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Hybrid Tips Optimizing mileage
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I think my gym has the worst kind of people. There are two parking lots, a smaller one in the front and a huge one in the back. There is always 2-3 cars in the front parking lots waiting for people to leave. But the only way to the rear parking lot is through the front one. I have to slalom through these parked cars to get to the rear parking lot, which has tons of empty spaces. I mean, come on people, you come to the gym to work out, to burn off that fat, but you can not walk 50 feet around the building to get to the gym? This defyes logic completley. These people are probably the ones who watch other people working out, and then complain that they have been going to the gym for 5 years and have not been able to achieve any result. Maybe it is because they watch people working out instead of working out, or maybe because they spent 30 minutes of their 1 hour work out time, waiting for a parking spot in the front.
For these people we should make a human hybrid, hook up some bisycle pedals in the car to the generator and make them charge the batteries by pedaling instead of just sitting there.
I'm driving a 2004 HCH with CVT.
These figures are pretty typical to what I usually see. Temps lower 40's, dry roads and no wind. I leave work at 1:00 AM onto practically abandoned roads.
1 Mile, 45MPG, Getting onto the freeway, speed limit is 55.
2 Miles, 45.4MPG, 55MPH
3 Miles, 46.5MPG, 58MPH
4 Miles, 47.6MPG, 56MPH
5 Miles, 48.8MPG, 57MPG
6 Miles, 48.8MPG, 56-52MPH, Pulling a 2 mile hill
10 Miles, 52.2MPG, 58MPG
15 Miles, 53.7MPG, 58MPH
20 Miles, 56.3MPG, 62-52MPH, Pulling a steep 3 mile hill.
25 Miles, 56.3MPG, Exiting freeway, speed limit is 45, average about 46MPH.
30 Miles, 56.7MPG
35 Miles, 58.6MPG
39.2 Miles, 60.5MPG
40 Miles, 61.3MPG
41 Miles, 61.6MPG
41.9 Miles, 62.8MPG
42 Miles, 62.8MPG
43 Miles, 63.5MPG, Begin pulling 1.9 miles of horrendous hills.
45 Miles, 62.8MPG
46 Miles, 64MPG
46.4 Miles, 64.3MPG, Final MPG figure as I arrive home.
I thought that some might possibly think that my road to home is mostly downhill, which it is not. Each way is basically a staircase of hills, with the peak about half way and lasting about 5 miles.
So today I brought my voice recorder along and made these notes. I reset the trip meter in the driveway, leaving for work at 4:30PM.
A thunderstorm had moved through the area a few hours before but the roads were mostly dried up and there was no wind to speak of, temps mid 60’s:
0MPG @ 0Miles In my driveway
40.8MPG @ 1 Mile
46.5MPG @ 2 Miles
53MPG @ 3 Miles
54.1MPG @ 4 Miles
52.6MPG @ 5 Miles
53MPG @ 6 Miles
54.5MPG @ 10 Miles
56.7MPG @ 15 Miles
59MPG @ 20 Miles
59.4MPG @ 23.4 Miles, about to get onto 65MPH limit freeway
60.1MPG @ 25 Miles
60.5MPG @ 30 Miles
61.3MPG @ 35 Miles
61.6MPG @ 40 Miles
63.4MPG @ 43 Miles, exiting freeway onto 5:30PM rush hour Atlanta city traffic.
62.8MPG @ 45 Miles
62.8MPG @ 45.2 Miles after climbing 4 stories of parking deck, parking and shut-down.
These figures are my typical statistics.
If I had to drive under the earlier thunderstorm & rain I’d likely parked with 55-60MPG. If a strong head wind would have prevailed I’d likely park in the lower 50’s.
I suspect that those of us who are in the upper 50’s low 60's tank average have about the same statistics?
I'll make my disclaimer:
These are my personal statistics and most will not get these results.
Most folks will average about 47MPG in their HCH.
