Yes, I'll definitely go to larger tires when it's time to replace the ones on my xB. Anything to get taller gearing, as 2800 rpm @ 55 mph is insane.

That's great mileage, Jan06xB. I got 46.8 mpg my first tank, and 48,4 mpg on my second. Third tank looks like it will be way down, but it's hard to tell with my Scangauge calibration jumping all over the place.

I'm not convinced yet about not shutting my engine off at stoplights. I figured that pulsing and gliding engine off v. pulsing and gliding engine on is the difference between 55 mpg and 44 mpg.

 

see once it gets to the point of turning your car on and off and tailgating semi trucks to increase mpg numbers... that's just ridiculous.

those people should be restrained and publicly humiliated in some fashion.

 

I don't have to tailgate to get my numbers - In fact I keep at least 3 seconds behind trucks but then some jerk pulls in between us and kicks up a rock or two.

If you look at the trip MPG at a stop light you will see the number drop about 0.1mpg every several seconds or longer depending upon how long your trip has been. It really doesn't impact much. Now starting it up again after a quick shutdown will spike the coolent temp in the engine and mine runs really weak - no power at all after a hot start plus it burns a lot more fuel after startup. I mean really 0.12gph for 1 minute is 0.256 oz per minute and at $2 per gallon it comes out to 0.4 cents a minute . . . let it RUN MAN! As far as coasting with the engine off - I don't know what operates the ABS but I know it takes some power from the battery and makes the headlights dim when it kicks in. Also power steering is very non-responsive with the engine off too - all it takes is one kid or a dog running out into the street and . . . you get my point? Leave it in 5th gear with no gas and the fuel is cut off anyway and eveything is kept HOT for immediate use if needed and you can even run the AC for free on a down hill - I usually crank it up in that situation and get a little extra cooling.

Looks like the rear tires are the tighter fit of the wheel wells with a little over an inch of clearance to the fender so I think just going up to the 65 series sidewall is a good choice. I can order some and see how they fit and if they don't work out sell them to my friend with a Prius. Actually I could pull her tire off and try it first too only they have a 5 bolt rim.

Tell you one other thing . . . anyone going with larger rims and lower profile tires will end up with a LOT heavier wheel and tire than the 15" rims. The low profile tires are over 22lbs and have the same outside diameter . . . must be a lot stiffer tire with more steel belts or something in them.

 

No one here is condoning or encouraging tailgating. When 70% of the speedsters passing me are tailgating the guy in front of them with less than a two second following distance, a guy going 55 mph in the slow lane is a hazard to no one.

Yesterday I was driving a rental car on I-10 in Phoenix, and slowed for a traffic slow-up (cops had a guy in handcuffs when we passed it). The moron behind me gunned his engine, passed me going 30 mph faster, and then realized he was going to rear end the stopped traffic in front of him. He locked his brakes, spun around backwards, and nearly hit the retaining wall. He sent up a huge blue cloud of smoke from the new flat spots on his tires. Speed causes way more accidents than slowness does.

 

Stuff like that makes me feel really good about the way I drive. Something to be said about NEVER having hit anyone in my entire life of driving - been hit 3 times from behind while stopped though twice in my Dad's car and now recently once in my xB - jerk backed up about 50 feet without looking right into my left rear quarter. I am still buffing out the over spray after the dealer body shop worked on it a month ago. And yeah the paint job was good but not as good as factory.

 

My calculation about pulsing and gliding engine on v. engine off was merely a mathematical calculation, not an actual driving experiment.

Fuel consumption at idle is only about .2 gal/hour, but it adds up. If a pulse and glider coasts 2/3 of the time, and it takes him 20 minutes to drive a 10 mile route, he'd consume an extra .2 gal X .33 hour X .66, or .044 gal on each test if he went in neutral with internal combustion engine on (NICE-On). At 55 MPG , he'd use .182 gal over his 10 mile (rounded) test drive. An additional .044 gal used for idling would cut his mileage to 10 mi/.225 gal, or 44 MPG , an 11 MPG penalty.

 

Oops. I meant to edit an earlier message, and ended up quoting it. now I can't figure out from this edit/delete choice, how to delete this message.

