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03-25-11, 05:02 PM
I've filled in more time with my netbook while waiting for trains etc, and this is the result. As requested it now includes other sorts of brakes than cantis - but I really don't know much about these, so more contributions are needed. Hints about discs and comments about v-brake modulation and v's vs mini-v's would be especially useful.
The Laws Of Brake
(With special attention to cantilevers.)
I. The Basics
1. Fit good good brake pads
Your brake can't slow down the tyre better than it can grip the rim. Kool Stop and Swiss Stop pads are specially favoured by cross riders. Both brands are colour coded: for riding in the wet with aluminium rims you need Kool Stop Pink (aka Salmon) or Swiss Stop Green pads.
2. Keep your rims clean
A green Scotchbrite pad works well for this. Dirty rims brake poorly and may wear out themselves and your pads more quickly.
3. Keep your pads clean
Give the inner surface a rub with something abrasive occasionally. (Making sure that you don't leave any abrasive particles behind!) This will get rid of particles of dirt and metal that will, again, reduce brake performance and increase wear.
4. Make sure that your cable path is a good one - and that your cables are too
Unnecessary kinks and bends cause friction, eating up "squeeze". sheldon brown
And never substitute gear cable for brake cable - it isn't strong enough.
5. Lube your cable inners as needed
If you have fancy expensive cables, check the manufacturer's recommendations first. Otherwise see:
http://www.ctc.org.uk/DesktopDefault.aspx?TabID=3824
http://www.bikeradar.com/gear/article/workshop-how-to-clean-and-lube-your-bike-18259/
I like GT85 as cable lube.
6. Know how to use your brakes
- Use your front brake aggressively. Once a tyre exceeds its traction limit in braking (or turning) then it will skid. And when you brake the back wheel loses traction - but the front wheel gains it. So strong braking has to come from the front wheel. Keep your arms "strong" but not rigid - i.e. don't let your weight move forwards but do allow the bars the freedom to let your bike make the small automatic steering corrections built into its geometry, and which are needed to keep it upright. (You do know that if you lock your arms and wrists while holding the bars that your bike will crash? Weird, isn' it?)
- Learn to hold your brakes at the edge that exists just before a skid. It is here that braking will be greatest. This will require a different amount of squeeze for each brake and the amount and balance of squeeze will depend on surface and slope. You have to learn to feel the bike's balance the skid point - especially for the rear. The only way to do this is the Carnegie Hall method - practice, practice, practice!
- The third secret of braking is that braking and steering both use up traction. You can do both, but not to the same extent you could do either alone. Again, practice.
II. Mechanical Advantage and Pull
1. Mechanical advantage and the problem of pull
You almost certainly know what leverage is. Mechanical advantage (MA) is a generalization of this. It can be achieved via levers, pulleys, gear systems, hydraulics and other means. It is simply the amplification of exerted force. If a system has an MA of two then twice as much force is exerted as put in.
There is a cost for mechanical advantage. When a lever doubles output force then the input force must travel twice the distance than it would if the two forces were equal. Imagine a lever that doubles MA: the input side of the lever must be made twice as long as the output side. So raising the output side one inch will require moving the input side two inches.
This same rule applies to all mechanical systems for increasing MA: Twice as much force, twice as much pull. Three times as much force, three times as much pull - etc, until infinity.
There are two consequences to this:
- Brakes and levers have to have matching pull, or the pads won't move far enough or will be too stiff to press really hard against the rims. Standard road brake drop bar levers are NOT pull compatible with regular v-brakes or most disc brakes, although there are ways of getting around this. See the section on each brake type.
- MA and pull are inevitably traded off against each other. People often mistake MA for braking power but it is only of part of it. Yes, if MA is too low then it won't be able to overcome the resistance of the brake pads - acting like rubber springs - to being squeezed against the rims. But if MA is set very high and pull very low then the pad will be squashed easily - but not very deeply! This means that little braking force will be exerted. Good braking requires good MA and adequate pull.
Good pull is also needed for clearance between rims and brake pads - if maximum pull is less than the clearance you have set, the pads won't even touch the rim when you bottom out the levers. The amount of clearance you need depends on the track you are riding. Smooth roads need very little clearance, but a muddy trail will coat your tyre with clumps of mud that will smash against your pads slowing you down.
