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Prius Tire Tuning - Page 15

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Posted by Daniel who wants to know on May 15, 2011, 7:06 pm

It has nothing to do with damaging the ICE, it has everything to do with
damaging the transaxle, though.  The lubricating oil/fluid pump for the
transaxle on NHW11 and NHW20 is driven by a shaft that extends from the
planet gear carrier of the PSD, through the center of MG2, to the pump which
is in the MG2 side cover just inside the driver's side wheel well (on LH
drive cars)  Since the PSD planet carrier is driven only by the  ICE, any
time it is off the trans is essentially unlubricated and relies on the
residual oil film in the bearings to keep it from self destructing.

Also for NHW11 and NHW20 there is no such thing as a speed where it
transitions from just electric to electric and gas, because the speed for
the transition cam be anywhere between 0 and the top speed of 105MPH
depending on throttle pedal position. If you hammer the throttle from a dead
stop it starts immediately, if you were to put it in drive and roll down a
mountain road without touching the pedal it might never burn a single drop.

What does always happen is that at 42MPH indicated the engine crank begins
to turn, even if it isn't burning any fuel, AKA the car transitions from
"stealth" mode to "warp stealth" mode.

Posted by bwilson4web on May 15, 2011, 7:41 pm
Hi Daniel,

. . .

Increasing the tire diameter doesn't change the ratio of ICE ON/OFF as
much as it lets the car slip down the road a little further ...
roughly in proportion to the decrease in wheel rotations.

The "42MPH indicated" remains the same but now the car is traveling at
45 mph true. <grins>

If we operated our Prius at the max in all cases, then the tire
diameter change would impact the limits. Fortunately, that isn't how I
drive. After all, getting 52 MPG in a 2003 Prius is not achieved by
running at the vehicle limits.

Bob Wilson

Posted by Neo on May 22, 2011, 2:30 pm
Thanks for the explanation.
This is still very new to me. (9_9)

Posted by bwilson4web on May 27, 2011, 5:22 pm
I was checking something else out and was amused to find this thread
over at PriusChat.com:

Several NHW11 owners noticing how the car has almost neutral
stability, 'wanders'.

Bob Wilson

Posted by News on May 27, 2011, 6:13 pm
 On 5/27/2011 1:22 PM, bwilson4web wrote:


There are many more like that, so much so that aftermarket strut brace
and flex plate/crossmember upgrades are available to stiffen the suspension.

Other than your earlier post, I've never seen mention of neutering the
problem via front-rear tire width differential or stagger.

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