[freeriding]

I have guide rsc on my bike, with bleeding edge, the 2017 model that should not have problems with the piston. However, yesterday, in a hot day, 35 celsius, and riding for much time in direct sunlight, the pads suddenly rubbed the brake disc a lot (i almost couldn't ride uphill), and the lever lost much of its travel. (only the rear brake)

I guess the sticky piston said hello to me
I really don't want to mess with it, changing piston etc, so i am thinking of changing just the rear brake
Do code rsc have the same problem?

 

[Udi]

Code on back with Guide on front will likely give L/R lever throw inconsistency, with same potential problems.
I'd just re-bleed your current brake and potentially consider cleaning and lubricating the pistons.

Long-term solution: non-SRAM brake.

 

[toodles]

I don't know what the hell happens in those levers, but in all the cases I've seen bleeding them hasn't fixed it. I think maybe they overheat and push the seal over-itself or something because cooling them down doesn't fix it. Stupid things.

I'm reluctant to recommend SRAM brakes for that reason.

 

[FarkinRyan]

Given that those are Guide RSCs what you have there is a 'feature', not a problem. It's designed to tell you when it's too hot outside to keep riding.

 

[freeriding]

so, code rsc have the same problems? Or nothing has been reported? Cause guides have been plagued with this shitty problem!

hope V4 will provide adequate braking power? i read the enduro mtb test, and v4 don't have that much decelarating power, like code, mt5, zee and are supposed to give you sorehands in long descents cause of lack of initial bite.

 

[toodles]

hope V4 will provide adequate braking power? i read the enduro mtb test, and v4 don't have that much decelarating power, like code, mt5, zee and are supposed to give you sorehands in long descents cause of lack of initial bite.

I switched from Guides to Hope V4s about 3 years ago and have never looked back. I've since switched to Hopes on all 3 bikes and can't see myself bothering to fuck around with rubbish brakes again. If you can afford them, get them.

 

[Udi]

hope V4 will provide adequate braking power? i read the enduro mtb test, and v4 don't have that much decelarating power, like code, mt5, zee and are supposed to give you sorehands in long descents cause of lack of initial bite.

If you want a reasonably reliable brake with decent stopping force, the V4 will work well.
I think you'll be pleasantly surprised, particularly in the long run compared to SRAM/Shimano.

The Enduro MTB test isn't hugely accurate so I wouldn't base your decision off that.

 

[freeriding]

i think it is quite accurate, it was performed in the hope lab.
Where did you buy them from? I am thinking of freeborn or ubyk.

Do they have at least the power/decceleration of the guides? (what pads are the best?)
sram brakes are over for me.

I want to ride or else, i might waited for eptember and the cura 4 pot.

 

[Udi]

i think it is quite accurate, it was performed in the hope lab.

It's not.

You should read through this entire thread:
http://ridemonkey.bikemag.com/threads/done-with-my-zee-brakeset-whats-next.280042/
It answers most of your questions, and will give you some options.

I think the Cura 4-pot (if you choose to wait) or Hope V4 will both be good options, just get them wherever they happen to be cheapest and available. V4 will stop as well as a working Guide (at least) in my experience, I don't think you have anything to worry about. The stock red semi-sintered pads are good in dry conditions (made by Galfer), but not good in wet. Their sintered pads are average but no worse than SRAM. If you ride in wet conditions use the sintered pads.

I don't own either brake, just that both brands build better quality brakes than current Shimano/SRAM.

 

[Electric_City]

Just because toodles is right and it deserves a second reading.

I switched from Guides to Hope V4s about 3 years ago and have never looked back. I've since switched to Hopes on all 3 bikes and can't see myself bothering to fuck around with rubbish brakes again. If you can afford them, get them.

 

[Wuffles]

i think it is quite accurate, it was performed in the hope lab.
Where did you buy them from? I am thinking of freeborn or ubyk.

Do they have at least the power/decceleration of the guides? (what pads are the best?)
sram brakes are over for me.

I want to ride or else, i might waited for eptember and the cura 4 pot.

Critical problem with the enduro test is it was performed at a constant force (can't remember the exact Newtons, but it came out to 11ish lbs). Yes, Hope's do not quite have the leverage that Saint's do, but unlike Saints the pistons will continue to actuate throughout the entire lever pull so the maximum force you can get out of them is greater, at least in my experience (Udi, do we have any data on piston travel in the frankenbrake spreadsheet?). You can pull Shimano brakes to the bar, and the force doesn't really increase past a certain point. With Hope, if you do actually manage to pull the lever to the bar your wheel is guaranteed to be locked tight.

