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"jim" <"sjedgingN0sp"@m@mwt.net> wrote in message
news:1141434475_67@sp6iad.superfeed.net...[color=blue]
>
>
> hob wrote:
>[color=green][color=darkred]
> > > Even a first year engineering student can tell you how hard braking[/color][/color][/color]
with[color=blue][color=green][color=darkred]
> > > the linkage turned hard over bends (warps) the rotor bell.[/color][/color]
>
> That's just plain silly.[/color]

It is only silly to those without brake engineering experience who assume
transverse forces into the rotor disc are negligible, or who attend pretty
weak schools.

I have designed and built several of the machines that test wheels,
tires, and linkages on motor vehicles for Ford and GM, and I can assure you
that there are forces imparted transversely to the rotor disc when the
linkage is not straight ahead and the brakes are applied.
Hi-speed photos of wheels heeling in hard braking turns show that that
cute little axle shaft holding on the wheel is aided in resisting total
failure by the caliper-and-disk. Looking at an accident where the wheel is
turned off the vehicle centerline axis at impact clearly shows the disk
assembly damage.

The rotor bell on a jeep wrangler is an excellent example for
illustration. Its linkage allows a greater angle off the vehicle axis than
on-road passenger vehicles, and the rotor is mounted off the axis of the
rotor disc. The mounting flange connecting the bell to the axle is
relatively thin material that is expected to deflect enough so as not to
reach the proportional limit.
Notice the size of the hold-down bolts and key-slider of the caliper
relative to the size of the axle and consider the moments imparted into the
axle-caliper-pin-rotor disk loop.
When the caliper is turned sideways to the direction of vehicle travel
and engaged, the momentum and resultant forces are no longer in the plane of
the rotor disk face, but rather across, and they become moments across the
bolts and keys, reacted into the face of the rotor (and across the face of
the disc itself) and the axle.
Hard turns and heavy braking will definitely warp that disk out of plane

The manifestation of transverse load is more pronounced in offset rotor
discs and with off-road where the greater limits lock to lock allow greater.
[color=blue]
>
>[color=green][color=darkred]
> > > (imagine 2 tons moving forward trying to go over a tire turned[/color][/color][/color]
sideways[color=blue][color=green][color=darkred]
> > > with the brake pads locked onto the rotor, a rotor designed for[/color][/color][/color]
transfer[color=blue][color=green]
> > of[color=darkred]
> > > force into floating claipers and transversely into the axle.[/color][/color]
>
> The caliper can move freely from side to side (floating calipers). There
> is no side load at all due to steering.
>[color=green][color=darkred]
> > > Guess how the force gets from the 2 ton moving vehicle mass into the[/color]
> > tire[color=darkred]
> > > tread in a turn-- through the shoes gripping the rotor and back into[/color][/color][/color]
the[color=blue][color=green][color=darkred]
> > > axle - forces across the rotor plane, unlike straight ahead braking,[/color][/color][/color]
where[color=blue][color=green][color=darkred]
> > > the forces are in the rotor plane)[/color][/color]
>
> This is fantasy. The wheel is mounted solid to the axle with the rotor
> sandwiched between.[/color]

You apparently are not familiar with force analysis. Any material receiving
a force deflects, the amount of deflection depending on the geometry, the
input force, and the material.
There is no such thing as "solid" in engineering, there is only relative
deflection.

The wheel is is mounted to the axle through a flexible bolt pattern and
the axle is a small diameter shaft that does deflect. A lot less straight
ahead than when turning.
It particularly deflects when the moment it sees is increased from the
weight and braking dynamic force acting in a plane parallel to the vehicle
axis an inch from the axle shaft mount arm in straight-ahead braking;
increased due to
1) the increased moment due to the wheel turned across the direction of
travel which causes the moment from the tread gripping the road to no longer
be "next to " the mounting plane in the plane of the wheel, but rather
across the plane of the disc: twenty times as great because of the
tread-to-mount distance of a transversely directed
(turned-to-plane-of-travel) force at the tread compared to the tread-to
mount-distance of an axially directed (straight-ahead-travel)force.
and
2) a greater dynamic braking input (greater from the leading turned wheel
getting more of the vehicle-braking dynamic forces from the resultant
moment, similar to the front wheels having more force than the rear in a
straight-shead stop)

Even if the axle would deflect it couldn't possibly[color=blue]
> deflect enough to exceed the side travel of the calipers. If the car is
> sliding sideways the brakes see no load at all because there would be no
> force to turn the wheels.[/color]
[color=blue]
> Heat build up is usually what causes rotors to warp.[/color]

Materials science one - heating steel does not warp steel- it removes
residual stresses of manufacture - annealing, etc. -and makes a more stable
part.

However, it is easier to bend a heated piece of metal than a cool one -
and any forces across the plane of the heated disc are more prone to
deforming the disc.

If you wish to warp a rotor, put in the force when the rotor is heated.
Heating a rotor will only warp it if it has residual stresses from
manufacturing that were not removed before truing.

