I've had my '04 Justa-Cooper for two weeks now, and I'm loving it. But I was a little disappointed when my gas mileage results came in: almost 23 MPG on the first tank (mostly city driving) and barely 27 on the second tank (mostly highway).

I noticed something, though: I have Falken 922 tires on there (195R16) and I think the car probably thinks it has 15" wheels. So this would mean my odometer is understating. The difference in wheel circumference from 15" to 16" is 6.7%, which accounts for almost 2 MPG.

Is there some way I can make my car's computer understand it has bigger wheels? And how much of my fuel economy am I losing to these tires?

I didn't buy a MINI because I wanted great gas mileage. But the numbers still seem a little low, so I'm wondering what's up.

Also, with regard to the computer, the "average speed" only shows about 3.5-4.0 mph. What's up with that?

 

There's so much more at play here than rim size.

More importantly, it is your tire size. Give me your tire sizes and let me know the "factory" tire size that should be on it and I can tell you a lot more about that.

But, weight of the tires and rims plays a huge factor. Adding weight to the tires increases rotational inertia, which slows your car down and makes it more difficult to spin your tires. This is much more important than just loading weight in your car. Taking 40lbs. from your wheels by choosing lighter tires and rims is like removing 400lbs. from your trunk.

And larger rims are almost always slower because from the center of the rim to the outside of the rim is larger and this also increases the amount of power needed to spin the tire.

If you want better gas mileage, switch to 15" lightweight rims, lighter tires, and keep your foot out of the gas......You'll find throttle response will seem to improve with a lighter wheel/rim setup also.

 

My wife's car did that when she went the first 6,000 miles without resetting the average speed. All of a sudden, the average dropped from twenty-something MPH down to 3-4 MPH. Try resetting the average speed display and see if it behaves after that.

 

Okay, so all the numbers for my tire size are 195/55R16 87V. I've done a little homework and found that this is in fact a "stock" size listed in the owner's manual, except for the "V" part which shouldn't matter anyway.

They're wider than the 175s (smallest on the list), but not the widest (205) listed.

So I think they're stock, but not base. Are the "V" rated tires heavier than a tires with a lower speed rating?

Here's a picture of what I've got:



Doesn't look like a particularly heavy rim to me...

*break* I'll try resetting the average speed and see what it does. I've wondered about resetting the whole computer, since some people say it helps MPG and the car is new to me, so it might be good to let it learn my driving habits from scratch. But I've driven it 500+ miles already, so I'm guessing it's probably already done about as much adjusting as it's going to do.

 

23 to 27 mpg mixed are very good numbers for the first gen cars. It's mostly driving style and proper tire inflation. Have you tried calculating the mpg with the odometer? The computer mpg can be off sometimes.

The three stock tire sizes for first gen MINIs have essentially the same revs per mile.

175/65/15 - 868.4
195/55/16 - 851.0
205/45/17 - 857.3

There is more variation as your tires wear than there would be between these sizes.

Also, about the ECU learning... It actually only adapts to changes in the car's condition and environment, not to driving style.

 

I've only ever calculated MPG based on the odometer. I think the odometer understates, though. What registered as a 15-miles-each-way drive to work in my '90 Toyota Camry is now a 14 mile drive in the MINI.

I'll check the tires just to make sure, but they look like they're properly inflated based on the shape at the bottom.

Another factor whose significance I may be underestimating is the constant use of air conditioning required by the climate here in the summer time. Doesn't seem to make much difference in my other cars, though.

I use 93 octane gas, but it's from a discounted and government-subsidized source (Navy Exchange), so that might have something to do with it, too.

From reading the other MPG threads on here, it looks like there are certainly people doing a whole lot worse. But there are also some doing much better, so I've still got to wonder. Think I'll try pulling a spark plug or two and poking around the ignition system a little to see how it's doing. It's only got 52,000 miles on it, so the plugs/wires/cap/rotor are probably all original.

 

Air conditioning use will certainly effect mpg more in these cars than it would in larger engined cars.

You could time yourself between mile markers on the interstate to see if your odometer is accurate. Mine is close enough. My Hanhart is more accurate than a digital stopwatch, so it wasn't device error. Any error could have been due to when I started/stopped timing.

 

195-55r16 is the same diameter..it is the OEM size...optional on the cooper, standard on the S (unless you had the optional sport package then you got 17' on an S, but the DIAMETER is still functionally the same...no changes were made in the computer!!).
You do have a wider tire than the cooper guys with the stock 15...so your MPG will never be as good...but you have better handling. Everything is a compromise. Some tires have lower or higher rolling resistance...that will affect MPG as will tire rim weight, driving style, and general car maintenance....spark plugs, air filter, o2 sensor, etc....

 

PS...your car has no cap or rotor..electronic ignition...
The coil can get a bit of corrosion on the tips....

