Anyone tried the Galfer big brake kit on their GS?

[Deleted account 211025001]

Sorry - braking force, as in pressure on the disc surface.

Increase (theoretically) the disc diameter to 500mm - apply the same hydraulic pressure - you’ll probably go into orbit. No increase in heat to the disc/caliper/pads though

AL

Agreed on the heat thing - but it sounds like Cardinal’s issue is heat which is the point I was (badly) trying to make ie he’llhave more powerful brakes but not address the heat issue it sounds like he’s having.

TBH though, I’m not sure that I know what I’m talking about

Andres

 

[Blackal]

Sounds like a heat related issue then, if it causes a soft lever after hard use, especially if it recovers once cooled down. The lever coming back to the bar suggests that the fluid is becoming compressible which I would have thought only normally happens if either the fluid itself, or moisture it has absorbed, boils, giving gas in the system - with gas being compressible unlike most liquids. More powerful brakes, unless they run a lot cooler, are not going to help if the fluid cannot exert sufficient pressure to operate them. Is there a higher grade fluid you could use which is compatible with the seals etc?

But - any moisture, when it changes phase to steam - will return to liquid phase under the increase in fluid pressure on braking.

The worst result of moisture at the callipers (the only area where heat is generated) - is the overflowing of the master-cylinder due to the expansion of the fluid(s) in the system.

Long term - any moisture may affect the pistons/callipers due to corrosion.


It sounds more like pad glazing under high temperature, which can be alleviated with a more appropriate pad material.

Al

 

[fred_jb]

Sorry - braking force, as in pressure on the disc surface.

Increase (theoretically) the disc diameter to 500mm - apply the same hydraulic pressure - you’ll probably go into orbit. No increase in heat to the disc/caliper/pads though

AL

Not sure about that. I hadn't thought about this before, but you are tracing out a longer path around the disk surface on the bigger disk, so although the force through the pads is the same, it is applied over more area per revolution which should mean more energy being dissipated into the brakes per revolution of the wheel.

At the end of the day a better brake setup, more or less by definition, must turn more kinetic (motion) energy into heat energy per unit of time, otherwise it is not going to slow you down any quicker. Whether it gets hotter depends on if it can dissipate the heat any more effectively than the original, which is unlikely if it uses the same pistons and calipers as the original, and if not will get hotter if used to the maximum.

 

[Blackal]

Not sure about that. I hadn't thought about this before, but you are tracing out a longer path around the disk surface on the bigger disk, so although the force through the pads is the same, it is applied over more area per revolution which might mean more energy being dissipated into the brakes per revolution of the wheel.

At the end of the day a better brake setup, more or less by definition, must turn more kinetic (motion) energy into heat energy per unit of time, otherwise it is not going to slow you down any quicker. Whether it gets hotter depends on if it can dissipate the heat any more effectively than the original, which is unlikely if it uses the same pistons and calipers and the original.

Think of it as mechanical advantage along the same lines as longer cranks on a pushbike does the same.

With the increased diameter disc, the hydraulic pressure is the same, but it has more "effect" only (why Buell went for a single rim-mounted disc). there is no additional heat.

 

[fred_jb]

Think of it as mechanical advantage along the same lines as longer cranks on a pushbike does the same.

With the increased diameter disc, the hydraulic pressure is the same, but it has more "effect" only (why Buell went for a single rim-mounted disc). there is no additional heat.

Not arguing that it is not more effective, but if it IS more effective then it IS going to produce more heat. If it slows you down quicker then it is turning more of one type of energy (kinetic) into another (heat) in a given period of time. This is the conservation of energy principle in Newton's First Law of Thermodynamics in action. You cannot just make energy disappear - you can only change it into a different form.

However, whether the extra heat energy makes the improved brakes get any hotter than the original system did depends on whether they can dissipate heat to the surrounding air any quicker. In the case of the OP's situation - though the new disks may cool slightly faster I doubt this would be enough to prevent extra heat soak into the pistons and calipers, and a consequent rise in fluid temperatures, assuming the better brakes are being used to their full potential.

 

[dean0n0]

Bigger discs will increase the giroscopic effect, whether you'd notice it, who knows...

 

[Bem]

Ooh er, I was thinking about the Galfer kit too, thinking that it would serve to improve sensitivity rather that any absolute overall stopping power (no means to measure this beyond seat of the pants).
However this is all getting a bit heavy for a bit of bling, esp. in the final approach to gift day!