YMWV
I use regular gas (major brand) with ethanol as gas stations stock. How do I get close to the mpg claims I've seen published here and elsewhere? What is the best acceleration (it seems allowing the electric motor to do a lot of work while the gas motor is not working hard would be ideal) pattern? Never allowing the electric to help would seem to lose the benefit of that available power that was recovered by braking.
My first tank was 38.4 MPG, but nine months later (today) my current tank is 54.8 MPG. I had a car that was already "broken in" because I bought it used with 4,823 miles on it.
You will learn the "sweet spots" when cruising at various speeds. You will learn how to "drive with a load" which is helpful in hilly areas such as you have described in your post.
Rain will ALWAYS knock your mpg down, because of the extra effort of the tires "pushing the water" out of their way and the extra weight of the rain on your car and in the undercarriage.
You will also find that the first few miles after a fillup are almost ALWAYS big numbers - one time I got 93.1 MPG for the first 3 miles after a fillup, when the car engine was warmed up to optimum operating temperature !!
Here are some general tips you can find here and elsewhere that might help you:
• Break in — almost universally people notice an improvement in mileage at about the 5000–6000 mile mark. It seems that the engine friction, wheel bearings and other moving parts 'loosen up' over that first 5k miles. Also, the High Voltage Nickel Metal Hydride (NiMH or HV) battery becomes more efficient over time. Also, switching to a full synthetic oil at around 5,000 miles will benefit your car and usually your MPG.
• Technique/style/learning curve — It is believed by many that the hybrid driver intuitively or through trial and error improves their own driving technique over time better take advantage of the most efficient modes of driving their car. Not all drivers do this, but it becomes almost a game. With time one learns to accellerate the vehicle in the most efficient manner. You learn to anticipate stops and begin coasting or gliding to those stops without wasting power to get there or putting undue stress on the brakes.
• Warmer temperatures — all praise to summer. Hybrids are at their most efficient in warm weather...particularly in that range of temperatures where A/C use is not necessary but where air temperatures are in a range that is 'comfortable' to the car and HV battery. Almost everyone sees a dramatic improvement in fuel economy in those summer months and reports of exceeding the EPA numbers begin to frequently appear on the forums!
• A/C use — there is a significant impact on mileage with A/C use. In the summer, try to just use the 'vent' setting or set the temperture to something b/w 78–81 degrees (depends on how much sunlight is shining directly into the vehicle as to what is comfortable enough).
• Weight in vehicle — Although most small articles won't make a major impact you should not carry unnecessary stuff in the car. If you always have the car full with the spouse and 3 kids and all their necessities of life it will negatively impact your mileage figures.
• Tire and road rolling resistance — The tire rolling resistance of the OEM tires is usually very low. If under inflated, however, that resistance increases creating a significant impact on gas mileage. Many hybrid drivers choose to use higher tire pressures than recommended to further improve fuel economy by a small amount and to improve tire wear, handling, and road hazard safety. Some argue that this causes an uncomfortably rough ride and might be a safety issue. Road rolling resistance is out of your control...but is a factor nonetheless. If you have rough roads, wet roads, gravel, etc. that increases rolling resistance and reduces mileage. Ideally dry smooth roads are best.
One special tip I personally use is to avoid highway travel whenever I can. My commute is all city streets, and my travels around the Phoenix area and the suburbs can usually be done on city streets, where my MPG is higher. Technically, my manual tranny HCH is rated at 51 MPG Hwy and 46 City, but I find that long, flat stretches of city streets can improve my MPG more quickly over the 51 MPG I am rated for on the higher speed highways.
Best advice is to read every post in this forum for a lot more helpful tips....It's a new way to drive !!
Here are a couple more thoughts, adding to what has already been written.
- I think when your temps get to around 70, you will notice a big difference, especially in city driving. I have noticed an increase of about 3mpg from our winter (40-50 degrees) to spring (60-70 degrees) in my city driving.
- When I'm on the highway, I try to (1) not use cruise control, and (2) find a car or cars going about my desired speed and follow them. I think this cuts down on the effect of wind resistance. Not drafting or being too close, but just following at a reasonable distance. I have found that going 75mph on my own yields about 3mpg worse mileage versus being in a system of cars going that same speed. So I just adjust my speed to someone going roughly my speed, and proceed. It is safer that way too, with less lane changes and passing trying to maintain MY speed.