 

[Udi]

Critical problem with the enduro test is it was performed at a constant force (can't remember the exact Newtons, but it came out to 11ish lbs). Yes, Hope's do not quite have the leverage that Saint's do, but unlike Saints the pistons will continue to actuate throughout the entire lever pull so the maximum force you can get out of them is greater, at least in my experience (Udi, do we have any data on piston travel in the frankenbrake spreadsheet?). You can pull Shimano brakes to the bar, and the force doesn't really increase past a certain point. With Hope, if you do actually manage to pull the lever to the bar your wheel is guaranteed to be locked tight.

Nah the latter part of your post is completely incorrect.

The Saint/Zee (and any other servowave brake) just use mechanical leverage modifiers, so it's the same principle as an LR curve on rear suspension. What happens is that at the start of the stroke the leverage is very low so you get a large amount of slave piston movement (to bring the pads close to the disc: low leverage = greater slave movement for given master movement + low force IF the brake was actually working, which it's not), but by the time the pads contact the disc the linkage has moved into its high-leverage profile. Less slave piston movement for a given master piston movement = higher leverage = higher peak force.

It's an absolutely brilliant idea, and it works EXACTLY as Shimano claim. The current Zee and Saint brakes (when working correctly) hands-down have more peak braking force than the Hope V4, this is calculable fact. Whatever you think you experienced suggests your Shimano brake had a problem. The Saint/Zee will generate more braking force (than the V4) at the point the pads engage, and at any point beyond that.

The Hope-V4-owner-spiel about "magically using unicorns to generate extra braking force as you press the lever more" is actually just how any normal brake works, in fact the "cam" on the V4 is just a dummy cam and does nothing to the leverage curve. Humans just like to justify their expensive purchases.

But I still did recommend the V4 / Cura4 (note: I own neither brake), and I would never run a Saint/Zee myself. Why? Because they fail, with multiple failure modes possible at both lever and caliper, and the manufacturing and materials quality (on both SRAM and Shimano) is far behind Hope, Formula, and Trickstuff. A brake that stops a little worse but does so consistently every time you hit it is far better than one that works brilliantly but only 90% of the time.

Regarding your spreadsheet questions, I think you have some gaps in your understanding to fill before any data would be useful to you. Of course piston travel is calculable, but your understanding (from what you said) is actually the complete opposite of reality, as per above explanation.

I also don't think the "critical" problem with the Enduro test is the constant force, I think the (much simpler!) problem is that they measured a million things at once (eg. what made it better, the brake or the pad?), and didn't mention normalizing things like engagement point (since peak force varies depending on lever angle and position). It's nice to see people attempting "testing", but a scientific experiment needs only one minor flaw to render the results not just "slightly wrong" but completely useless. Normalization (lack thereof) is the key problem with this test.

Hope you don't take it the wrong way, I'm not one to sugar-coat deliveries. If more people measured their brakes for my spreadsheet, we'd have more useful data to analyse. I have brakes I am incredibly happy with so while I occasionally add things to the sheet in hopes it might benefit someone, I have nothing to gain from it (monetary or otherwise).

 

[Wuffles]

Nah the latter part of your post is completely incorrect.

The Saint/Zee (and any other servowave brake) just use mechanical leverage modifiers, so it's the same principle as an LR curve on rear suspension. What happens is that at the start of the stroke the leverage is very low so you get a large amount of slave piston movement (to bring the pads close to the disc: low leverage = greater slave movement for given master movement + low force IF the brake was actually working, which it's not), but by the time the pads contact the disc the linkage has moved into its high-leverage profile. Less slave piston movement for a given master piston movement = higher leverage = higher peak force.

It's an absolutely brilliant idea, and it works EXACTLY as Shimano claim. The current Zee and Saint brakes (when working correctly) hands-down have more peak braking force than the Hope V4, this is calculable fact. Whatever you think you experienced suggests your Shimano brake had a problem. The Saint/Zee will generate more braking force (than the V4) at the point the pads engage, and at any point beyond that.

The Hope-V4-owner-spiel about "magically using unicorns to generate extra braking force as you press the lever more" is actually just how any normal brake works, in fact the "cam" on the V4 is just a dummy cam and does nothing to the leverage curve. Humans just like to justify their expensive purchases.

But I still did recommend the V4 / Cura4 (note: I own neither brake), and I would never run a Saint/Zee myself. Why? Because they fail, with multiple failure modes possible at both lever and caliper, and the manufacturing and materials quality (on both SRAM and Shimano) is far behind Hope, Formula, and Trickstuff. A brake that stops a little worse but does so consistently every time you hit it is far better than one that works brilliantly but only 90% of the time.

Regarding your spreadsheet questions, I think you have some gaps in your understanding to fill before any data would be useful to you. Of course piston travel is calculable, but your understanding (from what you said) is actually the complete opposite of reality, as per above explanation.

