I replaced the following:
Front brake: a brand new Magura MT4 (pre-bled) brake with brand new pads installed
Front rotor: replaced it with a brand new Magura HC Storm 203mm rotor
I used the correct adapter (160mm PM to 203mm from Shimano) for mounting the caliper to my fork (Shimano part number SM-MS-f203P/P).
I cleaned the rotor with brake cleaner (Würth brake cleaner and a clean rag) before installing the disc. I only handled the disc/pads with clean gloves on and tried not to touch the braking surfaces..
Note: The "reach adjustment" screw is screwed all the way in, meaning the lever is as far away from the bars as it possibly can be. I don't think I should be able to press the lever this close to the handlebars using only one finger, please see photos below.
The brake lever feels a bit spongy even though it's brand new. When I press the lever with 2 fingers I can easily press it against my ring finger, which is then clamped in between the lever and grip.
The brake lever in neutral position looks like this:
The brake pads touch the disc when the lever is at approximately this position:
With one finger pressing very hard this is the furthest I can push in the brake lever. towards the bars:
Are Magura brakes supposed to be this spongy?
I tested it out whilst riding just now and even with the brake lever approx 3mm from the grip (pressing very hard with two fingers) I barely slow down. For comparison on dry tarmac I can currently slow down approx 2 to 3 times as fast with the rear brake - which indicates how bad the front brake is working.
When trying to brake hard (by pressing hard with 2 fingers on the lever) I can hear some noise from the disc brake and the handlebars vibrate a bit but the deceleration is very, very underwhelming (especially for 203mm rotor).
I tried with two different brake pad sets: the original set that came with the Magura brake and some aftermarket pads made by BBB. No noticeable difference in performance.
After the first test I also cleaned the rotor with lots of methylated spirits (it was suggested online this was a good cleaner), I though perhaps somehow the brake cleaner had made my braking performance worse so I wanted to try and clean it off. After cleaning with methylated spirits still the same. I also replaced the pads after the first test after having cleaned the disc with methylated spirits in case the brake cleaner had somehow messed up my brake pads.
Whilst testing I braked approx 40 times as hard as I could (not able to lift rear wheel or coming close to doing so.) No difference in performance before and after.
I vibrated the brake line with a funnel on the reservoir port of the brake lever in order to get potentially trapped air bubbles out (even though this shouldn't be needed since this is a brand new brake), this made no difference to the 'sponginess' of the brake lever. It felt the same before and after (I made sure to elevate the lever well above the caliper whilst doing so).
I don't think the brake is defective but perhaps it could be. I've read that some Magura levers tend to be quite spongy. Before buying the MT4 I bought a (also brand new) Magura MT5, this one felt even more like a sponge (Bob). That lever I could easily press against my grip with 2 fingers with not a lot of effort. I exchanged that brake for the currently installed MT4 since I believed the MT5 was meant to be a lot more firm and therefore must have been defective.
Here is a photo of how much I could press the brake lever towards the bar (with quite a lot of force from that one finger) on the Magura MT5 brake:
What could be wrong / what could be causing this issue?
What could I try to improve braking performance?
Should I choose a different disc with different hole pattern in order to get more braking power? Or is the pattern I currently have on my 203mm disc just fine?
Are there any tests I can perform to see if the problem lies with the brake (if so which part of the brake) or with the rotor or with something else?
Should I clean the rotor better? If so how/with what?
Will the braking performance improve with more braking? do the brake pads/discs need some time to be 'bedded in' ? If so what would be the fasted way to achieve this (bedding in)? And how long should it take approximately?
Disc rotor: Magura Storm HC 203mm
Pads: The ones that came with the MT4 brake
Note: There appears to be a lot of brake dust on the caliper for just approx 20km of riding (I did a little trip to test the brake properly), is this normal? If not what might be causing the excessive (?) brake dust?