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-   -   Can I improve BB7 rear disc braking on Co-Motion Speedster? (https://www.bikeforums.net/tandem-cycling/1163784-can-i-improve-bb7-rear-disc-braking-co-motion-speedster.html)

sapporoguy 01-07-19 07:56 PM

Can I improve BB7 rear disc braking on Co-Motion Speedster?
 
Hi all,
We have a 2005 Co-Motion Speedster with Avid BB7 road caliper and Avid 203mm rear disc (pix below), Deore brifters. New pads, new cables, adjusted.
Braking is ok, but doesn't seem better than V-brakes.
Can I do anything with this setup to improve rear braking?
Or new disc? Or replace with TRP Spyre or HY/RD or such?
Thanks!
https://cimg6.ibsrv.net/gimg/bikefor...ac1ce201bf.jpg
https://cimg7.ibsrv.net/gimg/bikefor...a307155b58.jpg

Alcanbrad 01-07-19 08:32 PM

We have a Co-Mo Carrera with TRP Spyres and a Primera co-pilot with BB7. We too found braking not to our desired level of effectiveness - we’re a 400 lb team and ride very hilly terrain.

i am not sure exactly what your issue is, but take a look at this thread https://www.bikeforums.net/tandem-cy...rformance.html I found that the return spring of both the spyres and bb7s was not strong enough to overcome the slack in the Long cable run to the rear so I had to keep the pads opened up far enough to keep the pads from rubbing resulting in not enough pull range to apply strong braking. On a fellow forum members suggestion I added a secondary return spring to the TRPs which allowed me to set the pads closer and the braking performance is now fantastic. We obtained the primera later, experienced same, added the springs and all is good now.

sapporoguy 01-07-19 11:21 PM


Originally Posted by Alcanbrad (Post 20737224)
i am not sure exactly what your issue is, but take a look at this thread https://www.bikeforums.net/tandem-cy...rformance.html I found that the return spring of both the spyres and bb7s was not strong enough to overcome the slack in the Long cable run to the rear


I did read that thread. We initially had the same problem described by the OP in that thread--mushy brake lever, with pads adjusted just shy of the disk the lever would pull all the way to the bars. At that point, adding a spring probably would have helped. But I found the brake cables were kinked in several places. I put new cables in-- and totally got rid of the mush. Very crisp action at the lever. Now there's zero drag of the brake pads with lever released, and the brakes are fully engaged with about 3/4-inch pull of the lever (measured at the bottom tip of the lever), with plenty of room left before the lever would hit the bars if it could. But with the lever pulled as hard as it will go, the stopping power isn't any better than v-brakes. I certainly can't skid the back tire. Maybe I'm expecting too much of the disc brakes? (never had a bike with them before)

Alcanbrad 01-08-19 05:18 AM

Our Carrera was our first bike with discs as well and I didn’t feel confident in them coming from an old Santana with canti’s and a drum brake.

i don’t believe you should have to be able to skid the rear wheel as the bike won’t lean forward as a half bike will. Others better schooled on the nuances of braking performance can comment.

after installing the spring I gained some confidence and now I am a true convert to disc brakes and feel more secure than I ever did with the old set up. I would suggest you give it some time. Try some aggressive braking tests with your stoker in safe situations to speed the development of the “feel” your bike will have.

alias5000 01-08-19 07:54 AM

W can certainly skid the rear wheel on our cannondale with 203mm BB7s and stock pads.
Did you do all the common steps in making sure your disc brakes are working as good as possible?
Any contamination on pads/rotors (alcohol cleaning, sanding), compressionless (or low compression) brake housing? Try better pads, if nothing else works, e.g. kool stops.

We can degenerate quite quickly, to the point where it's more an issue to not surprise-throw off the stocker in tricky situations.

