[Mudpuppy]

Why why why?
I don't expect disk brake performance but it would be nice if I could lock up the rear wheel without really trying hard.
I think I'm running a modulever and maybe tektro brakes.

 

[stringcheese]

Try to align the pads to the rim a little better. After that, if you feel like they still could be better, sand paper the pads a little to give it a better surface. Before you try any of this make sure the rims are clean, that would be a problem too.

 

[shootr]

actually there can be a number of reasons, so I will try to break it down...

for a long time people believed that rim brakes worked by the advesive nature of rubber compounds in the pads and that heat was not a factor. ( in disc systems it is common knowledge that stopping power occurs due to a transformation of the kinetic energy into heat via friction which is dissapated by the rotor)...
Well it has be fairly recently been proven that rim brakes work EXACTLY the same, except that the heat is dissapated through the rim itself.
Here is where some of the problem first starts. did you ever notice that bikes with chrome plated wheels always brake better?? this is because the plating is nickle and chromium, both excellent conductors of heat, which makes it easy for the developed frictional heat to transfer to the rim and be dissapaited....unfortunately anodized coatings are relatively POOR conductors of heat and make it difficult for the transfer to occur, instead the pad loads itself with the energy and is ineffective. that is why when the anodizing rubs off on the rim it starts working better, also why the brakes may feel slightly better on damp days (fluids conduct heat fairly well).

Now that we have generically covered that issue I will move on to another, the angle of pad placement.
to effectively brake you must provide the greatest available amount of contact area between the frictional surfaces, this means that the pad must contact the rim completely and evenly, THROUGHOUT the braking process. depending on the location and design of your brake assembly you may either have to toe the pad in or out (in most cases in) so that the torsional leverage does not lift the trailing edge but rather force the leading edge into contact, this also goes for the case of pad angle it should be such that when the torque is applied it will rotate onto the rim surface rather than away...

If this is hard to understand I will provide an example.
I will use the front brake of a bike with a cantilever setup.

the wheel is rotating forward away from the brake and when the brake is applied, it will try to drive the pad forward, if the pad is set level what will happen is that the front of the pad will actually lift away from the rim because it is trying to move with the rim, that is why in this case you would toe the pad in so that this force makes the pad turn into the rim instead of away, as well in this example the pivot for the brakes is ABOVE the pads meaning that when the brake is applied it will try to rotate the pad upwards toward the tire (opposite on V brakes) meaning that you would want the pad turned slightly downward at the front, so that the torque levels it, otherwise the front of the pad will ride up and rub the tire instead of the rim.

Now to the final part of the braking equation...system friction.
(edit: this is important as a high level of friction in the system uses the leverage energy you apply, making it feel as though you are forcing the pad very hard against the rim when in actuality there is very little contact pressure)
Unfortunatly this is often the most overlooked variable. in your system your cable length and bend radii shoudl be such that they introduce the least amount of drag possible, in addition the pivot points on the braking mechanisms should move freely without stiction or bind, and finally and just as important but MOST often ignored is "system throw".. this is the distance that the mechanism travels during use, the alignment and adjustment should be such that the brake actually applies at the point of highest leverage, or just after that, NEVER before, in every type of brake mechanism there is a peak in the leverage, and this should be utilized... Most people place their pads far to close to "reduce their lever throw", which is completely wrong, a lever should be selected that provides the ratio desired to achieve the correct feel. Pad travel should be dictated by caliper design.

If this is all said and done you should actually find that at low speed a rim brake will actually have far superior performance relative to a disc, as it has a leverage advantage that a disc can never match (being at the edge of the wheel).

Now I have made most of this discussion fairly rudimentary, so anybody feel free to add a more sofisticated explanation.

good luck with your brakes.

