Ben I'm very interested in this at the moment. I have a 2005 STR and the best "indicated" mileage I've ever seen is way below that, even when I was being a lol on long trips. The actual mileage was even worse. Are you quoting numbers from the on-board fuel system computer? Even so my computer never displays average fuel economy numbers like that. Are you quoting the instantaneous ones or what?

 

Wow you are attentive. If I rotated tires (mostly impossible on my cars) every time I changed oil that would run into a lot of money. First because I change my own oil and second because quite a few of my cars cannot have the tires rotated or the wheels are just too darn big for me to also do that during an oil change. My 99 K2500 Suburban would be a good example. So I'd be paying for an oil change and tire rotation. A good service shop isn't cheap and cheap service shops like Walmart, Costco, Bj's etc. end up being very expensive in the long run. Part of it's my own fault for having cars with performance oriented tires. Those never last very long and even if the tread is still OK other issues develop which cause a highly tuned suspension system to "not like" the older tires. My sable wagon IS one that is extremely forgiving and the tires do seem to wear a long time. Currently, I drive a lot on poor roads which also doesn't help the situation.

So it really depends on the vehicle in question. If one is getting 50K miles out of tires on an STR then you're also probably robbing yourself of a quiet, good riding/driving car.

 

I do it all myself, in my own driveway. I'm not willing to pay other people to do anything that I can easily do....

 

Got two S-types, both 3.0L in the stable. They both average 19 mpg on "school duty" which consists of 3/4 mile <40 mph to 5 mi. of highway, 60-70 mph, then 3 miles of stop and go, in-line for kid drop off, etc. fair amount of idling. Same thing in backwards order in the afternoon. Too small for most highway trips, but on the rare occasions one or the other gets out to pin its ears back, I see 29-31 mpg at 70-80.

With respect to Post #9....wow...egads...it's been a long time since I was mud-bogging Jeeps and calculating the effect on rpm of the various gear ratios we had to choose from in deciding which gear to run in any particular hole...but I think!!! hope I'm right here...

MPH = (Tire OD" X RPM) / (336 X Final Drive Ratio)

336 is supposed to be the constant that accounts for converting inches/min to MPH if I remembered the formula correctly. I'm pretty solid on the value = 336, just fuzzy on where in the equation it goes...too tired and lazy to derive it this evening.

SO: If all you changed was tires, you can calculate the impact by comparing the inflated outer diameter of the old vs. new.

drag due to air-resistance increases as the square of the speed, so if the new tires are taller, you are going some amount faster at a given indicated speed. It won't be; but to make the math easy, assume your new tires carry you twice as fast across the earth for a given rpm as your old ones, then the drag due to pushing air is increased fourfold. Tire diameter is all that matters (on tire dimensions) for indicated speed, width would affect drag due to rolling resistance.

 

I get like 280 miles out of a tank... It is what it is really. These claims of 30+ mpg have me amazed. These guys driving 45 degrees downhill both ways or something? Do they get the car to 70 never exceeding 2000 rpm, set the cruise and putt along in the right lane and don't ever touch the brakes till they get where they are going?

I agree the whole ethanol / E85 programs are vast wastes of resources, but the government is so behind... Billions in farm subsidies have been given to basically cut gas with grain alcohol and reduce it's energy content, while people are allowed to starve and the price of food has doubled.

I also don't agree that at least in Jersey, with our 15% "MTBE" winter blend, that we really do anything to help the environment. E85 (85% ethanol, 15% gas) has an octane rating of about 105. It burns a lot quicker / hotter than gasoline. BUT it has a lot less stored energy - roughly 75% of the BTU value, so it requires a 30-40% greater volume of fuel to make the same power. The only thing it really does is help the engine get to operating temp quicker, theoretically getting out of closed loop faster and speeding up operation of the cats... It's one thing to have these new "flex fuel" cars that are designed to run on E85, which I have only seen at a couple pumps in Jersey, and another thing to cut gas with alcohol.

I know a lot of the race guys make "race fuel" by mixing E85 and regular 87 octane gas. In equal parts it gives you about a 100 octane mixture, which is great for preventing detonation (and lean conditions), and only about 15% lower energy storage (which can be compensated for in tuning). Once again, this is an arena for high compression, or forced induction engines that do not run well on 93 octane premium (or you have to take timing out of to avoid pinging). I haven't tried this on my drag car, (which is at 14:1 and struggles to start, and idle) but I was thinking about it next season. Usually spraying brake cleaner into the carb will get it to fire, and you have to dual pedal it on the street to keep it idling. I'd have to bump the carb's jets up a couple sizes. But no big deal there.

