jstonebarger wrote:
lyrrad wrote:
That diagram simply shows mechanical advantage ratio and has nothing to do with modulation.
Modulation is the feedback at the lever and lack of friction in the system allowing very fine adjustments to power applied to the pads unhindered by stiction...
So is modulation measurable? In modern disc setups, is modulation improved (over various rim disk systems) by the disc pad and rotor itself or by the hydraulic controls? Do you agree that modulation varies from one disc brake setup to another? Why or how?
Modulation gains in disc systems over conventional rim brakes come from multiple reasons.
Obviously the big one is hydraulics lack of cable friction and housing flex. So the same can be had from hydraulic rim brakes in this regard.
Another major one is the very much higher clamping forces of discs so that pads are made from very solid material, so more hand pressure means more braking, unlike rubber rim pads that compress and loose a lot of the hand force to merely squishing. This is why even cable discs can be very good compared to same level rim brake.
Rim brakes have long levers to reach around the tyre to the rim, flexy no matter what you do. Disc brakes have a very compact setup with no tyre to reach around, so very little flex.
Disc pads can be run extremely close compared to a rim brake, so designers are free to make use of what would have been wasted lever movement on a rim brake which must run with reasonable rim clearance.
This is not a modulation thing, but it is the reason that disc brakes can be made very powerful as the full lever movement can be used for braking and not waste the first third or half to rim clearance.
Because the disc setup does not squish pads and flex long arms, there is no loss of power in the extreme high power end of travel, so that more of the lever movement can be devoted to more common partial braking inputs, whereas a rim brake needs to keep a fair portion of the lever travel available to allow for flex under full power braking.
Differing disc brake feel can come from many sources also.
Shimano XT trail brakes can feel a bit on/off to those that are not used to them, they actually modulate very well, but the short lever movement made possible by the varying pivot point of the lever (servo wave) brings the pads in contact very quickly and then the lever enters into a very high power mode that catches some users moving from lesser powerful brakes to these brakes.
Organic pads also tend to have very high initial bite compared to metallic or semi metallic pads, so pads can play a large role in the feel of the brake, just like rim brakes.
Some pads have high initial bite but don't gain power linearly at high forces, so different lever feel, but the modulation is still there.
Many people (most) mix and match the meaning of modulation with lever ratios, so the conversation gets very confusing when you have no idea if the reviewer is talking lever ratios or actual modulation.
Poor modulation is just a shit brake to use at the limit, no matter the lever pull.
Good modulation is a great brake to use at the limit, no matter the lever pull.
It's just some great modulating brakes with short lever pull take a while for you to reset your brain to the extreme power available.
But a poor modulating brake is never good near the limit as fine control is masked by flex and friction losses.
Notice that this conversation has nothing whatsoever to do with being able to lock the wheel, just simply the ability for fine control at the limit where it is required most.
You know the times, over cooked it coming into the corner (or simply out braked your mates to get position or that dickhead dived right into your line forcing you to change to a slower line.) and need to keep braking at the limit whilst negotiating the corner on the limit, this is where modulation shines.