2. Single speeds and bar con bikes can get easy compatibility by using v-brake road levers
Special v-brake compatible drop bar levers are available. These will work directly with standard v-brakes and disc brakes. These levers do NOT include shifter controllers, but if you're riding singlespeed or with bar cons they may be a good choice.
III. Cantilevers
Cantilevers - aka "cantis" - are the standard cross brake for good reason. They allow wide tyre clearance and can be easily adjusted to give different combinations of MA, pull and clearance as needed for conditions - so on a dry course clearance can be cut to a minimum and power to a maximum, and on a muddy course clearance can be increased at the cost of full-on braking power. Many people also think that cantis give the best modulation (the ability to apply controlled amounts of braking) of any rim brake.
However cantis can cause problems. People complain of low power, squealing brakes, and even dangerously destabilizing fork judder. All these problems can be easily and cheaply cured, but most people - including the mechanics in most all bike shops - don't know how. So read on!
1. The ultimate reference and other useful links
The definitive analysis and reference on Mechanical Advantage and tuning:
http://www.circleacycles.com/cantilevers/canti-geometry.pdf
Accompanying MA calculator app:
http://www.circleacycles.com/cantilevers/
Squeal and judder:
http://velonews.competitor.com/2010/09/cyclocross/technical-qa-with-lennard-zinn-return-to-cross_101807
2. Types of cantilever
Cantilevers can be classed in several types according to the angle of the arm that holds the cable.
Narrow profile cantilevers (aka low profile) a
...Are as you'd expect - narrow! Their arms reach up and hardly go the side at all.
- Easy to fit the rear where a brake with protruding arms might catch the riders heels while he pedals.
- Very sensitive to set-up and are the least capable of getting good mud clearance while achieving good power.
- Getting good MA can require a very low straddle cable. This can interfere with a mudguard - or even with a tyre if your bike is set-up as a monster crosser.
Medium cantis
...Are between the narrows and wides.They're not widely favoured at the moment - a wide at the front and a narrow at the back is more common.
Wide profile cantis (aka high profile)
...Have arms that are more or less horizontal.
- Best ability to be set for good mud clearance while keeping decent braking power and are very popular as front brakes.
- Straddle cables can be set relatively high and MA will still be good
- Can stick out too much to be a good rear brake - they may catch your heel while pedalling or your shoulder while carrying your bike.
Super wide cantis
...Have arms that slope downwards. These are now historical curiosities only but should still be mentioned as the straddle cable tuning guide that follows won't work for them.
4. Adjusting power and pull: straddle cables and tuning
- The main way to tune your cantis is to adjust the length and height of your straddle cable. Shortening the straddle cable will give you more mechanical advantage but yield less pad movement for the same lever movement. As always, you need to find your personal preference. (Lowering the yoke/ shortening the straddle cable to increase MA always works for all canti types except super-wides.)
- Shimano cantis have pre-set straddle cables aka "z-wires". In this set-up the main brake cable runs directly to one brake arm and a yoke with a short cable of fixed length clips on to activate the other. These are known as z-wires and come in various lengths. Searching for "tektro z-wires" can help find them on the net.
- Other cantis come with a more tuneable straddle cable that runs from one arm to another. This cable runs through a yoke or "cable hanger" that attaches to the main brake cable. Shimano brakes can be converted to this set-up with a few minutes work.
- Mild warning: in theory, your main front brake cable can snap, in which case a non z-wire straddle will flop down and catch in the tread of your tyre, causing a very sudden stop. You can prevent this by checking your brake cable for fraying or by installing something to stop the straddle from falling that far.
- If you want maximum braking power then tune so that your pads will be set for the smallest amount of clearance that is tolerable given the terrain you are riding.
- My experience is that adding a fork mounted hanger will improve power and modulation. This makes sense - the less unnecessary flex there is a cable system, the better it should be at transmitting force.
5. Squeal and judder
See http://velonews.competitor.com/2010/09/cyclocross/technical-qa-with-lennard-zinn-return-to-cross_101807
Judder - and sometimes squealing (but this has other causes too) - is caused when your fork flexes during braking. As the fork flexes it can alter brake cable tension - which in turn alters how hard the bike is braking, which then alters the degree to which the fork has flexed - and around and around the cycle goes.
The cure is easy: stop either the fork from flexing (there are ultra rigid forks that don't flex - this is an easy solution but not a cheap one!) or stop the cable from flexing when the fork does by fitting a fork mounted cantilever hanger (aka FMCH from now on) instead of - or as well as - the more usual stem mounted hanger.