OneIsAllYouNeed 01-08-19 09:47 AM

First upgrade should be to compressionless brake housing or disc-brake specific brake housing. I recommend Jagwire Pro Compressionless brake housing. If that's not sufficient, the TRP Hy/RD would be a solid upgrade over the spongy BB7.

mtseymour 01-08-19 09:57 AM


Originally Posted by sapporoguy (Post 20737414)
But with the lever pulled as hard as it will go, the stopping power isn't any better than v-brakes. I certainly can't skid the back tire. Maybe I'm expecting too much of the disc brakes? (never had a bike with them before)

You're expecting too much from the BB7 (and other mechanical disc brakes) because they're obsolete. They all rely on a single piston to push the rotor against a fixed pad. The Spyre is slightly better because it uses two pistons to squeeze pads against the rotor.

If you go into any bike shop, you'll see that the vast majority disc-equipped single bikes use hydraulic disc brakes. I don't know of any new single bike that use the BB7. Hydraulic calipers use 2 or 4 pistons to squeeze the brake pads against the rotor. More importantly, the hydraulic calipers multiply your braking power. It's easy to lock up your wheels with one finger! Also, hydraulic disc brakes auto-center and have no cable friction.

I don't understand why tandem teams (with twice the weight of single bikes) continue to use obsolete brakes like the BB7 when the Hy/Rd (cable-actuated, hydraulic calipers) and full hydraulic brakes (eg. Shimano BR-R8070) are available at reasonable prices.

sapporoguy 01-08-19 10:22 AM

I have some new Jagwire Pro housing in my box of bike goodies--will try that along with sanding the rotor and swapping pads before giving up on it.
Hydraulic does sound compelling.

Alcanbrad 01-08-19 10:38 AM


Originally Posted by mtseymour (Post 20737811)
You're expecting too much from the BB7 (and other mechanical disc brakes) because they're obsolete.
...

I don't understand why tandem teams (with twice the weight of single bikes) continue to use obsolete brakes like the BB7 when the Hy/Rd (cable-actuated, hydraulic calipers) and full hydraulic brakes (eg. Shimano BR-R8070) are available at reasonable prices.

One word: Money

The cost of upgrading from mechanical to hydraulic is a big nut, especially if you are starting from a 10 speed triple, your only viable options are 11 speed double - This adds the cost of a full drivetrain and new brifters.

mtseymour 01-08-19 10:55 AM


Originally Posted by Alcanbrad (Post 20737893)
One word: Money

The cost of upgrading from mechanical to hydraulic is a big nut, especially if you are starting from a 10 speed triple, your only viable options are 11 speed double - This adds the cost of a full drivetrain and new brifters.

The TRP Hy/Rd list price $125, but it's easy to find them on sale for $100. The Hy/Rd does't require any changes to brifters, drivetrain or rotors. You have to decide if $200 per tandem is a "big nut" for significantly better braking and ease of use. I use full hydraulic brakes (Shimano R785, Shimano XTR, Hayes Stroker Trail) on several bikes and the Hy/Rd is reasonably close in performance. We would do steep descents on the Hy/Rd, but not on the BB7.

You're right that full hydraulic brakes require more expensive changes and are probably more suitable for new tandems rather than retrofits.

Alcanbrad 01-08-19 11:04 AM

My comment was focused on the conversion to full hydraulic. I do agree, spending $200 on a tandem is easier then opening a door :roflmao: We have BB7's on our travel tandem (which we bought used). I have noticed some vibrations from the front rotors on hard braking, however, we have not put many miles on that bike yet, perhaps this is something I need to think about.

