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post #11 of 33 (permalink) Old 07-29-2008, 08:47 AM
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Default Re: Tire Pressure 42PSI front 40PSI Back - Why?

Are you seriously questioning whether increasing tire pressure increases mpg?!?

PA P

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post #12 of 33 (permalink) Old 07-29-2008, 11:09 AM
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Default Re: Tire Pressure 42PSI front 40PSI Back - Why?

i have up the tire pressure driving 30 miles 55 60 am getting 38 42 mpg took trip 2 weekends ago mfd stated 60 mpg did the math 33 mpg. am driving light foot looking ahead coasting not breaking millage less than i would have expected
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post #13 of 33 (permalink) Old 07-29-2008, 01:46 PM Thread Starter
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Default Re: Tire Pressure 42PSI front 40PSI Back - Why?

Hi PA Prius,

I really continue to be impressed by your number 60MPG/60Miles/Hour especially that your car seems really loaded (4 people) and still you are getting these impressive numbers.

Questions are:
Now I wonder if there is manufacturing spread, meaning that Toyota will ship the product if the car efficiency is greater than 48MPG. For me, I always get 52 MPG on the freeway which I normally drive for an hour to get to San Francisco. So I had always considered myself "lucky" in a sense that I might have gotten a car at the superior side of the spectrum.

I put in more air this weekend, increaseed the pressure to roughly mid 40's for all 4 tires. I wasn't very precise...so that's why I've said "mid 40's"
And I didnt notice that my MPG went up at all, in fact I actually think it dropped a bit. And those tires are original tires that came when I bought the car brand new. What tires are you using?

Thanks!
JCPrius2008
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post #14 of 33 (permalink) Old 07-29-2008, 02:57 PM
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Default Re: Tire Pressure 42PSI front 40PSI Back - Why?

Quote:
Originally Posted by JCPrius2008
Hi PA Prius,

I really continue to be impressed by your number 60MPG/60Miles/Hour especially that your car seems really loaded (4 people) and still you are getting these impressive numbers.

Questions are:
Now I wonder if there is manufacturing spread, meaning that Toyota will ship the product if the car efficiency is greater than 48MPG. For me, I always get 52 MPG on the freeway which I normally drive for an hour to get to San Francisco. So I had always considered myself "lucky" in a sense that I might have gotten a car at the superior side of the spectrum.

I put in more air this weekend, increaseed the pressure to roughly mid 40's for all 4 tires. I wasn't very precise...so that's why I've said "mid 40's"
And I didnt notice that my MPG went up at all, in fact I actually think it dropped a bit. And those tires are original tires that came when I bought the car brand new. What tires are you using?

Thanks!
JCPrius2008
I am using Goodyear Integrities, which I'm sure is the same you have. Mine are about at the end of their life. I'm guessing they'll make it until I put the snow tires on this winter. That to say that my tires are getting pretty smooth, which decreases their rolling resistance. I read on Michelin's website that tires improve their rolling resistance by 25% through the life of the tire.

I see you have a 2008. How many miles are on it? If the car is still young I'm sure your gas mileage will improve as you get more miles on it and as the tires become worn.

One weekend's driving likely won't give you a good picture of whether your mileage changes by increasing tire pressure. There are too many variables-- weather, length and type of trips made, etc. My next door neighbor got an '08 and was on a trip from PA to FL. I e-mailed him mid-trip and told him about my tire pressure. He put his from mid-30's up to 50 and then reported an increase of 5 mpg. That sounds a bit high to me. I haven't checked back with him for how that is looking longer-term.

I do drive very conservativly. I use the cruise control on the highway if the roads are fairly flat and not too much traffic. If not, I think I can do better without. Or sometimes on hills I'll leave the cruise on but tap it down two or three mph as I approach the crest of a hill and then increase it again going down.

PA P

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2004 Lifetime mpg: 52.3 actual / 53.3 MFD 60.7cs
ScanGuage II Sharkfin Amsoil 0/30 56/54
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post #15 of 33 (permalink) Old 07-29-2008, 03:07 PM Thread Starter
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Default Re: Tire Pressure 42PSI front 40PSI Back - Why?

Hi PA Prius,

Oh yeah, it's a new car....I bought it in January 2008 and currently I have 7500 miles on it already, yeah not much I know.
My tires came with the car when I bought it and yes I guess I could label them as still "brand new" since I only covered 7500 miles roughly so far.


What year of Prius do you and how your mileage so far?

Oh yeah, what gas are you using? I recently went from Chevron 87 to Shell 87 and I notice I do a little better with Shell.

So, I'm also wondering where you are from. I guess the places where you drive your car to really make a difference.
I'm from the San Francisco Bay Area. Traffic is bad here and the roads ain't all that flat and smooth even on freeway.
However I think I'm a good driver, accelerate slowly, pulse/glide if I can, ....etc.

Thanks!
Joe
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post #16 of 33 (permalink) Old 07-29-2008, 03:26 PM
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Default Re: Tire Pressure 42PSI front 40PSI Back - Why?

Quote:
Originally Posted by JCPrius2008
Hi PA Prius,

Oh yeah, it's a new car....I bought it in January 2008 and currently I have 7500 miles on it already, yeah not much I know.
My tires came with the car when I bought it and yes I guess I could label them as still "brand new" since I only covered 7500 miles roughly so far.


What year of Prius do you and how your mileage so far?

Oh yeah, what gas are you using? I recently went from Chevron 87 to Shell 87 and I notice I do a little better with Shell.

