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Prius Tire Tuning - Page 3

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Posted by bwilson4web on May 15, 2011, 7:22 pm

Poor baby, stepped into it again, I see. You are such my bitch.

The ABS prevent the wheels from locking up which helps them achieve
maximum braking and avoids loss of control. Quite effective, the tires
are working fine and no problem braking. So this is what the NHTSA
published in DOT HS 808 206, December 1994:

"The fundamental safety problem addressed by ABS is that few drivers
are able to optimize the pressure they apply on the brake pedal, given
a sudden emergency situation or unexpectedly slippery surface. When
excessive pedal pressure locks the wheels, the vehicle can yaw out of
the driver's control (rear-wheel lockup), or go straight ahead,
impossible to steer (front-wheel lockup). On most, but not all, road
surfaces, a skidding vehicle needs a longer distance to stop than a
vehicle with the brakes applied and wheels still rolling. The
objective of ABS is to take over the optimization task from the
driver. A four-wheel system is intended to keep all the wheels rolling
during panic braking, to prevent yawing, to allow steering throughout
the emergency and, on many surfaces, to shorten the stopping distance.
The combination of efficient stopping and steering is intended to help
the driver avoid mobile and fixed obstacles. . . ."

The ABS works just fine, tested, with the larger diameter tires and
there is no apparent change in stopping distance. In fact the NHTSA
has a number of reports on ABS and stopping distance:

DOT HS 808 875, "NHTSA Light Vehicle Antilock Brake System Research
Program Task 4: A Test Track Study of Light Vehicle ABS Performance
Over a Broad Range of Surfaces and Maneuvers." which states:

"This study found that for most stopping maneuvers on most surfaces,
ABS-assisted full pedall brake applications stops were shorter than
those made with the ABS disabled. The one systematic exception was on
loose gravel ..." well I don't drive on loose gravel so no problem.

Then there is the SAE 1999-01-1287 "A Comprehensive Light Vehicle
Antilock Brake System Test Track Performance Evaluation"

"For most stopping maneuvers, made on most test surfaces, ABS-assisted
panic stops were found to be shorter than those made with best effort
or full pedal applications with the ABS disabled. . . ."

Except for your lying, fake outrage,  blow it out your ass troll. The
ABS works perfectly fine and the car braking is as before, no change.
"Such a moroon" - Bugs Bunny

Bob Wilson

Posted by Elmo P. Shagnasty on May 17, 2011, 9:04 pm
In article

<snort> SURE, bob.  SURE.

So far so good.

So what does any of that have to do with braking distance?

You were asked, quite directly:  "did you ever measure how the tire
sizes might effect the braking distance?"  And your answer was, as
quoted above:  "Not yet since I'm trusting the ABS to moderate the
braking force."

You have yet to provide any connection between your willingness or
ability to measure braking distance and the fact that ABS is functioning.

Of course, there's a reason for that:  there's no connection between the
two.  You just spouted random words that didn't answer the question at

Why was that, Bob?  Was it because you don't want to answer the question?

Posted by bwilson4web on May 19, 2011, 12:50 pm

Yesterday, we had one of those stop sign controlled incidents where
the car on the right assumed I also had a stop sign but I had a yield,
the right of way. So they started to pull in front of me. I mashed the
brake and felt the reassuring, ABS buzz as the car stopped with a lot
of space to spare. Excellent braking!

Testing done and passed! <GRINS>

The physics remains the same. The tire foot print is the same as all
Sumitomo tires are at 51 psi and kept there. They are all T4 style so
the tread patterns are identical. Best of all, ABS braking keeps each
tire right at edge of maximum braking based upon rpm changes which is
independent of diameter and the car remains fully in control.
Yesterday's test was just like all earlier, emergency braking
incidents, no drama, rapid stopping.

So Elmo, where is your report showing that tire diameter has any
effect on stopping distance?

You don't have any, our fool tool.

Bob Wilson

Posted by News on May 19, 2011, 1:07 pm
 On 5/19/2011 8:50 AM, bwilson4web wrote:

REFERENCE: J.W. Daws, “Technical Considerations for Plus Sizing,”
submitted for presentation at the 2008 International Tire Exhibition and
Conference, September 16-18, 2008, Akron, OH

"General Motors Corporation stated in a recent publication [“Plus-sized
Problem?”, Tire Business, July 19, 2004] that wheels used for their
upgrade packages have the “same mass, same offset, same width, same
mounting flange, same tire pressure monitoring requirements, same brake
clearance, [and] same dimensional tolerances” as the original equipment
wheels. Implicit in this tight specification are the impacts of the
plus-sized fitment on anti-lock brake systems, electronic stability
control systems, and so on. Obviously, a wheel with the same mass at a
larger OD has a larger rotational inertia than the OE wheel. Generally,
as wheel diameter increases, the mass of the tire and wheel for equal
load capacity generally increases, as does the inertia of the rotating
system. This change in unsprung weight may affect the response of the
suspension system. The change in rotational inertia may affect the
response of systems like antilock braking and electronic stability
control. Tire pressure monitoring based on antilock brake sensors may
also be affected by changes in tire size and vertical stiffness. At this
time, there is a significant lack of public domain data available to
assess these effects."

Posted by bwilson4web on May 19, 2011, 5:17 pm

I found the paper and am reading it now. But I'm struck by this

". . . conventional wisdom usually suggests that any difference should
be within +/- 3% of the original equipment tire . . ."

Based upon tire revs per mile, here is how the tires rate versus the
OEM tire, 902 rev/mile, 1102 lbs:

175/65R14 - 919  -1.9%, 1019 lbs
175/70R14 - 886  +1.8%, 1102 lbs
195/70R14 - 849  +5.9%, 1321 lbs

Per "conventional wisdom," the first two tires straddle the OEM tire.
The 195/70R14 is oversized but the rest of the article discusses
stability testing. I'll have to read it closely to see what their test
articles were doing and compare it to the Sumitomos.

One good thing is the 195/70R14 is the largest tire that can fit on
the NHW11 Prius. There is one I skipped over:

185/70R14 - 867 +3.9%, 1201 lbs

If someone is concerned about the 195/70R14, the next size down,
185/70R14 would work too.

BTW, thanks for the reference to "The Tire Society." I wasn't aware of
them and they look to be serious people.

Bob Wilson

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