I never saw the benefit of the TRP Hy/Rd over the Spyres other than the self adjusting nature of hydraulic brakes. Am I missing something?

tandem rider 01-08-19 12:16 PM

I clean the rotosr with alcohol every 2 - 3 hundred miles. If the pads get too much road dirt and oil on them, then replace the pads. As with new pads or rotors, cleaning with take a few miles for the pads to seat and work well. I also find the metallic (sintered) pads work better than the organic (resin or semi metallic) pads. As mentioned before, compressionless housing is important along with correct adjustment. Because the Avid BB7 has one piston and the TRP Spyre has two pistons, the adjustment will be different.

mtseymour 01-08-19 05:50 PM

https://cimg5.ibsrv.net/gimg/bikefor...a2df0a08a4.jpg

Originally Posted by Alcanbrad (Post 20737955)
My comment was focused on the conversion to full hydraulic. I do agree, spending $200 on a tandem is easier then opening a door :roflmao: We have BB7's on our travel tandem (which we bought used). I have noticed some vibrations from the front rotors on hard braking, however, we have not put many miles on that bike yet, perhaps this is something I need to think about.

I never saw the benefit of the TRP Hy/Rd over the Spyres other than the self adjusting nature of hydraulic brakes. Am I missing something?

There is a fundamental difference between the Spyre and Hy/Rd due to "mechanical advantage" or leverage. Although the Hy/Rd is cable-actuated, it has a Master piston and two caliper pistons to close the brake pads. According to Pascal's Law, .pressure exerted on a piston produces an equal increase in pressure on another piston in a hydraulic system. If caliper pistons have an area 10 times that of the master cylinder (actuated by a brake lever), the braking force is multiplied 10 times. This is the basic principle behind heavy hydraulic lifts, car brakes, and truck brakes. This is why it's easy to get 1-finger braking with full hydraulic brakes. Attached is a diagram of the master and caliper piston in a hydraulic system.

Since Spyre lacks "mechanical advantage", it won't come close to a full hydraulic brake (eg. R785). The Hy/Rd comes second because it suffers from cable friction and smaller hydraulic capacity. The Sypre is a distant third, and is rarely found on new single bikes of good quality.

PMK 01-09-19 06:02 AM


Originally Posted by mtseymour (Post 20738580)
https://cimg5.ibsrv.net/gimg/bikefor...a2df0a08a4.jpg


There is a fundamental difference between the Spyre and Hy/Rd due to "mechanical advantage" or leverage. Although the Hy/Rd is cable-actuated, it has a Master piston and two caliper pistons to close the brake pads. According to Pascal's Law, .pressure exerted on a piston produces an equal increase in pressure on another piston in a hydraulic system. If caliper pistons have an area 10 times that of the master cylinder (actuated by a brake lever), the braking force is multiplied 10 times. This is the basic principle behind heavy hydraulic lifts, car brakes, and truck brakes. This is why it's easy to get 1-finger braking with full hydraulic brakes. Attached is a diagram of the master and caliper piston in a hydraulic system.

Since Spyre lacks "mechanical advantage", it won't come close to a full hydraulic brake (eg. R785). The Hy/Rd comes second because it suffers from cable friction and smaller hydraulic capacity. The Sypre is a distant third, and is rarely found on new single bikes of good quality.

Fully understand hydraulics and the ability of hydraulics to multiply force.

The downside to multiply hydraulic force is the requirement of piston A vs Piston B linear travel. Multiplied you no longer have short stroke, but longer stroke.

PMK 01-09-19 06:28 AM

Avid BB7 brakes can work very well. Recently I just purchased a used single bike with them. The previous owner had done a poor and incorrect installation in regards to mounting the caliper brackets and the calipers to the frame / fork.

I assume the caliper brackets are installed correctly, are the correct size relative to the disc and are for the correct location.

Often, when installing the calipers themselves, the caliper is positioned too far outboard. Possible reasons are the frame or fork tab placement / location mandates a couple of shims to reposition the caliper bracket inboard more, or simply time was not taken in regards to endure the calipers inboard edge is not acting as the braking friction surface. In short, when the brake is applied, the disc could be rubbing the caliper and not truly contacting the brake pad itself.

As routine maintenance, regardless of hydraulic or mechanical brakes, it is advisable to clean the friction surfaces. I know that alcohol is often the recommended cleaner of choice, but honestly it is inferior to proper brake products such as Brake Cleaner from the auto parts store.

