Clever person needed

[ARGOJIM]

But we are having fun thinking about it, right?

If we hold that Rod's assertion is true, that is, that the energy exchange is the same regardless of the technique, then he is right, the heat is the same and it will make no difference whether you hold it or snub it.

I'm no physicist, engineer or even a traditionally schooled mechanic but the friction factor translates to heat, hence more drag= more heat . When the brakes are jerked in short bursts there would be less heat than a sweeping/dragging turn would create due to the time the brakes are actually applying friction. With both the pad and the disc slipping both pieces create and retain heat while in the sweeping turn the heat continues to create heat until the pressure is released, while in the jerky turn the heat stops generating to the entire disc and begins to cool the rest of the disc where pressure/friction is not applied.

No matter the case I prefer a smooth ride feathering and even sometimes riding the brakes through the trails, my machine has 1045hrs on original discs and second set of brakes and trans has never been apart.

[Rock Doctor]

But we are having fun thinking about it, right?

If we hold that Rod's assertion is true, that is, that the energy exchange is the same regardless of the technique, then he is right, the heat is the same and it will make no difference whether you hold it or snub it.

If I want to do a 180 deg turn, and do it in a long sweeping turn, I will generate heat.....correct?
If I want to do a 180 deg turn, and do it in one "Jerk", locking the brake on one side through the turn, I will generate almost no heat......correct?



There are so many ways to make a turn, I'm getting confused now. Sometimes I'm loaded so heavy that I have no choice to make jerky turns in some terrain

RD

[Stoneyridgeboy]

I don't know who this jerk is, but I've got a good, sharp cleaver ready. Just call.

[Old Tucker]

This is a great tread, sure gets the O gears turning. But wait I think I heard a squeak. I better get one more beer and oil that little squeak. I do not know how much heat it has created or energy I have used. But what the heck, I turn my argo as smooth as I can. And if it creates more heat (so be it).
Sure beats sitting around and watching the TV.

[rodp]

But we are having fun thinking about it, right?

If we hold that Rod's assertion is true, that is, that the energy exchange is the same regardless of the technique, then he is right, the heat is the same and it will make no difference whether you hold it or snub it.

Exactly, it was a purely theoretical question, something to get the grey matter working. I feather the brakes, but not to the point of over heating, as do most others I think.
So really what it boils down to (pun intended) is not the heat generated, because this will remain a constant, but heat absorbed by the mechanical parts.

[JohnF]

... When the brakes are jerked in short bursts there would be less heat than a sweeping/dragging turn would create due to the time the brakes are actually applying friction.

Not so... Remember that RodP said that all other parts of the system are held constant. If we don't hold them constant (because they aren't - as I explained) then things are as you say and have experienced and your intuition is on track.

So, let's remodel the constant case so it might make a little more sense:

You are at the top of a 6% 6 mile grade in a soapbox derby car that has perfect bearings, no wind drag, and the tires have perfect friction to the road surface. It is built so that you have a single brake on an axle. You wish to reach the bottom in 12 minutes and want to be perfectly stopped right at the bottom.

Should you hold or snub the brake?

With both the pad and the disc slipping both pieces create and retain heat while in the sweeping turn the heat continues to create heat until the pressure is released, while in the jerky turn the heat stops generating to the entire disc and begins to cool the rest of the disc where pressure/friction is not applied.

I think this is a great expression of the bit of intuition that was bugging Rod. The physics says that if the energy delta is the same then the heat to dissipate is the same and it does not matter whether you add that heat constantly to the rotor or in bits - it should feel just as hot. (And it doesn't???)

[Note: I too feather when I can for ride quality]

If I want to do a 180 deg turn, and do it in a long sweeping turn, I will generate heat.....correct?

Yep.

If I want to do a 180 deg turn, and do it in one "Jerk", locking the brake on one side through the turn, I will generate almost no heat......correct?

Nope. I didn't mention earlier (because I assumed Rod was wondering why the brakes don't heat up so much) that you still create heat - but it's in the tires and road surface when you skid the tires.

