tire pressure

I don't know about your first queston. For tire pressure, I like to go over the recommended, but I try to find a good balance between ride quality and efficiency. Still want good emergency handling and braking performance at the pressures you end up running.

In my 2009 I went 4 PSI over all around, but didn't like it above that. Too stiff and bumpy.

Just a thought, but over time you can use a tread depth gage to see how the wear is coming along across the tire. Gages are cheap.

I bought a 1 gallon air compressor for garage, but not much air storage. I can put a few pounds in maybe 2 tires, then have to plug in again.

 

I am not sure about the TPMS in the Prius v, the other two Prius versions just have a warning light indicating one of the four tires is low. The v will almost certainly be the same. I understand that the individual wheel sensors do report actual pressure back to the control unit but we have no way to access that data.

Interesting question about increased mpg with increased pressure. I am pretty sure mpg does increase all the way from the Toyota suggested pressure up to the max on the sidewall, but I haven't done enough tests to know for sure if the increase is linear or not. I suspect from my own observations it is not linear. I think you get a bigger jump in mileage from say 35 up to 40 psi than you do from 40 to 45. Others may be able to add their observations.

I usually try to find a compromise between ride and mileage and use a tread depth gage as Cycledrum mentioned. My gen3 Prius OEM tires, which I normally inflated to somwhere between 42 to 48 psi for the 42000 miles I used them, were worn a little more on the outside of the tread than in the center. I have observed the same type of wear on other vehicles I have owned as well. I think with good quality radial tires with good stiff belts the center will not wear faster in the center even with maximum pressure. On my tires, probably due to the roads I drive on, the outside and to a lesser degree the inside tread wears a little faster due to cornering forces.

 

yeah, the v is the same, no individual pressure display that I've found yet (there's undoubtedly some lights on/lights off/lock/unlock/rub tummy/pat head combination that gets you access to a display, there always is

After setting to a higher pressure, be sure to re-initialize the TPMS so that it alerts on a drop from that pressure rather than from the lower standard pressure. The instructions for initialization are in the owner's manual.

Peter+

 

If the roads are rough or wet, over inflating the tires to
the maximum sidewall tire pressure will give you a bumpy
ride and there's not likely to be any MPG gain. If the main road
conditions are poor, then the tires benefit from a lower
pressure setting which allow for more tire deformity-flexibility.
Hence for poor road conditions, tire pressure should not be
any higher than 5 psi over the recommended psi on the inside
of the door panel but no less than the recommended psi.

If the roads are smooth and dry, over inflating the tires to
the maximum sidewall tire pressure can increase the maximum
MPG that can be achieved (summertime MPG ) by 10%
if you drive gently but normally OR up to about 30% if
the Prius is aggressively hypermiled.

For example, in the summer, a 2010 Prius type III using
10% ethanol blend gasoline with its tire pressure set
to 44/42 psi - if accelerated gently, allowed to coast
to a stop most of the time, driven on a trip of
+60 minutes, and driven over a very smooth and dry
asphalt road then should get between 55mpg to 63 mpg.
The same car with the tire pressure set to 35/33psi
and driven the same way will get from 50mpg to 55mpg.
The same car with the tire pressure set to 50/48 psi
and driven in the same fashion will most of the time
get about 63mpg to 73 mpg. If the Prius burns 100%
gasoline instead of 10% ethanol blend gasoline (E10)
the MPGs go up 10% higher. If the Prius is driven
in below 40F temperatures its MPG can drops as much
as 20%.

hope this helps

Walter Lee
(Cleanmpg.com mileage log "HyperDrive 1")
2010 Prius Type 3,Blue Ribbon/Dk Grey, oem floormats
Yokohama avid S33
(front tire pressure =50psi, rear tire pressure =48 psi)
ScangaugeII (FwT, GPH, RPM, SoC)
100% grill blocking
Odeometer = 16500 miles, overall 60.5mpg
last tank 67.5 mpg/692miles/10.2gallons 87oct E10/Oct 22 2011
best tank 70.9 mpg/727miles/10.2gallons 87oct E10/Sep 29 2011
worst tank 52.3mpg/428miles/08.2gallons 87oct E10/Dec 27 2010

 

Nitrogen if it's "free", regular air if it's "free". As in it isn't worth even a $1 to pay for nitrogen in your tires.

 

If someone wants to put 100% nitrogen in your tires for free let them, it won't hurt. Otherwise use the stuff we breath it's 78% N2 anyway.

 

Great info (and by the way Blue Ribbon is my favorite Prius paint color) but I'm trying to make it more readable

one minor assumption is that those are the OEM tires which are S33D not S33. If so they have a sidewall max of 44 PSI and they are LRR tires.

I'd sum it up as

fwiw I drive my Gen II close to your 50/48 example (I do a 3 PSI differential front to back at that high of a PSI) and my tires (Avid ENVigor) have higher rolling resistance and I see numbers closer to your 44/42 psi example even though I'm running 50/47.

Though maybe that is because my trip length is only 15 miles so I'm not getting the full benefit of long range driving.

* I think of it as the northeast corridor but the big W calls it the "Northeast megalopolis".

 

I suggest that you just use regular air.

Instead spend your money on a
high quality tire pressure gauge from
the local auto/tire shop so you could check your tire pressure
yourself ( just to verify that's everything is okay)

If you are a DIY kind of person then a 12VDC or mechanical
tire air pump is a good investment. I've got a inexpensive
mechanical air pump from harbor frieght - its a real workout
just to keep my tires at the correct pressure....

If you want to spend even more $$$$ to get better MPGs

1) ScangaugeII - this is only worth it if you want to
hypermile or if you want to do grill blocking.

