Brake caliper flex

Runtothehills

Bar Shaker wrote:

I am sorry but you are delusional. Let me put this into a simple exercise that you may be able to understand, with objects that you may have close to you in the office, or at school. Perhaps you have a clear plastic 12" (300mm) ruler. Hold one the bottom end between your thumb and index finger so that the ruler is vertical. Now push the top end sideways so it bends the ruler.

Repeat this exercise with a less flexible ruler, such as an engineering scale rule.

How does the force transfer to your finger and thumb?

Your comment above is that the flexibility makes no difference to the force that results but as we can see the stiffer ruler applies much more force for a given lateral load at the other end of the ruler.

Imagine if your caliper arms were made out of the same bendy plastic as your ruler. Would you be able to apply:
1) Less pad pressure
2) More pad pressure
3) The same amount of pad pressure a a forged alloy arm would apply

The same, assuming you didn't get to the end of the travel of the lever (which you would).

The force transfer (mostly moment) to your finger and thumb is less for the same DEFLECTION applied at the top, if the same FORCE is applied then the forces are the same. Read this link and tell me where the stiffness of the object affects the equilibrium conditions -it doesn't. You seem to be confusing forces and deflections.

http://www.s-cool.co.uk/a-level/physics ... conditions

With the ruler example what happens if you twist your finger and thumb and measure the force at the top. You're saying that the bendy ruler absorbs the energy so the force I feel at the top will be lower right? So for the bendy ruler the applied moment at the bottom results in a lower observed force at the top, but you've said for a given force at the top the moment at the bottom is lower. So the force is lower than the one due to the moment which is lower than one due to the the force?

Simially if I sit on a see-saw I need someone of equal mass on the other end to balance my weight: the forces must balance. If it's a really bendy see-saw that doesn't change, I don't magically need someone of less mass because the see-saw has 'absorbed' some of the force (plus if I did they'd need someone of lower mass to balance them so we'd both need to be lighter than each other...hmmm).

Daz555

ednino wrote:

I've got Ultegra brakes, loads better than my old Tiagras. The Ultegra pads are still crap in the wet though

I have 2013 Tiagras and they are excellent. Coming from years of mountain biking and hydraulic disks I was very surprised with how good they were.

Bar Shaker

Runtothehills wrote:

Bar Shaker wrote:

I am sorry but you are delusional. Let me put this into a simple exercise that you may be able to understand, with objects that you may have close to you in the office, or at school. Perhaps you have a clear plastic 12" (300mm) ruler. Hold one the bottom end between your thumb and index finger so that the ruler is vertical. Now push the top end sideways so it bends the ruler.

Repeat this exercise with a less flexible ruler, such as an engineering scale rule.

How does the force transfer to your finger and thumb?

Your comment above is that the flexibility makes no difference to the force that results but as we can see the stiffer ruler applies much more force for a given lateral load at the other end of the ruler.

Imagine if your caliper arms were made out of the same bendy plastic as your ruler. Would you be able to apply:
1) Less pad pressure
2) More pad pressure
3) The same amount of pad pressure a a forged alloy arm would apply

The same, assuming you didn't get to the end of the travel of the lever (which you would).

The force transfer (mostly moment) to your finger and thumb is less for the same DEFLECTION applied at the top, if the same FORCE is applied then the forces are the same. Read this link and tell me where the stiffness of the object affects the equilibrium conditions -it doesn't. You seem to be confusing forces and deflections.

http://www.s-cool.co.uk/a-level/physics ... conditions

With the ruler example what happens if you twist your finger and thumb and measure the force at the top. You're saying that the bendy ruler absorbs the energy so the force I feel at the top will be lower right? So for the bendy ruler the applied moment at the bottom results in a lower observed force at the top, but you've said for a given force at the top the moment at the bottom is lower. So the force is lower than the one due to the moment which is lower than one due to the the force?

Simially if I sit on a see-saw I need someone of equal mass on the other end to balance my weight: the forces must balance. If it's a really bendy see-saw that doesn't change, I don't magically need someone of less mass because the see-saw has 'absorbed' some of the force (plus if I did they'd need someone of lower mass to balance them so we'd both need to be lighter than each other...hmmm).

No, no, no.