- Drive slow (50)
- Watch the instant MPG bar, and keep it in lean-burn mode (above 70) while cruising.
- At stops, switch to neutral at 20mph to engage engine-stop. Accelerate using full throttle (full throttle is more efficient...no air restriction)
.
I drive an insight, and average 90+ mpg overall using the above techniques. With the Civic, I estimate I could get 60-65 mpg.
troy
Test full throttle start MPG against a gradual increase in speed.
See what you get.
At 20K miles, I noticed that the mileage was dropping off, I checked the air filter and it was modestly dirty. I hunted down (another story) and replaced the filter and found 2 MPG. Remember, a five percent difference makes 52.5 as opposed to 50 mpg.
I also have an Escape hybrid AWD, which my wife drives. I hate the CVT.
-Charlie...
I'm on my third tank of gas and so far I've gotten 40.1, 43.3 and currently I'm at 44.9
MPG.
Question # 1 Is there a single place where all the Hypermiler tips have been collected?
My Commute. I drive 50 miles to work and 50 miles back. The whole ride is from Albany Oregon to Eugene Oregon. My trip brings me on 47 miles of freeway and 3 miles of city. My path gains 200 feet with a few gradule ups & downs.
My best mpg was 51 just after a fill and following a semi @ 58 mph (about 50 feet behind). I managed to maintain it for 150 miles. Then city driving dropped it to my current 44.9
My city miles are supposed to be more efficient than my highway miles, but I'm not finding that to be the case.
I would love to get hypermiles! Slow is OK when it doesn't interfer with normal traffic flow. I refuse to impose rude driving on others.
Question # 2 How are you folks doing it? (please don't start another "coasting"debate)
Thanks All
gr8
Having just traveled Interstate 5 from Portland to California, that section you drive seems to be going 75 MPH plus much of the time. If you get 40-45 MPG at 75 MPH that is not too bad.
My commute is at 6:00 AM and 7:30 PM. The fast push isn't there when I am.
I travel under 65. Lately I'm trying speeds around 60. 40 to 45 seems low from what I'm reading. Maybe it will get better after 5-6K
I almost forgot. Welcome to the Forum. How far are you from Scio. I just sold some acreage out there. I had bought it from my grandparents back in the late 1960s. I still have an Uncle & Aunt that live in Scio.
I think you will find yourself learning the tricks of hypermiling as time goes by. I just have a hard time not going with the flow, no matter how fast they are traveling.
The owner of Civic hybrid came into the shop looking to get the FE tires (reduced rolling resistance to improve mileage). My buddy tells me they are more expensive than a standard tire by a fair amount, but the owner wanted to maximize his mileage. About two weeks later, he came back in to purchase a set of standard tires because he was having real issues with traction and handling.
Anyone else have this experience? It seems to make sense to me that there's a real trade off there and that it really would come down to safety vs incremental increase in mileage performance.
P.S. I love my hybrid today more than ever. I have averaged only $43 per month in fuel, and that is including a 2568 mile road trip in December. Hang in there !!
I used to be a worst MPG offender and drove my last car in a way that did only about 16MPG!
I could have hung onto my old guzzler a couple more years but I would have missed out on a few thousand $$ in fuel savings, and would have continued to ride in my +10 year old, damaged, broken AC ugly car.
My 1st tank 17 months ago was also about 45, and after 38,000 miles my lifetime average is over 60MPG in my '04 CVT. Some other drivers are doing better than I am at efficiency and can really attest to what these cars are capable of.
You are already doing almost the average for most Civic Hybrid drivers, (Especially with your very first tank) so I'd say you are well on your way for great things.
I learned most of my tips from the Insight hypermilers and found great tips for training all around the net.
One great thing about learning how to drive for efficiency is that it can be transferred to any other car you drive as well. For example we've increased our 2001 Grand Caravan's average MPG by almost 8.
