The Best Brakes For Arm Pump - Let's Go Racing Season 2, Episode 3 13

How do you figure out what brakes are the best? For Brian Cahal, arm pump is the biggest deciding factor on what makes a brake race-worthy. Brian has no component sponsors this season and is in a unique position as a professional rider to test and evaluate critical parts he will put on his Forbidden Dreadnaught for the EWS race season. In this video, Brian tries brakes from SRAM, Shimano, and TRP to find out what blends modulation, power, and consistence the best.
Credit: Brian Cahal
Related:
Shimano
SRAM
Troy Lee Designs
Maxxis
TRP
Forbidden
Brian Cahal
Let's Go Racing
13 comments

View replies to: The Best Brakes For Arm Pump - Let's Go Racing Season 2, Episode 3

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Suns_PSD
2 years ago
Enjoying these.

I will say that Dominion A4s are by far the best mass produced brakes.

I prefer my Trickstuff brakes, but only just.
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Milton 26"
2 years ago
I've been running shimanos for the last 10 years. First 2 piston xts on trail bike and saints on dh bike. now saints on trail bike and zee on dh bike. I'm happy with ergonomics, power and heat reat resistance (no issues even on 2 piston xt on 3000 ft descends in summer and runnig basic shimano metal pads and slx rotors 200&180mmm). modulation for me is ok, could be better though. but I ave to bleed them every couple of months to keep a consistent lever feel. also the piston travel is very uneven if the pads are worn, maybe part of the issue.

would like to try shigura next with magura rotors. though trp is also high on my list. also the new formua brakes feel great, I think Cura is the current model. the also use mineral oil. but zee is pretty much unbeatable in terms of value.

best brake for me would probably be trickstuff piccola hd. I've been rinding with the trickstuff employees the other day (headquarter here in Freiburg Germany), great guys and great company. still not willing to pay this much for a brake though. maybe the can make mass produced version in the future with help of dt swiss to reduce the pirces
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jbv
2 years ago
all i know for sure, modern mtb brakes are pretty amazing. hard to go wrong, but at the elite level, i can see how you could get very particular. Shimano Zee's for years, now XT 4p on the last couple bikes and i have no complaints at all.
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Primoz
2 years ago
Here's a weird idea to give the Codes more power and less arm pump... Run the factory bleed???

If you run the pads closer to the rotor by adding oil through the bleeding edge (making them 'touchier through less pad clearance, same goes for a skinnier bleed block), you're also out of whack on the swing link leverage characteristic.

Think of it like a suspension leverage ratio characteristics (because it's basically the same) - you never get to the sweet bottomless feel of the progressive end stroke, you always run in the weird beginning stroke charactristic.

Bleed them like they are supposed to be bled and use the full capabilities of the swing link. Otherwise just run a cheaper Code R set.
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bstens
2 years ago
Primoz, do you mind extrapolating on how you would run the factory bleed (not over filling via bleeding edge), while maintaining a short throw? Or is that counter to what the Swing link is designed for and thus, users would just need to "deal with it"?
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Primoz
2 years ago
I'd say it's a 'deal with it' situation...

The swing link gives you a lot of pad movement and a lot of power. You're fairly limited in how much either you can get from your finger (as in lots of power, no pad clearance or lots of pad clearance, no power), unless you move that around a bit, which is what the swing link does. I can go all the way to 11 with the nerdiness, but I intentionally held back. If you want the 11, just say so.

Is the short lever throw personal preference or a necessity because of short fingers or something similar?
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Primoz
2 years ago
Okay, put on your beer bottle bottom glasses, we're getting nerdy!

This is of course my theory and thinking, I've never designed a braking system so I don't know if this is fact or fiction, but it kinda seems to check out. Though if you ask a 'world cup levele mechanic' on Pinkbike, the swing link does nothing.

Anywho, hydraulic brakes are essentially a simple hydraulic machine. As per wiki's article, this is the most important picture in the story (stolen and reuploaded due to the size of the original picture and keeping only the relevant part):


That force amplification part is the key. Want more power? Make the master piston (in the lever) smaller or the pistons in the caliper larger. Thus more force. The problem is that fluid volume is constant. The more you increase the ratio between the master and slave (caliper) pistons, the less travel the caliper pistons will have. As I've mentioned, the force and travel of a finger is fairly set, thus the travel and force on the master cylinder are fairly set as well. You only have so much 'energy' available. Thus, with a brake with no swing links, you can have pad clearance or power, but not both at the same time. The area under the graph is fixed and the same in all three cases (a relative 2) and is what would happen in a link-less system if you were to tune piston diameters only:


Now, if we were to extrapolate this to suspension, this would be a simple single pivot bike with a coil shock, like an Orange. Ideally even a coil sprung fork (as those are even more linear) - what you see is what you get. Want more small bump sensitivity? Run a lighter spring. Want more deep travel support? Run a heavier spring. Want both? Weeeeell... You can go for an air spring. Still want to run that sweet coil? Well, if we're talking about the rear suspension, you can play around with some more links and create a linkage (keyword here), that gives you more force on the shock with the small stuff (so it's more active) and less force deep in the travel. You're still running the same spring for example, same travel, same stroke on the shock, etc., it's just spread around a bit. Through the leverage curve.