By your argument, a rubber crowbar would be just as effective as a steel one.

If you take your bendy see-saw argument further and put two heavy blokes on it, one who is 120kg and one who is 115kg, who would be up in the air? The answer is neither as they would both be sitting on the floor. The reason is that the see-saw isn't stiff enough to transfer the lifting load required to lift 115kg. If we replace him with a 70kg chap, he will rise up 1m off the ground. If we remove him from the seat completely, the seat will go up 2m as there is nothing to bend against.

And that is exactly the argument here. A stiff caliper will let us put much more force into pressing the brake pad into the rim and this will give better braking ability.

Once your brake lever force exceeds the stiffness of the caliper arms, any extra effort goes into bending the arm with a no amount of this going into extra pad pressure.

If you were right, we have all wasted money on stiff levers, strong cables and stiff calipers, when any old stretchy/bendy rubbish would have done the same braking job.

Surely you must be able to see this.

rayjay

Top end brake review ,,,drool, admire, dream, use the credit card but don't tell the wife or just cry thinking that those AX Lightness brakes cost more than my whole bike.

http://fairwheelbikes.com/forum/viewtopic.php?p=93806

Runtothehills

Bar Shaker wrote:

Once your brake lever force exceeds the stiffness of the caliper arms, any extra effort goes into bending the arm with a no amount of this going into extra pad pressure.

If you were right, we have all wasted money on stiff levers, strong cables and stiff calipers, when any old stretchy/bendy rubbish would have done the same braking job.

Can I just ask is the sentence 'Once your brake lever force exceeds the stiffness of the caliper arms' a typing error or does it actually make sense to you?

If it does make sense to you then there's no point in us having this discussion as I'm assuming a working knowledge of the underlying physics. I can point you in the direction of some stuff that explains how forces and moments work and how they relate to deflections (through stiffness): what you've written there makes about as much sense as 'when my height exceeds my weight' or 'which is longer: 1 kilogram or 1 pound per square inch?'. Force and stiffness are different things, they can't be compared directly.

Also if you read what I said earlier in the thread I nver said that stiffer brakes were a waste of money: I said that a stiffer caliper could offer benefits in terms of modulation and lever 'feel' but, assuming the brakes are set up properly so you don't run out of travel on the brake lever, will not give a different force on the pad for a given force on the lever. The V-brakes on my hybrid are noticably more flexible and feel spongier than the brakes on my road bike (which is unpleasant) but can still send me over the handlebars, no lack of power there.

rayjay

Runtothehills wrote:

Bar Shaker wrote:

Once your brake lever force exceeds the stiffness of the caliper arms, any extra effort goes into bending the arm with a no amount of this going into extra pad pressure.

If you were right, we have all wasted money on stiff levers, strong cables and stiff calipers, when any old stretchy/bendy rubbish would have done the same braking job.

Can I just ask is the sentence 'Once your brake lever force exceeds the stiffness of the caliper arms' a typing error or does it actually make sense to you?

If it does make sense to you then there's no point in us having this discussion as I'm assuming a working knowledge of the underlying physics. I can point you in the direction of some stuff that explains how forces and moments work and how they relate to deflections (through stiffness): what you've written there makes about as much sense as 'when my height exceeds my weight' or 'which is longer: 1 kilogram or 1 pound per square inch?'. Force and stiffness are different things, they can't be compared directly.

Also if you read what I said earlier in the thread I nver said that stiffer brakes were a waste of money: I said that a stiffer caliper could offer benefits in terms of modulation and lever 'feel' but, assuming the brakes are set up properly so you don't run out of travel on the brake lever, will not give a different force on the pad for a given force on the lever. The V-brakes on my hybrid are noticably more flexible and feel spongier than the brakes on my road bike (which is unpleasant) but can still send me over the handlebars, no lack of power there.

I think what Bar Shaker is saying ,,,,,if you have a huge amount of force on the caliper and that force is enough to make the caliper bend or flex then that force is not putting any pressure on to the pad.
So there is no need to make extra stiff calipers.

For what its worth I used to run some KCNC CB1 brakes, very light but rubbish stopping power.
I switched the pads out to Gooey pads that are more sponge like, and they worked much better.

