15 more PSI = 7% better MPG
 

I filled up last night and this tank was the first tank with the tires pumped up to 45 PSI. I originally had them at 30 PSI. This is my 4th fillup this month, and the others have been around 41-42 MPG. For the tank the only thing that changed was the tire pressure, and I managed 45 MPG. Thats about 3 MPG, or 7%.

I think I can do a little better on the next tank, as 50 miles of this tank were still on 30 PSI. No driving techniques or modifications on this tank. I have one rule, speed limit is 60 mph. I'm going to do a couple more tanks at 44 PSI, then a few at 60 PSI to see what effect it has. By that time I should be ready for my alternator delete (almost done, just need the battery) and power steering delete. With those mods I hope to be around 50 MPG without any advanced driving techniques or aero mods.

Update 8/20/2013
3 tank average at 30 PSI = 41.4 MPG
5 tank average at 45 PSi = 45.4 MPG

(4 / 41.4) x 100 = 9.6 % gain

https://lh5.googleusercontent.com/-r.../graph5944.PNG

That's a good increase, But I think you should change the topic title from 15 to 45 PSI.

Nice. Definitely ask MetroMPG to change the subject line for you to "45" instead of "15". What was the previous pressure? What is max sidewall?

Sorry guys, meant to say "15 more PSI", it is changed.

Original was 30 PSI front and rear. Now it's 45 PSI front and rear. Max sidewall is 44 PSI.

Suggests confirmation of what MetroMPG showed in his test: big gains from maintaining max sidewall. He also saw further gains from going as much as 6 psi above sidewall. I go all the way up to 16 over sidewall after warming the tires and at peak daily ambient temps, partly so that cold tires and cold mornings will not likely see psi below maybe 10 psi over sidewall.

I plan on going to 55 or 60 after this current tank. I want to see the difference in fuel economy compared to how harsh the ride gets. I'm perfectly satisfied with the ride at 45 PSI. I can feel more bumps, but I am the type of person that likes to feel the road when I drive so it doesn't bother me a bit. And the girlfriend didn't notice, so that is always a good thing!

One more thing I should mention, lean burn is not working on my car, so there is further potential when I get that working again.

So don't tell her (ever). It might start to bother her. Leave well enough alone.

Yah. LB would be a big bonus. It tends to replace P&G, I think. Someone with experience behind the wheel of one with working LB will chime-in I hope.

Congrats on the improvement!

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Agreed: lean burn, used properly, is a good replacement for high/medium speed P&G, and far less troublesome.

You'll want to investigate aero mods though (at least the stealth ones), to "widen" your lean burn envelope by reducing engine load at your 60 mph target speed.

The alternator delete will help there too, provided the computer stays happy with the reduced voltage.

Here's the link to the PSI testing I did:

http://ecomodder.com/forum/showthrea...tire-2721.html

That thread contains results for a 1999 Camry, 1998 Firefly (Metro), and my 1992 Metro EV.



http://metrompg.com/posts/photos/met...scale-1200.jpg

http://forkenswift.com/album/8-chart...arious-psi.gif

Thanks and it's alright. I've made mistakes too.

As illustrated above tire pressure can make or break you!! I noted a great improvement in our Toyota minivan when I pumped up the tires to 45 PSI from 20~30 PSI... it was good for roughly 3 more highway MPG.

where are you filling your tires at? Do you have a compressor at home? I was going to go up to 45 lbs on the truck today but the dinky compressor at the gas station wouldn't pump more than 35 lbs

Try another gas station? Most keep their compressors at 100+PSI, at least over here.

Or you can buy a small compressor that plugs into your cigarette lighter for not much money. I don't leave home without one.


Different vehicles react differently to different tire pressures. I had a ranger and it had to be at 32-35 PSI, any higher and it would be bouncing all over the road. I have a versa now which seems to handle better at 40 PSI than the recommended 32.

And another thing to remember is if you are driving off the black top or on broken surfaces the higher your tire pressure the more susceptible you are to flats.

Our newer stations have air stations that will fill the 51 lb on the truck. Might try a newer station or one with a new air station.

I also have a very slow compressor from AutoZone that will "go up to 300 lb", but it takes forever to get to 42.

Joggernot

The Sheetz gas station a few miles away from me has an air compressor which will go up to 70, Easily.

I don't follow this forum much so this might have been covered but I have reservations about over-pressuring tires. First, it seems to me that some of the pressures quoted on this thread sounds like a blowout in the making. Second, I would imagine that very high pressures would make for uneven tire wear, negating the savings of fuel consumption from more frequent tire changes.