Use safety protection as needed.

Being lazy, you might try a clean cloth, dampened in brake cleaner, then wip the disc surface while rotating the the disc.

I may do the disc wipe at an event or as needed.

Ideally, and this is not difficult, learn to remove the brake pads, and without changing their locations, use the brake cleaner to wash the brake pads.

The best stopping power is from metalic pads. Organic pads can work, but are not as powerful. Over the years, I have tried / tested various pad setups, typically on our Ventana mountain tandem. I find that oem Avid pads work very well. Similar in performance are EBC metalic pads. Pretty certain the EBC is HH compound but I may have that confused with moto stuff.

If I had one complaint regarding Avid BB brakes, it is the spring that acts as an anti vibration / anti rattle device between the pads. As a spring it works fine. However, at the tip of each finger on the spring is an audible wear indicator. If you use the audible indicator to replace brake pads, they still retain a lot of life that is wasted. With that said, I typically use needle nose pliers and straigthen the audible indicator to disable it.

As a last consideration, understand that there are differences between Avid BB brakes. Avid offers BB7m or even the newer series BB75m for mountain bikes.

BB7r is the road version. The difference is the helix that actuates the brakes. The helix profile determines the brake lever to be used.

The very early Avid brakes, and you may have these tended to like an added return spring. My opinion is they are not as nice as the later versions. Newer versions also have adjustable spring force capability and do not require added springs provided the cable is good / clean.

Yamato72 01-09-19 12:42 PM

We have BB7s on our Cannondale and I've gotten them dialed in to my satisfaction. The biggest improvement was changing to Jagwire compressionless brake housing with a new cable. Next, I bought a truing fork to straighten the rotor (if you have blips then you have to adjust the caliper out too much to stop the rotor from dragging). Then I cleaned the glazing off the pads with 220 grit sandpaper. Lastly, I cleaned the rotor surface with acetone. The cable and housing fixed most of the sponginess in the brakes, and truing the rotor fixed the rest of it. Cleaning the pads and rotor helps a bit but mostly stops squeaking. We are a nearly 400lb team and I have no braking issues anymore.

Adding a helper spring did not make a difference for me.
And don't grease the housings when you install the cable either. Don't know where I picked up that "tip."

mtseymour 01-09-19 01:20 PM


Originally Posted by PMK (Post 20739150)

The downside to multiply hydraulic force is the requirement of piston A vs Piston B linear travel. Multiplied you no longer have short stroke, but longer stroke.

There is NO downside. Hydraulic brakes have been around so long that mfgs will use the optimal piston sizes for braking power and modulation. With both cable-actuated hydraulic (eg. HY/Rd) and full hydraulic brakes (eg. R785), there is enough reach and engagement adjustment at the lever stroke is appropriate. I've used over a dozen hydraulic brakes and lever stroke length has never been an issue. Here's a typical review on the Hy/Rd:

"The HY-RD definitely outperforms any mechanical disc brake Iíve ridden, surpasses TRPís own Parabox brake system, and comes close to the Formula R1-based 324 Labs system weíve spent a good amount of time on. It also looks a lot more elegant than any handlebar or steerer tube-mounted system, at a weight competitive to the popular standard, the Avid BB7 mechanical disc brake. (CX manazine):"

PMK 01-10-19 07:29 AM


Originally Posted by mtseymour (Post 20739789)
There is NO downside. Hydraulic brakes have been around so long that mfgs will use the optimal piston sizes for braking power and modulation. With both cable-actuated hydraulic (eg. HY/Rd) and full hydraulic brakes (eg. R785), there is enough reach and engagement adjustment at the lever stroke is appropriate. I've used over a dozen hydraulic brakes and lever stroke length has never been an issue. Here's a typical review on the Hy/Rd:

"The HY-RD definitely outperforms any mechanical disc brake Iíve ridden, surpasses TRPís own Parabox brake system, and comes close to the Formula R1-based 324 Labs system weíve spent a good amount of time on. It also looks a lot more elegant than any handlebar or steerer tube-mounted system, at a weight competitive to the popular standard, the Avid BB7 mechanical disc brake. (CX manazine):"

My reply was not focused on a manufacturer selecting the proper ratio of piston diameters, but rather in reference to your reference material of how hydraulics operate and you representing how hydraulics operate with no downside.