That's what the swing link does. As in not linear. I've used the y=x^2 function as a showcase, in reality it would be a function of sines or cosines, but it still shows the point I'm trying to get across:


The squared function achieves a relative pad clearance of ~1,8, almost as much as the goldilocks, with a final braking power of ~3,3, almost as much as the powerful variant. The area under the graph is the same as with the other three variants.
This is what the linkage in the lever enables.

If we look at how the pads move in relation to the movement of the lever (master piston) and what that means for the maximum available power, we get this:


It's simple to see that if you make the brake more 'responsive' through less stroke, that you influence the available power by A LOT. Just look how much power is left with a relative lever stroke of 1 (vs. how much the pistons in the caliper moved).

Why a simple linkage does this? Think of it as a wedge:


The bottom link is the lever, the top link actuates the piston. As you can see, starting off with the first situation, the movements will be fairly similar, x rotation of the lever will give almost x rotation of the other link. Once the lever link starts wedging itself under the top link (middle and then right situation), the top link will barely move for quite a bit of rotation of the bottom link (lever). That gives you the additional power when the pads touch the rotor. I.e. the wedge. If the pad clearance is not what it was designed to be, you're stuck in the middle situation. Kind of like trying to fell a tree by hammering a wedge into the cut sideways. You can swing that hammer and you will get it in a bit, but it won't do much.

I do have to add, the brake lever itself is a mechanism that you can also tune. Make the lever longer on the finger side and shorter on the piston side and you will get more force on the piston. But that will also give you less piston travel (as I said, finger stroke is finite) and you are back to square one, do you change the lever to caliper ratio to keep the pad clearance or use the higher power? So the lever itself, if it doesn't have a linkage between it and the piston, doesn't change things when it comes to the complete system (from the finger to the rotor).

So, keeping decent pad clearance (to prevent brakes rubbing) to get power, you need stronger finger(s) or a linkage and tune that correctly. Or a bigger rotor.

I hope it's fairly clear.
Also, Cascade Components might have a say (with some practical experience backing it up) regarding all of this considering the products they now sell.
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Malky79
2 years ago
Thanks for the info Primoz. I wonder if you are able to help me with the following?
Does using 2mm discs with Code RSC adversely affect the swing link leverage?
When bleeding the brakes, do you think there a better way other than Srams procedure of setting lever 75-80mm from the centreline of the bar and contact point adjustment wound all the way out? I'm getting a good bleed following the instructions, but not happy with the lever feel at the moment - just feel I'm having to pull to hard to brake hard, causing hand fatigue.
Cheers.
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Primoz
2 years ago
Oof, can't really comment on that one as I don't know how everything is setup, but if the pistons can move 0,2 mm back (0,1 mm for each piston) from the factory bleed position, at the worst, you'd need a 0,2 mm thicker bleedblock and it'd be completely the same (doing a factory specified bleed and pushing the pads 0,2 mm further apart might overfill the system and squeeze the pistons back towards the rotor).

As soon as you shave 0,1 mm off each pad you'll for sure be good to go though.

Considering it's a setup you already have, try to find something that's 0,1 mm or 0,2 mm thick. Slap some tape on your bleedblock and measure it before and after to see the effect it has. Not duct tape though, that's layered and it might move around, compress, etc. And do it with an open master cylinder bleedport with a syringe in there so the oil will have some place to go when you are pushing the pistons apart.
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Malky79
2 years ago
Thanks for the suggestion Primoz. I've got metal foil tape I can add to the bleed block. Cheers.
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CascadeComponents
2 years ago
As long as you reset the pistons/bleed to a block thicker than your rotor and pads, it doesn't matter how thick your rotors are. Lever throw will be the same. The only time thicker rotors decrease lever throw is if you just swap a thin rotor for a thicker one and do nothing else. This is effectively the same as over filling your brakes so it eventually goes away.
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CascadeComponents
2 years ago
Yeah this pretty much sums it up. The swing link has less mechanical advantage over the master cylinder initially and then ramps towards more mechanical advantage. That allows the bit of lever stroke that closes up the gap between the pads and the rotor to be relatively short. If you over fill the lever to make the brakes touchier then you end up with something that 1. needs to be maintained or the feel will go away and 2. is primarily in the portion of lever throw where the swing link has less mechanical advantage. The cams we make work by decreasing the mechanical advantage the lever has over the master cylinder initially so that the gap between the pads and the rotor can be closed even faster then they ramp up as usual.
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