Prius Tire Tuning

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Old 13 May 2011, 04:36 pm   #1 (permalink)
bwilson4web
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Default Prius Tire Tuning

One of the interesting aspects of a Prius is the effect of different
tire sizes for performance tuning. Recently someone asked 'what is the
largest tire' and 'what are the effects on mileage' so this is what I
shared:

* * *
I have experience with Sumitomo:

175/65R14 (919 revs/mile) - what Toyota service centers sell as
replacement tires. I got 50,000 miles from first set and only an
unrepairable puncture led to their retirement.GPS and mile markers all
confirmed the actual was a little generous and the actual speed a
little lower. But this was taken as the 'stock tire' from Toyota. This
goes a long way to explaining another reason why Prius may be
perceived as being slow ... their speedometers are showing a faster
than true speed.

175/70R14 (886 revs/mile) - this first pair tested revealed a slight
stability improvement on a 750 mile trip to Madison WI and back. I
drove up with the smaller 175/65R14 on front and 175/70R14 on the
back. At Madison, I swapped front and back so the larger 175/70R14 was
on the front and that was when I noticed the slightly improved,
straight-line stability. GPS and mile markers show the speed and MPG
are less than 1% from true. I really think these are the best tire for
the car.

195/70R14 (849 revs/mile) - a pair are now my front tires and the
175/70R14 are the rear. Again, my perception is more stability and
certainly it is not so flighty. However, it indicates ~6% slower speed
than actual (47 mph indicated is 50 mph true) and lower MPG. However,
when I correct for the true MPG, there has been no loss. Best of all,
the true hybrid transition speed has gone from 42 mph to just under 45
mph. This means I keep up with traffic and the engine continues to
shutdown when it can. <grins>

Here is an image of the spreadsheet showing what I was looking for:
http://hiwaay.net/~bzwilson/prius/pri_tire_100.jpg
(GPS and mile marker testing showed the 175/70TR14 brings the
indicated and measured MPG to within 1% of true)

I wanted to find the largest possible tire that could fit on an NHW11
Prius. Of the candidates, the 195/70TR14 was the largest so I bought
one and mounted it to see if it would fit in the rear wheel well ...
it did. I then drove around looking for speed bumps and dips to make
sure it didn't rub ... it worked fine. So I ordered a second one and
put both on the front.

* * *
Now I have to be careful and use my GPS speedometer or always subtract
6% from the indicated to know my true speed. I also have to adjust my
mileage records by 6%. But so far, there has not been a loss of
vehicle MPG other than I catch myself driving a little faster now.
<grins>

The Prius has a threshold speed, 42 mph for the NHW11, that above that
speed, the engine runs all the time. Below that speed, the engine can
shutdown. With the larger tires, I can travel 40 mph with traffic and
the engine will shutdown whenever it can giving better mileage at this
speed. But above 45 mph true, drag rules and the car only gets 52 MPG
at 65 mph which still beats the snot out of gassers and diesels:

http://hiwaay.net/~bzwilson/prius/edmunds_020.jpg

Bob Wilson
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Old 14 May 2011, 11:12 am   #2 (permalink)
Elmo P. Shagnasty
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Default Re: Prius Tire Tuning

In article
<84875d09-c525-4359-b1be-cedf3f75b54e@c1g2000yqe.googlegroups.com>,
bwilson4web <bwilson4web@gmail.com> wrote:

> But above 45 mph true, drag rules and the car only gets 52 MPG
> at 65 mph which still beats the snot out of gassers and diesels:


The Prius is a gasser too, Bob--or have you forgotten that already?
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Old 14 May 2011, 12:58 pm   #3 (permalink)
bwilson4web
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Default Re: Prius Tire Tuning

On May 14, 10:12*am, "Elmo P. Shagnasty" <el...@nastydesigns.com>
wrote:
> In article
> <84875d09-c525-4359-b1be-cedf3f75b...@c1g2000yqe.googlegroups.com>,
>
> *bwilson4web <bwilson4...@gmail.com> wrote:
> > But above 45 mph true, drag rules and the car only gets 52 MPG
> > at 65 mph which still beats the snot out of gassers and diesels:

>
> My boyfriend has left me and my anal herpies has cleared up. Please be mylover.


No Elmo, this is a Prius technical site, not a dating service.

