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Pads retract based on piston seal rollback, not on master cylinder volume. It's a common myth, one I believed until I started deep diving into brake bleeds because of persistent issues bleeding brakes. Here's a video explanation: https://youtu.be/mPptmoy0u3s?si=t8CNIRP7x5uGnBrf

Cavitation occurs when a pressure drop causes the local pressure to fall below the vapor pressure of the fluid. In the scenario you described, fluid was being aspirated by retracting a piston, which introduced a pressure drop due to flow restriction. At low actuation speeds, the flow rate was low enough that the vacuum generated could still draw the fluid through the system without issue. However, at higher actuation speeds, the pressure drop became large enough for the local pressure to fall below the fluid’s vapor pressure, releasing dissolved gases into the closed system and introducing bubbles. I’m not sure...

You're addressing two issues at the same time here. Absolutely the inner diameter of the hoses and ports matter in this case, if you create a choke point you can easily end up with inconsistent bite point etc due to the fluid not managing to move fast enough pull the caliper pistons back before they are activated again. However, the the point about the larger caliper pistons moving more oil back through the hose to the master lever is not correct. The amount of oil that moves up and down the hoses is solely dictated by the master cylinder. The...

Speaking to this point: " Downsizing one set of the pistons decreases the amount of fluid trying to return so may not create the same restriction or at least alleviate it some. " I would have to think it has more to do with smaller seals creating less friction. The amount of oil moving back and forth is dictated by the master cylinder, not the size of the caliper pistons (the smaller the pistons, the more distance they move for the same amount of lever travel). Also, if a big piston gets stuck even a little bit, it would affect...

That’s like, your opinion, man.

If someone is going 30mph up a multi use trail blowing past hikers I don’t think hikers are gonna care if the rider has been going 30mph for 10 seconds or 10 minutes

100% agree with you and the difference is even more stark on an e-bike having used 2 different sets of XTR 4 piston brakes with new rotors and pads on 2 bikes compared to 1 set of Mavens on a 3rd bike. As a larger rider (250lb kitted + ~50lb e-bike) the XTRs routinely have me worried on long descents and I develop significantly more arm pump compared Mavens. I’ve also never noticed the Maven lever resistance being any issue, but it could be because I’m a larger person, and I don’t doubt many others claiming the lever resistance is...

XTR uses a single piece caliper, XT and SLX don't. Could be a factor in the difference. As for the constant finger force and comparing different brakes, I know it adds a lot more testing, but maybe testing at two of maybe even three finger force levels would make sense. Maybe some brakes are not really linear and the 4 kg force isn't enough to really show them for what they are? EDIT: I see the second part was already mentioned...

Kinda derailing this thread now, but a couple of counter arguments: -XTR, XT, and SLX aren't "wildly" different in the results, there's about 10% decrease in recorded power between each of them with stock pads (they didn't test XT and SLX with the Sinter pads). Since they used the average of 20 decelerations, I would say there is some underlying (=real) reason for the differences. -TRP's DH-R EVO always felt a bit low on brake-power-to-finger-power ratio for me, compared to several other brakes... -remember that they tested with constant power at the lever (4 kg of force on the levers...

@Evwan @iceman2058 backlink Different rotors = different cooling.