advertisement
Forums

The Forum is sponsored by 
 

AAPL stock: Click Here

You are currently viewing the Tips and Deals forum
Am I doing it wrong? (Prius question)
Posted by: PeterB
Date: November 06, 2011 01:48PM
Hi everyone,

I've had my new (used) Prius for I guess about a month or two now, and I seem to only be getting about 32MPG, according to the display panel.

Not knowing any better, and not having read up on it thoroughly yet, I've been driving the car almost entirely in "Eco Mode".

What I've also been noticing-- the battery seems to be getting pretty well charged driving this way, but it almost always gives me a message that EV Mode is not available, if I try to switch to it.

Am I doing it wrong? smiling bouncing smiley




Freya says, 'Hello from NOLA, baby!' (Laissez bon temps rouler!)
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: GGD
Date: November 06, 2011 02:06PM
I have the previous generation, so I'm not sure what Eco Mode is and I don't have EV mode, but to get 32MPG and a fully charged battery seems like the gas engine is running constantly. This could be due to driving behavior or accessory usage.

In mine, continuous use of the heater or A/C can cause the gas engine to run more and kills MPG.

You also need to be very light on the gas pedal, and let the car coast a bit when you get up to speed. There is sort of a fine line between very slight acceleration which runs the gas engine and coasting or maintaining the current speed which runs the electric engine. If you watch some of the MPG and power source displays while you drive you can get a better feel for how the car reacts and feels and make slight adjustments to your driving behavior.

Also check your tire inflation, many Prius owners keep them at about 40psi
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: dad@home
Date: November 06, 2011 02:19PM
Probably your driving style.

A couple years ago Top Gear (the BBC version) did a demonstration on their track where they compared a Prius and a BMW 3 series. The Prius was in front and driven flat out. Full acceleration; full braking as though they were trying to get a good time on their track. The BMW simply followed the Prius.

The Prius got 13mpg and the BMW got 24mpg.

I have a 2005 Prius that I converted to a plug in using a 10kWh Li battery pack.
If I drive it I get about 120mpg. If son number 2 drives it he gets 75-80mpg. My daughter (a budding Mario Andretti) gets only 55-60mpg.

Without the supplemental battery pack I suspect she would be getting 30mpg or less.


BTW have you checked your tire pressure?

dad
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: PeterB
Date: November 06, 2011 02:20PM
Quote
GGD
In mine, continuous use of the heater or A/C can cause the gas engine to run more and kills MPG.

Ahh, that could be it... it's almost impossible down here NOT to have the A/C on... that kinda sucks...

The tire inflation-- that's a good thought though. I think mine are maybe 32psi?

Edit: oh, and as far as driving behavior's concerned, yes, it's mostly urban stop-and-go type driving, and unfortunately needs to be occasionally a bit heavy on the gas pedal, because of the overly aggressive drivers here...




Freya says, 'Hello from NOLA, baby!' (Laissez bon temps rouler!)



Edited 1 time(s). Last edit at 11/06/2011 02:21PM by PeterB.
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: M A V I C
Date: November 06, 2011 02:58PM
Quote
GGD
You also need to be very light on the gas pedal, and let the car coast a bit when you get up to speed.

I can't stand this type of driving so very much. Whenever I see a prius coming up in front of me, I have to get around it. For example, merging on the freeway behind on prius is almost always a near death experience. They're doing 35-40 while trying to merge with traffic doing ~60, and I'm behind them... sometimes if the onramp is wide enough I'll punch it and get around them before we get to merging.

I am always amazed when they not only do this, but then they promptly cut over across all lanes of traffic, causing all lanes and many dozens of cars to slam on their brakes. Then they setup camp in the left lane at 10 under. All to save themselves a little bit more gas.