I also don't think the "critical" problem with the Enduro test is the constant force, I think the (much simpler!) problem is that they measured a million things at once (eg. what made it better, the brake or the pad?), and didn't mention normalizing things like engagement point (since peak force varies depending on lever angle and position). It's nice to see people attempting "testing", but a scientific experiment needs only one minor flaw to render the results not just "slightly wrong" but completely useless. Normalization (lack thereof) is the key problem with this test.

Hope you don't take it the wrong way, I'm not one to sugar-coat deliveries. If more people measured their brakes for my spreadsheet, we'd have more useful data to analyse. I have brakes I am incredibly happy with so while I occasionally add things to the sheet in hopes it might benefit someone, I have nothing to gain from it (monetary or otherwise).

Err... I may have been slightly buzzed and chosen words poorly, but not incorrect.

Servowave is a variable leverage design that changes the instantaneous mechanical leverage the brake lever has over the master cylinder piston by changing the pivot point/fulcrum of the lever as it moves through it's throw. Video just so we're on the same page: https://www.pinkbike.com/video/428742/ I agree that it works exactly as Shimano claims.

The mechanical leverage of a brake system's input device is completely separate from the hydraulic leverage of the brake system, which is defined by the ratio of master and slave piston areas. Servowave only effects the mechanical leverage of the lever on the master cylinder piston, it does not and cannot change the hydraulic leverage ratio.

When you say Shimano brakes can generate more braking force, I agree that yes, they have a greater hydraulic leverage ratio than Hopes (comparing M820s to V4s here), as well as a greater mechanical leverage ratio, and therefore a greater total leverage ratio. But leverage ratio is not force, it is a ratio of forces. This is where piston travel is important, because I strongly suspect that while Shimano has a greater mechanical leverage, Hope has a longer master cylinder piston travel (we know from the frankenbike sheet the master cylinder piston on Hope is bigger than Shimano). So while it may take more effort than Shimano, the capacity for work (force x distance) is greater on Hope. Greater work equals higher pressure, which when applied to the caliper piston, equals greater force. Hence why you can pull Shimano brakes to the bar with some effort, but you can pull a harder on a Hope lever, not get to the bar, and still lock your wheel.

That's also why I'm picking out lever force as the worst part of the test. I am only mildly interested in the response of each brake from a 50N input, because that's just a measurement of instantaneous leverage. I am much more interested in how hard you can squeeze the lever before you stop seeing increases in braking power at the caliper.

 

[Udi]

This is where piston travel is important, because I strongly suspect that while Shimano has a greater mechanical leverage, Hope has a longer master cylinder piston travel (we know from the frankenbike sheet the master cylinder piston on Hope is bigger than Shimano). So while it may take more effort than Shimano, the capacity for work (force x distance) is greater on Hope. Greater work equals higher pressure, which when applied to the caliper piston, equals greater force. Hence why you can pull Shimano brakes to the bar with some effort, but you can pull a harder on a Hope lever, not get to the bar, and still lock your wheel

You are ignoring and dismissing everything I wrote (I still don't think you understand it either), and bringing up a completely unrelated point, which is what happens when the MC runs out of physical travel / displacement. This should never happen on any brake (during practical usage), if the lever is physically hitting the grip or running out of stroke then the reach needs to be set further out.

You are also implying that lever stroke before hitting grip equals MC piston peak displacement capacity with no mention of reach setting.

This also has absolutely nothing to do with peak force for a *given* (i.e. a fixed peak) level of lever force input. Now I can see why you are flared up about the Enduro brake test's constant lever force input. Can you not understand the simple concept that if you need greater input (finger) force for a given stopping force, then that brake is just weaker?

By your logic, a Formula T1 (for example) is superior to a Hope V4 again, because those brakes have substantially less dead-stroke than both the V4 and M820, which means you can "pull harder on the lever, not get to the bar, and keep developing infinite force". In reality though, the brake just generates less peak force, so it's just a weaker brake.

The mechanical leverage of a brake system's input device is completely separate from the hydraulic leverage of the brake system, which is defined by the ratio of master and slave piston areas.

Are you seriously assuming I don't know this, when my spreadsheet defines and separates exactly these things for individual calculation?

But leverage ratio is not force, it is a ratio of forces.

Where did I say leverage ratio was a force?
Read my post again, I think you're just arguing for the sake of arguing, this is nonsense.

 

[Udi]

Err... I may have been slightly buzzed and chosen words poorly, but not incorrect.

but unlike Saints the pistons will continue to actuate throughout the entire lever pull so the maximum force you can get out of them is greater

This is flat out incorrect, no wording issue.

You can pull Shimano brakes to the bar, and the force doesn't really increase past a certain point. With Hope, if you do actually manage to pull the lever to the bar your wheel is guaranteed to be locked tight.

Again, this is misleading at best.
You are confusing available/usable stroke distance (after free-stroke distance) with the actual leverage (combined mech/hydraulic) and force characteristics of the brake.