So, I'm also wondering where you are from. I guess the places where you drive your car to really make a difference.
I'm from the San Francisco Bay Area. Traffic is bad here and the roads ain't all that flat and smooth even on freeway.
However I think I'm a good driver, accelerate slowly, pulse/glide if I can, ....etc.

Thanks!
Joe
Mine is an '04. I got it used in '06 with 41,000 miles on it for $16,500. It now has 92,000 miles on it and I could probably get the same price for it!

I'm in southeast PA, rolling hills and fairly decent roads. I'm sure the traffic is less than yours.

I use whatever cheap gas I can find.

PA P

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ScanGuage II Sharkfin Amsoil 0/30 56/54
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post #17 of 33 (permalink) Old 07-29-2008, 06:18 PM
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Default Re: Tire Pressure 42PSI front 40PSI Back - Why?

Quote:
Originally Posted by PA Prius
Are you seriously questioning whether increasing tire pressure increases mpg?!?

PA P
.
.Not in the least!
I'm simply trying to point out that tires are very important in how a car handles and Toyota has done an awfull lot of testing before coming to the figures selected and printed on the sticker on the door posts.
We all know there are a thousand "gimmic's" that can be used to get better gas milage. And we all often find circumstances when we do something (like "stomping" on it to get around that little old lady) that we really know is foolish and going to cost us at the pump. When I read posts about folks getting 60 MPG in a Prius loaded to max I sort of smile and wonder where that awufully long hill is!
I've driven my car (an "04") what I would realalistically call normally for over three years and have been very happy with my "consistant" 44 MPG.
Sixty MPG, I have never seen. And I do recognise what type of small, "relatively as light as the designer can make it" type car I am driving. It already goes "hippiot- hop" enough on washboard type streets for me to ever make it worse just to save a couple miles per gallon.
I'll grant you that air preasure is a cheap way of designing a suspension system but these cars are definately not Ferrari's, Beemers or Jaguars. Toyota settled on what I consider a higher than usual tire pressure for an important reason and I hope the one that slides into me attempting to stop on a wet street isn't doing so because someone looking for a few extra MPG hasn't "over inflated" his tires.
Changing designed tire pressures definately does change things. Some for the better and some for the worse. I'll take Toyota's word that they have chosen the "all around" better figure since it has remained the same for the past four years.



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post #18 of 33 (permalink) Old 07-29-2008, 07:32 PM
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Default Re: Tire Pressure 42PSI front 40PSI Back - Why?

Hyperion, I agree that Toyota had the big picture in mind when making their psi recommendations. As I stated earlier I drive very conservatively and especially so if the road is wet. From your comment, "Tire pressures are extremely important in this. You will be changing much more than the 'possibly' higher milage figure, if you do even that. I did not find it so!" it sounded like you were thinking that raising psi does not raise mpg, which I don't think is questionable. The amount can surely be questioned.

The mileage I've reported is from my MFD. As you can see by my taglines, my actual is exactly 1 mpg less than the MFD, so the numbers in my earlier posts here are slightly overstated.

I wouldn't consider raising tire pressure a gimmick. Block heaters would come closer to that category for me because those who use them are raising their mpg with the use of electricity which does not show up in their mpg. It could be it pays off, I don't know.

As far as smiling and the awfully long hill.... I'd be smiling too if I could find a down hill that stretched both ways on a round trip, such as ours this past weekend to the shore and back, or three weeks ago from PA to IN and back. You'll probably smile even more when I say our family of four got 49.74 mpg (actual) average on our 7,500 mile cross country camping trip last summer- with roof rack, and yes the AC was on.

PA P

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post #19 of 33 (permalink) Old 07-29-2008, 10:26 PM
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Default Re: Tire Pressure 42PSI front 40PSI Back - Why?

Darn good numbers with a roof rack



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post #20 of 33 (permalink) Old 07-30-2008, 09:19 AM
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Default Re: Tire Pressure 42PSI front 40PSI Back - Why?

Hyperion noted:

"I'll grant you that air preasure is a cheap way of designing a suspension system but these cars are definately not Ferrari's, Beemers or Jaguars. Toyota settled on what I consider a higher than usual tire pressure for an important reason and I hope the one that slides into me attempting to stop on a wet street isn't doing so because someone looking for a few extra MPG hasn't "over inflated" his tires."

Hyperion,

I do not know what your experience is when assessing 'normal tire pressures', but my 3 Porsches all stated 36F/44R, my Pontiac TransAM GT was 38/38, ....all manufacturers' recommendations.

Large commercial truck tires regularly run 65PSI light, and 100PSI loaded..

(In fact, I have not seen tire pressures as low as 25PSI since the bias belt days of the 1950/1960s.)

As to Toyota (or any manufacturer for that matter), most set recommended pressures to compromise between performance, mileage, safety, and comfort/noise. I very much doubt that any Toyota engineer or Goodyear engineer will ever state the reasons or recommend any different settings for fear of being sued, so relying on 'official' representation is moot.

In my opinion, tire pressure alone has little to do with suspension changes, but tire size modification does and should be factored in. Going to 'Plus one or Plus two' usually requires alignment and castor/camber adjustments to compensate for vertical suspension movement and toe-in/toe-out.

Most of us have discovered that the current 'recommended pressures' are too low to even place a flat footprint to the road; tire wear seems to occur on both inner and outer edges, implying underinflation at 35/33. Tire fatigue occurs, typically, due to sidewall flex more than center tread failure. In your wet weather scenario, low pressure is just as evil as over pressure; in fact, low pressures can trap water and increase the likelihood of aquaplaning because the tread cannot properly sipe the water away from the tread.

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