 

[hardtail_schmuk]

^^what he said. Kool-stop pads and chrome rims are your friends

 

[bru]

Yep, chrome rims and kool stops. I didn't know what braking was until I ordered some salmon kool stop phatpads. It also helps if you have clean cable routing. No kinks or tight bends makes a huge difference. My current setup is rediculously complex but it works. Tech 77 lever to primo pervert to gyro, to dual lower cables with homemade london mod to 996 brakes with salmon phatpads on a primo chrome rim, all held together with shift housing. With 5 seperate cables and 10 barrel adjusters, it takes some work to tune but you can one finger everything. Regular upper cables and some knarps would probably work better though. I swear by chrome rims, phatpads, shift housing, and dual lower cables(if you run a gyro).

 

[BMXman]

Originally posted by Mudpuppy
Why why why?
I don't expect disk brake performance but it would be nice if I could lock up the rear wheel without really trying hard.
I think I'm running a modulever and maybe tektro brakes.

what kind of rims are you using?...I would maybe step up to 990's also and a standard lever....modulever seems to be a lot of hype to me.....D

 

[Sideways]

Originally posted by shootr
actually there can be a number of reasons, so I will try to break it down...

for a long time people believed that rim brakes worked by the advesive nature of rubber compounds in the pads and that heat was not a factor. ( in disc systems it is common knowledge that stopping power occurs due to a transformation of the kinetic energy into heat via friction which is dissapated by the rotor)...
Well it has be fairly recently been proven that rim brakes work EXACTLY the same, except that the heat is dissapated through the rim itself.
Here is where some of the problem first starts. did you ever notice that bikes with chrome plated wheels always brake better?? this is because the plating is nickle and chromium, both excellent conductors of heat, which makes it easy for the developed frictional heat to transfer to the rim and be dissapaited....unfortunately anodized coatings are relatively POOR conductors of heat and make it difficult for the transfer to occur, instead the pad loads itself with the energy and is ineffective. that is why when the anodizing rubs off on the rim it starts working better, also why the brakes may feel slightly better on damp days (fluids conduct heat fairly well).
....

No.
I'm not sure where you read that stuff.
Go ahead and ignore it.

To optimize brake performance,

Maximize:
1) Cf of the pad and the rim,

2) The compressive force of the pads against opposing sides of the rim.

Minimize:

3) Deflection and elongation of brake components

4) Friction of mechanical systems.

Do this by:

1) Use chrome rims and good brake pads

2) Set up the cables and arms so that all levers act at 90deg
(sin90=1, sin0=0)

3) Minimize length of housing,
minimize length of cable,
use a stiff brake lever,
use stiff brake arms,
use good brake pads,
use a stout rim,
have the pads hit low on the rim.

4) Grease all pivot points, lube cables and housing.



Simplicity is the hallmark of good engineering.

 

[Mudpuppy]

Sorry I haven't replied. I forgot I even posted this.

I think my rims are painted black.

I should buy new pads.

I bought it used and just have whatever came with it on.

 

[hardtail_schmuk]

Originally posted by Mudpuppy
Sorry I haven't replied. I forgot I even posted this.

I think my rims are painted black.

I should buy new pads.

I bought it used and just have whatever came with it on.

Black rims are crap for braking, so it might not be the pads

 

[Sideways]

Originally posted by hardtail_schmuk


Black rims are crap for braking, so it might not be the pads

Yep. It don't make a darn what else is right and good.
Black rims suck on BMX bikes.
Go chrome or go home.

 

[WTGPhoben]

I'll second the shifter housing. Gives a much stiffer feel than brake housing, but be careful to inspect it regularly for cracks, as it is more suceptible to catastrophic failure than brake housing.

 

[bru]

Another thing I love about shifter housing is that it doesn't stretch when pulled. I remember when I wasn't running a gyro, wrapping brake housing around the bars (I left enough cable to a barspin either way) would make the brakes a lot tighter and the housing itself would kink quite easily. With shift housing it is harder to kink and feels the same wound around the bar as it does straight. You are right though, when it fails it explodes

 

[shootr]

Originally posted by Sideways


No.
I'm not sure where you read that stuff.
Go ahead and ignore it.