Runtothehills

rayjay wrote:

I think what Bar Shaker is saying ,,,,,if you have a huge amount of force on the caliper and that force is enough to make the caliper bend or flex then that force is not putting any pressure on to the pad.
So there is no need to make extra stiff calipers.

Bar shaker can you confirm this is the gist of what you meant?: if so I can look up those resources because it's wrong.

The bottom line is forces have to balance and moments have to balance: the stiffness of a system does not change that. Deformation (such as bending) takes energy out of a system, but the force is still transfered. If you're convinced that what I've said is wrong get worried: every bridge, building, car, aeroplane or pretty much anything else built by an engineer assumes that I am right.

ps. if you've found something that won't deform when a force is applied can you let my physicist friends know - they always assume they're using light inextensible string: it makes things simpler but doesn't actually exist.

rickeverett

The sooner we move to disks the better IMO.

lesfirth

Runtothehills wrote:

rayjay wrote:

I think what Bar Shaker is saying ,,,,,if you have a huge amount of force on the caliper and that force is enough to make the caliper bend or flex then that force is not putting any pressure on to the pad.
So there is no need to make extra stiff calipers.

Bar shaker can you confirm this is the gist of what you meant?: if so I can look up those resources because it's wrong.

The bottom line is forces have to balance and moments have to balance: the stiffness of a system does not change that. Deformation (such as bending) takes energy out of a system, but the force is still transfered. If you're convinced that what I've said is wrong get worried: every bridge, building, car, aeroplane or pretty much anything else built by an engineer assumes that I am right.

ps. if you've found something that won't deform when a force is applied can you let my physicist friends know - they always assume they're using light inextensible string: it makes things simpler but doesn't actually exist.

Dead right runtothehills.

After following this topic I am amazed how many people have managed to get through our education system and managed to avoid a bit of basic applied mechanics. To some people it is even common sense. There have been enough attempts explain what is happening so I wont.

As long as the calipers don't flex to the extent that your brake lever reaches your bars it does not matter.The only way to get better brakes is by fitting different pads.

The other bit some people don't seem to get is that because Dura Ace calipers are more expensive than Sora it does not make them any better at doing their job. If you think your best bike has better brakes than your Sora hack bike its because it has different pads.

Runtothehills

Thanks for the support lesfirth - I was beginning to despair a little (although I must admit I've forgotten when I learnt stuff so can't comment on our education system - I'm pretty sure I knew this most of this stuff before uni (studied engineering) but whether it was A-level or GCSE stuff I don't know).

Bar Shaker

Lets get back to my rubber crowbar then. Please explain why it is just as effective as a steel one.

rolf_f

Bar Shaker wrote:

Lets get back to my rubber crowbar then. Please explain why it is just as effective as a steel one.

If it makes you feel better, I'm sure we would all agree that your rubber crowbar would be just as effective as a rubber brake caliper. The problem is that you don't seem to understand that we are talking about metal items here ie whether a more flexible metal brake caliper is as effective as a less flexible brake caliper. Metal is a lot less flexible than rubber surprisingly enough! Applying a brake lever connected to a rubber caliper would just result in the lever running out of movement before the force has been exerted. If the rubber caliper was so massively fat (or your crowbar was so massively fat) that it didn't bend very much when you applied the force, then it would work in the same way. But that just highlights that the material itself doesn't matter - just the way it is used.

Runtothehills

Bar Shaker wrote:

Lets get back to my rubber crowbar then. Please explain why it is just as effective as a steel one.

Please read what I've written, read what lesfirth has written. For the same FORCE applied to the end a rubber crowbar will be as effective as a steel one. However you can apply a much greater force to a steel one for two reasons:

1: At some you'll start pushing against the wall when you get a critical deflection with the rubber crowbar (this is equivalent to the brake levers hitting the handlebar). The crowbar won't be 'absorbing force', you'll be pushing against the wall and crowbar.

2: Tensile strength: the tensile strength of structural steel is about 500 MPa, rubber is about 15 MPa. Note that yield strength and stiffness are only loosely related. Most ceramics are wonderfully stiff but you don't make a crowbar out of them.

If either of these apply to your brake calipers do something: for the first re-adjust your brakes, for the second complain as your brakes have just yielded.