Fork Mounted Cable Hangers
- These need a hole in the fork crown to mount. If the crown lacks such a hole and is metal then you can (carefully) drill one. But do NOT ever drill into a carbon fibre fork crown!
- Some carbon forks come with a built-in hanger.
- If you have problems finding a hanger, order or Internet search for the Kona Design Front Hanger BP1272F
- A hanger can get in the way of running a front fender/mudguard. This may be less of a problem with a wide canti as it will let you use a higher yoke position which may let you route the straddle around the outside of the fender. Or you could use an MTB style fender that clips on to your down tube instead of the fork.
If you can't mount an FMCH and don't want to run v-brakes or buy a new fork
Try lots of toe-in, a very tight headset, and even trimming your brake pads down.
6. Common mistakes
Some people tune so that their cantis feel hard and definite. This is a mistake. Cantis should feel somewhat soft and rubbery, from the feedback of the brakepad being squashed against the rim. Cantis only feel hard if MA is set too low to squash the pad. However, not all soft cantis are correctly tuned! A soft canti may have good MA but too little movement.
Some people believe that the straddle cable should make a right angle with a line from the point where the cable attaches to the brake arm to the point where the pads will touch the rim. This is wrong. See "The Ultimate Reference" to understand why.
7. Recommended brakes
Remember: don't judge a cantilever as lacking power until you have installed a decent pad, tuned the straddle cable, and if necessary fitted a fork mounted hanger! Almost all cantilevers can be transformed this way and even the best cantilevers will usually perform poorly without these tweaks.
- The Tektro CR520 & CR720 are reasonably priced and very effective wide cantis.
- Shimano makes a number of good narrow cantis at a range of prices.
- The Avid Shorty Ultimate, Paul's Touring and Paul's Retro are all well-regarded high-end brakes . Although it is arguable that a canti (which is after all nothing but a lever and a return spring) is so simple a device that there is little point in paying a high price.
IV. Mini V-Brakes
Mini-v brakes sacrifice the adjustability, clearance and (perhaps - opinions vary) modulation of cantis for easier set-up and a lack of fork judder. They may be a good choice for you if your bike doesn't have to race through mud very often. Because they are pull compatible with road levers they can be fitted to a crosser without any special tricks.
Hints
If your mini-v's squeal then read the Cantilever section and use the tactics discuss there - toe-in, a tight headeset, and a fork mounted hanger.
Advantages
Easy set up. No risk of judder.
Disadvantages
Poor clearance; questionable modulation.
Recommended brakes
Tektro RX5 - 85mm arm length
Tektro RX6 - 90mm arm length, so should give slight more MA and less modulation
TRP CX9 - 90mm arm length. TRP = Tektro Racing Products... I suspect this will behave almost identically to the RX6, despite costing 4 times as much!
V. Fullsize V-Brakes
Fullsize v's have all the characteristics of mini-v's except pull compatibility. This can be provided using a "Travel Agent" or "V-Daptor". See:
http://www.phred.org/~alex/bikes/brakes.html (http://www.phred.org/%7Ealex/bikes/brakes.html).
If you decide to use a v-brake and adaptor, consider using it only at the front and keeping a canti at the back: most braking (and virtually all canti braking problems) happens at the front, and adaptors at the back may tend to clog with mud.
Advantages
Easy set up. No risk of judder.
Disadvantages
Poor clearance; need an adaptor; questionable modulation. Why not use a mini-v?
Hints
If your v's squeal then read the Cantilever section and use the tactics discuss there - toe-in, a tight headeset, and a fork mounted hanger.
Recommended brakes
The Avid Single Digit 7 is considered an all-time classic.
VI. Disc Brakes
Disc brakes require special mounts on the fork and frame and special wheels. They also add weight and may be harder to service than rim brakes. However they are powerful, modulate well, ignore mud on the rim and make clearance a non-issue. Standard disc brakes are not compatible with road levers. However you should be able to fix this using one of the adaptors made for v-brakes. And there are special road brake compatible disc brakes too.
Road lever compatible discs
These exist. Check carefully what you are buying!
Adaptors can be used with mechanical MTB discs
Treat as with fullsize v-brakes.
It can be worth fitting a disc fork even if your frame can't take a disc at the back.
Most of your braking happens at the front, so most of the benefit of discs comes from fitting a disc fork.