The biggest problem with Ethanol in fuels, especially primarly ethanol based fuels is their tendency to attack steel and especially rubber fuel lines. Basically the entire fuel system has to be stainless steel to avoid problems in the long run.

George

 

Hmmm is it really possible to get 30+ on S type 3.0
i have 2005 STR.. and the best i get on ave MPG is around 21....

does tire pressure.. oil change and rotating tire regularly make that much of a difference?

 

Factors influencing miles per gallon.
1) Is your reading true? The only safe way is to use the brim-brim or full tank to full tank method, where you divide the actual fuel used as shown by the pump by the miles covered. Pumps can be relied upon to be accurate as weights&measures check them for calibration every month or so. You can't really rely on vehicle's own computer-check as even the latest ones aren't partic. accurate. So your left with the mileometer as the only "iffy" possibility.
2) The dead weight of the car is the biggest influence on mpg, partic. in city driving. S-types are getting on for two tons, so you have to see your mpg. figure in that light.
3) Engine type, whether petrol or diesel, all other things being the same, the diesel will always win on this one, especially in city traffic.
4) The driver has a big influence on mpg., especially in city driving. Anticipating stoppages such as traffic lights, jams etc. will pay off. The driver could drive on the motorway/interstate at 60mph which is economical, or he could drive at 90mph which is certainly not. This is because the power needed to propel the car through the air resistance goes up as the square of the increase in speed. I.e. it will take four times the power if you double the speed -- slightly complicated by other factors, but this mainly applies. All that extra power has to come from somewhere -- the petrol. Cars that are capable of 200mph and can do that speed somewhere are always thirsty, around 3 to 4mpg.
5) Vehicle maintenance, tyres and tyre pressures. As indicated before, tyres with 'clingy' rubber will give you a short braking distance, but poorer mpg. "Eco" tyres will provide a better mpg, but less 'cling' and longer braking distance.

So...if you want the very best fuel economy, buy a light car of less than a ton, get it with the diesel engine option, and drive it in a planned way in town and at no more than 60mph on the motor way/interstate. Some cars like this (e.g. VW diesel Polo) will just about return 70mpgUK with the right economy-minded driver. JAGUARS ARE NOT IN THIS CATEGORY!
Leedsman.

 

Leedsman,

Did you ever see the top gear diesel fuel economy challenge from a few years past? Each of the 3 drivers had his choice of car, but he had to make a 750 mile trip from France to a lighting ceremony in Britain. Forgive my ignorance of the names.

Hammond picked a VW polo 1.3 blue motion, James May, a Subaru wagon diesel.

Jeremy Clarkson shows up in a full size Jag XJ Diesel. He basically has the attitude that none of these cars can make it on this kind of journey on tank of diesel, so it's a moot point so I might as well travel in style and comfort.
He also drove it like he stole it, while the others were trying to be extremely careful an cautious with their driving. In the end Clarkson lost to Hammond, but only because he lost confidence in the car and was afraid he was about to run out of diesel. Afterwards, when they examined the cars, the Jag actually had enough diesel left in it to go another 120 miles....

So apparently if you get the right one they aren't that bad. The only diesels on this side of the ponds are some occasional VW's, Large trucks, farm equipment, and large pickup trucks. Mercedes has started bringing some over under it's bluetec line, but the US has Largely shunned diesel passenger cars as a oddity. None of the luxury makers have even tried otherwise to bring diesels over here.

George

 

THose guys are great! On another "economy special" they drove a Prius 'round their track flat-out for 20 miles or so, and a BMW M3 with the task: "Just keep up with the Prius."

On fillup, the Prius register 17something MPG whilst the BMW was over 19.

 

You guys watch Top gear? Amazing!
Did you get the latest yet (shown here on Tues), with Ferrari 458, MB SLS AMG & 911 GT3 RS?

They cheated a bit with the Prius (nicknamed pious) but hey it was kinda funny.

 

I have watched it on and off... We don't have it broadcast here, we get BBC America, which doesn't show it (cause apparently Americans don't like cars - Probably a directive from Clarkson himself, seeing his disdain for all things from the former colonies). So We're limited to the internet and some productive pirates to procure episodes for our enjoyment.

You guys broadcasting in High Definition yet? I have yet to download an episode in HD.

If you want to laugh, and I mean shake your head and laugh, download and watch the new American version. They say imitation is the sincerest form of flattery, but they might as well have dusted off the old scripts... Pre James May. While this might sound good to someone who has never seen the original, it's like are you kidding me to someone who has been a fan for years.
The other problem is that the 3 cast members just don't have the chemistry that Clarkson, Hammond and May do. It seems forced, and almost if they don't even really like each other.