Edit: what Rolf F said, and pdw. Thanks guys: my faith in our education system is being restored.

pdw

Nobody said it was "as effective" - you incorrectly extrapolated that idea. What people have told you is that if you apply a force at one end of a lever, the resulting force at the other end is independent of how flexible the lever is.

The reason a rubber crow bar is not as effective is because you'll find it very hard to apply the necessary force. At the very high forces that you typically use with a crow bar, a rubber one will bend to the point that the end at which you are applying the force hits something. This is exactly equivalent to running out of lever travel if you have a very flexible brake caliper. But, until this happens, the same force applied at end of a rubber crowbar will result in more deflection, but the same force as, a steel crowbar.

Same argument applies to your see-saw analogy:

If your 70kg person is up in the air, the force from the see saw acting on him to hold him there is (approximately) 700 Newtons. This is the case whether the see-saw is very bendy, and holding him 2cm off the ground, or completely stiff and holding him 2 metres off the ground. This holds true unless the see saw is so bendy that he hits the ground, at which point he is supported by both the ground and the see-saw, and the force applied by the see-saw will be less than 700N.

rayjay

Did anyone get hurt on the see saw? 2 metres is quite high , did he/she get dizzy?

what about having brakes made out of bones...could that work?

fwgx

Well I didn't imagine this topic would take the turn it had.
I was more interested in whether other people's brakes that they are happy with display the same flexing or not.
Anyway, I ended up getting some 105 calipers that I fitted late last night. There is still a little flex, but not as much. I have only ridden 2 miles on it so far, but down the 15% hill that approaches a roundabout at the bottom they were noticeably better than my previous calipers. A lot more power. Gave me more confidence on the brakes than previously. Almost as good as the v-brakes on my hybrid bike.

Bar Shaker

So provided that are 'stiff enough' there is no advantage in them being forged or made from exotic alloys etc and certainly no point in spending more than £20 on them.

OK, I concede.

rolf_f

Bar Shaker wrote:

So provided that are 'stiff enough' there is no advantage in them being forged or made from exotic alloys etc and certainly no point in spending more than £20 on them.

OK, I concede.

The Weinmann Centre pulls I experienced on one bike flexed so much that to retain optimum leverage on the brake lever required minimum clearance between pad and rim which in turn meant it was almost impossible to hook the straddle wire on once the rim was inplace. In that case, the braking certainly felt inferior and I did at the time blame the bendiness of the caliper itself. Now I suspect that I just wasn't exerting enough leverage on the lever with it being too close to the bar at maximum pressure..

But otherwise, it's still down to the geometry of the levers (which is probably mostly constant within a manufacturers range) and the pads. It's a couple of alloy arms and a spring. If they centre nicely, you're probably 99.5% there. But bling is nice!

If you genuinely do concede, at least you have to respect the effectiveness of the manufacturers propaganda! BTW - I did check up what Campagnolo said in their specs in the 2010 catalogue I have. Basically, irrc Veloce and Centaur mentioned forged arms (but the higher groupsets mentioned nothing on this) - otherwise Record mentioned ball bearing pivots and SR titanium fittings. Otherwise there are various minor finish differences that identify each level but aren't of much performance siginficance. None of these things, from Veloce to Super Record, would actually have an impact on braking performance. Wiggle charge £30 for Veloce and £210 for Super Record.

lesfirth

fwgx wrote:

Well I didn't imagine this topic would take the turn it had.
I was more interested in whether other people's brakes that they are happy with display the same flexing or not.
Anyway, I ended up getting some 105 calipers that I fitted late last night. There is still a little flex, but not as much. I have only ridden 2 miles on it so far, but down the 15% hill that approaches a roundabout at the bottom they were noticeably better than my previous calipers. A lot more power. Gave me more confidence on the brakes than previously. Almost as good as the v-brakes on my hybrid bike.

Look in the mirror every morning for the next six months and repeat ten times to yourself " The difference is in the pads."

topdude

Well it seems to be the general opinion that it doesn't matter if brake calipers are flexy as the braking force is still applied to the rim.
Why then is there so much talk about having a stiff frame / crankset / wheels :?

taon24

topdude wrote:

Well it seems to be the general opinion that it doesn't matter if brake calipers are flexy as the braking force is still applied to the rim.
Why then is there so much talk about having a stiff frame / crankset / wheels :?