Bob Wilson
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Old 14 May 2011, 02:00 pm   #4 (permalink)
Elmo P. Shagnasty
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Default Re: Prius Tire Tuning

In article
<b4cd65fa-e99e-4dc6-b537-c9e5469c8677@hg8g2000vbb.googlegroups.com>,
bwilson4web <bwilson4web@gmail.com> wrote:

> On May 14, 10:12*am, "Elmo P. Shagnasty" <el...@nastydesigns.com>
> wrote:
> > In article
> > <84875d09-c525-4359-b1be-cedf3f75b...@c1g2000yqe.googlegroups.com>,
> >
> > *bwilson4web <bwilson4...@gmail.com> wrote:
> > > But above 45 mph true, drag rules and the car only gets 52 MPG
> > > at 65 mph which still beats the snot out of gassers and diesels:

> >
> > My boyfriend has left me and my anal herpies has cleared up. Please be my
> > lover.

>
> No Elmo, this is a Prius technical site, not a dating service.
>
> Bob Wilson


hehehehe So Bob *does* lie and make things up in order to try to make
himself look better to the ignorant others in the world.
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Old 14 May 2011, 03:21 pm   #5 (permalink)
bwilson4web
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Default Re: Prius Tire Tuning

On May 14, 1:00*pm, "Elmo P. Shagnasty" <el...@nastydesigns.com>
wrote:
> In article
> <b4cd65fa-e99e-4dc6-b537-c9e5469c8...@hg8g2000vbb.googlegroups.com>,
>
>
>
>
>
> *bwilson4web <bwilson4...@gmail.com> wrote:
> > On May 14, 10:12*am, "Elmo P. Shagnasty" <el...@nastydesigns.com>
> > wrote:
> > > In article
> > > <84875d09-c525-4359-b1be-cedf3f75b...@c1g2000yqe.googlegroups.com>,

>
> > > *bwilson4web <bwilson4...@gmail.com> wrote:
> > > > But above 45 mph true, drag rules and the car only gets 52 MPG
> > > > at 65 mph which still beats the snot out of gassers and diesels:

>
> > > My boyfriend has left me and my anal herpies has cleared up. Please be my
> > > lover.

>
> > No Elmo, this is a Prius technical site, not a dating service.

>
> > Bob Wilson

>
> hehehehe *You've figured me out. I'm so gay.


<SIGH>You really should head over to the alt. sex sites. They will
welcome you with open flys.

Bob Wilson

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Old 14 May 2011, 03:41 pm   #6 (permalink)
Elmo P. Shagnasty
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Default Re: Prius Tire Tuning

In article
<423f0aa6-26b5-4f9c-88bd-ffcf501050e0@w21g2000yqm.googlegroups.com>,
bwilson4web <bwilson4web@gmail.com> wrote:

> On May 14, 1:00*pm, "Elmo P. Shagnasty" <el...@nastydesigns.com>
> wrote:
> > In article
> > <b4cd65fa-e99e-4dc6-b537-c9e5469c8...@hg8g2000vbb.googlegroups.com>,
> >
> >
> >
> >
> >
> > *bwilson4web <bwilson4...@gmail.com> wrote:
> > > On May 14, 10:12*am, "Elmo P. Shagnasty" <el...@nastydesigns.com>
> > > wrote:
> > > > In article
> > > > <84875d09-c525-4359-b1be-cedf3f75b...@c1g2000yqe.googlegroups.com>,

> >
> > > > *bwilson4web <bwilson4...@gmail.com> wrote:
> > > > > But above 45 mph true, drag rules and the car only gets 52 MPG
> > > > > at 65 mph which still beats the snot out of gassers and diesels:

> >
> > > > My boyfriend has left me and my anal herpies has cleared up. Please be
> > > > my
> > > > lover.

> >
> > > No Elmo, this is a Prius technical site, not a dating service.

> >
> > > Bob Wilson

> >
> > hehehehe *You've figured me out. I'm so gay.

>
> <SIGH>You really should head over to the alt. sex sites. They will
> welcome you with open flys.
>
> Bob Wilson


What's that I said, Bob?
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Old 14 May 2011, 05:53 pm   #7 (permalink)
bwilson4web
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Default Re: Prius Tire Tuning

On May 14, 2:41*pm, "Elmo P. Shagnasty" <el...@nastydesigns.com>
wrote:
> In article

.. . .
>
> What's that I said, Bob?


Well I'm so glad you asked. We were discussing Prius tire tuning ...
matching the right tire side for optimum performance. To summarize:

o too small - the speedometer indicates higher than true which results
in slow speeds that reduce drag and improve actual MPG. However, it
also leads Prius drivers to being slower than other traffic and
inflates the indicated MPG. It is also associated with 'skitterish'
handling as it needs more driver attention.

o just right - the speedometer is right on as is the indicated MPG.
Slightly larger diameter leads to more straight-line stability.

o oversized - the speedometer indicates lower than true speed which
can result in more drag and a loss of true MPG. Also, the indicated
MPG is lower. However, straight-line stability and handling is
improved.