Help MacInTouch: Buy from Amazon? use this link [amazon.com]
Mac News & Info: [macintouch.com] [macnn.com] [tuaw.com]
Mac Benchmarks: [barefeats.com]
Used Mac Stuff [FS/T]: LowEndMac Swap List
Mac Software Updates: [macupdate.com]
Fonts: [dafont.com] [fontspace.com]
Online Computer Store With Mac Support: [macsales.com]
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: Acer
Date: November 06, 2011 03:18PM
EV mode button only works at parking lot speeds. I have found it to be largely useless.

Look up "warp mode" or "stealth mode." (The terminology is not used consistently.) It's where you drive just slow enough to keep the gas engine off, but using the maximum power from the battery, which is true EV mode, but without the button. Sometimes you have to punch the accelerator up a bit then back off--this makes the gas engine shut off. Especially at faster city speeds, ca 40-50 MPH, learning to work the battery in this manner can really help MPG.

e.g., [boardreader.com]

FWIW, my actual measured MPG after 17000 miles is 44.5 MPG. I find the onboard display to overestimate MPG by a good 5%.



Edited 1 time(s). Last edit at 11/06/2011 03:22PM by Acer.
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: zeppo2
Date: November 06, 2011 03:57PM
I have the same Prius, run the AC almost all year long, and drive 70 on the freeway and average 46 mpg. This only changes if we drive up into the mountains--it's very flat where we are. Might be worth having the Prius checked out.
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: bazookaman
Date: November 06, 2011 05:31PM
Quote
M A V I C
Quote
GGD
You also need to be very light on the gas pedal, and let the car coast a bit when you get up to speed.

I can't stand this type of driving so very much. Whenever I see a prius coming up in front of me, I have to get around it. For example, merging on the freeway behind on prius is almost always a near death experience. They're doing 35-40 while trying to merge with traffic doing ~60, and I'm behind them... sometimes if the onramp is wide enough I'll punch it and get around them before we get to merging.

I am always amazed when they not only do this, but then they promptly cut over across all lanes of traffic, causing all lanes and many dozens of cars to slam on their brakes. Then they setup camp in the left lane at 10 under. All to save themselves a little bit more gas.

yes. those people are a menace.




__________________________________
There’s a guy wearing overalls with no shirt.
Which I think we all know is the International uniform for the last guy you’ll ever see.
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: Markintosh
Date: November 06, 2011 05:34PM
Hmmm...Prius at 32 mpg and I have an AWD Toyota Matrix that cost half as much and it gets 30 mpg with AWD as an added bonus....that does not seem right.



“Live your life, love your life, don’t regret…live, learn and move forward positively.” – CR Johnson
Loving life in Lake Tahoe, CA
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: Billybob
Date: November 06, 2011 05:48PM
Not sure what year your Prius is, but I have a 2010 Prius. I typically get over 50mpg, and the heavier the traffic--the more stop-and-go it is--the better the gas mileage. Early Oct. I went through 1/2 a tank of gas at just under 55mpg. I filled up and reset the trip odometer because I felt like I was too conscious of my driving. And no, I'm not the idiot who creeps onto the freeway at 35-50mph. I do floor it when I merge at highway speeds–and the 2010 Prius has surprisingly good pickup when pushed–, I just don't go onto the highway very often.

32PSI seems awfully low. I think the tires are rated for 40PSI, and when I bother to check, I typically overinflate my tires by a pound or two (yes, I got flamed for doing this last year, so let's not revisit that discussion).

I live in Florida, so I keep the AC going a lot, although I usually turn it off in the morning when it's cooler.

Suffice to say that you really have to 1) try hard to go under 40mpg, 2) drive almost all your miles on the freeway–in which case, why do you have a Prius?– and constantly engage in hard accelerations, or 3) there is something very wrong with your vehicle.

I'd take it in.
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: M A V I C
Date: November 06, 2011 06:33PM
Quote
Billybob
I think the tires are rated for 40PSI, and when I bother to check, I typically overinflate my tires by a pound or two (yes, I got flamed for doing this last year, so let's not revisit that discussion).