 

Idle time would be 2/3 of 20 minutes or .22hours x 0.12 g/h if warmed up or .0264 gallons additional gas for 55mpg and 10 miles 10/55 = 0.181 gallons less 0.0264 or 64mpg yeah a savings but in reality the engine being turned off and on again that much in 10 miles may not be worth it - your odometer ECU shuts down etc. and the engine cools off running less efficiently when started again for the pulse possibly running a little richer wasting the fuel you are trying to save.
BTW at a constant 25mph I get 60mpg or more anyway with the engine on so . . . the point of diminishing returns has been reached where the cost of the ignition switch and the wear on the cluch offsets the savings in fuel. As an example I drove back from the Cape one late afternoon and went by the old Rt 6 because of head winds there is more protection than by 195 which is wide open. I got 49mpg for the trip back about 80 miles but it took about an hour longer to save a few tenths of a gallon of gas. I enjoyed the trip more and saved some gas but really not practical in everyday driving.

 

I've never seen .12 GPH at idle. Both my Nissan and my Scion idle at .22 GPH when warmed up, and at about .55-.60 GPH when stone cold. It does sound like a comparison test might be justified.

I doubt my xB can achieve 60 mpg at a steady 25 mph, but I haven't tested it yet. I agree that anyone can get about 80% of the benefits of hypermiling just from slowing down, coasting, and minimizing pressure on the gas pedal. The last 20% is hard core stuff.

 

Yeah I am not sure of the 0.12 gph yet as I have not filled the tank a second time and adjusted the fill amount factor since the upgrade but my engine once warmed up will drop down to a 680rpm idle and get really quiet and at that point it is 0.12gph - turn on the lights and it goes up to 0.15gph so you can see the load from the alternator. Gives me an idea to connect an external charger to off load more of the alternator and see if I can get the fuel rate even lower. Some of my lower burn rate maybe from Iridium plugs 0.044" and the Synlube in the engine having less friction at low rpm than conventional and synthetic oils. Last night I saw engine braking with fuel cutoff down to 15 mph in 5th gear - I though it was only good down to 20mph but it was 15mph on the ScanGauge digital read out - gps corrected.
What is wild on the two decimal places for fuel is just how sensitive the gas pedal is . . . I can make the 0.01 digit move one at a time and it really is a light touch on the pedal to do it.

 

I couldn't resist - had to go out and test the theories. 10 mile North-south route with one turnaround, 75 degrees, dry, 10 mph west wind. Country road, no traffic.

25 mph steady - 44.5 mpg
25-40 mph P&G glides in neutral, engine on - 49.1 mpg
25-40 mph P&G gliding engine off - 52.8 mpg

 

So, on flat roads P&G with the engine on is good for mileage and best for the car's starter.

 

P&G is good for mileage. It's harder on the clutch than on the starter. though, as I bump start. You get about a 10% mileage improvement with P&G. Switching the engine off only adds another 6%

 

They'll fit. 185/65R15 is the stock size on the JDM bB. They went to the lower profile for the US vehicles for some unknown reason.

I'm pondering going to 195/65R15 to drop my RPMs a bit more.

 

check the size again - the 195 is just wider and the 65 is the side wall height - you want 70 series for lower rpm.

 

The 65 is the ratio of sidewall height to width, so a 195 tire will be about 13mm larger in diameter than a 185 tire.

The stock sidewall ratio is 60, so a 65 will be about 18.5mm larger in diameter than a 60.

Combine these effects and you get an increase in diameter of about 30mm or a bit more than an inch.

a 70 series would be taller still, but there is a matter of clearance in the wheelwell.

 

I thought that is how it works but TireRack says the 60 is the side wall height and not a ratio unless I read it wrong.

 

I need to buy new tires this year so I'm curious to know what size would be best in terms of mileage.

My best tank ever was 47.4mpg before I gave up hypermiling.

 

This might explain it better www.goodyeartires.com/kyt/readingATire/

 

Something else to consider when using larger tires - going up a size adds about 2-3 lbs to the tire and from TireRack this little gem is interesting:

http://www.tirerack.com/tires/tirete...jsp?techid=175

"Larger tires require more rubber and longer reinforcing cords than smaller tires. Therefore within a single tire model line, there is typically a relationship between tire size, weight and the resulting rolling resistance force where larger tires have more rolling resistance than smaller tires."