I actually know exactly why you are confusing (or combining) these things, because in practical usage the M820 certainly does have a very long free-stroke (not ideal), which means that at a realistic reach setting (especially for riders with small hands / short fingers, who physically can't run the reach very far out) there is a chance the lever could contact the grip before a) developing peak useful braking force, and b) before the MC itself runs out of travel. If the brake is old or problematic then the likelihood of this occurring is increased further. However this does not reflect actual MC travel. if you want to see / understand actual MC travel, you need to wind the reach quite far out. Then you can explore your little W=Fd scenario more accurately.

Sidenote: obviously reach setting affects mechanical leverage too because the lever blade angle will be different at engagement point (and for realistic operation range) depending on the reach setting. Another aspect hard to normalize with a test like Enduro Mag conducted.

However, for the sake of analysing brakes, see the Formula counterexample I gave.
You can choose to believe what you like, but the V4 is just flat out a weaker brake than the M820. I think there is much more to a brake than peak force which is why I still recommended the V4 - however I do not agree with deluding others into thinking "this product is actually better at everything" by unicorning the brake's minor flaw into a positive trait.

The V4 is a better brake all round because it has decent peak force, generous pad size, reasonable free-stroke (better than M820 for sure) which means reach setting doesn't have to be crazy far out, and has higher build quality so less prone to failure / variation after a few years.

 

[Jm_]

So it’s Hayes HFX9 then?

 

[Flo33]

So while it may take more effort than Shimano, the capacity for work (force x distance) is greater on Hope. Greater work equals higher pressure, which when applied to the caliper piston, equals greater force. Hence why you can pull Shimano brakes to the bar with some effort, but you can pull a harder on a Hope lever, not get to the bar, and still lock your wheel.

What's the point in being able to displace more fluid when the force needed to and the distance needed to do so is higher on the one brake?

Force x at the lever results in force y at the pads. If force x hast to be higher to reach force y on a brake, than it's a weaker brake. Period.

Servo wave is a really good idea, it combines the advantages of a high hydraulic leverage late in the travel and a low lever throw through the lower lever leverage at the beginning of the levers travel.

 

[marshalolson]

@Udi just to confirm,

Formula R0 Racing is still monkey approved on trail bikes with bigger rotors (200 F & 180 R)?

Just use EBC red pads vs frying the stock sintered ones?

 

[Udi]

@Udi just to confirm,
Formula R0 Racing is still monkey approved on trail bikes with bigger rotors (200 F & 180 R)?
Just use EBC red pads vs frying the stock sintered ones?

I think that's a decent option, especially if you have a source for EBC red and they work for your needs. I really liked those pads, though they wear a bit fast. Certainly eliminates the small pad glazing issues.

I'd go for 203mm F/R, the Formula rotor with alloy carrier is incredibly light anyway, 143g@203 and on 650b with that brake I'd prefer to max things out. I wouldn't recommend them for a 29er.

I haven't run them in a while, but HAB is a more recent user, and I think Flo33 might have a pair too, so perhaps PM them if you want more up to date thoughts.

 

[marshalolson]

I think that's a decent option, especially if you have a source for EBC red and they work for your needs. I really liked those pads, though they wear a bit fast. Certainly eliminates the small pad glazing issues.

I'd go for 203mm F/R, the Formula rotor with alloy carrier is incredibly light anyway, 143g@203 and on 650b with that brake I'd prefer to max things out. I wouldn't recommend them for a 29er.

I haven't run them in a while, but HAB is a more recent user, and I think Flo33 might have a pair too, so perhaps PM them if you want more up to date thoughts.

Awesome thanks man, will look at bumping to an 200 R. I am coming from M810’s on 180’s.

Like the EBC Red in the dry/dusty Utah riding here. Burn em up every month, but they end up lasting longer/less maintenance than most sintered pads, since they don’t glaze.

Appreciate it

 

[Udi]

Awesome thanks man, will look at bumping to an 200 R. I am coming from M810’s on 180’s.

Like the EBC Red in the dry/dusty Utah riding here. Burn em up every month, but they end up lasting longer/less maintenance than most sintered pads, since they don’t glaze.

We're on the same page, clearly!
I first tried those pads back in 2004, and then again for Europe/PDS in 2011, each time I've loved them right until they hit the backing. You'll lose a little bite + peak stopping force from M810 to ROR (even with the rotor bump) but you're clearly already onto that, with the bigger rotors it'll be close.

Depending on how much you care about weight, the the Hope V4 is another good option for you, and the stock Galfer Red pads are very similar to the EBC Red, especially in those conditions. Stock with the braided hoses they weigh the same as M810s, but ~35g/end lighter if you switch to normal plastic hoses.

Of course the ROR is way lighter (one of the lightest brakes in existence!) so that's the benefit for the sacrifices in peak force and pad size. The V4 is probably a bit closer to the M810 for stopping, and pad area is the same. Both good brakes in their own right.