 

[fred_jb]

But - any moisture, when it changes phase to steam - will return to liquid phase under the increase in fluid pressure on braking.Al

Well it is not necessarily just water in the fluid which turns to a gas (water vapour) but the fluid itself could if it gets hot enough. I suppose that with enough applied pressure it will turn back to liquid, but applying sufficient pressure to change the high volume gas back to a low volume liquid takes up all the lever movement, without transmitting much force to the pads - why would the pads move and exert pressure on the disk when there are nice soft bubbles of gas in the system that can be squashed instead?

 

[Deleted account 191119001]

Thanks guys - good advice on fluid - hadn’t realised that 5.1 was silicone free. I had bought 5 but was then advised it wasn’t compatible so just used the bmw stuff.

Would I need an abs flush changing to 5.1?

Hope this helps, credit to the op who made the video

 

[tanneman]

The bigger disc is just an extension of the torque arm. With the same pressure applied to the disc at a longer distance from the axle will have more torque Torque=Force x Distance from centre). I do wonder if the 320mm disc will allow the calipers to be fitted on a 19'' front wheel.

The pressure applied at the brake lever is proportional to the volume of fluid displaced when applying the brakes. Hyd Pressure=Force / Area where the pressure is the same in all directions. Since you have air bubbles the area has increased and hence the hyd pressure has decreased. The air bubble is the same surface area as the diameter of the brake pipe.

 

[Blackal]

The bigger disc is just an extension of the torque arm. With the same pressure applied to the disc at a longer distance from the axle will have more torque Torque=Force x Distance from centre). I do wonder if the 320mm disc will allow the calipers to be fitted on a 19'' front wheel.

The pressure applied at the brake lever is proportional to the volume of fluid displaced when applying the brakes. Hyd Pressure=Force / Area where the pressure is the same in all directions. Since you have air bubbles the area has increased and hence the hyd pressure has decreased. The air bubble is the same surface area as the diameter of the brake pipe.

It’s essentially a static system. You can’t have variance in pressure just because there is an air bubble present.

 

[batman1]

I think that the RT-LC has larger diameter front discs to help pull up the extra weight of the RT, so there should be enough parts in the BMW LC parts bins to put something together that would work.

However I think that the standard GS LC brakes are pretty dam good, and more than adequate for the fastest road rider so perhaps you need to fit some fresh descents pads.

 

[Cardinal]

BMW Gs 911 tool for ABS flush £461 !!!!

I agree that heat is my enemy. Anyone know if bigger / two pot callipers from s1000 range would be compatible?

 

[Neil W]

Read my post I have had the 320mm rt discs fitted to my old gsa lc and with the 7.5mm spacers the brembo caipers fit the standard spoke wheels with no clearance issues.

I have no doubt they would have worked fine and possibly produce better braking

I chose because of an impending warranty claim for other issues not to run the bike in that configuration

 

[ReGenesis]

The bigger disc is just an extension of the torque arm. With the same pressure applied to the disc at a longer distance from the axle will have more torque Torque=Force x Distance from centre). I do wonder if the 320mm disc will allow the calipers to be fitted on a 19'' front wheel.
.

320mm is the standard size on al superbikes running 17” wheels and has been for a long time.
A 19” will have no problem.

My CRF450R has. 320mm Galfer on the 17” supermoto front.

 

[tanneman]

It’s essentially a static system. You can’t have variance in pressure just because there is an air bubble present.

Ah yes, You are compressing the air first before you effectively move the pistons.

 

[tanneman]

320mm is the standard size on al superbikes running 17” wheels and has been for a long time.
A 19” will have no problem.

My CRF450R has. 320mm Galfer on the 17” supermoto front.

Ok, the op has cast wheels. On the GSA with the spoked wheels this can be a problem as the cross spoke is to the outside of the rim.

 

[ReGenesis]

Talon/Excel supermoto wheels are spoked 17”.
There should still be no issues as the discs are always outboard of the rest of the hub and rim.
Unless for some ridiculous reason the hubs are narrower with the discs inside the footprint of the rim then they’ll fit.

 

[steveC]

I agree. You will reduce the effective piston pressure because the air will compress. Thats until it reaches the point when when the force applied decides the path of least resistance is pushing the pistons out. That condition is a variable according to the amount of air in the system.

Another variable in the system is expansion of the flexible brake lines.

The suggestion of 5.1 fluid with a higher boil temp sounds a good starting point. I didn't realise it was compatible.

As Mr Slow a brick on a bit of string provides adequate stopping power for my riding style.

Ah yes, You are compressing the air first before you effectively move the pistons.