To optimize brake performance,

Maximize:
1) Cf of the pad and the rim,

2) The compressive force of the pads against opposing sides of the rim.

Minimize:

3) Deflection and elongation of brake components

4) Friction of mechanical systems.

Do this by:

1) Use chrome rims and good brake pads

2) Set up the cables and arms so that all levers act at 90deg
(sin90=1, sin0=0)

3) Minimize length of housing,
minimize length of cable,
use a stiff brake lever,
use stiff brake arms,
use good brake pads,
use a stout rim,
have the pads hit low on the rim.

4) Grease all pivot points, lube cables and housing.



Simplicity is the hallmark of good engineering.

I hate to sound antagonistic, but I think that if you re=read my WHOLE post you will see that you stated what I had already stated. And if you believe that a higher Coefficient of friction is the major determining force for braking, you might want to try using a silicon carbide stopping surface, something with a grit of around 80...that would provide you with a MUCH higher CofF but I assure you that it would not provide you with greater braking force, I do not make this claim because of some fancifal flights of fatasy, I have been involved in performance friction materials for most of my carreer, and as such have had the opportunity to specifically study and work with brakes and braking performance as a central subject of study...

But feel free to tell me how wrong I am, just don't do it by regurgitating what I have already said.

 

[Sideways]

Originally posted by shootr


I hate to sound antagonistic, but I think that if you re=read my WHOLE post you will see that you stated what I had already stated. And if you believe that a higher Coefficient of friction is the major determining force for braking, you might want to try using a silicon carbide stopping surface, something with a grit of around 80...that would provide you with a MUCH higher CofF but I assure you that it would not provide you with greater braking force, I do not make this claim because of some fancifal flights of fatasy, I have been involved in performance friction materials for most of my carreer, and as such have had the opportunity to specifically study and work with brakes and braking performance as a central subject of study...

But feel free to tell me how wrong I am, just don't do it by regurgitating what I have already said.

Why would I want to re-read your wordy post?
Maybe you missed my final statement.

BTW: "Grit" and Cf are unrelated.

 

[Sideways]

Originally posted by shootr
actually there can be a number of reasons, so I will try to break it down...

1. in disc systems it is common knowledge that stopping power occurs due to a transformation of the kinetic energy into heat via friction which is dissapated by the rotor)...

This is not common knowledge. You may be thinking about brake fade prevention. You do not want temperatures that will cause brake fluid to boil and pads to degass.
However, most high performance pads rely on higher temperatures to achieve maximum frictional performance.

2. Well it has be fairly recently been proven that rim brakes work EXACTLY the same, except that the heat is dissapated through the rim itself.

Rim brakes also work on the principals of friction. Not heat dissipation. If what you are trying to say were correct, rim manufactures everywhere would build rims with additional surface area. Like a radiator.

3. Here is where some of the problem first starts. did you ever notice that bikes with chrome plated wheels always brake better?? this is because the plating is nickle and chromium, both excellent conductors of heat, which makes it easy for the developed frictional heat to transfer to the rim and be dissapaited....

Thermal conductivity of nickel: 421 BTU-in/hr-ft²-°F
Thermal conductivity of aluminum: 1160 BTU-in/hr-ft²-°F

As you can see, aluminum is by far a superior conductor of heat. The nickel plating on aluminum rims increases friction, that’s all.

4. unfortunately anodized coatings are relatively POOR conductors of heat and make it difficult for the transfer to occur, instead the pad loads itself with the energy and is ineffective. that is why when the anodizing rubs off on the rim it starts working better,

Anodizing adds very little thickness. Check your equations. You’ll see that its thermal properties are negligible.
Anyways, it's friction that's important. Sorry to beat a dead horse.

5. also why the brakes may feel slightly better on damp days (fluids conduct heat fairly well).

