You're not serious??? It's like snake oil!

 

For the gigantic aircraft tires, nitrogen may be beneficial. For any automotive tire, however, it's just another gimmick designed to squeeze more money from your wallet....

 

Hows so? that 20% other gases in air, cause density fluxuations in the inflated tire.

If its hogwash why is it mandated by the FAA?

I have my Private with a glider rating. so Im fairly familiar with the FAR's.

furthermore how can it be hog wash snake oil if there is less pressure fluxuation with temprature, and since the molecules are actually larger and uniform they dont leak out.

Where do you think happens to helium gas when its in a rubber or mylar balloon?

Now I really think its rediculous what the actual benefits and the hype have done to drive the prices up.

I mean seriously average joe can create thier own filling station at home.

Just need a harbor frieght vaccuum pump, a cyclinder of nitrogren which is availible commercially stateside. such as BOC-GAS or AIR-GAS cheap a regulator and fill to your hearts content.

 

Thats what I always thought it was a way to cut down on the pressure changing with temperature.

 

jagv8, not only do I beg to differ with ya, but it has already been "performed": It's possible for a more powerful engine in the same chassis as a N/A engine to deliver superior mpg. In fact there are cases where the larger engine fared better than a smaller displacement engine in the same chassis. Examples of "Moving the Mass More Efficently" (MMME) due to more power was evident in the Ford Econoline vans and Mercury Marquise. At a steady 55 mph V8 models delivered 1-2 mpg more than the 6 bangers. The STR chugs through a 2.88 final drive ratio versus the 6 banger "S" 3.25's. Anyone would agree 400 hp @ 410 lb/ft torque makes it easier to move the mass than both the N/A V8 and V6. Somewhere in the powerband/final drive ratio/speed equation; an STR may deliver superior fuel economy.

 

There maybe "cases where" but here I was talking only about the S-Type NA & SC V8. I agree that there MAY (because I don't know for certain that it's not true) be somewhere the STR has superior fuel economy, but so far we have no data to say so and we do have data to say it doesn't.

On nitrogen, the environmental issues (temperatures, pressures etc) on aircraft tires are rather different to cars and also any reduction of fire risk for an aircraft tends to be viewed far more seriously than for a car. So nitrogen for aircraft doesn't by any means imply it's worth doing for cars. If someone can put it in the tires for free, sure go for it. I wouldn't pay.

 

I mention "May" repeatiley in my posts instead of "Will". Somewhere in an STR's powerband there may be a window of opportunity for it to surpass the N/A engine in mpg at a specific speed. Perhaps on the low end or midrange of the power/speed equation. Agree; no data collected evaluating this hypothesis. Also advize to allow this discussion to die before the eyes roll.

 

I guess value is in the perception of beholder. I'd pay $5-10 for the evcuation and fill for nitrogen but that's all. Any more and it's a waste of money it only helps ensure a constant tire pressure

 

Good point! I get Sammy Hagar syndrome way too easily.

 

I've done stretches that long using cruise control when I could but I can't get that kind of mileage in my 2005 STR. You're getting at least 2.5 mpg better than I ever did. So maybe it's just too fun of a car to drive and even though I'm not driving it hard I'm not being a little old lady either ... ?

 

No

 

I have a 36 mile mixed HWY/CTY commute every day to work. About 21 miles of it is all highway. I was averaging 19.8 MPG in my '06 STR. At first I thought there was a problem but then it dawned on me.......I start it up in the morning and let it run for 15 minutes while it gets the inside all toasty and I finish getting my daughter ready. Then I take her to daycare where I leave the car running for another 10-15 minutes and again when I pick her up......all the while it's getting 0 MPG while in park. It sits in idle for a good 35-45 minutes a day. Starting monday I'm going to just start her up and go and shut her down when I drop my daughter off and pick her up. I'll do that all wekk and see what I get. I also noticed my tires were at 34psi where they should be at 40psi, so I filled them up.

I'll let y'all know how it turns out.

 

Yep John...you'll def. notice better fuel mileage when ya shut her down instead of ideling.

 

One of the oft unspoken advantages of nitrogen is it's freedom from water. Sometimes my humidity indicator here gets to around 50%, what effect is on mpg I don't know, but there will certainly be an effect on tyre pressures when they get hot during sustained high speeds.
Leedsman.

 

I am a new member and I am not trying to flame anyone here, but...

Could anyone explain the science behind "more power moving a mass more efficiently"?

Seeing that the cars weigh nearly the same, getting them to 55 mph with the least amount of power possible would create the most efficient result.

If you stuck a 1.4 liter civic engine in the STR, and set it at 55 mph, it would blow away a stock STR in terms of MPG. Where as if you stuck an H1 motor in the STR, set it at 55, it would attain terrible gas mileage. Better yet, throw a tractor trailer engine on in and calculate the gas mileage.


The bottom line here is the speed difference. Wind resistance on cars grows at an exponential rate. That 7 mph difference is where all of the gas went. Had you driven the exact same speed, I am sure the MPG would have been very comparable. I would really like to see the difference, go for another drive!! Differences in gearing ratios and the light boost at low rpms are the only possible advantages.

This is why trains achieve such amazing efficiency. A huge mass, with minimal power for the job, as well as low wind resistance and rolling friction. Metal on metal has much less resistance than rubber on concrete.

 

That which Olsic says about fuel-burning efficiency in a car is substantially correct, both theoretically and in my experience, practically too. I've had approaching 100 cars in my lifetime, often the same model with different engines; it's always been the case there that the smaller engine was noticeably more fuel-efficient than the larger. Same body, same driver, same driving techniques.
And as I've said so many times, if fuel-efficiency is your top priority, you shouldn't drive a Jag! Get a super-economy car by all means, but you won't like driving it -- you'll want your Jag. back....
Leedsman.
p.s. The comments about rail-locomotion are quite correct too. Railway/road locomotives spend much of their time not being driven at all, i.e. coasting due to the rolling-efficiency of the steel tyre on steel rails. Not much grip though...

 

It doesn't contradict the last 2 posts but some are rather surprised that the 4.2 NA is hardly any worse mpg than the 3.0. At a given speed it'll be doing different rpm and the rear diff is different so comparisons are apples and oranges really.

As the STR has more "stuff" (SC and its drive belt, you name it) I'd expect it to get lower mpg than the 4.2 NA and I believe that's the case.

I very much agree you'd hardly buy these cars with mpg as a focus!

However, there are a couple of 3.0 owners on the UK forum who are convinced their cars get considerably less mpg than other 3.0s and would love to find why. This thread, for example http://www.jaguarforum.co.uk/viewtopic.php?f=16&t=53435

 

I will hazard a guess I'll never know exactly how fuel efficient my STR could ever be, since I'm unable to control myself behind the wheel most of the time and bury the skinny pedal every chance I get.

I figure the N/A is a little lighter due to not having the S/C bits lumped on top of the V8, although that could be offset by the weight of the driver or how much crap they have rolling around in the trunk. So maybe the STR could get better MPG if it was mostly empty with a lighter driver....but who is going to find out? The skinny pedal beckons....

 

Getting down to the nitty gritty here. This is going to start sounding like a Toyota Prius forum.


I believe, at the molecular level, my brand of wax has a smaller drag coefficient than any of your guys' wax. Meaning I get .0237234 MPG more.


If you are averaging above 18 MPG, with a heavy foot every now and then, be happy.

Get to know your car, know what your average is, and just watch for any drastic loss in MPG. <--- So you know if something might be wrong.


....forgot to mention, farting into your gas tank improves your gas mileage, it's science.

 

+1 on checking there's no sudden unexplained mpg change.