A frame builder maybe able to add disc mounts to a metal frame.
Ask one!
Hydraulic adaptor
You might be able to get hardware that lets you use your mechanical road levers with hydraulic MTB brakes:
http://www.bikeradar.com/news/article/eurobike-2010-trickstuff-cyclo-cross-disc-brake-converter-27723/
VII. Interrupter aka cross levers
These handy things go on the flat part of your bar to give you an on-the-tops braking position.
- If fitted correctly they shouldn't reduce power
- They won't have a problem working with v-brakes if an adaptor has been fitted
- Getting the cable path right so that power and modulation aren't reduce can be tricky. Using compressionless braking cable may help. Do not confuse this with the more common compressionless gear cable - this is not strong enough for use with brakes.
VIII. Brake boosters
Powerful rim brakes can cause their mounts to flex reducing power and modulation. Brake boosters are U-shaped pieces of metal or carbon fibre that arch over the wheel to join the mounts together, reinforcing them. Much more popular among mountain bikers.
IX Problem Solver
When multiple solutions exist I've listed the cheaper ones first. I've recommended the CR720 and RX5 when a specific brake seemed useful not because either is a favourite of mine but because they are almost universally liked and cost very little.
If your brakes are cantilevers and they aren't powerful enough
- Learn to use your front brake aggressively, clean your pads and rims, fit better brake pads, check the cable path is good, tune the straddle cable, fit a fork mounted brake hanger
- Fit a Tektro CR720 to the front and adjust the straddle again
- Fit a mini-v brake to the front - probably a Tektro RX5
If your brakes are NOT cantilevers and they aren't powerful enough
- Learn to use your front brake aggressively, clean your pads and rims, fit better brake pads, check the cable path is good, lower the straddle cable, fit a fork mounted brake hanger
- If you are using a full-size v-brake make sure you are using the pull adaptor correctly
If your brakes squeal or cause fork judder
- Increase brake pad toe-in, fit a fork mounted hanger, shorten your brake pads, tighten your headset
- Fit a mini-v brake to the front - probably a Tektro RX5
If you need more pad-rim clearance than your current brake will give you
- Fit a wide profile cantilever, probably a Tektro CR720
--------------------------------
My thanks to everyone who has contributed so far, either in this thread or in the previous ones that I mined. I'll add names of contributors in the next edit, really!
The Laws Of Brake
(With special attention to cantilevers.)
I. The Basics
1. Fit good good brake pads
Your brake can't slow down the tyre better than it can grip the rim. Kool Stop and Swiss Stop pads are specially favoured by cross riders. Both brands are colour coded: for riding in the wet with aluminium rims you need Kool Stop Pink (aka Salmon) or Swiss Stop Green pads.
2. Keep your rims clean
A green Scotchbrite pad works well for this. Dirty rims brake poorly and may wear out themselves and your pads more quickly.
3. Keep your pads clean
Give the inner surface a rub with something abrasive occasionally. (Making sure that you don't leave any abrasive particles behind!) This will get rid of particles of dirt and metal that will, again, reduce brake performance and increase wear.
4. Make sure that your cable path is a good one - and that your cables are too
Unnecessary kinks and bends cause friction, eating up "squeeze". sheldon brown
And never substitute gear cable for brake cable - it isn't strong enough.
5. Lube your cable inners as needed
If you have fancy expensive cables, check the manufacturer's recommendations first. Otherwise see:
http://www.ctc.org.uk/DesktopDefault.aspx?TabID=3824
http://www.bikeradar.com/gear/article/workshop-how-to-clean-and-lube-your-bike-18259/
I like GT85 as cable lube.
6. Know how to use your brakes
- Use your front brake aggressively. Once a tyre exceeds its traction limit in braking (or turning) then it will skid. And when you brake the back wheel loses traction - but the front wheel gains it. So strong braking has to come from the front wheel. Keep your arms "strong" but not rigid - i.e. don't let your weight move forwards but do allow the bars the freedom to let your bike make the small automatic steering corrections built into its geometry, and which are needed to keep it upright. (You do know that if you lock your arms and wrists while holding the bars that your bike will crash? Weird, isn' it?)
- Learn to hold your brakes at the edge that exists just before a skid. It is here that braking will be greatest. This will require a different amount of squeeze for each brake and the amount and balance of squeeze will depend on surface and slope. You have to learn to feel the bike's balance the skid point - especially for the rear. The only way to do this is the Carnegie Hall method - practice, practice, practice!