Good luck either way!

 

[Wuffles]

You are ignoring and dismissing everything I wrote (I still don't think you understand it either), and bringing up a completely unrelated point, which is what happens when the MC runs out of physical travel / displacement. This should never happen on any brake (during practical usage), if the lever is physically hitting the grip or running out of stroke then the reach needs to be set further out.

You are also implying that lever stroke before hitting grip equals MC piston peak displacement capacity with no mention of reach setting.

This also has absolutely nothing to do with peak force for a *given* (i.e. a fixed peak) level of lever force input. Now I can see why you are flared up about the Enduro brake test's constant lever force input. Can you not understand the simple concept that if you need greater input (finger) force for a given stopping force, then that brake is just weaker?

By your logic, a Formula T1 (for example) is superior to a Hope V4 again, because those brakes have substantially less dead-stroke than both the V4 and M820, which means you can "pull harder on the lever, not get to the bar, and keep developing infinite force". In reality though, the brake just generates less peak force, so it's just a weaker brake.


Are you seriously assuming I don't know this, when my spreadsheet defines and separates exactly these things for individual calculation?


Where did I say leverage ratio was a force?
Read my post again, I think you're just arguing for the sake of arguing, this is nonsense.

This is flat out incorrect, no wording issue.


Again, this is misleading at best.
You are confusing available/usable stroke distance (after free-stroke distance) with the actual leverage (combined mech/hydraulic) and force characteristics of the brake.

I actually know exactly why you are confusing (or combining) these things, because in practical usage the M820 certainly does have a very long free-stroke (not ideal), which means that at a realistic reach setting (especially for riders with small hands / short fingers, who physically can't run the reach very far out) there is a chance the lever could contact the grip before a) developing peak useful braking force, and b) before the MC itself runs out of travel. If the brake is old or problematic then the likelihood of this occurring is increased further. However this does not reflect actual MC travel. if you want to see / understand actual MC travel, you need to wind the reach quite far out. Then you can explore your little W=Fd scenario more accurately.

Sidenote: obviously reach setting affects mechanical leverage too because the lever blade angle will be different at engagement point (and for realistic operation range) depending on the reach setting. Another aspect hard to normalize with a test like Enduro Mag conducted.

However, for the sake of analysing brakes, see the Formula counterexample I gave.
You can choose to believe what you like, but the V4 is just flat out a weaker brake than the M820. I think there is much more to a brake than peak force which is why I still recommended the V4 - however I do not agree with deluding others into thinking "this product is actually better at everything" by unicorning the brake's minor flaw into a positive trait.

The V4 is a better brake all round because it has decent peak force, generous pad size, reasonable free-stroke (better than M820 for sure) which means reach setting doesn't have to be crazy far out, and has higher build quality so less prone to failure / variation after a few years.

Lets dive into this, but first a few clarifications.

One: I am reading what you write very carefully. Which is why, when I see something that is amiss, I bring it up. This is not a dismissal, it is an attempt at improving all of our understandings. Be open to the possibility that you are not god's perfect child, and may be wrong about something every once in a while.

Two: I have a preference for the way Hope's feel. This does not mean I'm pretending it magically does everything better, and as you can read in previous posts I certainly concede there are other brands that are superior in other areas. Your claim of "magic unicorn dust" is your own shitty projection on some internet straw man, now knock it the fuck off.

Okay- to begin with, master cylinder bore and travel, and the corresponding capacity of a hydraulic system to do work is not an unrelated point as you dismiss it, but is in fact rather goddam important. Why is it important? Because the the force a caliper puts on the pads is directly due to the pressure of the system. With no external factors, the pressure of a hydraulic system is solely a function of the work the master cylinder puts into the system. This is a basic principle of physics, called P-v work.

...what happens when the MC runs out of physical travel / displacement. This should never happen on any brake (during practical usage), if the lever is physically hitting the grip or running out of stroke then the reach needs to be set further out.

You are also implying that lever stroke before hitting grip equals MC piston peak displacement capacity with no mention of reach setting.

For an MTB brake, master cylinder displacement is limited by the geometry of the MC piston body and the kinematics of the lever stroke. Ideally the piston stroke does not bottom out, but unfortunately practical engineering considerations get in the way.

Look at this video of a transparent M820 display show model paused at 25 seconds:

Notice the MC return spring is bottomed out? That's an internal mechanical stop on piston travel, and monkeying around with reach won't do anything to change it. Sure you could use a less tight spring, but you still run into the other issue: leverage ratio vs work, and this is where we're having communication difficulties.

YCan you not understand the simple concept that if you need greater input (finger) force for a given stopping force, then that brake is just weaker?