 

Haha, yeah, I figured out the cap-and-rotor thing shortly after that last post. I'm thinking about changing or at least checking the plugs. I'm guessing that since the car has 52,000 miles on it, they're probably original. I have a 14mm hex spark plug socket, but I've seen a lot of folks on here say I really need a 12-point socket... and maybe a torque wrench, if they're not too pricey.

I do like the tires I've got on there. I still haven't gotten them to slip on a turn. I get scared before they do...

 

Don't worry about getting a 12-point socket - they don't offer any advantage over a 6-point when you're using them with a ratchet wrench on something that's easy to get to like a spark plug.

Do buy or borrow a torque wrench, though. Too much torque and you'll strip the threads in the head, and too little torque could result in the spark plug loosening up and being blown out of the head by the engine compression.

Lastly, put a little "anti-seize" on the plug threads before you install them. Putting a steel-threaded spark plug into an aluminum cylinder head and then leaving it there for 50-75k miles is just asking for trouble the next time you try to remove it, because you can get corrosion and galling between the dissimilar metals that will essentially "weld" the plug in place.

 

Do you have the auto or manual transmission?

 

Okay, I decided to splurge and get a basic ($25) torque wrench from Sears and take a look at my plugs. Here's the #1 cylinder's spark plug:



In my limited experience, it looks like a plug from a healthy engine with about 50,000 miles or so on it.

All the other plugs looked just like this one. The ignition wires were dated "2003", so I'm guessing nobody's touched any of that stuff since the car was built. I pulled the first two off the ignition coil, and all the contacts looked clean and corrosion-free.

I think I'm going to at least replace the plugs. It's not terribly expensive, it's easy (thanks to my nifty new torque wrench), and I figure after 52,000 miles it's probably about time. And it'll make me feel better, right?

Now I just gotta figure out where to get 'em. Autozone can special order some NGK Laser-Iridiums for about $9 a piece that have the same four-pronged thingy on the business end. They look just like the OEM BKR6QUPs... but is there somewhere I can get the actual OEM ones for a good price? If I've gotta order them, I might as well order the exact ones I want...

I'm also going to put some air in the tires today, just to make sure. Gotta get my baby running in top form, you know? Love this stupid car... :P

 

Actual OEM's are $$$....they have BMW or MINI printed on the insulator....so getting the NGK equivalent or better is IMO better. But the # of the plug is still on the side...so you can get the plugs, same type, but no Special marking on the insulator......
IMO the car came with a multi tipped plug, I'd stick with it, but the lazer iridiums are tough to beat. Great plug. Run them in my other car. Run the NGK equivalent, but cooler, due to my mods in platinum.
Sounds like you are doing it right....the TQ wrench is VERY useful!!

 

The ones that Autozone can order have the same part number (3199) as the OE-spec NGKs and are identical in appearance to the NGKs currently installed. My local BAP-GEON store doesn't even have to order them (40 on the shelf, according to website) and they sell 'em a few cents cheaper.

Question now is, do I really need to replace the plugs? I'll put the picture here for comparison, but this might warrant a new thread...



Thanks!

 

Most folks will do a plug change every year or two as a cheap "tune-up". Amazing what changing out the plugs can do for a car.

 

You may also want to put in a new set of plug wires.

Alot of heat has been into those OEM wires so why not do that also.

Since you are using so called Cheap Gas, I would put in a bottle of fuel injector cleaner to make sure the injectors are not alittle plugged up.

 

We had a recent discussion about odometers and speedometers being off. One of our club members determined the speedo is off (as I have), but he determined his odometer was right on. A GPS was used for comparison.

 

If my plugs looked like that, I would replace them.

What is the # of the plugs at Auto Zone? I'd love to find the OEM replacements for the 4 prongs. I have the single iridiums right now from Advance Auto Parts, but want to take them back.

Of course, I need to find a heat range colder also.

 

Just got 4 new NGK BKR6EQUP plugs (part number 3199) from Advance Auto for $6.99 each! The $6.99 is a website price, but they were able to match it in store (they wanted $7.99). They're four-prong, NGK platinum plugs which are as far as I can tell identical to the OE. Advance had them in stock, Auto Zone could order them (they just call them "Laser Platinum" and don't know about the BKR6EQUP name). BAP-GEON had them in stock, and I imagine a store specializing in import parts would be more likely to actually have them.

But the "3199" seems to be the number everybody knows...

 

The BKR7EQUP are NGK # 4285.

Good luck finding anyone with them in stock. I called Advance Auto Parts, Napa and Auto Zone in 2 cities and nobody had them and they couldn't order them.

Looks like I'm calling Way up......

 

Yes, the MINI speedometers are notoriously "optimistic", but the odometers are pretty much spot-on as long as you have stock-diameter tires. When I checked mine via GPS, I think the speedometer was off by about five percent but the odometer was within a tenth of a percent.

A MINI speedometer can read high by slightly more than 10% and still be "within spec", but fortunately most peoples' MINIs aren't that far off.