Firstly I think we decided it was minimal difference. You could probably feel the difference (less cable pull to brake engaging fully), so it might 'feel' nicer. However the force produced was equal, so the stopping effect was equal.

A stiff frame potentially reduces the side to side movement of the human body sat on top. The mass of a person is much higher than with callipers so a greater amount of force will be involved in moving the body side to side if the frame flexes. Brake callipers weigh ~0.2kg. A human is ~70kg. Therefore a human will be absorbing 350x the force if a frame is moving them around. The actually effect is likely to be relatively minimal, but might feel different

With Cranksets it will be about feel. I suspect the flexing is mostly irrelevant.

With Wheels you want to avoid the wheel deforming and the brakes rubbing which is the big cost.

rolf_f

topdude wrote:

Why then is there so much talk about having a stiff frame / crankset / wheels :?

Because it is a measurable that technology gradually improves on. ie as the manufacturers get better at making frames they can make them stiffer for the same weight. And that therefore is something they can make a big deal about. Of course, there is rarely mention of the fact that you might not want an incredibly stiff frame - certainly, a light rider will experience a harsher ride on a stiff frame than a heavier person. So really, the logical marketing approach would be to push stiff frames for heavier people and vice versa which would be quite beneficial. But that is much less sexy than marketing stiffness in extra super performance terms - which is most of the time quite unbeneficial.

stueys

lesfirth wrote:

Runtothehills wrote:

rayjay wrote:

I think what Bar Shaker is saying ,,,,,if you have a huge amount of force on the caliper and that force is enough to make the caliper bend or flex then that force is not putting any pressure on to the pad.
So there is no need to make extra stiff calipers.

Bar shaker can you confirm this is the gist of what you meant?: if so I can look up those resources because it's wrong.

The bottom line is forces have to balance and moments have to balance: the stiffness of a system does not change that. Deformation (such as bending) takes energy out of a system, but the force is still transfered. If you're convinced that what I've said is wrong get worried: every bridge, building, car, aeroplane or pretty much anything else built by an engineer assumes that I am right.

ps. if you've found something that won't deform when a force is applied can you let my physicist friends know - they always assume they're using light inextensible string: it makes things simpler but doesn't actually exist.

Dead right runtothehills.

After following this topic I am amazed how many people have managed to get through our education system and managed to avoid a bit of basic applied mechanics. To some people it is even common sense. There have been enough attempts explain what is happening so I wont.

As long as the calipers don't flex to the extent that your brake lever reaches your bars it does not matter.The only way to get better brakes is by fitting different pads.

The other bit some people don't seem to get is that because Dura Ace calipers are more expensive than Sora it does not make them any better at doing their job. If you think your best bike has better brakes than your Sora hack bike its because it has different pads.

I'll repeat my post from earlier,I have swissstop pads on both my road bikes. Dura ace on one, Tigara on the other. The DA bike outperforms the Tiagra brakes in every respect, especially in the wet. My winter bike is now running my old mavic elites so I've even ridden the same wheels on both bikes.

lesfirth

Stueys wrote:

lesfirth wrote:

Runtothehills wrote:

rayjay wrote:

I think what Bar Shaker is saying ,,,,,if you have a huge amount of force on the caliper and that force is enough to make the caliper bend or flex then that force is not putting any pressure on to the pad.
So there is no need to make extra stiff calipers.

Bar shaker can you confirm this is the gist of what you meant?: if so I can look up those resources because it's wrong.

The bottom line is forces have to balance and moments have to balance: the stiffness of a system does not change that. Deformation (such as bending) takes energy out of a system, but the force is still transfered. If you're convinced that what I've said is wrong get worried: every bridge, building, car, aeroplane or pretty much anything else built by an engineer assumes that I am right.

ps. if you've found something that won't deform when a force is applied can you let my physicist friends know - they always assume they're using light inextensible string: it makes things simpler but doesn't actually exist.

Dead right runtothehills.

After following this topic I am amazed how many people have managed to get through our education system and managed to avoid a bit of basic applied mechanics. To some people it is even common sense. There have been enough attempts explain what is happening so I wont.

As long as the calipers don't flex to the extent that your brake lever reaches your bars it does not matter.The only way to get better brakes is by fitting different pads.

