Not really. The overall diameter of the tire should be close to what the 16" rims had slapped on them.... maybe 55 series tires? I dunno. In anycase, it should be very close therefore no difference in MPG in terms of tire diameter. You may in fact be getting worse mileage now because those 18s have to be heavier than the stock wheels. Heavier = more effort to move them = more gas used. The difference shouldn't be more than 1-3 mpg though.

 

It really is all a matter of gearing. My last car, a 4-cyl '98 Accord was geared the same as in 4th gear as my Protege was in 5th. Consequently, it actually got better highway mileage (about 30-32 mpg @ 75mph vs 28-30 mpg for the Protege) than the Protege. Back when the the speed limits were 55mph, the Protege was still geared too short, and I got about 30-32mpg on the highway. My friend with a '90 LX auto reported getting close to 40mpg at a steady 55mph, taching about 2000rpm.

But, most 4-cylinders won't hit their top speed in 5th gear, like Proteges do. I for one have always wished for a much taller 5th gear. Spinning 4k @ 80 mph is silly. There are very few freeway grades that I can't climb in 5th gear even when loaded (and at 10,000 feet).

But, driving around Yellowstone last year, I got 38 mpg, because I couldn't legally drive more than 45mph (and who's in a hurry in Yellowstone).

 

Ive compared different cars sometimes, with comparable engines and power, and some are a lot better on gas than others.

I think in the case of the MAzda, gearing is a factor, as they rev entirely to much while highway cruising. I would gladly downshift to pass or go up a hill and enjoy better mileage than drive around in 5th gear at 4000 RPM!

But for me, the Mazda is the slowest and least powerful car Ive ever owned (im 34 and I have had 11 different vehicles) so it is a dream on gas to me regardless....

Anyway, besides gearing, there are a lot of engineering differences in engines, and a lot of factors could determine gas mileage differences..

 

I think the exhaust manifold/1st cat has a lot to do with the low fuel economy/engine efficiency. When I installed the OBX header, there was significanly less engine braking when laying off the pedal. When cruising, less pedal was needed to maintain a speed. And yes, fuel economy did go up.

The gearing is probably the biggest problem though. The Saturn that we traded in for the P5 regularly hit 40mpg. On the freeway, the tach rarely passed the 2.5k mark. My Grand Prix GTP at 1/2 ton heavier than the P5, also managed 30+mpg on the freeway. The only time it passed 3k RPM was when making its low 13 sec 1/4 mile passes.

 

i do quite a few trips to and from california, so i have a good idea about this one.

i/h/e on my 2002.5 p5, going 80mph at 3500 rpms. i average right under 31mpg. on a day with not so much headwind coming into california, i can get up to 32mpg. on the way back, (going from basically 0 elevation to a little over 2000 feet), i get 30mpg. same speed. tire pressure's at 40psi on 205/40/17. engine specs are 130horse/135tq pulling about 2900 pounds with me in the car and my stuff.

now with my beater 96 civic ex, going 80mph at 3200 or 3300 rpms, i averaged 35mpg. i had a dirty as all hell stock air filter that was so black the filter element looked like it was black instead of the yellow it really was. the car is also in desperate need of an oil change and spark plug replacement. tire pressure was at 35psi on 185/65/14. engine specs are 127hp/106tq pulling 2600 pounds.

i'd get pretty much the same mileage on 6 gallons now in the civic as i did on 7 gallons in the p5. i've figured i'm now saving $10 (give or take a few dollars depending on gas prices) a trip on gas alone.

i'll let you guys know how the car does this weekend after it got a tuneup.


edit: i forgot to mention the p5 had 30K miles on it and the civic now sits pretty at 96K miles.

and as to the original question of mazda's engine... the fs-de has been in existence in some form since circa 1993 on the 626. i'm not sure about this, but before being put in the 626, there were renditions of the block in the mazda series trucks. hence, we don't get the crazy gas mileage from the newer economy motors from other makes.

 

i wonder if anyone will have better mileage in another 3 years?

 

That's true, but I don't think warmer air will decrease fuel consumption. Considering only temperature, HP is a function of the square root of the change in absolute temperature of the intake air. Assume an ambient intake air temperature of 59 deg F at cruise in closed loop. The density of the intake air as "read" by the MAF sensor will trigger an injector pulse duration that maintains the stoichiometric A/F ratio. Further assume a throttle opening X is required to produce enough HP to maintain a 65 MPH cruising speed.

Now assume an ambient intake air temperature of 77 deg F with the same conditions. The less dense intake air will therefore require less fuel be added to maintain stoich than in the first case. But at the same throttle opening X in this case, the HP output will be less. Therefore, in order to maintain the same 65 MPH cruising speed as in the first case, the throttle opening will have to be increased to X+ in order to provide the same HP. Thus, fuel consumption will rise again overcoming the effects of the less dense air.

IMO, the relatively poor fuel mileage of the Protege is due to its relatively low overall gear ratio (high numerical ratio) in 5th gear.

 

Does anyone make gears for the Protege yet? They do it for Domestic Muscle, why not us?

 

I dont know about that goldstar I got a record low milage of 16 mpg in the winter, now at least im in the 20's.
I would like to point out that Im really trying to get the milage up now. Full tune up and hyper ground goes in today maybe tomorow.

I would like to point out I have a 1.6l

 

I got 29.5 last two tanks in my '03 MSP.

 

30 ish 03 LX.

BTW, a stock 97 Saturn SL1 with a wieght reduction will take out a Miata. Ive seen it. Its Laughable. Dont doubt the saturns man...

SO WHAT if the damn thing is basically all plastic. I mean, I hear the frame is just blow molded plastic. Anyway.. i donno. Ive been up for 49 hours and had 3 pots of coffee in the last 20 mins. Ramble ramble

 

98 protege 1.5 5spd 50 miles each way commute 1/2 75mph 1/2 60mph never less than 35 mpg ( once I'm on the highway I don't have to downshift for 50 miles)

 

Have to think major factor in ambient temp v fuel mileage is air density/ increased drag

 

Holy Lazarus, Batman! Resurrected for the second time!

BTW, in case you didn't read the whole thread, 3rd gens get crappy MPG.
It's the price paid for a little extra low-end torque.