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Prius Tire Tuning - Page 9

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Posted by bwilson4web on May 22, 2011, 9:22 pm
. . .

It has been more than fun and an example of how to train a troll. Your
profile used to automatically delete postings after a week. Now you've
turned it off so the record remains. This means the nasty crap you
used to post is unlikely to return. Key to ending that bad habit is to
not quote your crap or better still ... 'enhance it.' Regardless, you
are finally taking responsibility and this is a good start.

Straw-men postings were and are simply replied with facts and data.
Instead of going down the rat-hole, use them to bring what the troll
lacks, fact based information . . . a teaching moment. As for arguing
nonsense, again, use each opportunity to bring reality, the facts and
data. So let's go back to Physics 101.

The larger diameter tires increase the polar moment of inertia. This
is the gyroscopic force that tends to hold a rotating mass steady. Sad
to say, the NHW11 steering geometry makes the car all but neutral even
with perfect, four wheel alignment. So increasing the tire diameter
converts the front wheels into more powerful gyroscopes which improves
straight-line tracking.

So the next challenge is to find the largest, 14", low rolling
resistance tire that can fit on an NHW11. That turns out to be the
195/70R14. It also has the lowest revolutions per mile, effectively
increasing the final gear ratio. This pays dividends by letting the
car cruse at faster true speeds while still running in engine cycling,
hybrid mode. But it also increases the moment arm of the wheels.

The larger diameter reduces maximum acceleration. But efficient
driving doesn't use maximum acceleration so this is not missed.
However, there is a risk that the brakes might not be able to keep up.
Fortunately, there is a maximum brake test, engage the ABS.

ABS works by sensing when the wheel is about to stop turning because
the brakes have enough power to lock them up. If the ABS failed to
engage, then the larger diameter tires would have exceeded the braking
power and be unsafe. So one of my first tests was a maximum brake
effort and sure enough the ABS worked.

Measuring stopping distance without having some reference makes no
sense. The Prius is not sold with a stopping distance specification.
Even after replacing the OEM tires, again, there is no standard for
stopping distance since it is really a function of the tires. That the
ABS engages is enough and the National Highway Traffic Safety
Administration said as much in "DOT HS 811 182":

". . . As long as the driver maintains firm pressure on the brake
pedal, ABS will automatically modulate the pressure at the wheels at a
level close to the optimum braking force short of lockup. . . ." (pp.

In fact, here is a stopping distance calculator and tire and wheel
diameter are not part of the inputs:
Only vehicle speed and coefficient of friction are needed. This is
physics 101 and I am more than willing to go through the math behind
this web page.

The ABS is activated by wheel rotation stopping or slowing down, not
the diameter of the tire. As long as the ABS is working, stopping
distance is not brake limited but a simple function of the tire tread,
compound, and road surface ... the coefficient of friction.

See, this how to train a troll. Get them to take responsibility and
always use their nonsense postings for a 'teaching moment.'

Bob Wilson

Posted by Elmo P. Shagnasty on May 23, 2011, 12:21 am
In article

I ask you again:  what "profile" are you talking about?

The record is clear:  you're a wacko.  The record gets clearer every
time you say something.

What "nasty crap" is that, bob?

Ah, you not only announce that you're a wacko, you announce it with
PRIDE.  Facts are yours to twist to your own desire, eh, bob?  "Enhance
it"?  You're not above out-and-out lying, and you've proven that every
time you post.

Tell us again how you don't have to have any data or facts regarding
braking performance on different size tires--that all that matters is
"it brakes fine" and/or "I let the ABS handle it".

You are saying that "it brakes fine" is a suitable substitute for actual
data.  Again, every time you post something, you show what a wacko you

Did you really say that?  Well, of course you did--you're an absolute

Measuring stopping distance of one tire against another is absolutely
meaningful, and it's how the REAL world does things.  But in your
fantasy world, you decide you can do anything you want and declare it to
be real and factual.

You're a wacko.

Yes, the stopping distance is a function of the tires.  And the ABS will
modulate the brake pressure at the wheels at a level close to the
optimum braking force FOR THE TIRE THAT'S INSTALLED--that is, the ABS
will not allow even the slickest and least sticky of tires to lock up.

What will happen is that braking distance will change based on the tire
itself, because as you say "stopping distance is a function of the

So if "stopping distance is a function of the tires" then why don't you
care what affect a different tire would have on stopping distance?  Why
do you put on a different size/model tire and declare it to be
satisfaction simply because "the car stopped"?

