both hands? I've had a similar perception about all of my cable actuated brakes, all of my bikes have a "sharper" feel on the front brake, and I do believe that the hand I use for the front brakes is a bit stronger then the other (after very unscientific tests), but none of that has been an issue for me. I'm always capable of locking the rear wheel, even leaning back all that is possible.
    – Jahaziel
    Commented May 3, 2022 at 23:23

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Rear hydraulic brakes are always a little bit softer feeling than fronts. My understanding of the reason is that the hose isn't 100% unable to bulge, the system is never 100% free of air, and/or the fluid isn't 100% unable to compress, despite all those numbers being close too 100, so the more hose and more fluid you have, the more softness creeps into the brake feel.

There's a mechanical skill/judgment call involved sometimes in being able to differentiate between normal rear brake feel and slight air contamination, and sometimes brakes wind up being bled because someone decided to be on the safe side. How I would approach it is ask if you were judging the rear brake feel independently of the front, when squeezing hard and fairly fast, does it give you that moment of firmness, where the free movement of fluid in the system has clearly been taken up and now you're squeezing against the flex/compression-resistant aspect of the system? Or does it transition straight to mush without a good moment of firmness? That's the symptom of a brake you should at least try bleeding.

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This sounds like an incomplete bleed. If you hang your bike vertically, try pulling the rear brake lever after it has sat overnight (front wheel up). if it feels extra bad that confirms it. Or if you notice that the brake feels better after a few 'pumps'.

That said, I had noticed with my SLX brakes that the front and rear had a different 'feel' possibly. Not that they acted differently at all, but felt different through the stroke of the lever. I thought it was possible it was the factory bleed, which wouldn't be the case for you, but perhaps there is something to it. Or possibly a difference in friction in the Pistons in the caliper or lever somehow.

On my Jamis dragon actually (separate M675 from above), I think the front brake ended up with too much oil from the factory bleed on the front. I couldn't get the pads open enough to not rub the disc. I put a bleed block in the caliper and opened the bleed screw on the lever and that pressure alone pushed a bunch of oil out. I closed it up and everything worked as it should have. Possibly something similar has happened in your case, but too little oil? (this could happen if the Pistons were too far retracted in caliper/lever not fully open during bleed)

side notes: Of course the front lever is going to provide more stopping power as it has greater mechanical advantage. Also some bikes have a larger front rotor. And never rule out quality control.

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The length of same braking hose should not influence braking power.

The material that hose is made from can influence braking power and/or modulation. If braking hose is poor quality or damaged, it can swell, expand. As a result, your braking pump has to push liquid not only to push brake cylinder, but also to fill enlarged hose volume.

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    But for a poor-quality/damaged hose, a longer hose will have a greater difference in volume (between relaxed and stretched) than a short one; therefore.
    – Will Vousden
    Commented Jan 4, 2017 at 14:05
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    Doesn't a longer hose contain a larger volume of oil, and even though the oil is hard to compress, somewhat more force is transferred into compressing oil instead of pressing the pads against the disc? Same goes for length: the hose isn't infinitely stiff. Just guessing here, also I don't know if the forces applied via the lever are high enough to even compress the oil and/or make the cable expand..
    – stijn
    Commented Jan 4, 2017 at 16:00
  • @stijn oil compress is negligible and does not play any role in such systems.
    – krzyski
    Commented Jan 4, 2017 at 16:07
  • Do you have any idea then what causes e.g. Magura rim brakes to be 'sluggish' after a couple of hours of continuous usage (i.e. lever has to be pulled closer to handlebars to achive same braking power, goes away over night again). Different type of oil?
    – stijn
    Commented Jan 4, 2017 at 16:13
  • @stijn probably you've boiled the liquid - continuous usage produce a lot of heat. When boiling, it produces gas, that is compressive.
    – krzyski
    Commented Jan 4, 2017 at 20:42

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