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Tyre Tread
6,320 posts
85 months
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walm said: OlberJ said: It doesnt pull down though. Of course it does. It may not actually move much but there is a boat-load of downward force. OlberJ said: It's the momentum of the sprung weight slowing down after the unsprung wheel that causes the car to pitch forward under braking. Absolutely, of course. Although as above when the calipers grip they pull the rest of the chassis down with them too. But IIRC Will was suggesting that switching the caliper from the leading edge of the disc to the trailing edge would apply a force in the opposite direction. i.e. you could put the front wheel caliper on the back of the disc and that would create a force that pulled the back of the car down. But if it were on the front of the caliper it would do the opposite and pull the front down. That's wrong. OlberJ said: If the brakes are at the middle of the car its to put weight between the axles, mid mounted. +1 Would it make any difference if the car were on, say, a conveyor belt?
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walm
3,441 posts
71 months
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Tyre Tread said: Would it make any difference if the car were on, say, a conveyor belt? This is a very good point. If it were we could see whether applying the brakes pulled the front of the car down. I suspect on their release it would spring back up and might even take off.
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OlberJ
11,953 posts
102 months
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Actually, that is a good point.
If the car was physically staying still but the conveyor belt and the wheels were going at the same speed, what would happen when it brakes (assuming the belt brakes at the exact same speed)?
Would the unsprung chassis be pulled down? If not, would the sprung mass even move?
Why not get 2 hub dynos and we can find out?
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Frimley111R
4,210 posts
103 months
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Why doesn't dust and pollen blow off my car as soon as I drive it?
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Sexual Chocolate
837 posts
13 months
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Why is my collegue taking ages to mail me some paper work so I can close my laptop and sod off for the weekend?
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V8mate
34,917 posts
58 months
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Sexual Chocolate said: Why is my collegue taking ages to mail me some paper work so I can close my laptop and sod off for the weekend? Because they hate you.
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CommanderJameson
20,672 posts
95 months
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Frimley111R said: Why doesn't dust and pollen blow off my car as soon as I drive it? Because you're not driving fast enough.
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OlberJ
11,953 posts
102 months
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OlberJ said: Actually, that is a good point.
If the car was physically staying still but the conveyor belt and the wheels were going at the same speed, what would happen when it brakes (assuming the belt brakes at the exact same speed)?
Would the unsprung chassis be pulled down? If not, would the sprung mass even move?
Why not get 2 hub dynos and we can find out? Infact, would a standard 4 wheel dyno not produce the effect we are after? Or even those brake testing machines in MOT centres?
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DeadMeat_UK
3,053 posts
151 months
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Why can 2 consecutive days, both with the same clear skies and the same amount of wind from the same direction result in different temperature weather?
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AstonZagato
3,228 posts
79 months
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Frimley111R said: Why doesn't dust and pollen blow off my car as soon as I drive it? I have always assumed an electrostatic charge plus pollen being a bit sticky.
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Fabric
3,043 posts
61 months
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OlberJ said: Actually, that is a good point.
If the car was physically staying still but the conveyor belt and the wheels were going at the same speed, what would happen when it brakes (assuming the belt brakes at the exact same speed)?
Would the unsprung chassis be pulled down? If not, would the sprung mass even move? Surely not, as the forces you're describing acting on the brakes are nothing more than a result of the cars forward inertia? Wouldn't all the "energy" through braking just be dissipated through the rollers themselves? I could be miles off on this, but it seems to be in a similar vein to seeing people sitting in the boot of powerful front engined RWD cars on dyno's in order to keep them from skipping off the rollers, since the forces normally present under physical acceleration of mass aren't there to transfer any weight/traction onto the rear axle. Conveyor belts, life's greatest mystery. 