One should go by what the car says the PSI should be at, not what the tires are rated at. As far as overinflation, that increases rolling resistance and shortens the tire life.




Help MacInTouch: Buy from Amazon? use this link [amazon.com]
Mac News & Info: [macintouch.com] [macnn.com] [tuaw.com]
Mac Benchmarks: [barefeats.com]
Used Mac Stuff [FS/T]: LowEndMac Swap List
Mac Software Updates: [macupdate.com]
Fonts: [dafont.com] [fontspace.com]
Online Computer Store With Mac Support: [macsales.com]
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: sekker
Date: November 06, 2011 07:02PM
Check your fuel. In MN, they are putting up to 20% ethanol in the blend. Gas mileage in my Civic Hybrid is quite a bit lower than what it was a year ago.
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: Kiva
Date: November 06, 2011 07:14PM
this would't account for all the error, but don't go off the MFD for mileage. You need to calculate an entire tank by hand. Sign up and use www.fuelly.com. It's kind of fun..

btw, I do have to say that my '03 TDI has about 165hp (goal is 200hp) and gets about 48mpg smiling smiley. talk about fun to drive...700+ miles/tank..



----------------------
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: Carm
Date: November 06, 2011 07:52PM
Know a few people here in the SoCal desert that have the AC on all the time and they get @#$%& mileage too. One works for the city(drives city prius vehicle) and the other outright owns it.

J. Carm
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: mrbigstuff
Date: November 06, 2011 08:18PM
Quote
Kiva
this would't account for all the error, but don't go off the MFD for mileage. You need to calculate an entire tank by hand. Sign up and use www.fuelly.com. It's kind of fun..

btw, I do have to say that my '03 TDI has about 165hp (goal is 200hp) and gets about 48mpg smiling smiley. talk about fun to drive...700+ miles/tank..

is the goal attainment through a larger turbocharger? I'm curious....

BTW, most Prii around these parts are driven quite fast. I'm not sure of what the point is when that's the case, but many on the highways, at least, are booking it.
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: Kiva
Date: November 06, 2011 08:33PM
ya, bigger turbo, injectors, intake, tuning smiling smiley They're fun cards to mod, keep reliable, and still get killer mpg's.



----------------------
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: RAMd®d
Date: November 06, 2011 08:47PM
You also need to be very light on the gas pedal, and let the car coast a bit when you get up to speed.

I drive like that in my mid/full size American car because I get the best mileage that way, and because I'm almost always in commute traffic and that's the only way a sane person can drive. In very light commutes I'll hold my speed at 55.

Fortunately, in CA only motorcycles, vehicles with two/three or more occupants, or all-electric vehicles can use the HOV lane during commute hours.

There are still hybrids that use the lane, and occasionally I see one pulled over getting the word. There are still a lot of other non-exempt vehicles violating the law.




When a good man is hurt,
all who would be called good
must suffer with him.

Everybody matters or nobody matters.

You and I have memories longer than the road that stretches out ahead.

There is no safety for honest men except
by believing all possible evil of evil men.

We don’t do focus groups. They just ensure that you don’t offend anyone, and produce bland inoffensive products. —Sir Jonathan Ive

-An armed society is a polite society.
And hope is a lousy defense.

You make me pull, I'll put you down.

Mister, that's a ten-gallon hat on a twenty-gallon head.

I *love* SIGs. It's Glocks I hate.
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: PeterB
Date: November 06, 2011 09:05PM
Thanks everyone. If you all remember, I bought it used certified, so there shouldn't have been anything wrong with it, but it is due for a service so I will ask them about this.




Freya says, 'Hello from NOLA, baby!' (Laissez bon temps rouler!)
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: Acer
Date: November 06, 2011 09:25PM
Diesel fuel is more energy-dense, which contributes to the higher mpg. Add in the mpg-reducing ethanol blends in gasoline handicap, and it's apples and oranges until you finish the spreadsheet.