2) engine block heater - if you have a garage/electric
outlet and are motivated enough to preheat your
engine 2 to 4 hours before you drive it - it can
do wonders at raising your MPG when the temps
drop below 40F

3. LRR tires - getting premium low rolling resistant tires
will set you back a pretty penny...


hope this helps

Walter

 

Yes I'm using OEM Yokohama Avid S33(D) Tires

I'm still learning how to hypermile...
I'm not an expert like Wayne Gerdes...
but I'm truly focus on hypermiling the 3rd gen Prius
and getting the best fuel efficiency I can
for the first 24 months.


it's really important to understand the MPG I posted were achieve at temperatures above 65F on smooth dry asphalt roads. If the roads are rough or wet or icy - the higher tire pressures will not only NOT achieve hi MPG --the extra rigidity will decrease the tire's road surface traction making the Prius harder to control. I'm going to drope lower my tire pressure from 50/48 -> 44/42 this week to increase my traction for November just in anticipation of more wet weather. If necessary I might lower the tire pressure again in December from 44/42 --> 40/38 - ( I'm still experimenting with tire pressure so I'm not sure where this all is going to take me)

hope this helps

Walter Lee
2010 Toyota Prius 3, Blue Ribbon/Dark Grey
Yokohama Avid S33D (50/48)

 

When a thin layer of water on the road causes a risk of hydroplaning, higher pressure reduces the risk. Or more accurately, higher tire pressure raises the speed at which hydroplaning begins.

Several past threads have pointers to NASA and other aviation articles about this.

 

Definitely something for the people with OEM tires to keep in mind.

Myself I'm running Avid Envigor tires which have much better traction than OEM tires so I'm willing to run higher PSI even under wet conditions. As to Icy I expect that takes care of itself due to air temperature lowering pressure.

I believe the rule of thumb is 10F drop in temp = 1 PSI drop in pressure.

I check my tire pressure in a garage as close to 70 degrees as possible (warmer in summer, cooler in winter), the pressure drops or rises with temp during use, all that matters is setting it in a reasonable range when the car has been sitting for several hours.

The PSI I choose from is:

50/47 high (short trips or warm winters)
48/45 med (long trips or summer use)
45/42 low (winter below freezing)

But I have 51 PSI sidewall max tires. If I had 44 PSI I'd probably make that

45/42 high
42/40 med
40/38 low

As to snow/ice, I figure between high traction aftermarket tires, ABS, traction control, and the natural PSI drop due to temps my PSI in a rare snowstorm wouldn't be a problem.

 

At maximum sidewall tire pressure, tires tend to give
their best performance with respect to hydroplaning
from what I understand - but my experience and reports
that I've read indicate that going over the maximum
sidewall tire pressure (which is what I have my tire
set at currently) can decrease the speed at which
hydroplaning occurs(lower tire road traction).

In the early part of the Winter of 2010, I had to make an
emergency stop from 35 mph to 0 mph on a curved banked
downhill grade of about 10 degrees (on a wet asphalt road) .
For less than 1/2 second - I felt a loss of road traction (the
antilock brakes kicked in and performed extremely well)
on my Yokohama Avid S33 which at that time was set
to 50psi/48 psi ( note: the max sidewall for Yokohama
Avid S33 tires is 44psi ). After that incident, I lowered
the tire pressures down to 40psi/38 psi - which still gave
reasonable good coasting performance during that
winter ( that winter I got about 53 mpg). I'm not too
sure if this setting was too low but I know that going
back under the max side wall tire pressue gave better
road traction than going over the max side wall.
Going over the max sidewall tire pressure is yet another
hypermiling trick that I am experimenting with. I don't
want to give the impression that raising the tire pressure
is some kind of freebie which can raise your fuel efficiency
without any effort at all - there is a sort of quid pro quo
to all this...there is a kind of equal exchange -
for everything you get you must give something back
of equal value.

However because it's winter time - I'm also with concerned
about ice, snow, sand, and road slush. These are solid
road irregularities rather than liquid - so its not hydroplaning
but the impact of solid road irregularities on road traction
and fuel efficiency. Early summer of 2011, a section of my
commute route was resurfaced. For over a month, that
section of the asphalt road was grooved (made rough and
uneven by having wavy trenches mechanically dug into
the road surface -sort of like the rumble strips that are put
between a super highway lane and the shoulder of the super
highway). The Prius ability to glide on this section of
the road dropped signficantly and fuel efficency
dropped too even with my tires set to 50psi/48psi.
It was only when the road was finally resurfaced that my MPG
went back to up for this section of the road. So I'm
pretty sure that the smoothness of the road counts - just
how much I'm not sure.

hope this helps

Walter Lee
(mileage log on Cleanmpg.com under "HyperDrive 1" )
2010 Toyota Prius Type3, Blue Ribbon/Dark Grey,oem floormats
Yokohama Avid S33(D) - currently set to 50psi/48psi
ScangaugeII (FwT, SoC, GPH, RPM)
100% grill blocking
Odeometer +16750, 60 mpg
Washington DC Area

 

Nicer tires do make a big difference.

Yes - wrt to regular concrete and asphalt roads
your recommended tire pressure setting should
perform well.

However - Mark57 (OK) reportedly found that an
even lower tire pressure setting of 38/36 psi
(IIRC he is using OEM with a max sidewall of 44psi)
was better for going long distances over badly
maintained roads and dirt roads.

 

This is exactly kind of the info I am looking for.

 

Anyone care to comment on the pressure difference front/rear? I tend to think it doesn't make any difference especially if you have a hundred pounds or so of "stuff" in the back, or your mother-in-law sitting in the back seat.

I have tried front/rear pressure differences of 0,1, and 2 pounds and I can tell no difference.

With the Michelin Primacy MXM4 tires (51 pound max) I have now I use about 45 pounds in all 4 and go up by 4 or 5 pounds for long trips.