For my third point I should qualify and say that I have a fair amount of experience working with tire pressures to change a cars handling characteristics, specifically in a racing environment. We can control understeer by lowering front tire pressure or raising the rear pressures. By raising the pressure, we are making the tire grip less. In normal driving conditions this is unimportant but in the event of an accident situation I want as much traction as possible to allow me to perform evasive maneuvers like hard braking or turning.

Having said that, one of the aspects of hypermiling is situational awareness which will have the added benefit of reducing the likelihood of an accident so maybe there is a balance there.

Just some points to ponder. I am all for hypermiling but not at the expense of safety.

CoClimber, I read that Diesel Dave has tires on his truck which are rated to go as high as 80 PSI safely.

6-ply truck tires are rated at 80 psi. My father-in-law ran these on his truck and ran 80 psi all over the USA towing a 5th wheel.

I wonder how it felt without the weight of that fifth wheel.

I would never think that auto engineers ever design with the thought of selling more tires. Therefore, they are considering safety (maybe including their own liability), handling and comfort. It would be wise to consider each of those when doing comparisons of tire pressures.

There are huge numbers of reasonable people who would simply not care if they spent an extra hundred dollars per month to have a more comfortable ride. And that's just one issue.

When I considered going over the max sidewall pressure, I thought it was interesting all tire brands seemed to use 44 or 51 PSI as the max. It seems those numbers are not necessarily based on the limits of the specific tire, but rather some industry standard. Are you going to tell me brand X and brand Y both designed their tire so that it could safely handle 51 PSI? And even if it was the true limit of the tire, the designers would have given it a pretty wide margin of error. Meaning if tests indicated that a tire will bubble or burst at 80 PSI, they are probably going to set the max pressure lower at maybe 60 PSI so that nobody even comes close to the actual limit. They would have to account for inaccurate filling station gauges and other factors.

And we have already discussed how center tread wear on over-inflated tires is not as true as many would seem to believe due to the modern construction of tires. Uneven wear is more likely due to poor tire maintenance like not rotating and not getting alignment checks.

But even with all that, MetroMPG already showed us that beyond 50 PSI the mpg gains taper off significantly. The benefit of running 60 PSI vs 50 PSI might not be worth the risk of going over the sidewall limit in some cases.

Hi, I like driving with LB. (Lean Burn) I only wish they would make a cruise control regulated by LB.

The trick with LB is lifting the gas pedal often causing the ECU to load the LB fuel map. The lift can very small as you will notice if you have a fuel gauge (FG) in your car. Just lift quickly and press it back down to the level you were at. Experiment to see how quickly you can do it. Quicker the better since you won't lose any speed. You don't have to lift all the way either.

By watching the FG you can see when you drop out of LB. Keep your eyes on the road though.

A neat trick is accelerating in LB by very slowly adding gas pedal pressure. If it is slow enough in pedal pressure the ECU is fooled into holding LB. It is easy to gain 5 mph in a Minuit.

When approaching a hill slow accelerate in LB if possible. Then hold the gas pedal absolutely still. This also fools the ECU in holding LB while going up hill. The vehicle speed drops and the fuel burn increases some, but stays in lean burn. You can prove it by pressing down on the gas pedal and watch the mpg drop.

My vehicle that I started with is The Beast. I added a FG to my Chevy Venture and improved my long distance driving by 10 mpg. :turtle:

The Beast (a 12000 lb motor home!) is in the Garage & Tools 15 mpg.

CrazyLee

Helps if you have at least an instant economy gauge (if you don't have an aftermarket one)... you can see the economy level spike and stay high if you lift and re-press.

Been doing that with the CR-V without really thinking about it. Fiddling with getting the car into lean-burn while cruising.

I was going to ask about the ride quality. I run my RAM's tires at 37-38 psi normally. Book says 35. Never thought of running max sidewall (44 psi). Tire wear still even?

Wish I'd thought of that before I bought new tires. Could have bought a higher load range...

Tire wear will not be even at higher pressure unless weight is added to press the tread surface flat once again. That is the actual factor involved.

More weight needs higher pressure in a given set of tires, but never enough to over-ride the maximum setting no matter what. The tire engineering takes into account the momentary increased load under a bounce condition or striking an object in the roadway, where the pressure will soar upward momentarily.

A tire designed for 80 psi will also expect a higher load. Without that load, the tire wear might become uneven.

It is far better to select a narrow tire width to increase mpg, IMHO, than to damage a wider tire by over-inflation. Trading mpg savings for an expensive tire replacement seems obviously counter-productive.

BTW, all tire pressure ratings are always assuming accurate measuring devices.

