You're right about the heat in Texas. The only months that DON'T have autocrosses are the peak summer months. We absolutely LIVE for the spring and fall autocrosses.

 

You say you now get 31mpg. Is that mixed driving or what? I get the same mpg in mine this summer as last (28 city, 34.4 hway). If the change in tires started the change in mpg that has to be it IMO. I keep mine at 38 psi (stock Dunlap RFs).

 

I recently learned that because of government incentives most of the gas stations around here are switching to Ethanol 'enhanced' gasoline. Also, I discovered that my station had already switched. That answered the question as to why my mileage recently dropped from a long time average of 30.4 mpg to 29.2 (mostly city driving). But I found a station on one of our local Indian reservations where they told me they would never switch to ethanol. I bought gas there and the mileage on my MCS went right back up to where it was before.

 

Ken, we've had ethanol all along--since before I got the MINI. The pumps in Texas must be labeled with the % in the fuel, and they all (except the new 85%) read "not more than 10%" or words to that effect. There is the slim possibility that it changed by a percentage point or two, but I doubt it. There is absolutely no doubt that ethanol makes your mileage go down the tubes, if you're comparing with and without. But that's the point--same station, same brand, same grade, same pump, even.

FWIW, I can go one county higher (opposite from where I generally want to go) to buy the full-blooded stuff. I don't go out of my way to get it, though my husband almost never fills our '64 Porsche 356 SC with ethanol fuel. (The old engines aren't happy with ethanol fuel.) If, on the other hand, I'm in a non-ethanol county, I make it a point to get it. Right now I'm on vacation, and in the span of Texas to D.C. I was able to fill up a couple of times in non-ethanol counties. Mileage promptly went back up. It's hard to do an apples to apples test on the trip, though, because we went from a primarily flat terrain profile to primarily hilly terrain. Still, we were happy to see it.

Yes, Newt, it's mixed. I live out at the end of a 5 mile long highway (55 mph), and it's pretty much high speed freeway from that point. I don't usually get into rush hour because I work out of my home and can schedule my doctor's appointments and such for non-peak hours. There's a minimum of low speed errand running, too. Most of it would be highway, though.

Okay, here's something new to add to the stew. I emailed Tire Rack to see what they thought, and the person who answered my letter said I had a slightly different tire size. Their website shows 195-55 as the OEM size, and that is the size I bought in the non-RF. Perhaps the early '07s came with a different size? Or does he mean that the difference between the tire size when worn and the tire size when new is significant? If the latter, that doesn't wash either, because from the time break-in was completed I'd settled into the 33 and change mpg, which held for over a year, when it fairly abruptly changed.

I see no one has commented on the coasting/noncoasting question.

 

Coasting (in neutral) would be against most Highway Safety Rules.

Although 'coasting' in gear does incurr the 'load' of turning the crankshaft, the fuel is off and by remaining in top gear as long as possible, you would minimize this 'load'. While Coasting in Neutral, your idling engine would be consuming fuel.

BTW Those Hypermylers are coasting with engines off to realize the maximum gain and that is not worthwhile for the danger.

All Automatic Transmission Cars would Prohibit towing (or coasting) with drive wheels on the ground, I have a MINIautomatic, but seem to recall that MINI prohibits this with Manual Transmission as well.

 

Did you install aftermarket exhaust ?

I know I lost about 3 MPGs after I installed my Megan Cat-back. Can't imagine how this happened ??

 

I don't know why coasting would be against highway rules. When I had my SAAB Sonett back in the early 70's, that was the way we drove. When your foot was off the gas, the car went into a coasting mode in neutral. Although it could be locked out (and we did when driving on snow or ice), this was the default position. I think there are some other cars coming from Europe that do the same thing. And what's wrong with that? After all, the engine is on, and there's no risk of the steering wheel locking, if that's what you're concerned about.