Thanks for the question, I needed a reason to summarize the thread,
Bob Wilson
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Old 15 May 2011, 07:59 am   #8 (permalink)
Neo
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Default Re: Prius Tire Tuning

On May 13, 4:36*pm, bwilson4web <bwilson4...@gmail.com> wrote:
> One of the interesting aspects of a Prius is the effect of different
> tire sizes for performance tuning. Recently someone asked 'what is the
> largest tire' and 'what are the effects on mileage' so this is what I
> shared:
>
> * * *
> I have experience with Sumitomo:
>
> 175/65R14 (919 revs/mile) - what Toyota service centers sell as
> replacement tires. I got 50,000 miles from first set and only an
> unrepairable puncture led to their retirement.GPS and mile markers all
> confirmed the actual was a little generous and the actual speed a
> little lower. But this was taken as the 'stock tire' from Toyota. This
> goes a long way to explaining another reason why Prius may be
> perceived as being slow ... their speedometers are showing a faster
> than true speed.
>
> 175/70R14 (886 revs/mile) - this first pair tested revealed a slight
> stability improvement on a 750 mile trip to Madison WI and back. I
> drove up with the smaller 175/65R14 on front and 175/70R14 on the
> back. At Madison, I swapped front and back so the larger 175/70R14 was
> on the front and that was when I noticed the slightly improved,
> straight-line stability. GPS and mile markers show the speed and MPG
> are less than 1% from true. I really think these are the best tire for
> the car.
>
> 195/70R14 (849 revs/mile) - a pair are now my front tires and the
> 175/70R14 are the rear. Again, my perception is more stability and
> certainly it is not so flighty. However, it indicates ~6% slower speed
> than actual (47 mph indicated is 50 mph true) and lower MPG. However,
> when I correct for the true MPG, there has been no loss. Best of all,
> the true hybrid transition speed has gone from 42 mph to just under 45
> mph. This means I keep up with traffic and the engine continues to
> shutdown when it can. <grins>
>
> Here is an image of the spreadsheet showing what I was looking for:http://hiwaay.net/~bzwilson/prius/pri_tire_100.jpg
> (GPS and mile marker testing showed the 175/70TR14 brings the
> indicated and measured MPG to within 1% of true)
>
> I wanted to find the largest possible tire that could fit on an NHW11
> Prius. Of the candidates, the 195/70TR14 was the largest so I bought
> one and mounted it to see if it would fit in the rear wheel well ...
> it did. I then drove around looking for speed bumps and dips to make
> sure it didn't rub ... it worked fine. So I ordered a second one and
> put both on the front.
>
> * * *
> Now I have to be careful and use my GPS speedometer or always subtract
> 6% from the indicated to know my true speed. I also have to adjust my
> mileage records by 6%. But so far, there has not been a loss of
> vehicle MPG other than I catch myself driving a little faster now.
> <grins>
>
> The Prius has a threshold speed, 42 mph for the NHW11, that above that
> speed, the engine runs all the time. Below that speed, the engine can
> shutdown. With the larger tires, I can travel 40 mph with traffic and
> the engine will shutdown whenever it can giving better mileage at this
> speed. But above 45 mph true, drag rules and the car only gets 52 MPG
> at 65 mph which still beats the snot out of gassers and diesels:
>
> http://hiwaay.net/~bzwilson/prius/edmunds_020.jpg
>
> Bob Wilson



Did you ever measure how the tire
sizes might effect the braking distance?

While I would suspect that the 195/70R14
would provide better traction which
would translate to better stability and
braking performance - how much better
might one expect?


It sounds like that these bigger tires
are fooling the ECU (which is still thinking
the prius is using the smaller tire size) to
allowing for a slightly higher velocity at
which the Prius changes from all electric
to electric and gas. If I recall correctly
that hybrid transition speed where the Prius
goes from all electric mode to running both
the electric motor and the ICE was to protect
the ICE from damage. While extending the
top speed for a Super Highway Mode Cycle
sound great - I am wondering if there are
any risk . While I suspect that Toyota has
probably engineered enough tolerance to
allow for your slight increase in speed -
I would suspect that going signficantly
higher may damage the ICE.