Now THAT's a miracle in itself.
Average litre per 100K 4.4 or 63/64 MPG (Canadian)
Also, on NPR one morning they had a short segment about how some cars had the lower rolling resistance tires as original equipment which improves their EPA numbers but owners generally don't buy them when the tires need to be replaced so it is another contributor to EPA numbers not being met in real life.
I'm glad Lexus made the decision they did. The safety trade-off isn't worth the extra mileage and it makes their EPA numbers more reflective of what we will get long term.
When my wife drives it, she takes the average down considerably (-anyone else hate to let others drive (ruin mpg stats) their hybrids?!) I will consider myself a pro hypermiler when I get to the 60 mark.
I've done everything suggested except check the air in the tires at re-fills. I'm due next week and hopefully that will make a difference. Everyone at work is really impressed with the car -I think this will catch on as prices for gas increase.
I have to drive a 4WD F250 Ford van at work, so I'm going to try these tips because it's got a small tank and gets @ 10-12 MPG!! I'm always at the pump!!
:shades:
It varies by car. My CR-V gets better mileage with brisk acceleration, but not with rapid acceleration. The Prius, on the other hand, uses electricity a slower speeds, and the further you go on pure electric, the better the MPG...
Last readout was 4.1 litres per 100K. or 68MPG Imperial ---reduce by 20% for the US Gallon = 54.4 MPG US. 65 miles per hour with cruise control.
So I'd recommend keeping the tires exactly at 44 PSI as recommended on the tire (please check your tire first, though, to make sure the rating is the same as my claim). No roof racks. 55 MPH is unbelievable. And, finally, I try to go with interstate highways rather than city traffic, because contrary to what the mandatory EPA Stickers claim, this car DOES get much better gas mileage on the highway than the city.
Also, check your headlights and any additional electrical load. That determines how fast the batteries drain, and in turn, how much the engine (stink box) has to run to recharge them.
That 44 PSI is DEFINITELY NOT "recommended on the tire" as you wrote. The number molded into the tire is the maximum pressure that its manufacturer specifed before it could possibly explode. It is extremely unsafe to overinflate your tires like that. The proper tire inflation pressure is printed on the vehicle manufacturer's sticker on the door frame. You should have read it.
Tire bursting pressure exceeds 100PSI. Tire MFG's have to maintain a safe bursting pressure above the cold rating, as the tire when hot can exceed an additional 10PSI.
My Dunlops are rated 51PSI cold pressure rating, and that's where I keep them (Even my Honda dealer sets them up for me that way under request).
The only noticeable change is higher MPG but lower comfort.
Why is it that even the tire MFG's websites suggest max cold pressure under certain circumstances? If they were at risk of explosion they wouldn't suggest anywhere near the cold pressure rating.
The best argument against it would be comfort and traction.
However, I take many very strong, hard turns to keep momentum and never slid, even while driving on water, leaves, sand, etc.
I even did a stopping distance test on wet pavement with my HCH back in Feb'04 when it was new and found little to no difference 32 vs 51 PSI.
I had my CAT software recall along with my 40K maintenance done and when I drove afterward my MPG dropped by 7-10. I soon realized that I forgot to suggest the higher pressure to the dealer- So I pumped them back up.
Last Friday night I set my personal record of 914miles on a single tank in my HCH CVT which calculated to 67 point something MPG. I couldn't have came near that on spongy tires that were inflated to just above half their cold rating.
You are correct in posting the recommended pressure is there in the door frame but I, along with many believe this low inflation figure is primarily for comfort, as not many people would buy a car with the harder ride under higher pressures.
After 45K miles there is no uneven or abnormal wear to my tires.
I can't find any tires labelled "low rolling resistance" tires
at either Michelin or Goodyear. The OEM bridgestones
aren't labelled LRR on bridgestone's website (which is
not helpful anyway).
I am looking for an LRR with higher treadwear than the 240 OEM ones
with a high PSI rating and decent grip in wet conditions.
Any ideas?
thanks.
My car has only about 100 miles total, so break-in is not needed to achieve high-mileage, although most people say it will get better by 3k miles.