Anyway, my mpg takes a significant hit in cold weather Pennsylvania, about 8 to 10mpg worth in the coldest sub-freeezing stretches. My commute is short, so I lose a lot to warming up.



Edited 1 time(s). Last edit at 11/06/2011 09:29PM by Acer.
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: Kiva
Date: November 06, 2011 10:28PM
Quote
Acer
Diesel fuel is more energy-dense, which contributes to the higher mpg. Add in the mpg-reducing ethanol blends in gasoline handicap, and it's apples and oranges until you finish the spreadsheet.
.

ok, i get the energy dense part, but can you explain the apples and oranges thing? I put in 15gal of fuel in and go 725 miles. The prius, in this case, puts the same fuel in and goes 480 miles. Factor in diesel's approx 20% premium cost, it's still cheaper to run.

and a heck of a lot more fun to drive...

As a side note, it's really hard to beat the prius 'around town'. My diesels only get about 32-35mpg around town...they love the highway.



----------------------
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: M A V I C
Date: November 06, 2011 10:31PM
Quote
PeterB
I bought it used certified, so there shouldn't have been anything wrong with it

That's a common misconception. Pretty much any car can end up being "certified." Sure they usually have an inspection checklist, but any two year old can check the boxes. Plenty of cars have been sold as "certified" that have tons of problems.




Help MacInTouch: Buy from Amazon? use this link [amazon.com]
Mac News & Info: [macintouch.com] [macnn.com] [tuaw.com]
Mac Benchmarks: [barefeats.com]
Used Mac Stuff [FS/T]: LowEndMac Swap List
Mac Software Updates: [macupdate.com]
Fonts: [dafont.com] [fontspace.com]
Online Computer Store With Mac Support: [macsales.com]
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: Acer
Date: November 07, 2011 12:19AM
Quote
Kiva
Quote
Acer
Diesel fuel is more energy-dense, which contributes to the higher mpg. Add in the mpg-reducing ethanol blends in gasoline handicap, and it's apples and oranges until you finish the spreadsheet.
.

ok, i get the energy dense part, but can you explain the apples and oranges thing? I put in 15gal of fuel in and go 725 miles. The prius, in this case, puts the same fuel in and goes 480 miles. Factor in diesel's approx 20% premium cost, it's still cheaper to run.

and a heck of a lot more fun to drive...

No argument on the fun to drive part!

As for the other, now you made me get out the spreadsheet when I was hoping a gloss would cover it. baseball bat smiley
I simply mean to say until you factor in the inherent differences between diesel and gasoline, just saying "I get XX mpg in my diesel, you get XX in your prius" is not a direct comparison. To do it precisely, we need a common unit: how many miles per Megajoule?

[bioenergy.ornl.gov]

121 MJ per gallon gasoline (pure) @ 44.5 MPG = 0.37 mi/MJ (to use my Prius MPG, because PeterB's mpg is not typical. And we'll forget that most of the time I have to use 10% ethanol here in PA, which is even lower in MJ)
138 MJ per gallon diesel @48 MPG = 0.35 mi/MJ (to use your result)

I win! big grin smiley

Of course, a good bit of the time, the Prius gasoline engine is not even on when coasting or idling. A hyrbid diesel would blow the Prius out of the water by mpg or "mpmj."



Edited 4 time(s). Last edit at 11/07/2011 12:24AM by Acer.
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: RAMd®d
Date: November 07, 2011 01:02AM
I win!

Indeed, LOL!

"I'ma get Excel on your ass."

A question though- will a diesel play well with Start/Stop technology?




When a good man is hurt,
all who would be called good
must suffer with him.

Everybody matters or nobody matters.

You and I have memories longer than the road that stretches out ahead.

There is no safety for honest men except
by believing all possible evil of evil men.

We don’t do focus groups. They just ensure that you don’t offend anyone, and produce bland inoffensive products. —Sir Jonathan Ive

-An armed society is a polite society.
And hope is a lousy defense.

You make me pull, I'll put you down.