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walm
3,441 posts
71 months
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Fabric said: Surely not, as the forces you're describing acting on the brakes are nothing more than a result of the cars forward inertia? There is a huge amount of rotational kinetic energy in any spinning wheel. When you apply the brakes on a dyno it's going to compress the springs. Again, imagine leaning out of the window and grabbing the spinning wheel - it's going to drag you out of the car whether it's on a dyno/conveyor belt or not. The confusion might be because the springs ALSO compress when you brake on a road because the car will rock forward as the slowing wheels will work against the momentum of the chassis. Since the centre of gravity is ABOVE the axles and it can't detatch from the wheels the energy transfers into the springs as they compress.
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V8mate
34,917 posts
58 months
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Fantastic discussion regarding the reasoning behind calliper positioning, chaps  Wish I'd asked it in its own thread now!
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TheEnd
12,084 posts
57 months
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AstonZagato said: Frimley111R said: Why doesn't dust and pollen blow off my car as soon as I drive it? I have always assumed an electrostatic charge plus pollen being a bit sticky. I'm sure it is down to laminar flow, and the closer it gets to a solid object, the less the speed is. An inch above the surface is the full airspeed, but the closer you get, it drops to zero.
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Fabric
3,043 posts
61 months
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walm said: There is a huge amount of rotational kinetic energy in any spinning wheel.
When you apply the brakes on a dyno it's going to compress the springs. I'm not disagreeing that the wheels will carry kinetic energy, but the majority of the "boat load" of force you mentioned that "pulls" the chassis when you're applying brakes on the road is energy transference from the cars inertial mass, surely? Unless you're applying power to the wheels whilst you also apply braking force, they're just going to be carrying their own (diminishing) rotational energy, which, if the car is static on a dyno, is going to be relatively minimal in comparison to the cars mass, no? What I'm trying to say, I suppose, is that any forces exerted upon the suspension from a rolling road, would be kinetic energy from the mass of the wheels, tyres, and braking system, rather than the car itself - and not very indicative of the real world dynamics of braking force upon the handling dynamics of a moving car. Ultimately, I have no idea what I'm talking about though.
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1point7bar
1,091 posts
17 months
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Doesn't the torque unloading into the chassis equal nearly FA compared with the torque being applied by the wheel being braked?
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OlberJ
11,953 posts
102 months
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walm said: There is a huge amount of rotational kinetic energy in any spinning wheel.
When you apply the brakes on a dyno it's going to compress the springs. Not through the braking of the wheel though. In fact if you take friction of tyre and surface out of the equation i don't think it would compress them at all. The caliper is fixed to the hub, the wheel is connected to the bearing located and in a fixed position to the hub. The only movement up or down, dependent on front or rear positioning is going to be in the flex of the steel and tyre deformation. It's unsprung, it won't move up or down or front or back from inertia/momentum when braking. Only the sprung mass will move when you brake.
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marshalla
8,018 posts
70 months
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Sexual Chocolate said: Why is my collegue taking ages to mail me some paper work so I can close my laptop and sod off for the weekend? He's waiting for matter teleportation to be invented first.
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AdeTuono
3,752 posts
96 months
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TheEnd said: AstonZagato said: Frimley111R said: Why doesn't dust and pollen blow off my car as soon as I drive it? I have always assumed an electrostatic charge plus pollen being a bit sticky. I'm sure it is down to laminar flow, and the closer it gets to a solid object, the less the speed is. An inch above the surface is the full airspeed, but the closer you get, it drops to zero. If that's the case, why does water on the surface of the car get blown backwards when travelling?
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GTIR
19,077 posts
135 months
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Hugo a Gogo said: kev b said: On a motorbike, braking hard will lift the rear wheel whether the calipers are fixed to the front or rear of the forks. Stomping on the rear brake only will not lift the front wheel. (Please,I know about leading link/trailing link/BMW wierd forks, lets stick with ordinary bikes.) it would if you were going backwards fast enough  No it wouldn't. Ever. Firstly, it's not powerful enough (one small disc, two pot caliper) and secondly it's mounted such that it has to lift more weight, engine, rider etc. Unless you were being fececious in which case, parp!
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