The Place

Hello,

As I mentioned in a previous thread, we are going to put a bias adjustment on our windle.

Ideally we can replace the master cylinder with a dual master cylinder with bias adjustment and use the original brake lever. If this doesn't work out, we will have to use a different fulcrum for the brake lever and mount the master cylinders elsewhere, this is where my question comes in.

I need to calculate the mechanical advantage (i.e. how much greater the force on the master cylinder is than the force created by my foot) provided by my current brake lever so that we can be sure that the new brake lever will exert the same pressure on the master cylinders. I am pretty good at maths, I can probably work it how, if only I knew how to work it out.

I don't suppose anyone has done any of this calculations before and can help me out a bit?

Regards

Dave

Would you not need to know how much force it takes from your hand or foot to operate the brakes first? Or am I over complicating things?

I don't think it matters how much force I use with my foot, I'm just interested in how much the force is multiplied (when it is applied to the master cylinder), so this multiplication can be duplicated by the new brake lever we manufacture.

I have attached a pic. What I want to work out is when I apply force to the brake lever (red arrow) how much force is applied to the master cylinder (green arrow).

Maybe I shouldn't be thinking so much about this? lol, but I don't really want to mess around when it is the brakes

Maybe you are.. Surely so long as the master cylinder bores are matched to the calipers your using, you won't have a problem?

Contact Wally at West Performance, as i know he does this type of system for disabled riders.

Well, as I understand it the brake lever assembly multiplies the force you apply with your foot, so in the event we need to make a new assembly I need the mechanical advantage to be the same as now.

If we end up with less than we have now, it might mean lesser braking performance as even though I could press the pedal as hard, less pressure is being applied to the master cylinder.

Is the compound lever giving me more mechanical advantage than one with a master cylinder plunger close to the fulcrum? Or less? My head hurts haha.

David have you got a better/ brighter picture of the system?
From what I can see of your leavers in the pic is you have a 3-1 ratio system,the leavers/pivots etc just allow for the positioning of the master cylinder assembly.

Could you just not measure pedal travel against travel at the cylinder rod and work out a ratio of that instead of measuring effort it's easier. Then there may be a formula to convert to effort.

My heads melted but I know what your getting at..
Try this link but you will need some figures and measurements
http://www.comfsm.fm/~dleeling/physics/torque.html

The ideal ratio is around 7 -1 so the lever needs to be 7 inch long to the pivot point and 1 inch the other side. 6 - 1 is ok but get as near to 7 - 1 as you can.

Whites wrote:Well, as I understand it the brake lever assembly multiplies the force you apply with your foot, so in the event we need to make a new assembly I need the mechanical advantage to be the same as now.

If we end up with less than we have now, it might mean lesser braking performance as even though I could press the pedal as hard, less pressure is being applied to the master cylinder.

Is the compound lever giving me more mechanical advantage than one with a master cylinder plunger close to the fulcrum? Or less? My head hurts haha.

Thinking more about it by putting x2 cylinders on in the same place using the same pedal linkage assy you automatically gain an advantage of 2-1 thus you should need half the effort you use now or am I over thinking

powerhouse wrote:

Whites wrote:Well, as I understand it the brake lever assembly multiplies the force you apply with your foot, so in the event we need to make a new assembly I need the mechanical advantage to be the same as now.

If we end up with less than we have now, it might mean lesser braking performance as even though I could press the pedal as hard, less pressure is being applied to the master cylinder.

Is the compound lever giving me more mechanical advantage than one with a master cylinder plunger close to the fulcrum? Or less? My head hurts haha.

Thinking more about it by putting x2 cylinders on in the same place using the same pedal linkage assy you automatically gain an advantage of 2-1 thus you should need half the effort you use now or am I over thinking

Would you not use 2 smaller bore cylinders anyway?

Just been in my workshop and looked at my windle. It has 2x cp2623-90 master cylinders fitted to give my bias if it helps.

Willow Racing wrote:The ideal ratio is around 7 -1 so the lever needs to be 7 inch long to the pivot point and 1 inch the other side. 6 - 1 is ok but get as near to 7 - 1 as you can.

Thanks for the info Dave, I have heard this quite a lot, 5 - 1, 6 - 1, 7 - 1. As you can see from the photo I have some compound leverage going on, so it has 2 pivots.

I could add up all the length on the input sides and all length on output side and then work out a ratio, I have no clue if this would be accurate though.

Also, the link between the two pivots is at an angle, although it is mostly in the same direction as the way the pedal travels, maybe it will transfer all pedal movement to the secondary lever?

powerhouse wrote:Thinking more about it by putting x2 cylinders on in the same place using the same pedal linkage assy you automatically gain an advantage of 2-1 thus you should need half the effort you use now or am I over thinking

The current master cylinder has a bigger hole feeding the front brakes than the side/rear. I assume this is how it provides a non-adjustable bias. I would assume we would need the same amount of force going to the master cylinders as we have now, just split between 2 rather than all into 1.

I will get a better picture next time I go to the workshop.

powerhouse wrote:Just been in my workshop and looked at my windle. It has 2x cp2623-90 master cylinders fitted to give my bias if it helps.

Thanks for the info, I'm not sure off the top of my head which ones we are looking at. I will find out.

I'm glad we decided to do this, as adjustable bias is better than non-adjustable, but it aint half a headache

In my humble opinion, I would measure a straight line from the pedal to the fulcrum, correct me if I'm wrong but that's how I would work out your current ratio.

When you mean hole do you mean the hole in the banjo bolt?
If so it may restrict flow when the pedal is pressed but the pressure will eventually and quite quickly be the same. Pressure restriction gives bias,not flow.