- The third secret of braking is that braking and steering both use up traction. You can do both, but not to the same extent you could do either alone. Again, practice.
II. Mechanical Advantage and Pull
1. Mechanical advantage and the problem of pull
You almost certainly know what leverage is. Mechanical advantage (MA) is a generalization of this. It can be achieved via levers, pulleys, gear systems, hydraulics and other means. It is simply the amplification of exerted force. If a system has an MA of two then twice as much force is exerted as put in.
There is a cost for mechanical advantage. When a lever doubles output force then the input force must travel twice the distance than it would if the two forces were equal. Imagine a lever that doubles MA: the input side of the lever must be made twice as long as the output side. So raising the output side one inch will require moving the input side two inches.
This same rule applies to all mechanical systems for increasing MA: Twice as much force, twice as much pull. Three times as much force, three times as much pull - etc, until infinity.
There are two consequences to this:
- Brakes and levers have to have matching pull, or the pads won't move far enough or will be too stiff to press really hard against the rims. Standard road brake drop bar levers are NOT pull compatible with regular v-brakes or most disc brakes, although there are ways of getting around this. See the section on each brake type.
- MA and pull are inevitably traded off against each other. People often mistake MA for braking power but it is only of part of it. Yes, if MA is too low then it won't be able to overcome the resistance of the brake pads - acting like rubber springs - to being squeezed against the rims. But if MA is set very high and pull very low then the pad will be squashed easily - but not very deeply! This means that little braking force will be exerted. Good braking requires good MA and adequate pull.
Good pull is also needed for clearance between rims and brake pads - if maximum pull is less than the clearance you have set, the pads won't even touch the rim when you bottom out the levers. The amount of clearance you need depends on the track you are riding. Smooth roads need very little clearance, but a muddy trail will coat your tyre with clumps of mud that will smash against your pads slowing you down.
2. Single speeds and bar con bikes can get easy compatibility by using v-brake road levers
Special v-brake compatible drop bar levers are available. These will work directly with standard v-brakes and disc brakes. These levers do NOT include shifter controllers, but if you're riding singlespeed or with bar cons they may be a good choice.
III. Cantilevers
Cantilevers - aka "cantis" - are the standard cross brake for good reason. They allow wide tyre clearance and can be easily adjusted to give different combinations of MA, pull and clearance as needed for conditions - so on a dry course clearance can be cut to a minimum and power to a maximum, and on a muddy course clearance can be increased at the cost of full-on braking power. Many people also think that cantis give the best modulation (the ability to apply controlled amounts of braking) of any rim brake.
However cantis can cause problems. People complain of low power, squealing brakes, and even dangerously destabilizing fork judder. All these problems can be easily and cheaply cured, but most people - including the mechanics in most all bike shops - don't know how. So read on!
1. The ultimate reference and other useful links
The definitive analysis and reference on Mechanical Advantage and tuning:
http://www.circleacycles.com/cantilevers/canti-geometry.pdf
Accompanying MA calculator app:
http://www.circleacycles.com/cantilevers/
Squeal and judder:
http://velonews.competitor.com/2010/09/cyclocross/technical-qa-with-lennard-zinn-return-to-cross_101807
2. Types of cantilever
Cantilevers can be classed in several types according to the angle of the arm that holds the cable.
Narrow profile cantilevers (aka low profile) a
...Are as you'd expect - narrow! Their arms reach up and hardly go the side at all.
- Easy to fit the rear where a brake with protruding arms might catch the riders heels while he pedals.
- Very sensitive to set-up and are the least capable of getting good mud clearance while achieving good power.
- Getting good MA can require a very low straddle cable. This can interfere with a mudguard - or even with a tyre if your bike is set-up as a monster crosser.
Medium cantis
...Are between the narrows and wides.They're not widely favoured at the moment - a wide at the front and a narrow at the back is more common.
Wide profile cantis (aka high profile)
...Have arms that are more or less horizontal.
- Best ability to be set for good mud clearance while keeping decent braking power and are very popular as front brakes.
- Straddle cables can be set relatively high and MA will still be good
- Can stick out too much to be a good rear brake - they may catch your heel while pedalling or your shoulder while carrying your bike.
Super wide cantis
...Have arms that slope downwards. These are now historical curiosities only but should still be mentioned as the straddle cable tuning guide that follows won't work for them.