Mister, that's a ten-gallon hat on a twenty-gallon head.

I *love* SIGs. It's Glocks I hate.
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: Winston
Date: November 07, 2011 04:32AM
Quote
M A V I C
One should go by what the car says the PSI should be at, not what the tires are rated at. As far as overinflation, that increases rolling resistance and shortens the tire life.

Not sure that's right. Manufacturers set PSI to balance rolling resistance against tire grip characteristics and wear life, as well as smoothness of the ride.

I think a higher PSI reduces rolling resistance, but at the expense of possibly reducing tire grip. Effect on tire life depends in part on how you drive. It will also give you a harsher ride.


Good luck.

- Winston



------------------------
Be seeing you.
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: Acer
Date: November 07, 2011 08:34AM
Quote
RAMd®d
I win!

Indeed, LOL!

"I'ma get Excel on your ass."

A question though- will a diesel play well with Start/Stop technology?

That is indeed the question. Have the Europeans done it? If not, I'm guessing there are still some technical hurdles to overcome. Imagine trying to start-stop a diesel in Minnesota winter...
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: Kiva
Date: November 07, 2011 08:55AM
haha...ok, now I get it..that was funny...

I guess my simple self puts a certain amount of $ in the car for fuel..one takes me 725 miles, the other 430 or whatever winking smiley

btw, re: tire pressure...run the highest you can without impacting the wear pattern or handling. That is typically about 80-90% of the max on the sidewall. But you have to check by running a chalkline across the tread, driving it, and seeing how it wears.

I've heard about diesel hybrids....but not sure where the research is on them. What kills me is that there are a bunch of great diesel cars in europe that don't meet US emissions standards. So, my neighbor can have his freaking SUV getting 12mpg, but we can't bring over the VW Polo Diesel which, I believe, gets 70mpg...LAME...



----------------------
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: AllGold
Date: November 07, 2011 05:36PM
Take a look at PriusChat.com or a similar forum to get current info on your model year.

I have a 2007 which is the previous generation so it may not apply to your Prius. Anyway, for my generation, the tire and car manufacturer rate the tires up to 40psi, and for the best handling, the rear tires are supposed to be inflated 2psi lower than the front (i.e., 40 front / 38 rear, 39/37, etc.). You will get noticeably better milage going from 32 to 40psi. You will also get better handling but at the cost of a rougher ride. Again, I'm not sure if any of that is valid for your model year.



Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: M A V I C
Date: November 07, 2011 10:23PM
Quote
Winston
Quote
M A V I C
One should go by what the car says the PSI should be at, not what the tires are rated at. As far as overinflation, that increases rolling resistance and shortens the tire life.

Not sure that's right. Manufacturers set PSI to balance rolling resistance against tire grip characteristics and wear life, as well as smoothness of the ride.

I think a higher PSI reduces rolling resistance, but at the expense of possibly reducing tire grip. Effect on tire life depends in part on how you drive. It will also give you a harsher ride.


Good luck.

- Winston

Which manufacturers are you talking about?

Going over the vehicle's spec causes the tread to not sit flat on the ground. Only the center of the tire makes contact, and thus the tires doesn't function as designed. So all of the tire mfg's design for rolling resistance, grip... go out the window. The center of the tire then sees a great deal more friction, which causes the tires to cup... the premature wear is caused by greater resistance.

[blog.tirerack.com]

overinflation will cause a tire to wear faster in the middle of the tire. This is due to the "ballooning" effect that occurs when a tire has too much air. Some drivers incorrectly inflate their tires to the maximum pressure listed on the sidewall. If a vehicle's tires are overinflated by 6 psi, they could be damaged more easily when running over potholes or debris in the road. The most common place to find the proper tire pressure for your vehicle is the sticker on the inside of the driver door or inside the gas filler door.

On my car, the fronts are supposed to be 38 and the rears 42. Max on these tires is 44. I've seen tires for my car that go up to 51, but I'm still supposed to run them at 38/42.