You don't even[color=blue]
> have to put the rotor on a car just toss it in a fire and it will warp.[/color]

Not if you keep the face-plane vertical.
[color=blue]
> Rust in the ventilation passages can also warp rotors. And frozen
> calipers can also warp rotors - not so much because of uneven force
> loads but uneven heat loads.[/color]

Not because of uneven heat loads per se, but because the calipers wear the
disc face unevenly.
A rotor that has frozen calipers will heat a "high spot" on one side of
the disc, and that high spot is easier to abrade when hot, so indirectly the
heat allowing more wear can contribute - but it is not the heat itself.
[color=blue]
>[color=green][color=darkred]
> > >
> > > Any experienced engineer will tell you that if there is a problem and[/color][/color][/color]
it[color=blue][color=green][color=darkred]
> > > goes way when you replace a part, the problem is gone.
> > > Was the problem the root cause and will it return? Well, if it[/color][/color][/color]
wasn't[color=blue][color=green]
> > part[color=darkred]
> > > of the problem, the problem would still be there in some form.
> > > However, if it is only part of the problem, the problem will later
> > > manifest the same symptoms (E.g, if the driver brakes hard in corners,[/color]
> > part[color=darkred]
> > > of the problem, the rotors will again bend/wear the faces so that in[/color][/color][/color]
time[color=blue][color=green][color=darkred]
> > > the plane of the rotor surfaces are no longer within tolerance, Before[/color][/color][/color]
the[color=blue][color=green][color=darkred]
> > > driver got in and warped the new rotors, the new rotors were just[/color][/color][/color]
fine)[color=blue][color=green][color=darkred]
> > >[/color][/color]
>
>
> This is nonsense. Excessive braking can result in warped rotors, but
> braking on turns has nothing to do with it.
>[/color]

See above. And hard braking during turns is the main cause of passenger
vehicle rotor damage.
[color=blue]
> -jim
>
>[color=green][color=darkred]
> > > ( Logically, when you change the rotor and then the problem goes[/color][/color][/color]
away,[color=blue][color=green]
> > the[color=darkred]
> > > problem is gone.)
> > >
> > > and it seems
> > > > nobody on this planet can really (reliably) tell the difference[/color][/color][/color]
between[color=blue][color=green][color=darkred]
> > > > brake friction materials (because there are no standards whatsoever)
> > > > according to
> > > > [url]http://www.performanceoiltechnology.com/brakingsystems.htm[/url]
> > >
> > >
> > > the man ought to read the specs in the vehicle manuals, which do[/color][/color][/color]
indeed[color=blue][color=green]
> > list[color=darkred]
> > > tolerances for rotors. And he ought to get some in depth background[/color][/color][/color]
first.[color=blue][color=green][color=darkred]
> > > The internet is full of half-aware self-promoters with partially[/color]
> > applied[color=darkred]
> > > theories. And AMSOIL, no less.
> > >
> > > FWIW - match mounting is a way to limit costly close tolerance[/color][/color][/color]
machining[color=blue][color=green]
> > in[color=darkred]
> > > many mating parts- you make hundreds of parts all alike, and then[/color][/color][/color]
measure[color=blue][color=green][color=darkred]
> > > them - some will be way off and get tossed, most will be within[/color][/color][/color]
tolerance[color=blue][color=green][color=darkred]
> > > and used according to their tolerance, and some may even be perfect.[/color][/color][/color]
It's[color=blue][color=green][color=darkred]
> > > cheaper than making each one perfect.
> > >
> > > I'll put this quote from them in here for the experienced engineers to[/color][/color][/color]
get[color=blue][color=green]
> > a[color=darkred]
> > > chcukle
> > >
> > > "DTV is when the rotor thickness is not the same all the way around[/color][/color][/color]
the[color=blue][color=green][color=darkred]
> > > rotor. DTV is typically caused by lateral runout. DTV can only be[/color]
> > measured[color=darkred]
> > > with very specialized laboratory testing equipment or with special on
> > > vehicle capacitance probes."
> > >
> > > right.... ( or like a shop caliper or shop "mic", as noted in the
> > > maintenance manuals.)
> > >
> > > Quote - "This [DTV] phenomenon is what many technicians refer to as
> > > "warping", however they actually think the rotor warped and needs
> > > replacement."
> > >
> > > OK, so what they are saying is that the rotor isn't warped ( and so[/color][/color][/color]
the[color=blue][color=green][color=darkred]
> > > rotor is true?) and the face of the rotor plane has just warped, and[/color][/color][/color]
so[color=blue][color=green]
> > they[color=darkred]
> > > are saying that
> > > instead of the rotor needing replacing because the thickness[/color][/color][/color]
varies,[color=blue][color=green]
> > the[color=darkred]
> > > rotor needs replacing because the thickness varies and the esoteric[/color][/color][/color]
DTV[color=blue][color=green][color=darkred]
> > > measurements are lab things .(or you could just get refacing done at a[/color]
> > brake[color=darkred]
> > > shop, if enough material is left).
> > >
> > > enough of quoting their home-spun humor....
> > >
> > > >
> > > > So, since I have horrible brake-induced wobble in my Toyota 4Runner,[/color][/color][/color]
how[color=blue][color=green][color=darkred]
> > > > DOES anyone buy the right parts given there are no regulations or
> > > > standards to protect us?
> > > >
> > >
> > > There are regulations - Check out the following standards for brake
> > > materials: DE3A, BEEP, NHTSA FMVSS-105
> > >
> > > > We may as well close our eyes and choose randomly for all the lack[/color][/color][/color]
of[color=blue][color=green][color=darkred]
> > > > standards. Which leaves me to my most important question, having to[/color]
> > trust[color=darkred]
> > > > in your judgement and experience (which I don't have).
> > > >
> > > > Where would YOU buy a good quality rotors & pads for a Toyota[/color][/color][/color]
4Runner?[color=blue][color=green][color=darkred]
> > > >
> > >
> > > From Toyota -
> > > why? aftermarket pads have few, if any standards. New-car brake[/color][/color][/color]
pads[color=blue][color=green][color=darkred]
> > > (OEM) have to meet NHTSA standards, and thus actually do stop better,[/color][/color][/color]
are[color=blue][color=green][color=darkred]
> > > more reliable, and the dust around the kids and dogs is less[/color][/color][/color]
hazardous.[color=blue][color=green][color=darkred]
> > >
> > > nuff free stuff
> > >
> > > > Stu
> > >
> > >[/color][/color]
>
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