Yes, when I'm coasting in neutral the engine is consuming gas, but is it a factor in the mpg decrease I've asked about? In some of the areas we went literally miles without a foot on the accelerator. As for remaining in gear, even in 6th the car slows quickly, and to my mind that wastes fuel.

Do you have a reference for your comment about MINI prohibiting coasting with a manual transmission?

 

Section 21710 of the California Vehicle Code: The driver of a motor vehicle when traveling on down grade upon any highway shall not coast with the gears of such vehicle in neutral.

 

just opinion here but 2-3 mpg isn't enough to allude to a major issue. it could be any number of things. I don't think tires would do it unless your alignment is way off. Could be air intake or ignition, oil condition or qty, weight in the car, etc. If it dropped 20% I'd say get scientific and get to a dealer ASAP but you're not quite there.

Just FYI observations for anyone reading this...

I have a roof mount bike rack that I now completely remove when I'm not transporting my bike as the extra wind resistance has a noticeable effect on mpg.

AC reduces mileage

Sport mode will significantly reduce mileage in an automatic but definitely also has an effect with a manual transmission as well, although to a lesser degree

Airflow mods make a huge difference in an R56 S only. I went from 31mpg average to 38 consistently... and I don't exactly have a light foot!

Keeping RPM in every gear between 2-3K with a light foot also helps a lot.

p.s. coasting is one of the crazier ideas i've read about on this interweb. consider the wear and tear and risks, distraction, etc. Unless you've got a hybrid, your car was not designed to be driven that way. Drafting certainly works, but after having a rock shatter my driver side window all over me as I drove down the freeway behind a truck (not drafting), I'll pass on that.

 

Sometimes I wish I had my old Sonett. It was amazing--pieces didn't magically fall off the car when coasting, the world didn't end, and cops didn't issue citations for it. It just was another way to go down the road...

 

There you have it. You thought that the tire change and the mileage drop coincided, and if in fact you replaced your tires with a slightly different size that explains it. Your speedo will be off a little too. You would have to look at the old set of tires to see what size they actually were. Case closed!

 

As for MINI and Towing requirements; it caught my eye as unusual, automatics have discouraged or prohibited towing for years,
but had not seen mention for manual gears. Probably saw it in my owners manual and since mine is automatic....

Some mid thirties autos Dodge & Desoto featured "Free-Wheeling"

Pull a **** on the dash and when you took your foot off the gas, the engine would idle and car would coast.

Their next bright idea was Fluid Drive ... all the slip and slush of an automatic, but you still had your clutch and stick

 

The team cars at TdF were stick. I don't know why.

 

Continental factory runflat 195/55VR16 have a O.D. of 24.4" and 844 revs per mile. Dunlap factory runflat 195/55VR16 is 24.5" and 853 revs per mile. The non-runflats are similar in size -- so within 1% of each other. That would only make about 1/3 of a mpg.

 

But is she 100% sure that she had that size oem tire? It could have been a slightly different size.

 

TireRack.com lists all the OEM runflats for 16" and 17" wheels. I assume she has 16" wheels. The tire size for 16" is 195/55-16. They are all within about 1% of each other in revs per mile. The 17" wheels are 205/45-17 and seem to vary from 844 to 868 revs per mile. That's 2.8%, and would account for less than 1 mpg.

 

Very good practice to watch out for any, unexplained change in factors like fuel economy.

Odometer accuracy could be confirmed by watching 'mile-posts' along a highway. Any change in tyres could effect rolling risistance as well as odometer, so that could compound the variations.

These Fuel Injection Systems (especially Turbo versions) run very high pressure in the Fuel lines, all the way from the Tank and then another return line back to the gas tank.

There could be a 'pin-hole' leak anywhere in this system, that might not be enough to drip, but still effect the mileage.

Any whiff of gas smell might likely be what to watch for, my Turbo LeBaron had a couple of these in its twenty years. New gas lines, but then found that it also required double clamps to be 'tight' enough.