So how is it done you may ask? I know I was asking this question and after much reading of these forums I got some hints but nobody ever spelled it out in a tutorial for us newbies. Just give me a few basic tricks to start with and hopefully I can learn after that.
First thing I did was pump my tires up to the sidewall maximum of 44 PSI.
My driving style ended up being like a semi truck with the exception that I used a little extra gas to get up to freeway speeds on the on-ramp.
I think I discovered a little "training wheels" kind of trick. I watched the little instantaneous mileage meter and never let it drop below 40 mpg after the initial accelleration to freeway speeds. This produced one moment up a long gentle hill when I was doing 46 mph, only one mph above posted minimum speed but the rest was over 50 mph, with most of it just under 60 (I only got over 60 a few times).
Fortunately there was a little old lady in front of me who was going only marginally faster than I was so I could pretend that she was the slow one. :-)
I discovered that downshifting is a bad thing, 5th gear always produced a higher instantaneous mileage than 4th, I don't know why, it just did. I never saw the downshift light go on and I was down to just over 1000 rpm in a few spots. In case you don't know, the HCH hybrid engine performs well at low rpms because the electric assist produces its highest torque in that range.
I also used the accellerate and coast trick (clutch down) for the short burst of stop and go that I had to endure. I used gentle but not too gentle accelleration for the go parts, I pressed the gas pedal until the assist just comes on (typically about four or five bars). So I avoided gas-only accelleration for the slow parts of my trip. The car can only do about five minutes of this before the battery drains, even with some regenerative breaking. I ended up getting the four charge bars in third gear near the end of the slow part. This was because the computer varies the assist based on the battery charge level and eventually drops to a mostly charge mode when the battery drops to about one third.
I coasted (clutch down but still in 5th gear) as much as possible on the downhills, I only used the accellerator when my speed was below 50 mph on downhills and I only used regenerative breaking when I needed to because in most cases the downhill was just enough to maintain speed. I learned not to let the engine run with the accellerator pressed to maintain speed on a downhill, you gain nothing and lose mpg.
I am not sure I could stand to drive like this all the time but at least now I know it is possible even over hills.
My trip had a long mild hill climb (about 5 miles one direction). After my little experiment I can see how on flat roads 55+ mpg average could be achieved without working too hard.
When I drive normally, sustaining 60-65 mph on that hill climb (but still driving gently), my mileage drops to about 45ish for the same round trip. If I was to push the car with my old driving habits (where I tried to sustain 68+ all the time regardless of hills) I suspect I would only get upper 30s to low 40s in gas mileage. My old car got 28 mpg when I pushed it and its best ever was about 34 mpg for a long sustained 65 mph trip.
Next, only put good gas (good brand of regular with a full detergent package) in your high-mileage car. I use Chevron. Cheap gas can hurt mpg and cause long-term problems too. I know people who had cars that wouldn't run well who solved all their problems merely by switching brands of gas.
Lastly, put regular gas in engines designed for regular gas. Putting premium in engines designed for regular may feel good for a while but it increases carbon buildup which will ultimately lead to pinging which will cause the computer to retard the timing and kill your mileage. And then you have to put in more premium to avoid the pinging, it is a vicious cycle that destroys engines designed for regular.
I have killed a few engines in my lifetime by putting premium in regular engines before a petro-chemical engineer finally set me straight.
As a bit of a counter-example, in my HCH, with cruise control set at 65 MPH, I always get over 50 MPG -- usually in the 52-53 range. Mine is a 2005 CVT. My colleagues at work who also have HCHs get the same. This is on relatively flat 65 MPH freeways through town. Tires at about 36 or 38 PSI.
YMMV, of course, but I just wanted to reiterate that if you just drive regularly at 65 MPH, without A/C of course, I believe you should be getting 50 MPG or more.
Watch out! You are at severe risk of getting bitten by the hypermiler bug :surprise:
When you have semi's tailgating and passing you because you are going too slow you know you are in trouble.
