Brake housing tech question

[NHAero]

As i posted in the Growtac thread, I just replaced the spliced Growtac-supplied compressionless housing with standard coiled brake housing on my Habanero and it seems to work fine and retains the stiff lever feel.

My question is, beyond preventing the brake lever from hitting the bars and thereby interfering with full application of the brakes, or, having the brake lever feel "mushy" when applied, what are the functional reasons for compressionless housing?

Is there any reason why (assuming the same cable and internal cable friction) the compressionless housing results in less force needing to be applied at the lever for a given amount of braking force at the caliper?

[Mark McM]

Originally Posted by NHAero

As i posted in the Growtac thread, I just replaced the spliced Growtac-supplied compressionless housing with standard coiled brake housing on my Habanero and it seems to work fine and retains the stiff lever feel.

My question is, beyond preventing the brake lever from hitting the bars and thereby interfering with full application of the brakes, or, having the brake lever feel "mushy" when applied, what are the functional reasons for compressionless housing?

Is there any reason why (assuming the same cable and internal cable friction) the compressionless housing results in less force needing to be applied at the lever for a given amount of braking force at the caliper?

Housing compression results in a little more cable travel, which in turn results in a little more friction, resulting in a little less force reaching the caliper. But the main difference is probably the loss of modulation, in which there is a loss of linearity between lever input and caliper reaction (due to compression and friction).

[NHAero]

Originally Posted by Mark McM

Housing compression results in a little more cable travel, which in turn results in a little more friction, resulting in a little less force reaching the caliper. But the main difference is probably the loss of modulation, in which there is a loss of linearity between lever input and caliper reaction (due to compression and friction).

Thanks for your response. Kind of my take too. Doesn't the friction force dissipate once the cable stops moving?

I think in the past I have mistaken a firm lever feel for better actual braking capability.

[Gabe77]

The main benefit is that many bikes today have full length housing runs - especially internally routed. The longer the housed cable run the more compression you get - the worse it is. In the olden days when the cable was fully housed back along the top tube to rear brakes there was a clearly worse brake feel than for the front one.

[hilanij]

Originally Posted by NHAero

As i posted in the Growtac thread, I just replaced the spliced Growtac-supplied compressionless housing with standard coiled brake housing on my Habanero and it seems to work fine and retains the stiff lever feel.

My question is, beyond preventing the brake lever from hitting the bars and thereby interfering with full application of the brakes, or, having the brake lever feel "mushy" when applied, what are the functional reasons for compressionless housing?

Is there any reason why (assuming the same cable and internal cable friction) the compressionless housing results in less force needing to be applied at the lever for a given amount of braking force at the caliper?

Based on my experience I would like to say yes, assuming the same cable and internal cable friction, compressionless housing can result in less force needing to be applied at the lever for a given amount of braking force at the caliper due to the reduced amount of housing compression.
When a brake lever is squeezed, the force applied to the cable is transmitted through the housing to the caliper. However, if the housing compresses under this force, some of the applied force is absorbed by the compression of the housing, rather than being fully transmitted to the caliper. This means that more force needs to be applied at the lever to generate the same amount of braking force at the caliper.
Compressionless housing, on the other hand, is designed to minimize or eliminate this compression, resulting in more direct transmission of force from the lever to the caliper. As a result, less force needs to be applied at the lever to generate the same amount of braking force at the caliper. This can make the brake system feel more responsive and require less effort from the rider to achieve the desired level of braking force.

[NHAero]

Originally Posted by hilanij

Based on my experience I would like to say yes, assuming the same cable and internal cable friction, compressionless housing can result in less force needing to be applied at the lever for a given amount of braking force at the caliper due to the reduced amount of housing compression.
When a brake lever is squeezed, the force applied to the cable is transmitted through the housing to the caliper. However, if the housing compresses under this force, some of the applied force is absorbed by the compression of the housing, rather than being fully transmitted to the caliper. This means that more force needs to be applied at the lever to generate the same amount of braking force at the caliper.
Compressionless housing, on the other hand, is designed to minimize or eliminate this compression, resulting in more direct transmission of force from the lever to the caliper. As a result, less force needs to be applied at the lever to generate the same amount of braking force at the caliper. This can make the brake system feel more responsive and require less effort from the rider to achieve the desired level of braking force.

Thank you for this reply. My conclusion, which may be incorrect, is that the force the housing "absorbs" is a constant, what changes is the deflection of that housing under the influence of the force. I wonder which of us is correct?

[dddd]

Many brake levers have some progressive leverage increase as the lever comes in toward the bar.

So any increase in housing compression would allow the lever to come in further as tension force being applied to the cable and brake increases.

The result of this would seem to be that the "softer" or longer cable housing may actually reduce the force at the lever that is needed to achieve any particular level of braking force.

A "spongier" cable housing will also reduce the peak of breakaway force of static friction in the cabling, because said breakaway occurs within a shorter length of housing at a time, instead of along the entire length of housing all at once. This spreads the static-to-dynamic friction transition over a longer span of lever travel, becoming more noticeable as the sliding surfaces become contaminated over the service interval.

Note that an increase of leverage at the lever may not be realized as a decrease in bio-mechanical perceived effort, since the hand muscles may find themselves working in a less effective range of motion as the lever comes fully inward. This "bite point" is of course adjustable by means of the cable adjuster (if tightening the cable tension doesn't also cause brake pad rub).

One way to firm up and really improve the feel of the brakes is to center the caliper such that the disc or rim does not visibly deflect even a little bit when the brake is applied. I commonly work on bikes where some increase in work (force X distance) pulling the lever is being imposed by the caliper needing some careful centering. I will closely eyeball the tire (or disc) adjacent to the stationary fork or frame (or disc caliper body), looking for any bit of lateral movement as the brake is applied, often finding great improvement (in perceived lever effort and brake modulation) just by more carefully centering the caliper.

The term "modulation" as I use it refers to three things; a lack of change in lever position as braking force is increased, a lack of friction between lever and brake pad, and good linear braking force as force on the particular brake pads is applied to whatever braking surface (rim or disc) is in use.

[Mark McM]

Originally Posted by NHAero

Thanks for your response. Kind of my take too. Doesn't the friction force dissipate once the cable stops moving?

The friction would dissipate if it were viscous friction (as for hydraulic systems), but in this case it is static friction between cable and housing. You may have noticed that replacing corroded & dirty cables & housings with smooth new cable & housings results in less lever force for a given brake force. The new cable/housing has lower static friction.[/QUOTE]