Fluids such as air, water, oil?
No. Dry brake surfaces are superior stoppers.
Ride some chrome rims through a puddle and see.

6. Now that we have generically covered that issue I will move on to another, the angle of pad placement.

Your arguments are anything but generic.

7. to effectively brake you must provide the greatest available amount of contact area between the frictional surfaces, this means that the pad must contact the rim completely and evenly, THROUGHOUT the braking process.

Frictional force is independent of surface area. Normal force and Cf are the only concerns.

8. Pad travel should be dictated by caliper design.

No, by available clearance. Depending on wheel wobble and dirt clearance, this is variable.

9. Now I have made most of this discussion fairly rudimentary, so anybody feel free to add a more sofisticated explanation.

You have done all but that. “Sophisticated” explanations are worthless. Therefore, I offered an easy to understand discussion on brake set up.

10. And if you believe that a higher Coefficient of friction is the major determining force for braking, you might want to try using a silicon carbide stopping surface, something with a grit of around 80...that would provide you with a MUCH higher CofF

Silicone Carbide is known for it’s hardness. That is why it shears a variety of materials so well and is commonly used for sanding paper. Hardness does not equal Cf.

But feel free to tell me how wrong I am, just don't do it by regurgitating what I have already said.

Thank you for making me feel free to do so.
Obviously I would not try to repeat the arguments that you have made.

 

[Dog Welder]

To run a gyro do you have to run a Odyssey Modulever? To me they feel like crap...I'd rather run a Shimano DX or shoot if I've got the cash a XTR. Can you rig either one of those to use a gyro? Or do you have to run a lever with a dual cable capability?

WOW Sideways...you sure you're not "Just Pete" ...the guy's just trying to pass on info...no need to go for the throat...Shootr's been providing this forum with great accurate information since its inception. Now what you two are doing is taking it to a whole new level that just about everyone but you two can understand, just to prove a point...this is the internet...both you guys are going to give each other an anerism.

But I have to say that I do agree with Shootrs argument about lever throw...its more difficult to apply power if your levers engage the pad right when you touch the lever vs when the levers/pad engage half way in. exactly the same principle as doing a pullup. What's harder? Doing a pullup at full extension? or doing a pulleup at only half extention....well if you had gym class back in high school you'd know the answer.

Peace...now if someone cans answer my question at the top of this post?

 

[Sideways]

Originally posted by Dog Welder
To run a gyro do you have to run a Odyssey Modulever? To me they feel like crap...I'd rather run a Shimano DX or shoot if I've got the cash a XTR. Can you rig either one of those to use a gyro? Or do you have to run a lever with a dual cable capability?

WOW Sideways...you sure you're not "Just Pete" ...the guy's just trying to pass on info...no need to go for the throat...Shootr's been providing this forum with great accurate information since its inception. Now what you two are doing is taking it to a whole new level that just about everyone but you two can understand, just to prove a point...this is the internet...both you guys are going to give each other an anerism.

But I have to say that I do agree with Shootrs argument about lever throw...its more difficult to apply power if your levers engage the pad right when you touch the lever vs when the levers/pad engage half way in. exactly the same principle as doing a pullup. What's harder? Doing a pullup at full extension? or doing a pulleup at only half extention....well if you had gym class back in high school you'd know the answer.

Peace...now if someone cans answer my question at the top of this post?

Detanglers (Gyros) are not desgined to be modulever specific. The modulever is just a lever with a special set of cables. The upper cables of detangler systems are made to work with all BMX levers. Use of V brakes and V brake componants does not work well with detangler systems.
Hope that helps.




Sorry if I called out shootr for passing along such crap info. I hope that his original post was not indicitive of his "great accurate information" that you speak of.

As to "lever throw": I see nowhere that shootr suggests how to actually set up the brakes. When I mentioned setting up all levers at 90deg, this also refers to the brake lever. It works for the same reasons that half way up pull ups are easier.