Walter Lee
2010 Toyota Prius III, Blue Ribbon/Dk Grey, OEM floormats
Yokohama Avid S33 (psi 48/44)
Scangauge II ( AVG, RPM, GPH, SoC)
no grill blocking

Dc/md/nova metro area hypermiler on training wheels
odeo 11800 miles, overall 58.7 mpg
last tank 4/19/2011, 598 miles of hilly urban/suburban, 9 gallons e10
87 oct regular, estimage FE=66 mpg

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Old 15 May 2011, 01:09 pm   #9 (permalink)
bwilson4web
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Default Re: Prius Tire Tuning

.. . .
>
> Did you ever measure how the tire
> sizes might effect the braking distance?


Not yet since I'm trusting the ABS to moderate the braking force. My
understanding is the ABS releases braking force when the wheel begins
to stop, keeping it in the peak braking force region, and this is
independent of the tire diameter.

> While I would suspect that the 195/70R14
> would provide better traction which
> would translate to better stability and
> braking *performance - how much better
> might one expect?


This is a hard problem as I don't have a good metric nor know of any,
the units of stability. Pretty much universal, the automotive
magazines and even TireRack use driver impressions. But two approaches
come to mind:

1) monitor the electric steering adjustment voltages over a straight-
line course
2) monitor the horizontal accelerations over a straight-line course

We still have a problem with absence of a known impulse that would
require a steering adjustment. Perhaps a vertical air foil that
oscillates between +5 and -5 angle of attack. Each transition would
move a force from one side to the other, a well defined force
application, and then the vehicle and steering response could be
measured.

> It sounds like that these bigger tires
> are fooling the ECU (which is still thinking
> the prius is using the smaller tire size) to
> allowing for a slightly higher velocity at
> which the Prius changes from all electric
> to electric and gas. *If I recall correctly
> that hybrid transition speed where the Prius
> goes from all electric mode to running both
> the electric motor and the ICE was to protect
> the ICE from damage. While extending the
> top speed for a Super Highway Mode Cycle
> sound great - I am wondering if there are
> any risk .


I thought about this before the experiment and came up with these
states:

acceleration - the amount of torque is engine and transmission limited
so I'm expecting slower, maximum acceleration. But I don't do hard
accelerations except when benchmarking the car. I just don't have
frequent requirements for maximum acceleration and the NHW11 at 13
seconds to reach 60 mph, is more like a truck than a sports car.

hill climb - the torque needed to climb even an 8% grade at 55 mph is
well within the capabilities of the existing car. I've done maximum
speed hill climbs and topped at 85 mph so I don't see a risk.

regenerative braking - will have a maximum reverse torque and the
larger diameter tire may lead to more mechanical braking. However, I
drive so as to minimize regenerative braking so no impact is expected.

> . . . While I suspect that Toyota has
> probably engineered enough tolerance to
> allow for your slight increase *in speed -
> I would suspect that going signficantly
> higher may damage the ICE.


What we've done is made the last gear, the tires, taller.

> Walter Lee
> 2010 Toyota Prius III, Blue Ribbon/Dk Grey, OEM floormats
> Yokohama Avid S33 (psi 48/44)
> Scangauge II ( AVG, RPM, GPH, SoC)
> no grill blocking
>
> Dc/md/nova metro area hypermiler on training wheels
> odeo 11800 miles, overall 58.7 mpg
> last tank 4/19/2011, 598 miles of hilly urban/suburban, 9 gallons e10
> 87 oct regular, estimage FE=66 mpg


I've only been testing these tires on our 2003 Prius. We have a 2010
Prius but while it remains on warranty, I'm keeping the new Prius
stock with one exception. I've started a 5K, 15K, 30K, and 60k,
transaxle oil change and test plan. I want to measure transaxle wear
over time and make sure I know the change interval based upon metrics.

Bob Wilson

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Old 15 May 2011, 01:49 pm   #10 (permalink)
Elmo P. Shagnasty
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Default Re: Prius Tire Tuning

In article
<223dc403-7573-4743-8878-c45038d2fe64@cu4g2000vbb.googlegroups.com>,
bwilson4web <bwilson4web@gmail.com> wrote:

> > Did you ever measure how the tire
> > sizes might effect the braking distance?

>
> Not yet since I'm trusting the ABS to moderate the braking force.


Ohmigod, did you really SAY that? That's a TOTAL non-sequitur.

The sole purpose of the ABS is to allow the tires to perform at their
maximum grip for the circumstances.

The purpose of the ABS is NOT to affect braking distance.

You alter the tire size but choose not to measure the car's performance
at the different tire sizes because....you're "trusting the ABS to
moderate the braking force"? As if that has anything at all to do with
measuring the braking distance?

Your pretty charts and graphs are all ****ed up, because you don't have
a clue what you're doing.
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