The foreground (How to do it).

Here's how to do improve your brakes and save cash for beers after the ride or whatever other foolish things one can do with excess discretionary income (?).

Start off by buying the parts. Buy an old straddle carrier, and a new (old style) straddle wire at your favorite hip bike shop. Go for new pads if your old ones are worn out. Buy Ritcheys - I've never used them myself, but they look real cool and Tom needs the money for home improvements I hear.

Then put it all on right. Throw the old stuff in the recycling bin. Adjust the brakes. Ride away. Stop on a dime. Don't go over the bars.

Look at them every now and then to make sure they're in good working order. Learn to appreciate the cycling magazines, Internet NewsGroups, and most of your friends for the entertainment and dark humor they provide. That's all. They are not engineers.

If this isn't enough for you, you'll find a bit more on the how and why of this project below.

V Brake Analysis - a simple calculation of the mechanical advantage of a V Brake

Standard Cantilever Brake Analysis - a not so simple calculation of the mechanical advantage of a cantilever brake. You will be able to see the scope of the calculation of a cable mechanism in a spreadsheet, and if you are ambitious you will be able to recreate the calculation. The spreadsheet is almost unreadable because it's big. There's a simple graph included that shows the results.

Modified Cantilever Brake Analysis - same as above, but more satisfying results.

What it looks like when you are done - a picture of tricked out cantilevers and a brief discussion to fill space and give me satisfaction

What goes wrong with standard cantilever brakes - a way to tell when somebody is jiving you about brakes, and what to look for when your brakes are not working so well.









XT V Brake Analysis

Here's some science screen captures of the spread sheets to show you what's going on.


Where:

L1 = OAL of the brake arm, center to center

L2 Max and Min = distance from pivot to pad attachment, center to center

This is the basic info for the XT V Brake. Note that the system leverage is twice what the simple leverage of the system is. The cable is connected between the arms, and half of a given mount of cable displacement moves the pivot of each arm one half of the total amount. 2x leverage in the system. Cables are wonderful things. The range of leverage in the system when it is connected to the V brake levers is from about 4.5 to 7:1. The leverage in the brakes on a given bike is fixed somewhere in this range and depends on the cantilever pivot location on the frame or fork.



















Standard XT Cantilever Brake Analysis


Where:

There are way too many inputs to define here.

This is really the same information for the cantilever as the first sheet showed for the V brake, but it's a more complicated calculation. The basic geometry is put in, locations, distances and angles, the main cable is displaced in small increments, and the pad motion in towards the rim is calculated. At the point where the distance between the pads is about the same as the rim width, the leverage is what you feel when you put the brakes on. The following graph shows it more clearly.


This graph shows the system leverage for standard XT cantilever brakes and V brakes. The line on the graph shows the changing system leverage as the cable is taken up at the lever for the cantilever brake. The brakes are set up in a way that is typical of a new bike. The critical point is reached when the distance between the pads is in the vicinity of the rim width - about 22mm or so.

The vertical arrows show the leverage for a V brake. The brake's leverage is relatively constant throughout the range of motion and it would be a boring horizontal line. The standard XT cantilever has less leverage than the V brake.

















Modified Cantilever Brake Analysis



This is the spreadsheet for a modified cantilever setup. The only changes made are possible with the hardware upgrades (retrogrades?) recommended above and otherwise the set up uses standard brake hardware. There are other things you can do to improve the system's performance, but none are easy.



This graph shows the results of the changes. The cantilever brake has leverage, lots of it, as promised. When the pads are separated by a distance that is about the same as the rim width, it has leverage that is just under the mean for the V brake. The feel on the bike is consistent with this analysis. The brake requires very little pulling force on the lever to lock the wheel.

There are two bars shown for the V Brake, the higher of which shows the system leverage with an older style lever for comparison.

Recall that the V brake leverage is not adjustable. The variation in each bar is caused by mounting the pad at each extreme of the pad mounting slot. You can't use this as a tuning parameter. You get what you get; you don't get to adjust it. This isn't bad, but don't think you can dial in the brakes this way. It depends on where the posts are on your bike.

I didn't take the analysis of the cantilever to this extreme. The pads in this case are close to the center of their slots. The cantilever brake has a leverage range that depends on the post location and is similar to range I show for the V brake.