To try to struggle free maybe I will do a few 0-60 runs and see if I can beat or match the edmunds rating of 12 seconds. :-)
But I might lose my mpg (what am I saying)...
My first few months of training my eyes were on the FCD alot more than now. Back then I was more interested in going faster, no matter if anyone was behind or not. Once the technique became routine (6 months or so) I was able to make speed adjustments when there were no cars behind.
I remember when I'd get there my back and leg was a little sore for a while because the drive (Watching FCD, speed, conditions, traffic, SOC, wind etc) was so intense that I'd stiffen my back and Right leg/foot muscles. I was literally on the edge of the seat at times. Learning to relax from this state was also a learning curve for me.
Now it's just routine but each drive presents different challenges.
Today's commute was good- I had a light tail wind and drier conditions and did 68.3MPG on the dash over my 46 miles. To date, I've driven 462 miles and 66.8MPG on this tank and still have 4 bars above half.
BTW
4-5 Hypermilers are in the Chicago area and having a MPG competition with a Prius 2 over an extremely hilly long course with 7 or so stop lights along the way. They're using one car for fairness and exceeding 100MPG. One of them routinely gets over 90MPG in their HCH for their normal daily commute..
Sorry I can't post a link here for Edmunds rules but this is simply amazing.
0-60 Time:
Back when my HCH was a couple of months old I used my wristwatch stopwatch and timed on flat, level dry pavement with full pack and it came slightly over 10.0 seconds for all three tries. Not bad.
o - when running the air in stop-and-go traffic, keep the thermostat at least one click above the minimum temprature, the auto-stop feature will engage more often if you do this, although cabin temperature will increase.
o - when breaking to a stop it seems better to choose a braking gear and stick with it all the way down rather than to downshift through the gears. There is a delay from when a gear is engaged to when the electronics starts drawing power in regenerative breaking so you lose a lot by shifting. I find both second and third gear go down pretty low before the regeneration cuts out.
o - when breaking, initially barely engage the break pedal, this will cause only regenerative breaking to be done. You will see the recharge indicator max out, you will feel decelleration increase also. When the recharge indicator drops (when the engine rpm drops too low to recover more energy) engage the clutch (allowing the auto-stop feature to engage), and increase break pedal pressure to engage the friction breaking.
With practice you will be able to time stops so that regenerative breaking will be maximized and friction breaking will be minimized. Even if you have to stop more rapidly using friction and regenerative breaking together the same technique applies.
Most of the breaking tips are unnecessary for the CVT except for the light break pedal pressure to maximize regenerative breaking, you guys have it easy. :-)
I tried my 0-60 times over the weekend, twice, one was 12 seconds, and one was around 11.5. This is consistent with reviewers who reported between 11.2 and 12.5 seconds.
CVT owners can expect 0-60 in ten seconds. I scratched my head over this one (briefly) and realized that the CVT probably offers a lower gear ratio than the manual does, thus offering a significantly better 0-60 time. The 5 spd gears are tall, no way to compensate for this with driving technique.
I imagine this is true across the board, passing, rolling starts, in every case the CVT probably offers more power and better regenerative breaking, which almost (but not quite) compensates for the efficiency loss of the automatic clutch. The only thing the manual gets you in the HCH is slightly more gas mileage, the illusion of more control, and lower sticker price.
me: You do know that tire pressure varies with temperature. So if you inflated them to 44 psi on a cool day, or a cooler time of day, your pressure at times is above 44 psi? Also you might want to consider how accurate the pressure gage was that you used.
Also since higher tire pressure means less contact area with the road, that's why you get better mileage, you've just decreased your traction for cornering and braking? I don't think the HCH really has that good of brakes or grip, to be lowering their performance further, do you? I'm sure you could get better mpg by lightening the vehicle too; but I suggest you keep the spare-tire, the jack, the airbags, the windshield washer fluid and such.
Mentioning gas though; your vehicle will be aboout 50 Lb lighter if you don't fill the tank over 1/2 way. Run your car between 1/8 and 1/2 full. That WILL help your mpg.
That's why it says 44psi cold pressure rating.