Help MacInTouch: Buy from Amazon? use this link [amazon.com]
Mac News & Info: [macintouch.com] [macnn.com] [tuaw.com]
Mac Benchmarks: [barefeats.com]
Used Mac Stuff [FS/T]: LowEndMac Swap List
Mac Software Updates: [macupdate.com]
Fonts: [dafont.com] [fontspace.com]
Online Computer Store With Mac Support: [macsales.com]
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: JoeH
Date: November 07, 2011 11:01PM
You have that backwards, under-pressure causes cupping and over-pressure will cause excess wear on the center of the tread. That said, most radials can be 2-5 psi over the listed pressure and still not get that type of center tread wear. As for the label in your car, that gives the manufacturers recommended pressure for the OEM tires or ones constructed almost exactly the same. Use a different tire and you may have to adjust the inflation pressure up or down.
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: Winston
Date: November 07, 2011 11:14PM
Quote
M A V I C
Quote
Winston
Quote
M A V I C
One should go by what the car says the PSI should be at, not what the tires are rated at. As far as overinflation, that increases rolling resistance and shortens the tire life.

Not sure that's right. Manufacturers set PSI to balance rolling resistance against tire grip characteristics and wear life, as well as smoothness of the ride.

I think a higher PSI reduces rolling resistance, but at the expense of possibly reducing tire grip. Effect on tire life depends in part on how you drive. It will also give you a harsher ride.


Good luck.

- Winston

Which manufacturers are you talking about?

Going over the vehicle's spec causes the tread to not sit flat on the ground. Only the center of the tire makes contact, and thus the tires doesn't function as designed. So all of the tire mfg's design for rolling resistance, grip... go out the window. The center of the tire then sees a great deal more friction, which causes the tires to cup... the premature wear is caused by greater resistance.

[blog.tirerack.com]

overinflation will cause a tire to wear faster in the middle of the tire. This is due to the "ballooning" effect that occurs when a tire has too much air. Some drivers incorrectly inflate their tires to the maximum pressure listed on the sidewall. If a vehicle's tires are overinflated by 6 psi, they could be damaged more easily when running over potholes or debris in the road. The most common place to find the proper tire pressure for your vehicle is the sticker on the inside of the driver door or inside the gas filler door.

I was talking about the automobile manufacturer.

I don't disagree that overinflation can cause greater wear in the center of the tire, but it will reduce rolling resistance, at least until the tires wear out. Haven't you ever ridden a bicycle with underinflated tires, then pumped them up? Much lower rolling resistance with higher inflation. I can always tell after I've added air to a car's tires, because it seems to move more easily.

One thing I don't understand is how use of the tires affects all this. Tire inflation is supposed to be set with cold tires. Driving warms them up, which increases the PSI inside. How much it increases should depend on how the car is being driven (lots of accelerating and stopping vs. steady state, high vs. low speed). I'd bet there are even differences if you are driving with the sun on one side of the car. I suspect that tires are designed to work under a variety of pressures as that's how they likely operate.

I remember reading an article about an advanced driving school that I think used Golf GTIs. They vastly overinflated the tires, because the way they were driving would "rip the tires off of the car" at lower pressures.


- W



------------------------
Be seeing you.
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: M A V I C
Date: November 08, 2011 12:16AM
Quote
JoeH
You have that backwards, under-pressure causes cupping and over-pressure will cause excess wear on the center of the tread.

Excess wear on the center of the tread IS cupping - it causes the tire wear to curve inward instead of being flat.

Quote

That said, most radials can be 2-5 psi over the listed pressure and still not get that type of center tread wear.

True, depending on the conditions when inflated and how they've changed. Plus it depends on the tire.

Quote

As for the label in your car, that gives the manufacturers recommended pressure for the OEM tires or ones constructed almost exactly the same. Use a different tire and you may have to adjust the inflation pressure up or down.