What it looks like when you are done:

The technician demonstrates the proper set up on the bike:

The straddle cable in this set up is about 135mm long (plus the extra that hangs out past the arm - cut it to 160 or 170mm overall, or just leave it long until you are done, then trim it to length.

Set the brakes up so that the bottom center of the carrier is about 25mm above a line drawn between the points where the straddle cable attaches to the arms about 12mm above the tire. Adjust the pads so that the arms are the correct distance apart at the top. Toe them in a little (1mm should do it, but you can experiment - too little and they squeal like pigs, too much and the brakes get mushy because the pads flex too much as they contact the rim and the toe in is taken up).

The able technician demonstrates the appropriate clearance between tire and straddle carrier. You may disagree with his assessment. If you do, set the carrier up as close as you think is reasonable 2 and keep the arms as wide as you can (again, within reason).

As you might have divined by now, I am not completely sold on the basic advantages of the more powerful brakes, V brake or cantilever. I can ride as well either way I think. Braking traction is generally limited by the tires, not my hand strength. Sometimes the extra leverage makes the brake overly sensitive and too easy to lock. Of course, the cantilever brakes can be adjusted so that they have leverage anywhere inbetween the maximum and the standard amounts. If I were doing 50mph downhills with constant hard braking, for a living, I would probably change my tune about powerful brakes, but the standard cantilevers, adjusted properly, suit my needs very well.

You don't have to get weird about the spreadsheets - we're not all Dilberts. The set up basics for any cantilever brake system:









What goes wrong with Standard Cantilever Brakes

Standard brakes are not very good when they are set up poorly, or when the pad and rim surfaces wear and degrade. They can be restored by maintaining them, replacing parts, or they can be improved easily by the changes shown above. I've heard riders say things like STX brakes suck, or these pads rule. These claims are not based on good science of course, and they are usually wrong. STX brakes work well, pads and all, when they are set up and maintained properly. You need to have the cables set right, the overall adjustment right, and you need to have reasonably fresh clean pads in them. That's all. Your bike may not have come with straddle cables that can be set up to perform well, and it may be up to you to improve it if you want good brakes.


The technician shows a visual indicator of sub-optimal brake setup.

Most claims about the performance differences between cantilever brake pads are easier to explain by observing the differences in the condition of the pads that were changed than they are on actual pad performance. Look at an old worn pad while it's still in the bike. It's caked with dried mud in what's left of the slots (poor friction), worn down so the arms are rotated in towards the center of the bike (poor leverage), and the long straddle cable pulls straight up on the arms (poor leverage). Compare this to the same bike set up with a brand new set of pads - fresh clean material, arms spread back out, mechanical advantage back up a bit. Of course the new pads will feel more powerful!

Try this sometime when you are rich and have time on your hands. Get new pads, several brands, set the brakes up carefully with each so there's no difference in leverage, and ride the bike. You will find that they are all very similar in power and feel. Set up well they stop. Set up poorly they don't. Set up by the recommendations above and they really stop.

Remember, if you set your brakes up following the hints and tips above, watch out when you grab the brake the first time. Take the bike on an easy cruise to get used to the brakes, not a technical death ride. Hang on tight. Have fun. 3

Oh yeah, now for the usual hedge to keep my ass out of any more trouble than necessary:

This is intended as humor and entertainment. We're not trying to sell you anything, and we're not trying to cause you to hurt yourself. I really don't want anybody to do anything that might lead to an injury and get pissed off, or worse.

And if that's not enough, some words to live by:

Don't do anything you don't understand to your brakes 4 or anything else for that matter.

The footnotes

(2) If you are going to look for somebody else to blame when things go wrong for you, and then you are going to try to sue them, keep the straddle carrier well away from the action and hang a safety wire from the bike to catch the straddle wire if something goes wrong.

(3) If you are going to look for somebody else to blame when things go wrong for you, and then you are going to try to sue them, don't ride with high powered brakes and don't ride in places where you might need them. Manage your risk at a very low level. Off road riding is probably not for you.

(4) If you are going to look for somebody else to blame when things go wrong for you, and then you are going to try to sue them, buy standard parts when you need them and only let your dealer service them for you. Manage your risk at a very low level. Off road riding is probably not for you.