Re: Cities Turning to Bicycles
Frank Krygowski wrote:
> Nate Nagel wrote:
>> Frank Krygowski wrote:
>>> Nate Nagel wrote:
>>>> Frank Krygowski wrote:
>>>>> If a person were to apply _real_ reading comprehension to your
>>>>> paragraph, they'd note that you never actually said what that car's
>>>>> headlights were, other than "not stock." Now are you seriously
>>>>> claiming that they gave you adequate visibility on a rural two-lane
>>>>> road at 75+ mph? Unless you'd hung driving lights all over the
>>>>> front end, I find that highly doubtful.
>>>> No, just everyday high-output halogens from the parts store, with a
>>>> properly maintained electrical system. It's not rocket science.
>> Just took a closer look at that site. There are some more glaring
>> (heh) errors in the assumptions they've made.
>> 1) the distances calculated for "reaction time" are based on a
>> reaction time of 1.5 seconds. If it takes you 1.5 seconds to
>> recognize a hazard and react to it, it's probably time for a motorized
>> 2) There's no mention at all of what headlights were used to calculate
>> the visible distance numbers, and as I and other posters have pointed
>> out, they were all based on some generic "low beam" headlight.
>> Obviously when one's driving at night on a mostly deserted road, one
>> is using high beams unless there's oncoming traffic or you are
>> approaching or being passed by traffic in the same direction.
>> 3) The site also assumes a coefficient of friction of 1.0 which is
>> fairly optimistic, about the only way that's achieved with normal
>> tires is on dry, clean asphalt. Granted, asphalt is becoming more and
>> more prevalent, but there are still a few concrete-paved highways left.
>> 4) "deceleration" is listed as 17.02 ft/s^2. What the heck? If the
>> coefficient of friction is 1.0, the deceleration of the vehicle should
>> be appx. 32 ft/s^2. sounds like a "rectal number" to me, and what's
>> worse, it's given four significant digits, implying a precision that
>> isn't there - deceleration can and indeed does vary even over the
>> course of one braking maneuver due to weight transfer and the fact
>> that a typical tire/road interface does not have a constant mu when
>> load varies greatly (and, of course, it changes with the degree of
>> slip of the tire vs. the road as well, but I'm assuming that we're
>> talking about a panic stop sith a skilled driver here, so only 5-10%
>> slip not 100% as in a locked wheel stop.)
> If you want to delve deeply into the psychology and physics, we can do
> it. But self-proclaimed "skilled drivers" are seldom as fast in
> reaction as they pretend. Unanticipated events take quite a while to
> The coefficient of friction = 1 is high no doubt; , and as is obvious
> from elementary physics, they're not basing the deceleration on that
so what are they basing it on then? Certainly not real world stopping
distances - they are way long. Check the back of any car mag for their
summary of the last couple years' road tests.
> But to get back to reality: Imagine your bias-ply tires after
> the first 100 feet of a panic stop from 75+ mph. The rubber temperature
> would be WAY up - in fact, you'd have left large amounts on the road -
> so the coefficient of friction has dropped tremendously.
a) I (why am I saying "I"? I wasn't driving, but you're completely
ignoring that fact) wouldn't have left "large amounts of rubber on the
road" - the best decel is usually found at maybe 5-10% slip, to leave
"large amounts of rubber" I would have to have locked the brakes up
b) You obviously know exactly squat about tires, as even if I did manage
to get the rubber temperature "WAY up" - that would be a GOOD THING.
The coefficient of friction does not "drop tremendously" with increased
temperature, it actually goes UP. If I'm wrong, you better tell all
those drag racers that they're just wasting fuel and tire rubber doing
all those long, smoky burnouts - they ought to be able to accelerate
faster if they just stage and go. The only detrimental effects of heat
in tires are shorter tread life, increased risk of a blowout if too-high
temperatures are maintained for a long period of time, and the risk of
"blistering" the tread. Reduced traction is generally not a problem.
> You don't know
> the road surface
No, *you* don't. I was there.
> - you may be trying to brake on a surface lubricated by
> road apples, further reducing "mu". Your car's weight is biased far
> forward, the rear is jacking up, and (correct me if I'm wrong) that
> Studebaker had no brake proportioning valve, so your rear brakes are
> likely locking.
You mean a major automotive mfgr. deliberately released a defective
product? Well, that's happened a few times before, but not in this
case. You're actually partly right - there's no prop valve, but they
did compensate for the increased line pressure required to activate the
front discs by fitting non-self-energizing drums in the rear as opposed
to the normal self-energizing type, and then making a power booster
standard equipment to reduce pedal effort, which would otherwise have
been high. As usual, if you overdo it with the brake pedal, the fronts
will still lock first.
> That means you're losing attitude control, and the rear
> has begun swinging around. The road has a camber (as do essentially all
> two-lanes) so you're drifting right.
Only if you've locked up any wheels.
> The only way to regain control is
> to reduce the deceleration rate, either by easing off the pedal or by
> rapidly pumping the brake. You're now trying to find that precise
> boundary between kinetic and static friction - which you haven't
> practiced in this car,
I wasn't driving. The driver has been driving Studes since they were
still in production.
> and which wouldn't help if you had, because the
> tire tread is now nearly molten,
again, were that possible, that would be a Good Thing
> and the hot rear drum brakes are
> behaving erratically.
That's the first almost-factual thing you've said in this post. The
real limiting factor in a panic stop, other than the tires, is the
temperature of the brake components. However, hot brakes don't "behave
erratically" - once they get above their optimum temperature, they just
don't work as well, commonly known as "brake fade." However,
contemporary road tests of similar vehicles are full of phrases like "no
perceptible brake fade in repeated stops from 80 MPH" etc. etc. etc. and
my own experiences driving these cars bear that out (not that I drive in
such a manner as to have required repeated hard stops from any
significant speed; but neither have I noticed any shortcomings with any
Stude braking system, disc or drum.)
> And to make matters worse, you've just peed your
> pants. If you do stop in time, you've got a mess to clean up.
> And that's how messy real life is, compared to the fantasies of boy
Again, you mean the 65 year old guy that was driving? The guy who owned
the car, and had a significant financial investment in it?
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