You're talking about leverage ratios. I said, and I quote "yes, they have a greater hydraulic leverage ratio than Hopes (comparing M820s to V4s here), as well as a greater mechanical leverage ratio, and therefore a greater total leverage ratio." You glossed right the fuck over it in your haste to denounce my poor understanding, but it's there in black and white dude. Read moar better.

Okay, so M820s have a bigger leverage ratio, and they deliver a correspondingly bigger caliper force for an input finger force. Why do all brakes not do this? Why do we not have tiny ass master cylinders and huge levers with fulcrums right at the very end to exert the maximum force on the MC piston? Why is it not leverage uber alles when it comes to brake design? Simple- work. Motha fuggin work.

Normalize the lever and caliper piston for a second and look only at master cylinder bore: all other things being equal, a smaller MC provides a larger hydraulic leverage ratio. So for any given displacement of the caliper piston, it takes less force on the MC piston. The flip side is that while it is easier to move the MC piston, you have to move it further. Now throw the lever back in: the same thing is true- a greater mechanical leverage ratio means it is easier to move the lever for any given force, but again you have to move it further.

Brake levers on a MTB have to work within a certain design envelope determined by human factors and cockpit geometry. You cannot make your brake lever throw longer than someone can bend their pointer finger, so that's a limitation. You cannot make your MC piston travel all that long, because it a) has to fit within a compact lever housing and b) is the load on the other end of the lever arm that your finger is pulling on. So since you are limited to a certain MC piston displacement, there is a certain maximum amount of work that the hydraulic system can do, which means there is a certain maximum pressure the system can reach, and thus a certain maximum amount of force the caliper pistons can put out. This is what is normally referred to as peak force, but maybe we should call it maximum force to avoid confusion with some other peak force.

So, in the context of the limitations of an MTB brake, higher leverage allows you to more easily achieve a certain caliper piston force by moving the lever and MC a longer distance. The converse is that since both lever throw and MC piston displacement are limited, a brake with lower leverage moving the same throw/piston travel distances will do more work. More work means higher pressure, which means more force at the caliper pistons, which means greater friction between the pads and rotor, which means more total braking power. That's just how physics work, it's not magical or anything.

 

[R_Pierce]

Im kind of surprised that I dont see Magura mentioned in many of these threads. Im currently on MT7's and they are some seriously solid brakes!

 

[jonKranked]

That's just how physics work, it's not magical or anything.

the bike industry lizards don't use physics, just magic. at least mostly magic.

 

[Flo33]

@Udi just to confirm,

Formula R0 Racing is still monkey approved on trail bikes with bigger rotors (200 F & 180 R)?

Just use EBC red pads vs frying the stock sintered ones?

As Udi said I'm running a pair of RORs with 203/180 Icetech rotors and am very happy with them. But I'm at 66 kg and relatively easy on brakes. We have a very wet season so far, so totally different conditions compared to yours I guess.

 

[slyfink]

Im kind of surprised that I dont see Magura mentioned in many of these threads. Im currently on MT7's and they are some seriously solid brakes!

ummm... I'm not gonna go through them all, but I'm pretty sure you will find them referred to in all of these threads:
http://ridemonkey.bikemag.com/threads/done-with-my-zee-brakeset-whats-next.280042/
http://ridemonkey.bikemag.com/threads/shimano-xt-brakes-for-downhill.280118/
http://ridemonkey.bikemag.com/threads/frankenbrakes-and-brake-improvement-discussion.274164/

maybe also look for "saintgura"...

 

[bagtagley]

This is interesting because I just started having an issue with my Guides where the front pads start to rub, and the lever throw goes to nil, and it seems to only happen when I've been in the sun. They're fine the next time I ride the bike, and I went several days before it happened again. I thought the sun part was just a coincidence, but this is a known issue?

 

[Wuffles]

What's the point in being able to displace more fluid when the force needed to and the distance needed to do so is higher on the one brake?

Force x at the lever results in force y at the pads. If force x hast to be higher to reach force y on a brake, than it's a weaker brake. Period.

Servo wave is a really good idea, it combines the advantages of a high hydraulic leverage late in the travel and a low lever throw through the lower lever leverage at the beginning of the levers travel.

You've forgotten Z, the displacement of the lever. Force X at the lever may result in force Y at the pads, but it does so over Z distance. And Z can't be longer than you can curl your finger. So if you've got the grip strength, you can get a lot bigger Y over the same Z with lower leverage. It all depends on what's important to you.

Servowave is indeed a thing. I am not partial to the grabby sensation it gives, but if that's your cup of tea, by all means rock it.

 

[Udi]

Notice the MC return spring is bottomed out? That's an internal mechanical stop on piston travel, and monkeying around with reach won't do anything to change it. Sure you could use a less tight spring, but you still run into the other issue: leverage ratio vs work, and this is where we're having communication difficulties.

We need to take a few steps back. This is the straw man, you're the sole builder.