That's what this all started with:  your own declaration that you saw no
need to measure braking distance with the different sizes of tires,
simply because you "let the ABS do its thing".  You apparently don't
even know the physics behind all of this, and/or are trying to flummox
the public--who, as you can see with Al Falfa, is full of ignorant
people--into thinking that your fantasy world has any basis in reality.

The NHTSA never said "that the ABS engages is enough".  You created
those words out of thin air, and then had the gall to quote a complete
non sequitur.

ABS most certainly will keep ANY wheel from locking up, because the
purpose of ABS is to maximize braking and control--and that is done
solely by keeping the tire on the edge of locking up, without actually
locking up.

But ABS has nothing to do with braking DISTANCE; as you yourself said,
that's a function of the TIRE.

You don't have a clue, but you sure do like to act as if you do.  And
then you strut around proudly because you've gotten other ignorant
people to follow you, the blind leading the blind.

Posted by bwilson4web on May 23, 2011, 2:01 am

The evidence is in the thread "Prius Power - 112 hours, 8 gallons"
where your silliness has faded in to obscurity . . . except for the
quotes. You are such a tool.

See that it doesn't and we'll all be happy.

Oh so soon, the troll mumbles "wacko" but then that is the way of a

Again, the mark of a sociopath who substitutes personal attack for
facts and data.

Fortunately, physics doesn't care for the claims of sociopath.

So instead of citing some stopping distance, just more ramblings of a

Well it has been a long and nasty road but eventually you are coming
around the how the real world works.

Fortunately Consumer Reports has already quantified Sumitomo T4
stopping using their 1-5 scale: 4/5 - dry pavement.

Exactly! The ABS normalizes any tire to stop as quickly as that tire
is capable.

Again, physics and the natural world don't care about the utter
nonsense of a sociopath.

Amazing, watching a sociopath try to make sense in the natural world.

Actually, it is just the sane dealing with a sociopath, a cornered one
at that. <GRINS>

You are so my bitch.

Bob Wilson

Posted by Elmo P. Shagnasty on May 23, 2011, 10:44 am
 In article

wow, Consumer Reports.  Is THAT the data you use for your pretty charts
and graphs??

And you say it so proudly.

...and from that you declared that there's no difference in braking
distance between tires, AND no need to bother to measure it.

And then when pushed, your idea of measuring it is...a Consumer Reports
rating of the tire from 1 to 5.

This has all been FASCINATING, bob.  It sure puts your pretty charts and
graphs into the proper perspective.

Posted by bwilson4web on May 23, 2011, 12:19 pm

It has and remains a useful exercise. Not only do we get to discuss
Prius tire tuning but also learned about "The Tire Society," a new
source of credible research papers. It is also shows how a troll's
posting can introduce additional technical content. Simply treat their
nonsense with ellipsis and thank them: 'Elmo' is so my bitch.

Based upon tire revs per mile and load, here is how the Sumitomo 14"
tires, all rated at 51 psi maximum sidewall versus the 44 psi, OEM

175/65R14 (OEM) -  902 rev/mile, 1102 lbs:

175/65R14 - 919, 1019 lbs, and smallest of the 14" series, tested
175/70R14 - 886, 1102 lbs, exact match on load, tested
 185/60R14 - 926, 1047 lbs, the highest revs/mile, untested
 185/65R14 - 902, 1124 lbs, closest to an exact match, untested
 185/70R14 - 867, 1201 lbs, untested
 195/60R14 - 907, 1135 lbs, untested
195/70R14 - 849, 1321 lbs, known to fit, likely the largest, tested

Looking at the list, the most interesting testing combination would

185/60R14 (926 revs/mi) vs 195/70R14 (849 revs/mi)

This would allow us to compare and contrast the smallest to largest
diameter tire. We already know the larger diameter tires improve
straight-line handling over the 175/65R14. But I just reviewed the
definition of caster angle:

"The pivot points of the steering are angled such that a line drawn
through them intersects the road surface slightly ahead of the contact
point of the wheel. The purpose of this is to provide a degree of self-
centering for the steering - the wheel casters around so as to trail
behind the axis of steering. This makes a car easier to drive and
improves its directional stability (reducing its tendency to wander).
Excessive caster angle will make the steering heavier and less
responsive, although, in racing, large caster angles are used to
improve camber gain in cornering. . . ." - Wikipedia

One of the effects of a larger diameter is to move the road surface
intersection further in front of the tire contact patch and increases
the effective caster. So in addition to the higher gyroscopic forces,
caster is also increased, a two-for-one advantage.

Given the different revs/mile of the Sumitomo 14" tires, there are
different degrees of handling. For those who want maximum stability,
195/70R14. If one wants a faster responding car, use 185/60R14.

Bob Wilson

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