BE CAREFUL GUYS! i drove on the hwy on a hot day with slightly over inflated tires and one tire started shaking and wobbling like crazy - turned out it developed a "bulge" - lucky it did not blow out completely. anyways, destroyed tire and $100-$150 out for the learning experience....not worth it imho...

The truck was set up for towing. Ride was rock hard without the 5th wheel. With it, the ride was very nice.

I ran the tires in my old scion at 63-64 cold...rode like **** but gained the 3mpg I lost by switching to "fuel max" tires over stock

Were said tires properly balanced? What pressure were you running and what was the sidewall max?

Aren't you concerned the having such high pressure in your tires will cause premature wear of the middle tread?

Depends on the car, depends on the tire.

On my R-Comp Advans, which are wide, sticky and have a treadwear rating of somewhere between "zero" and "negative infinity", running over 35 psi... yes... friggin' 35... will wear down the center blocks quickly unless you drove it like you stole it and exit each corner at 1g lateral.

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On my truck and CR-V, we run 45 to 50 with absolutely no problem.

Absolutely true.

Plenty of 1st generation Insight owners run their cars' Bridgestone RE92's at pressures *well, well above* what cbaber does... and still they generally wear the shoulder treads first... even on cars that spend the majority of their time on the highway.

It's not a given that pressure higher than placard = increased center wear. Depends on the car, depends on the tire. It hasn't happened to me on 3 different cars, 3 different tires.

Adding another one to the count; I ran at least 10psi over the manufacturer recommended 32psi, up to and including max sidewall (51 psi), in the OEM tires on my Fit, and they wore evenly.

What was the weight? Was the vehicle carrying more than stock?

Thanks for clarifying! That makes sense.

Were you asking me? I dunno, a fit weighs around 2500 lbs or so. I never carry any animals in it beyond the occasional cat to/from the vet. I've used it to carry humans, and a remarkably large amount of non-living stuff as well.

Some cats get heavy.
http://assets.carwow.co.uk/blog/Chee...side-car-2.jpg

@wdb, Yes I was, as well as anyone else with over-inflated tires. The issue I wonder about is whether or not some might have more weight than stock or carry more as rule. That would make increased tire pressure necessary, and not considered as over-inflated at all. Therefore, tire wear would be even automatically.

There are many times we might need to carry larger loads and increase the tire pressure, or need increased traction for a short way and decrease the tire pressure accordingly.

I would like everyone to mention their loads when discussing increased pressure.

it's an eco forum......nobody is pumping up to carry a 'load'. in fact the real question is "who has lightened their car weight?"

I for one reduced the wieght on theQ45 about 100 lbs.
The only time I add weight was when traveling to texas 3 times a year for a 2-3 week stay.

Not really. The purpose of getting better fuel economy must be coupled with getting useful work done. (The best fuel economy is probably a human-powered bicycle or similar. And that would be pretty useless work.)

If anyone is trying to get better economy, and he is driving by himself in a vehicle with more than one passenger space, he does not understand the concept of real energy savings to begin with. We are then just playing around with little bits and pieces of the puzzle. Interesting maybe, but not particularly helpful over all.

After all, don't people go to a lot of extra work to make their cars more aerodynamic? That just usually adds weight. It would be far better to shrink or expand the vehicle based upon space needed.

If one is not going to do that, then calculations of weight when adjusting tire pressure are a very reasonable part of the formula. Today I might just be driving myself, but tomorrow I might be taking the family and a full car of vacation stuff on a very long trip.

We can no more ignore weight then we can aerodynamics or rolling resistance or time or speed or any other part of the equation. Weight will always play a part in the whole discussion; especially when considerations of tire wear are concerned.

BTW, it is actually an eco-mod forum. ;)

In any of those cases I would be running the same pressure in my tires.

Higher pressure (up to a point) = better fuel economy. The fact that I might also desire higher pressures when carrying a heavy load is, at best, secondary to my decision.

In addition, based on the experiences, links, and other information presented on this forum, I personally have come to the conclusion that higher tire pressure and uneven tire wear are largely unrelated. You are of course welcome to believe as you will, but you should be aware that folks here place a lot more faith in evidence than than they do in conjecture.

Many posts are based on personal conjecture without scientific proof. In addition, there is a lot of anecdotal evidence. As such, there are no scientific conclusions to be made.

Actually, scientific evidence can be based upon the overwhelming weight of evidence, and that evidence clearly shows the over-inflation, just like under-inflation, causes uneven tire wear over the life of the tire. There is absolutely no evidence to the contrary.

BTW, I use no beliefs; I use facts. ;)