4. Adjusting power and pull: straddle cables and tuning
- The main way to tune your cantis is to adjust the length and height of your straddle cable. Shortening the straddle cable will give you more mechanical advantage but yield less pad movement for the same lever movement. As always, you need to find your personal preference. (Lowering the yoke/ shortening the straddle cable to increase MA always works for all canti types except super-wides.)
- Shimano cantis have pre-set straddle cables aka "z-wires". In this set-up the main brake cable runs directly to one brake arm and a yoke with a short cable of fixed length clips on to activate the other. These are known as z-wires and come in various lengths. Searching for "tektro z-wires" can help find them on the net.
- Other cantis come with a more tuneable straddle cable that runs from one arm to another. This cable runs through a yoke or "cable hanger" that attaches to the main brake cable. Shimano brakes can be converted to this set-up with a few minutes work.
- Mild warning: in theory, your main front brake cable can snap, in which case a non z-wire straddle will flop down and catch in the tread of your tyre, causing a very sudden stop. You can prevent this by checking your brake cable for fraying or by installing something to stop the straddle from falling that far.
- If you want maximum braking power then tune so that your pads will be set for the smallest amount of clearance that is tolerable given the terrain you are riding.
- My experience is that adding a fork mounted hanger will improve power and modulation. This makes sense - the less unnecessary flex there is a cable system, the better it should be at transmitting force.
5. Squeal and judder
See http://velonews.competitor.com/2010/09/cyclocross/technical-qa-with-lennard-zinn-return-to-cross_101807
Judder - and sometimes squealing (but this has other causes too) - is caused when your fork flexes during braking. As the fork flexes it can alter brake cable tension - which in turn alters how hard the bike is braking, which then alters the degree to which the fork has flexed - and around and around the cycle goes.
The cure is easy: stop either the fork from flexing (there are ultra rigid forks that don't flex - this is an easy solution but not a cheap one!) or stop the cable from flexing when the fork does by fitting a fork mounted cantilever hanger (aka FMCH from now on) instead of - or as well as - the more usual stem mounted hanger.
Fork Mounted Cable Hangers
- These need a hole in the fork crown to mount. If the crown lacks such a hole and is metal then you can (carefully) drill one. But do NOT ever drill into a carbon fibre fork crown!
- Some carbon forks come with a built-in hanger.
- If you have problems finding a hanger, order or Internet search for the Kona Design Front Hanger BP1272F
- A hanger can get in the way of running a front fender/mudguard. This may be less of a problem with a wide canti as it will let you use a higher yoke position which may let you route the straddle around the outside of the fender. Or you could use an MTB style fender that clips on to your down tube instead of the fork.
If you can't mount an FMCH and don't want to run v-brakes or buy a new fork
Try lots of toe-in, a very tight headset, and even trimming your brake pads down.
6. Common mistakes
Some people tune so that their cantis feel hard and definite. This is a mistake. Cantis should feel somewhat soft and rubbery, from the feedback of the brakepad being squashed against the rim. Cantis only feel hard if MA is set too low to squash the pad. However, not all soft cantis are correctly tuned! A soft canti may have good MA but too little movement.
Some people believe that the straddle cable should make a right angle with a line from the point where the cable attaches to the brake arm to the point where the pads will touch the rim. This is wrong. See "The Ultimate Reference" to understand why.
7. Recommended brakes
Remember: don't judge a cantilever as lacking power until you have installed a decent pad, tuned the straddle cable, and if necessary fitted a fork mounted hanger! Almost all cantilevers can be transformed this way and even the best cantilevers will usually perform poorly without these tweaks.
- The Tektro CR520 & CR720 are reasonably priced and very effective wide cantis.
- Shimano makes a number of good narrow cantis at a range of prices.
- The Avid Shorty Ultimate, Paul's Touring and Paul's Retro are all well-regarded high-end brakes . Although it is arguable that a canti (which is after all nothing but a lever and a return spring) is so simple a device that there is little point in paying a high price.
IV. Mini V-Brakes
Mini-v brakes sacrifice the adjustability, clearance and (perhaps - opinions vary) modulation of cantis for easier set-up and a lack of fork judder. They may be a good choice for you if your bike doesn't have to race through mud very often. Because they are pull compatible with road levers they can be fitted to a crosser without any special tricks.