Not so, as the tirerack link points out. Generally the MFGs have no clue which tire is going to be OE on the car. It can vary depending on market. Use a tire that's in spec with the car, and you'll want to stick with what the car says.

Even the tire MFGs say to go by what the car says: [www.dunloptires.com]
PROPER INFLATION
SAFETY WARNING:
[...] Follow Owner's Manual and tire placard in vehicle.





Help MacInTouch: Buy from Amazon? use this link [amazon.com]
Mac News & Info: [macintouch.com] [macnn.com] [tuaw.com]
Mac Benchmarks: [barefeats.com]
Used Mac Stuff [FS/T]: LowEndMac Swap List
Mac Software Updates: [macupdate.com]
Fonts: [dafont.com] [fontspace.com]
Online Computer Store With Mac Support: [macsales.com]
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: M A V I C
Date: November 08, 2011 12:21AM
Quote
Winston
I don't disagree that overinflation can cause greater wear in the center of the tire, but it will reduce rolling resistance, at least until the tires wear out.

Think about it: what causes something to wear faster? More friction. The greater the friction, the less the rolling resistance.

Quote

Haven't you ever ridden a bicycle with underinflated tires, then pumped them up? Much lower rolling resistance with higher inflation. I can always tell after I've added air to a car's tires, because it seems to move more easily.

Eh, your comparison is only accurate between under inflated and properly inflated tires. Take a road tire that's at 120psi, add another 20% to it and you're not going to notice a difference.

Quote

I suspect that tires are designed to work under a variety of pressures as that's how they likely operate.

Yes, they are. So if you start off overinflated, it's only going to go above what it's designed to work at.

Quote

I remember reading an article about an advanced driving school that I think used Golf GTIs. They vastly overinflated the tires, because the way they were driving would "rip the tires off of the car" at lower pressures.

Sounds like they were using the wrong tire setup. The rim width was too narrow for the sidewall height under the driving conditions.




Help MacInTouch: Buy from Amazon? use this link [amazon.com]
Mac News & Info: [macintouch.com] [macnn.com] [tuaw.com]
Mac Benchmarks: [barefeats.com]
Used Mac Stuff [FS/T]: LowEndMac Swap List
Mac Software Updates: [macupdate.com]
Fonts: [dafont.com] [fontspace.com]
Online Computer Store With Mac Support: [macsales.com]
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: Winston
Date: November 08, 2011 07:32AM
Quote
M A V I C
Quote
Winston
I don't disagree that overinflation can cause greater wear in the center of the tire, but it will reduce rolling resistance, at least until the tires wear out.

Think about it: what causes something to wear faster? More friction. The greater the friction, the less the rolling resistance.

The tire would only wear more in the center. There is less contact area, so less friction, so less overall wear.


Quote

Quote

Haven't you ever ridden a bicycle with underinflated tires, then pumped them up? Much lower rolling resistance with higher inflation. I can always tell after I've added air to a car's tires, because it seems to move more easily.

Eh, your comparison is only accurate between under inflated and properly inflated tires. Take a road tire that's at 120psi, add another 20% to it and you're not going to notice a difference.

As I said, auto manufacturers trade off several factors when they set the PSI for a car. I suspect that in some cases they set a lower PSI for ride characteristics and in others a higher PSI for mileage. I think there is a safe working range.

Otherwise why could you put a set of tires on one car and have 32 PSI as the auto manufacturer recommendation, and the same tires on another car have 35 PSI as the recommendation? The manufacturers have made different tradeoffs. (I suspect suspension layout plays a part too.)


Quote

Quote

I suspect that tires are designed to work under a variety of pressures as that's how they likely operate.

Yes, they are. So if you start off overinflated, it's only going to go above what it's designed to work at.

I don't think that's true unless you go over the PSI rating on the sidewall of the tire.


Quote

Quote

I remember reading an article about an advanced driving school that I think used Golf GTIs. They vastly overinflated the tires, because the way they were driving would "rip the tires off of the car" at lower pressures.