The other bit some people don't seem to get is that because Dura Ace calipers are more expensive than Sora it does not make them any better at doing their job. If you think your best bike has better brakes than your Sora hack bike its because it has different pads.

I'll repeat my post from earlier,I have swissstop pads on both my road bikes. Dura ace on one, Tigara on the other. The DA bike outperforms the Tiagra brakes in every respect, especially in the wet. My winter bike is now running my old mavic elites so I've even ridden the same wheels on both bikes.

I am not doubting your observation but I would be interested if you or anybody else could give me a technical/ engineering reason why.

topdude

I am not doubting your observation but I would be interested if you or anybody else could give me a technical/ engineering reason why.

Is it possible that 105 / ultegra / DA calipers are physically larger than the cheaper tektro / tiagra ?
Tektro / tiagra certainly look more compact to me but not having owned them all i have not been able to make a direct comparison ?
If the leverage is longer that would explain the better performance of 105 / ultegra / DA.

rolf_f

topdude wrote:

I am not doubting your observation but I would be interested if you or anybody else could give me a technical/ engineering reason why.

Is it possible that 105 / ultegra / DA calipers are physically larger than the cheaper tektro / tiagra ?
Tektro / tiagra certainly look more compact to me but not having owned them all i have not been able to make a direct comparison ?
If the leverage is longer that would explain the better performance of 105 / ultegra / DA.

I guess different leverages will give a different feel but I'd be surprised if that had much impact on stopping power. I did a test of the brake performance of my various bikes - stopping from about 20mph on a downslope in the dry. First time I tried to stop my Look, I nearly went over the handlebars. If your brakes give you enough power that the rear wheel loses contact with the ground, then there isn't really anything you can do to improve them whatever calipers you use (unless you put on lots of weight of course - that'll keep the back end planted!). Maybe if there are differences between different the Shimano calipers, you need to be heavy to benefit from them.

fwgx

Rolf F wrote:

Maybe if there are differences between different the Shimano calipers, you need to be heavy to benefit from them.

6'5" and around 15 stone here. It's difficult to stop me once rolling

Bar Shaker

topdude wrote:

I am not doubting your observation but I would be interested if you or anybody else could give me a technical/ engineering reason why.

Is it possible that 105 / ultegra / DA calipers are physically larger than the cheaper tektro / tiagra ?
Tektro / tiagra certainly look more compact to me but not having owned them all i have not been able to make a direct comparison ?
If the leverage is longer that would explain the better performance of 105 / ultegra / DA.

My experience is the same.

If I had not read this thread I would have carried on thinking that by bending something, I was wasting energy that could have somehow been used for something else.

As the thread has developed, it also seems that it doesn't matter how bendy any part of your bike is as bendy bikes perform just as well as stiff bikes.

I am so glad I read this before buying expensive stiff components, when cheap plastic ones would clearly suffice.

rolf_f

Bar Shaker wrote:

topdude wrote:

I am not doubting your observation but I would be interested if you or anybody else could give me a technical/ engineering reason why.

Is it possible that 105 / ultegra / DA calipers are physically larger than the cheaper tektro / tiagra ?
Tektro / tiagra certainly look more compact to me but not having owned them all i have not been able to make a direct comparison ?
If the leverage is longer that would explain the better performance of 105 / ultegra / DA.

My experience is the same.

If I had not read this thread I would have carried on thinking that by bending something, I was wasting energy that could have somehow been used for something else.

As the thread has developed, it also seems that it doesn't matter how bendy any part of your bike is as bendy bikes perform just as well as stiff bikes.

I am so glad I read this before buying expensive stiff components, when cheap plastic ones would clearly suffice.

Do you still not get it? Honestly!

* Clue - flex in the calipers (and pads themselves) does mean you move your fingers more than you might otherwise have to. If that bothers you, use really hard pads and keep them close to the rims. Or better still, get disc brakes. The energy you are losing squeezing the brake levers onto your ever so slightly more flexible calipers (which may be improving the feel) is inconsequential compared to that you would lose pedalling a bendy frame. Just because one thing doesn't benefit from being bendy doesn't mean others don't either. If you find you can measure a performance loss due to increased brake lever movement, then you've made a good case for your argument.