The additional pressure is considered by the tire companies.
"you've just decreased your traction for cornering and braking"
I'm not sure about other tires but I've done braking tests with Honda's recommended 32PSI vs the fuel saving 51PSI in the Dunlops. Over several tries on each pressure there was no measurable difference on wet puddly pavement..
I take some very hard turns to keep momentum and never once lost traction even on sand, leaves etc.
"I don't think the HCH really has that good of brakes or grip"
What is your information source or is this opinion?
If an opinion, how was that formed?
The harder tires will produced a harder ride, though.
me: yes, but as I said the cold pressure varies with when you do it. If it's 6am and the temp is 60F and you fill the tires to 44psi that is the cold pressure. If the temp. then increases to 90F at 3pm the cold pressure in that tire is then going to be 47psi. The cold pressure is going to increase roughly 1 psi with every 10F increase in the air temp. So it does matter what the air temp. is when you fill the tires.
The air-temp. is not critical if you're inflating the tires to the recommended 30-32 psi as you're not near the limit, but when you're inflating them to the max., I'd say it is critical.
you: What is your information source or is this opinion?
If an opinion, how was that formed?
me: http://www.intellichoice.com/reports/vehicleReport/vehicle_nmb/12605/section/specs/type/us- - - ed. 0.77 on the skidpad and 136 ft. braking from 60 mph are not world class numbers.
You may also like to read this about high pressure in your tires. http://www.cars.com/go/advice/Story.jsp?section=ct&subject=adv&story=ctTire
Seen in these forums: 1 PSI difference for every ten degree temperature difference. Not enough to get worked up about.
I carry a seperate gauge, but gas station gauges are usually within a pound or two.
The half-tank idea sounds pretty cool actually.
Traction does not go down linearly as patch size decreases, because the increased downward force per square inch compensates by increasing friction.
misterme's braking test shows us the compensation is pretty good.
In these forums people are reporting reduced gas mileage (about 7 mpg highway) when PSI is dropped from 50ish to 30ish.
Dropping rear tire pressure a bit might make sense, but I would only do it to avoid oversteering (unlikely this car oversteers).
For wet roads, higher tire pressure reduces hydroplaning in addition to reducing wet traction, so neither too high nor too low PSI is optimal for wet safety.
I suspect that far more can be accomplished by using tires that have good wet and dry traction than by varying PSI by small amounts.
Now a more informed decision can be made. Giving up a bit of traction for a small increase in mileage by increasing PSI is ok by me. But I will never knowingly put a tire that performs poorly in wet conditions on my car.
me: I'm not an expert on tire pressure, as I've shown in that link "it's what I've read" from reputable sources.
I've never seen an auto manufacturer recommend anywhere near the maximum tire manufacturer pressure for their vehicles. I'd guess there is a liability issue with pushing the safety limits of the tire. Certainly the engineers of the tires and the engineers that design the vehicles know better than us.
Certainly an auto manufacturer has a lot of incentive from a CAFE perspective as to what mix of large to small cars they could build, if they could increase their fleet mpg. But they don't recommend high tire pressures. The vehicles are designed, including the alignment and camber of the wheels to perform best at the recommended tire pressure.
I would not recommend to anyone any modification that decreases their safety, even if it was an increase of 1mm to their braking distance.
you: I have heard that some people put over 50PSI in their cars.
me: and hopefully no one gets the idea to fill their tires with hydrogen because it is lighter than the N2/O2 mix of air. ;-)
me: Thank you; I hope it wasn't already brought up. And it is safer than having a fuller gasoline tank too if you're in an accident. A smaller, slower fire is preferable. ;-)
Let's digress -- I saw a TV show once ("myth-busters", I think) that demonstrated that it took a couple thousand helium-filled balloons to lift a small child.
"Prius Drivers Demonstrate 110 MPG"
http://www.evworld.com/view.cfm?section=communique&newsid=9134&url=http://www.post-gazette- .com/pg/05220/550484.stm
i wonder... is the Gerdes mentioned in this article Wayne here in Edmunds?