Your entire claim is based on your personal experience where a Shimano lever hit the grip and ran out of lever travel. You implied that this simultaneously means that the MC piston ran out of travel, which is not the case on a correctly working and correctly set up Shimano brake. If the reach is set too close (i.e. initial/static lever position) OR if there is a problem with the brake, it is easily possible to have a scenario where the lever stops against the grip before the MC has hit mechanical end of stroke. This is why these factors matter.

Okay, so M820s have a bigger leverage ratio, and they deliver a correspondingly bigger caliper force for an input finger force. Why do all brakes not do this? Why do we not have tiny ass master cylinders and huge levers with fulcrums right at the very end to exert the maximum force on the MC piston? Why is it not leverage uber alles when it comes to brake design? Simple- work. Motha fuggin work.

No.

1. You say "bigger leverage ratio", which suggests a constant. The mechanical leverage on a brake is a curve, and in the case of Servo-Wave, an atypical curve - which is key to answering your questions with actual facts rather than "simple motha fuggin work".
   
2. All brakes don't do what SW does, that's exactly why most brakes (including the V4) can't do what the M820 does.
   
3. The hydraulic leverage ratio is constant on every brake discussed in this thread (linear piston displacements), but the mechanical leverage ratio is a variable curve.
   
4. The reason we can't just increase leverage indefinitely is because our lever displacement is limited by hand geometry, this part you understand. However what we can do (via SW) is distribute our actual leverage value, such that the instantaneous mechanical leverage value is incredibly high at the pad contact point, much higher than on a non-SW brake.
   
5. If you wanted to achieve the same instantaneous mechanical leverage value (at contact) on a non-SW brake (assuming identical hydraulic leverage), it would simply have far too long a throw, because it would "waste" too much finger displacement to get the pads to the rotor in the first place. The reason for this is because without SW, the LR curve is restricted to being far closer to linear - which means if you have a high instantaneous leverage value at pad contact, the rest of the stroke will be proportionally high also. High leverage AND close-to-constant leverage means large input displacement! SW on the other hand generates huge slave displacement for small MC displacement initially, allowing the remainder of the MC stroke (past contact, the important part) to operate at much higher overall leverage.
   
   
   
   As you can see, at the PONTO DE CONTATO, our leverage ratio on the SW brake can be much higher. If you take the integral of our approximated curves, you'd see they are very similar - meaning that SW allows similar total finger displacement while having far higher leverage at the PONTO where we actually need it. Obviously the "regular" brake in real life has some curvature also, but I think this graph still makes things clear.

 

[Bikael Molton]

Are any other manufacturers using servowave-type mechanisms? I think the Shimano v-brake application is close to 20years old.

We need to take a few steps back. This is the straw man, you're the sole builder.

Your entire claim is based on your personal experience where a Shimano lever hit the grip and ran out of lever travel. You implied that this simultaneously means that the MC piston ran out of travel, which is not the case on a correctly working and correctly set up Shimano brake. If the reach is set too close (i.e. initial/static lever position) OR if there is a problem with the brake, it is easily possible to have a scenario where the lever stops against the grip before the MC has hit mechanical end of stroke. This is why these factors matter.



No.

1. You say "bigger leverage ratio", which suggests a constant. The mechanical leverage on a brake is a curve, and in the case of Servo-Wave, an atypical curve - which is key to answering your questions with actual facts rather than "simple motha fuggin work".
   
2. All brakes don't do what SW does, that's exactly why most brakes (including the V4) can't do what the M820 does.
   
3. The hydraulic leverage ratio is constant on every brake discussed in this thread (linear piston displacements), but the mechanical leverage ratio is a variable curve.
   
4. The reason we can't just increase leverage indefinitely is because our lever displacement is limited by hand geometry, this part you understand. However what we can do (via SW) is distribute our actual leverage value, such that the instantaneous mechanical leverage value is incredibly high at the pad contact point, much higher than on a non-SW brake.
   
5. If you wanted to achieve the same instantaneous mechanical leverage value (at contact) on a non-SW brake (assuming identical hydraulic leverage), it would simply have far too long a throw, because it would "waste" too much finger displacement to get the pads to the rotor in the first place. The reason for this is because without SW, the LR curve is restricted to being far closer to linear - which means if you have a high instantaneous leverage value at pad contact, the rest of the stroke will be proportionally high also. High leverage AND close-to-constant leverage means large input displacement! SW on the other hand generates huge slave displacement for small MC displacement initially, allowing the remainder of the MC stroke (past contact, the important part) to operate at much higher overall leverage.
   View attachment 129015
   As you can see, at the PONTO DE CONTATO, our leverage ratio on the SW brake can be much higher. If you take the integral of our approximated curves, you'd see they are very similar - meaning that SW allows similar total finger displacement while having far higher leverage at the PONTO where we actually need it. Obviously the "regular" brake in real life has some curvature also, but I think this graph still makes things clear.