Sounds like they were using the wrong tire setup. The rim width was too narrow for the sidewall height under the driving conditions.

I probably exaggerated when I said "vastly" overinflated. This was a number of years ago, and I don't think today's low-profile street tires were available. But it's been long enough that I admit I don't remember the details exactly.


- W



------------------------
Be seeing you.
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: M A V I C
Date: November 08, 2011 10:29PM
Quote
Winston
The tire would only wear more in the center. There is less contact area, so less friction, so less overall wear.

Have you seen this actually happen? Take tires that normally go 40k miles, over inflate them. You'll get about 10k before the middle half is worn through. When the tire can contact all the surface area evenly, it has a MUCH longer wear life. Grossly over inflated tires may only see a few thousand miles before they're worn out.

Quote

As I said, auto manufacturers trade off several factors when they set the PSI for a car. I suspect that in some cases they set a lower PSI for ride characteristics and in others a higher PSI for mileage. I think there is a safe working range.

They set the range and choose a tire based on what will wear evenly.

Quote

Otherwise why could you put a set of tires on one car and have 32 PSI as the auto manufacturer recommendation, and the same tires on another car have 35 PSI as the recommendation?

Among other characteristics, the weight of the vehicle.

Quote

I don't think that's true unless you go over the PSI rating on the sidewall of the tire.

Again, it completely depends on the car. If the car's ratings put it at the higher end of the load range, you would be correct.

That all said, I've cited both tire experts (tirerack) and a tire MFG (dunlop) both saying to follow the inflation rating of the vehicle, not what the sidewall says. What domain expertise do you have that enables you know better than them?




Help MacInTouch: Buy from Amazon? use this link [amazon.com]
Mac News & Info: [macintouch.com] [macnn.com] [tuaw.com]
Mac Benchmarks: [barefeats.com]
Used Mac Stuff [FS/T]: LowEndMac Swap List
Mac Software Updates: [macupdate.com]
Fonts: [dafont.com] [fontspace.com]
Online Computer Store With Mac Support: [macsales.com]
Options:  Reply • Quote
Re: Am I doing it wrong? (Prius question)
Posted by: Winston
Date: November 08, 2011 10:54PM
M A V I C -

I think we are covering slightly different things. I don't dispute that over inflating tires will cause them to wear out faster. I am not advocating to use the sidewall max. pressure as a guide for inflating tires.

I also don't dispute that there are other reasons not to overinflate. But the wear will be on a smaller portion of the tires than the full surface. There will be less contact area with the road surface, and therefore less total friction, so lower rolling resistance. The tires would also be "harder" from the additional pressure.

If you took two identical cars, with new tires, and inflated one to the car manufacturer's specifcation and the other a pound or two above that specification, then checked gas mileage on the two cars, the one with higher PSI would get better gas mileage, all else equal. If your sole consideration is mileage, tires with higher inflation pressure will have a lower rolling resistance.

But I agree the one with higher PSI would likely wear the tires out faster if the pressure differential is maintained.


I wonder, since most people never check their tire pressure, and as a result run most of the time on under-inflated tires, if tires should be slightly overinflated for most people on the occasions when they are in fact checked (say at 6 month rotations). I wonder if that would result in a better average inflation for those who never check tire pressure. (This is based solely on a goal of maximizing tire life, not mileage or safety or ride or other characteristics. I'm just wondering if it would cause the average tire to wear more evenly.)

I'd love to have a system on our cars that indicated when tire pressure is low. The one car we have with some kind of a system seems to only measure when there is a big differential between tires, not when all of them are a few PSI low.


- W



------------------------
Be seeing you.



Edited 1 time(s). Last edit at 11/08/2011 10:58PM by Winston.
Options:  Reply • Quote
Sorry, only registered users may post in this forum.

Click here to login

Online Users

Guests: 180
Record Number of Users: 186 on February 20, 2020
Record Number of Guests: 5122 on October 03, 2020