185/75 - MPG improvement?

[Eggman]

A taller profile would effectively reduce rpm by 400 per my initial example, as the tire size is essentially a final gear...

Taller profile as in the whole car sits higher, thus affecting aerodynamics. Tire size, not so much.

[gone.a]

Too bad the Enasaves are so darn noisy. I dont care about their grip, I am a slow, defensive and boring driver. I might as well be 33 going on 87. But tire noise is still annoying. With those tires pumped up a bit and on level ground you can give the car a mean look and it will start to roll away.

[cyclopathic]

.Not sure what you mean by ESP. What do you mean by saying 'turn it off?'

Electronic stability program, there is a button with sliding car left from steering wheel to turn it off. ESP is glorified ABS, in addition it detects wheel spin from different wheel rotation speed and steering wheel position and applies brake to spinning wheel.

I've looked at the gap and it looks like 185/75 which is ~2.5" bigger diameter than OEM will be likely rubbing; the gap between tire and fender is 2 fingers

[philavine]

I recently upsized to 175/70 14's thinking that they would provide more stability (less wandering) and the 5.3 % increase in diameter would improve mpg's by that much compensating for the loss of mpgs from the 165's. W/ the ensaves I've been getting 45mpg+ around town and 42-45 mpg at 70 mph, ('14, mt, 26k mi). It still wanders a bit but less so. Have to watch the speedo as I'm actually going 5.3% faster than it says. But who goes over the speed limit in a Mirage?
I did this upsizing based on an experiment I did, swapping in a set of wheels/tires 185/70 14's (borrowed from my '94 del sol) They not only improved the appearance but did improve stability. The only problem was that when I went over a driveway entrance they would bottom out in the rear. Not sure if it was the tires, the wheels were 6 inch wide and the offset wasn't too much different than the ES's wheels. But I did like the drive.

[flatbroke]

I know everyone wants to improve fuel mileage if possible, but there really is no easy, simple method that doesn't have a fairly large downside. The engineers at Mitsu have worked long and hard to bring this car as far along as they have. Sometimes you just have to stop and be thankful and appreciative for the incredible cars we have.

[MetroMPG]

The Mirage is definitely an efficient package, but there's always room for improvement.

there really is no easy, simple method that doesn't have a fairly large downside.

Depends on your definition of "downside". There are some mods that will improve efficiency with little to no downside (eg. better undertray, lip spoiler, just to name a couple).

Others definitely have trade-offs (eg. taller gearing will affect acceleration; taller tires may affect wheel well clearance; additional grille blocking requires you to monitor coolant temps more closely or add an alert if the fan is running more often; some aero mods arguably make the car look weird).

Of course the biggest efficiency gains are to be found by modifying the nut behind the wheel.

But to say "the engineers did all they can" isn't right either.

[palebeachbum]

New member here, just picked up a new/used Mirage, currently at about 30K miles and looking into first set of new tires.

I do a lot of highway driving at about 70-75 mph and would like to see lower rpms and better mpg (I could go slower, I know). Was wondering if larger tires (and their effective re-gearing) would help? For sake of discussion lets not worry about the spedo or mileage indicator being off.

For example a 185/75 tire would do about 78mph when the stocks would be doing 70 mph and reduce rpm by about 400.

Question is
1- Would it even fit?
2- Is there any mpg advantage under steady state highway driving in switching to a larger diameter or does the increased width negate this?

The increased width negates the larger diameter. You're not doing yourself any favors. The smaller the contact patch of the tire, the better the MPG. This is why the stock tires are so skinny. It maximizes the MPG. Unfortunately it also throws road grip out the window. I switched to wider tires. Much improved handling. However the fuel economy has also suffered as a result.

[flatbroke]

The Mirage is definitely an efficient package, but there's always room for improvement.



Depends on your definition of "downside". There are some mods that will improve efficiency with little to no downside (eg. better undertray, lip spoiler, just to name a couple).

Others definitely have trade-offs (eg. taller gearing will affect acceleration; taller tires may affect wheel well clearance; additional grille blocking requires you to monitor coolant temps more closely or add an alert if the fan is running more often; some aero mods arguably make the car look weird).

Of course the biggest efficiency gains are to be found by modifying the nut behind the wheel.

But to say "the engineers did all they can" isn't right either.

The vast majority of these will show little to no gain and can easily be negated by a windy day or a day that requires the a/c to run more than normal. Anyone that thinks these cars aren't tuned right to the nth degree to get maximum fuel mileage with a blend of quality driving and safety is only kidding themselves. Pretty soon the old fuel line magnets and air cleaner vortex inserts will come out.....http://www.popularmechanics.com/cars/a310/1802932/

[Eggman]

The vast majority of these will show little to no gain and can easily be negated by a windy day or a day that requires the a/c to run more than normal.

I'm not sure I follow you here. Whether these modifications are used or not, driving in windy or hot conditions can increase fuel consumption.

[Eggman]

For example, refer to this thread: ECO Mod: Howto reduce level of enrichment when cold

Forum member foama details a modification to Mitsubishi's engineering that reduces the Mirage fuel consumption on a cold start by making the ECU think the engine is warmer than it really is. According to foama, it reduces the amount of fuel used until the engine reaches operating temperature.

While I'm not advocating such a modification, and I'm not sure I would do this (for warranty reasons) it sure seems like Mitsubishi could have made such a similar modification to improve fuel consumption by editing their ECU program.