But, for this discussion, Correct - because the turn got really easy once the tires started to skid - at least as far as the brake is concerned.

Sometimes I'm loaded so heavy that I have no choice to make jerky turns in some terrain.

I have that problem too when I go to higher elevations. In fact, at some point I can't even make a turn unless I snub it around. I no longer have the power to feather a turn because a feathered turn takes more energy.

Exactly, it was a purely theoretical question, ...

Sometimes people say theoretical to imply that an explanation makes book sense but doesn't apply to the real world. If that's what you are thinking here then you are wrong - this is really what is happening - not theoretical at all.

... I feather the brakes, but not to the point of over heating, as do most others I think.

If two people make the same turn with the same equipment (these are constants) and one overheats the brakes and the other does not, then the energy in the two systems is not equal. Maybe one drives at a faster ground speed and needs to overcome higher inertia in the turn...

So really what it boils down to (pun intended) is not the heat generated, because this will remain a constant, but heat absorbed by the mechanical parts.

Heat absorbed (or , what we are really talking about - the ability of a brake system to shed heat) is also constant. This gets into Jim's discussion a bit; oh, and we can use Old Tucker's torch too!

Say we need to pass 4 BTU of energy through a brake rotor in a 10 minute period. The rotor system is designed to shed .4 BTU a minute and it's a perfect system.

If we add all 4 BTU at the very first instant (big torch flame) at the end of 10 minutes it will be ...

If we pulse heat into the brake starting from the very first instant such that the average heat added to the brake equals .4 BTU a minute then at the end the brake will be...

If we add a constant .4 BTU a minute to the brake for 10 minutes then at the end the brake will be...

If we wait 10 minutes and add all 4 BTU at the very last instant then the brake will be...

[rodp]

Sometimes people say theoretical to imply that an explanation makes book sense but doesn't apply to the real world. If that's what you are thinking here then you are wrong - this is really what is happening - not theoretical at all.

I suppose hypothetical would have been a better choice of word.

Nope. I didn't mention earlier (because I assumed Rod was wondering why the brakes don't heat up so much) that you still create heat - but it's in the tires and road surface when you skid the tires.

So, no matter how you turn the energy is dissipated through both brakes and tyres, but if you feather then a larger proportion is through the brakes ? If you brake hard and slew turn then a larger proportion is through the tyres? Hadn't even considered tyres sharing the heat.

If we add all 4 BTU at the very first instant (big torch flame) at the end of 10 minutes it will be ...

If we pulse heat into the brake starting from the very first instant such that the average heat added to the brake equals .4 BTU a minute then at the end the brake will be...

If we add a constant .4 BTU a minute to the brake for 10 minutes then at the end the brake will be...

If we wait 10 minutes and add all 4 BTU at the very last instant then the brake will be...

Sorry, this just hasn't registered with me.

I do appreciate you taking the time to answer these questions John, and all other input is appreciated and welcome. The problem I have is my head asks questions my education can't answer, bit of a bummer really

[JohnF]

... Sorry, this just hasn't registered with me.

Ah, now that I read it, it does seem confusing. I should have put question marks instead of ellipsis. The idea was to leave the answer blank so that the group could fill it in with whatever feels intuitively right and see where that leads.

I do appreciate you taking the time to answer these questions John, and all other input is appreciated and welcome. The problem I have is my head asks questions my education can't answer, bit of a bummer really

Hey, I appreciate the discussion too. Keeps the brain muscle trim.

And, education doesn't end until you die. The head asking what you don't already know makes it so.

[rodp]

Ah, now that I read it, it does seem confusing. I should have put question marks instead of ellipsis. The idea was to leave the answer blank so that the group could fill it in with whatever feels intuitively right and see where that leads.

Ah, with it now, good thinking.

If we wait 10 minutes and add all 4 BTU at the very last instant then the brake will be...

This my guess for retaining most heat at the end of ten minutes, the brake just isn't designed to shed this amount of heat, therefore, assuming the brake's absorbed the heat most of it should be retained.

Come on gents, any thoughts ???

[Sol]

Has anyone seen my car keys?