Hydraulic brakes on bicycles have improved many levels since the early production versions in the 1990s. Not saying hydraulic brakes are superior or inferior, simply another choice to get you stopped.

Each design and method of actuating, plus each manufacturer has their quirks. Properly setup, Avid BBs are very worthy, The Avid RS brakes on my inspired trials bicycle are a good match for the levers to my fingers ergonomics and accoplish powerful braking. The Shimano XT brakes on my wifes LIV Advanced Pique 1, she loves, where I find the rate linkage notchy and do not like the feel when I am on that bike. My Scorpa has AJP brakes, my KTM uses Brembos, and the Can Am Spyder uses Brembos. Each setup and system has its own merits and demerits. Not so much quoted from a magazine article, but relative to riding and using the brakes.

Not important to you, both our Co-Motion and Ventana both use Avid BB series brakes, and when adjusted well, never leak fluid and have more than enough stopping capability with good modulation at the levers.

Pretty certain, with a touch of effort, minimal if no expense, and care setting up, the original post will have very good brakes.

PMK 01-10-19 07:40 AM


Originally Posted by Yamato72 (Post 20739732)
We have BB7s on our Cannondale and I've gotten them dialed in to my satisfaction. The biggest improvement was changing to Jagwire compressionless brake housing with a new cable. Next, I bought a truing fork to straighten the rotor (if you have blips then you have to adjust the caliper out too much to stop the rotor from dragging). Then I cleaned the glazing off the pads with 220 grit sandpaper. Lastly, I cleaned the rotor surface with acetone. The cable and housing fixed most of the sponginess in the brakes, and truing the rotor fixed the rest of it. Cleaning the pads and rotor helps a bit but mostly stops squeaking. We are a nearly 400lb team and I have no braking issues anymore.

Adding a helper spring did not make a difference for me.
And don't grease the housings when you install the cable either. Don't know where I picked up that "tip."

Agree. Attention to a few details gets results. Acetone does well to clean the surfaces of metalic pads also. Not a fan to read when people substitute acetone based nail polish remover for true acetone.

The tool for truing the discs works well. Sadly, with non floating discs, we often induce small amounts of wobble from heat and distortion. Unless truly bent, I leave well enough alone.

Not sure how you cut your cable housings, I typically rough cut to length with Park cable cutters, then final cut with a cut off wheel or ensure the ends are flat on a belt sander or similar. Obviously, reopening the inner liner with a scribe after cutting and squaring.

Deglazing the discs work very well to help burnish the pads quickly. Also after burnishing, the remaing texture reduces, even prevents shudder from the disc being too polished.

Everything you posted is great advice.

Yamato72 01-10-19 08:32 AM


Originally Posted by PMK (Post 20740958)
The tool for truing the discs works well. Sadly, with non floating discs, we often induce small amounts of wobble from heat and distortion. Unless truly bent, I leave well enough alone.

Yes it is a royal pain to try to straighten them, but worth the effort to me since it lets me get the pads that little bit closer to the rotor surface.


Originally Posted by PMK (Post 20740958)
Not sure how you cut your cable housings, I typically rough cut to length with Park cable cutters, then final cut with a cut off wheel or ensure the ends are flat on a belt sander or similar. Obviously, reopening the inner liner with a scribe after cutting and squaring.

I use a dedicated cable cutter and dress the ends with a Dremel. Flaring the end of the liner is important too as it's very stiff on these housings.