George

 

http://www.streetfire.net/video/top-...-1_2100196.htm

Wish I'd known beforehand they were filming it. I speak "Hillbilly" fluently and would've offered to ride along as translator. ....not sure they'd understand my brand of English, though...

but back to topic Leedsman makes a thorough treatment of the factors affecting fuel economy (though I'd argue if his methods outlined in 1) are employed judiciously, you'll arrive at litres/100 km -actually, Gal/mi which would be < 1 even for supercars driven briskly causing one to scratch one's head and re-figure) but I believe few on this board are interested in scrunching up behind the wheel of an econobox and gingerly pedaling around for 50-70 mpg. Rather, we seem to have S-Typer's with long histories of 20 mpg and below and others reporting 30+. Understandibly, the low-mileage guys are wondering "what's up?" Can't speak for the V-8's, though I suspect they'd be as economical as the 6's if not moreso, but from personal experience using the fill-to-fill method on 2 different 3.0L's...I see both sides. Stop and go or even a bunch of short trips that are 80% highway will keep you below 20, whereas sustained highway runs with limited stop's will push you toward 30 and beyond. My experience is that the computers are not that bad, normally trying to make you feel better by about 1 -1.5 mpg, depending upon how you handle the resets.

 

HD - yes.
I didn't know BBC America existed. May as well broadcast TG then.

It's not exactly a car programme... comedy, maybe?

 

Top Gear is shown on BBC Canada on a daily basis, sometimes two different episodes per day shown at different times. The stuff we get is at least 6-8 months out of date (just like Coronation Street) so you'll have to wait for us to catch up.

I don't agree with the 'they only bash American cars' mantra, they trash just about everything equally. Sh*t is sh*t in their eyes. Just watch any episode where they discuss the S-Type. Almost put me off buying one 'til I learned to put their opinions in perspective.

Back on topic- tire pressure does make a significant difference in fuel economy, rotating tires and frequent oil changes do not. Trying to diagnose lower fuel mileage based on one tank's worth is pretty well futile. Too many variables.

Don't forget also the apples and oranges comparison of MPG using Imperial gallons to MPG using US gallons. On the other hand, I roll along quite happily at my 7L/100Km average with the 4.2L V8.

 

You should try different brands of gasoline. I have done this! filled up at the same pump twice just to get a better comparison, and doing the same run to work with 3 different brands of gas miles per gallon ranged from 26.2 mpg to 28.6 depending on the brand of gas. This test was not with my jag but I don't think it would make a difference on the better brand for overall mpg. Three of my cars run on premium gas 93 octane, 2008 Audi A3 s-line, 2004 S-type-R, and my 1985 Bmw M6 turbo these all drink the good stuff, my work car 1996 Honda accord drinks the draft. I have done this test more than once because of such a difference, but the outcome is always the same. I think it has to do with the percentage of ethanol in the gas! Next time you fill up try this and see if it makes a difference for you. I won't mention brands by name but the best for me USED TO HAVE ULTRA 94 (if you no what I mean you no the brand) So merry Christmas every one and try your own comparison. Paul

 

Well I'll be damned...

I went on the BBC America website here:
http://www.bbcamerica.com/tvschedule.jsp

If you select top gear, there are several episodes available per day, including what appears to be Most of season 15 on Monday.

My damn DVR iphone app isn't smart enough to find it because of the new US Version.

Time to start manually programming the DVR... Thank god for the terrabyte external hard drive.

George

 

OMG Now I'm furious....

I just realized why my iphone app wont find Top Gear on BBC America.

It's because our stupid cable company (Cablevision.. UGH) doesn't HAVE BBC America, but rather some other channel called "BBC world news". (Which comes up on the menu as BBC).

So, my apologies to Mr. Clarkson and my inference that his bias towards America was the reason why we don't get it. In fact I rather fancy his opinions that country music is rubbish and Nascar sucks. LOL.

George

 

No, we don't get the series until later... BBC America just started showing them uncut here. So, our show is an hour and a half where yours is an hour..Since they have to put in the commercials here...

Anyway, I have every episode..And yes I saw the recent special where they came to America (once again). This time they were much "nicer" about it..LOL... At least they addressed the whole "Stig" issue..LOL

So, here is a great website where you can see them all....

http://www.finalgear.com/

 

OMG you are my new best friend! Thank you for that site... Now to get a torrent client on my home theater PC and off we go!

 

Very off topic - apologies to the OP - but it's good to hear you get/watch TG