Hints
If your mini-v's squeal then read the Cantilever section and use the tactics discuss there - toe-in, a tight headeset, and a fork mounted hanger.
Advantages
Easy set up. No risk of judder.
Disadvantages
Poor clearance; questionable modulation.
Recommended brakes
Tektro RX5 - 85mm arm length
Tektro RX6 - 90mm arm length, so should give slight more MA and less modulation
TRP CX9 - 90mm arm length. TRP = Tektro Racing Products... I suspect this will behave almost identically to the RX6, despite costing 4 times as much!
V. Fullsize V-Brakes
Fullsize v's have all the characteristics of mini-v's except pull compatibility. This can be provided using a "Travel Agent" or "V-Daptor". See:
http://www.phred.org/~alex/bikes/brakes.html (http://www.phred.org/%7Ealex/bikes/brakes.html).
If you decide to use a v-brake and adaptor, consider using it only at the front and keeping a canti at the back: most braking (and virtually all canti braking problems) happens at the front, and adaptors at the back may tend to clog with mud.
Advantages
Easy set up. No risk of judder.
Disadvantages
Poor clearance; need an adaptor; questionable modulation. Why not use a mini-v?
Hints
If your v's squeal then read the Cantilever section and use the tactics discuss there - toe-in, a tight headeset, and a fork mounted hanger.
Recommended brakes
The Avid Single Digit 7 is considered an all-time classic.
VI. Disc Brakes
Disc brakes require special mounts on the fork and frame and special wheels. They also add weight and may be harder to service than rim brakes. However they are powerful, modulate well, ignore mud on the rim and make clearance a non-issue. Standard disc brakes are not compatible with road levers. However you should be able to fix this using one of the adaptors made for v-brakes. And there are special road brake compatible disc brakes too.
Road lever compatible discs
These exist. Check carefully what you are buying!
Adaptors can be used with mechanical MTB discs
Treat as with fullsize v-brakes.
It can be worth fitting a disc fork even if your frame can't take a disc at the back.
Most of your braking happens at the front, so most of the benefit of discs comes from fitting a disc fork.
A frame builder maybe able to add disc mounts to a metal frame.
Ask one!
Hydraulic adaptor
You might be able to get hardware that lets you use your mechanical road levers with hydraulic MTB brakes:
http://www.bikeradar.com/news/article/eurobike-2010-trickstuff-cyclo-cross-disc-brake-converter-27723/
VII. Interrupter aka cross levers
These handy things go on the flat part of your bar to give you an on-the-tops braking position.
- If fitted correctly they shouldn't reduce power
- They won't have a problem working with v-brakes if an adaptor has been fitted
- Getting the cable path right so that power and modulation aren't reduce can be tricky. Using compressionless braking cable may help. Do not confuse this with the more common compressionless gear cable - this is not strong enough for use with brakes.
VIII. Brake boosters
Powerful rim brakes can cause their mounts to flex reducing power and modulation. Brake boosters are U-shaped pieces of metal or carbon fibre that arch over the wheel to join the mounts together, reinforcing them. Much more popular among mountain bikers.
IX Problem Solver
When multiple solutions exist I've listed the cheaper ones first. I've recommended the CR720 and RX5 when a specific brake seemed useful not because either is a favourite of mine but because they are almost universally liked and cost very little.
If your brakes are cantilevers and they aren't powerful enough
- Learn to use your front brake aggressively, clean your pads and rims, fit better brake pads, check the cable path is good, tune the straddle cable, fit a fork mounted brake hanger
- Fit a Tektro CR720 to the front and adjust the straddle again
- Fit a mini-v brake to the front - probably a Tektro RX5
If your brakes are NOT cantilevers and they aren't powerful enough
- Learn to use your front brake aggressively, clean your pads and rims, fit better brake pads, check the cable path is good, lower the straddle cable, fit a fork mounted brake hanger
- If you are using a full-size v-brake make sure you are using the pull adaptor correctly
If your brakes squeal or cause fork judder
- Increase brake pad toe-in, fit a fork mounted hanger, shorten your brake pads, tighten your headset
- Fit a mini-v brake to the front - probably a Tektro RX5
If you need more pad-rim clearance than your current brake will give you
- Fit a wide profile cantilever, probably a Tektro CR720
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My thanks to everyone who has contributed so far, either in this thread or in the previous ones that I mined. I'll add names of contributors in the next edit, really!