 

[Flo33]

Shimano already used it in 1992 XT cantilever brake levers. There is a thread here with some info and pics of it posted by myself.

 

[Wuffles]

We need to take a few steps back. This is the straw man, you're the sole builder.

Your entire claim is based on your personal experience where a Shimano lever hit the grip and ran out of lever travel. You implied that this simultaneously means that the MC piston ran out of travel, which is not the case on a correctly working and correctly set up Shimano brake. If the reach is set too close (i.e. initial/static lever position) OR if there is a problem with the brake, it is easily possible to have a scenario where the lever stops against the grip before the MC has hit mechanical end of stroke. This is why these factors matter.

I agree, lets take a few steps back and start as basic as we can, first principles.

My claim starts with a Shimano levers running out of travel and exploring the implications thereof- let's set aside the issue of MC travel capability for the moment as well.

Are we good with Shimano and Hope (lets say M820 to V4 Tech 3) having the same hydraulic leverage ratio? It looks like the sheet was updated today, and both the 820 and V4 run 10 mm masters with 18/16 slave pistons. So they're identical for hydraulic leverage- great, makes one less variable to worry about.

Now lets look at that nice Servowave graph from Shimano (english version here: https://bike.shimano.com/en-EU/technologies/component/details/servo-wave-action.html for anyone totally baffled by Porteguese).

They show that Servowave has a low initial leverage before pad contact in order to minimize free stroke- perfect, fully granted and I don't think we disagree there.

And then it shows that once the pads contact the rotor, the whole system operates at a higher leverage than a non-servowave lever. This is, as you say, the important part. Again, we agree

And we also agree that you can only have a certain brake lever throw, because fingers are only so long.

So let's dig into leverage vs work. Do you agree energy is always conserved? I hope so, because to suggest otherwise is to suggest the universe is broken. The principle of leverage follows directly from the principle of conservation of energy. That is, on a Lever Arm, F1D1 must always be equal to F2D2, because force x distance = work = energy, and it is always conserved; it cannot be any other way.

Now Shimano has chosen, as they show in their graph, to have a higher leverage ratio than a non-servowave brake once the pads have engaged. Another way to say this is it takes less force on the lever to generate a given force on the master cylinder than a non-servowave lever. Great, I'm lazy and all for easier. That's the big selling point of Shimano, it's less effort to achieve a given force.

But there's no such thing as a free lunch, especially not in physics.

Remember that we agree you can only have a certain brake lever throw, so our distance is limited by the size of our fingers. Over the distance of any given rider's lever throw, a brake that takes less force to actuate does less work than one that takes more force, because force x distance = work = energy. So where is this energy going? It goes into pressurizing the brake system, either because a bigger master cylinder is being pushed, or, as I suspect is the case with Hope v Shimano, the master cylinder is being pushed a longer distance. So all that extra energy (force x distance) you are using in pulling a lower leverage ratio brake is not disappearing, it can't disappear- it goes into pressurizing the brake fluid to a greater degree, which means greater slave piston force, therefore greater pad friction, and thus greater braking force.

High leverage is a double-edged sword. It makes achieving a given braking force easier, but because we can only move a lever so far it also means our maximum possible force is lower. The tradeoffs between the two is up to the individual rider, but it is a necessary consequence of Conservation of Energy that for a given distance (say one finger curl), a lower leverage brake will do more work and therefore develop higher system pressures than a higher leverage brake, it cannot be any other way.

 

[Flo33]

In a correct working brake there should be no travel in the MC beyond contact point, fluids are incompressible. So all that is happening is an increase in force/pressure/force and your work goes into heat.

 

[Udi]

The "lunch not being free" is hidden in the low-leverage initial travel, which is why SW brakes have a firm initial lever action to get past. This is a clever optimisation because you are only pushing the pads through air (not against the rotor) during this part of the stroke (free-stroke region), so it's negligible effort.

I mentioned taking the integral of the two LR curves prior to the point of contact to mathematically illustrate how the overall stroke can remain the same. In laymen's terms: by using lower leverage when the brake is doing nothing, we can use higher leverage when the brake is doing something; and still maintain similar total stroke. No laws of physics are broken.

So where is this energy going? It goes into pressurizing the brake system, either because a bigger master cylinder is being pushed, or, as I suspect is the case with Hope v Shimano, the master cylinder is being pushed a longer distance. So all that extra energy (force x distance) you are using in pulling a lower leverage ratio brake

So all that extra energy (force x distance) you are using in pulling a lower leverage ratio brake

So all that extra energy you are using

using

extra

energy

As I've said all along, the brake which generates lower peak force (V4) takes more effort to stop with than the brake which generates higher peak force (M820). What a surprise.

Excellent work figuring out exactly how you were wrong.

/thread.