Pay attention to cable routing, too, on our Cannondale the cable housing was routed outside and over the chainstay, which put a severe bend to it right as it got to the caliper. Re-routing it inside the chainstay straightened things out.

fietsbob 01-10-19 04:51 PM

One advantage to full hydraulic is hose length does not decrease the performance..

so the sole Hydraulic Rim brake maker, Magura is the best V brake made.. & it gets even better on rear wheels..


that being Said, I put HyRd in place of the BB7 on my single bike,,,

sapporoguy 01-11-19 11:50 PM

Thanks, all, for a hugely informative responses. Tomorrow (Saturday) I'm going to start wringing out my existing system as some have suggested. I have Jagwire housing and will get Jagwire cables at my LBS. Then will sand/clean rotors. I have acetone (my favorite cleaner. does anyone else guiltily enjoy smelling it just a little?)
Can anyone point me to a good procedure for sanding rotors? What grade and composition of paper? wet/dry? pattern? I have a random orbital sander--maybe use that?

PMK 01-12-19 04:30 AM


Originally Posted by sapporoguy (Post 20743966)
Thanks, all, for a hugely informative responses. Tomorrow (Saturday) I'm going to start wringing out my existing system as some have suggested. I have Jagwire housing and will get Jagwire cables at my LBS. Then will sand/clean rotors. I have acetone (my favorite cleaner. does anyone else guiltily enjoy smelling it just a little?)
Can anyone point me to a good procedure for sanding rotors? What grade and composition of paper? wet/dry? pattern? I have a random orbital sander--maybe use that?

While you have it apart, ensure you have metalic brake pads and not organic or semi metallics.

Sanding the discs, your sander, if electric and for woodworking, it may not be best. If you have an automotive type random orbital sander that may work better. Ideally, your finished surface will get a texture similar to honeing a cylinder in an engine. Doubtful you will get the pattern, but the roughness matters.

Without using the powered sander, my suggestion is a sanding block. Avoid hand sanding without the block, the finish will be inconsistent.

Read up on how to initially position the fixed pad. Many people start with the fixed pad incorrectly positioned, and have calipers in the less than ideal location left to right.

Dealing with the spherical alignment washers is kind of a pain and takes time. On both the off road and road tandems I found that even when aligned well, with use the caliper can ever so slowly move. For us, I have gone to a flat washer stack of matching height. This may or may not be best for you, how well they aligned the caliper mount during manufacture of the frame plays into this.

Also, realize that the brake pads and rotors need to bed in, so initially braking may seem soft and less effective. Usually, ten or so hard stops and then make minor pad adjustments gets you dialed in.


alias5000 01-12-19 08:58 AM

In extend to the previous reply, a few comments from my side:
The best way to set up BB5s that I found is this:
- Loosen the spherical bolts.
- Unclamp the cable from the caliper (BB 7: fully open up the outboard adjustment knob and then dial it in 1-2 clicks. With this, you might be able to work without the business card mentioned below)
- Put a business card between outboard pad and rotor
- turn the red inside adjustment knob all the way in such that the caliper firmly holds on the the rotor. Make sure, the caliper is free to move around the spherical bolts and only held by the rotor.
- tighten up the spherical bolts
- loosen up the inside adjustment knob and adjust it such that it just does not rub the rotor anymore. The business card should achieve this for the outboard side. If not, play with the outboard adjustment know.
- attach the cable again, make sure there is not slack, but also do not (significantly) preload the cable.

I hand sanded my rotors with fine sand paper and cleaned with alcohol afterwards. Would agree with previous comments, but together with all other measures I was able to get a good braking power out of my discs afterwards this way.

sapporoguy 01-12-19 12:30 PM

Two avid rotors came with this tandem. Pix below. Condition being equal, is one model preferable?https://cimg1.ibsrv.net/gimg/bikefor...a9b415c49.jpeghttps://cimg2.ibsrv.net/gimg/bikefor...1e305d693.jpeg


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