Hey, I'm getting 19 mpg!!!

[Red Regal T]

For about a year and a half I was getting 17-18 mpg, tankful after tankful. For some reason a couple months ago it dropped to under 15. I was and . I had installed a stretch intercooler and went to 27 1/2" tall tires. That's when my mpg went down. Didn't make sense a taller tire would hurt my mpg. I figured on the opposite. For the 19 mpg I am now getting, I installed a 2 1/2" hooker catback system w/ Summit turbo muffs, TH downpipe, and put my shorter 26" tires back on. I'm but .

 

[Evans Ward]

Hey John.... 19 MPG is fantastic for one of these cars! I get 15 MPG combined road/city mileage and that is driving mostly like I have an egg under the gas pedal. And when I get on it some.... mileage really suffers. Of course, I didn't purchase my car for a gas miser. My car is within normal tuning parameters courtesy of SM and TL too.

Evans Ward
Macon, GA
87 Turbo-T
70 GS455

 

[VIN7]

John, did you take into account that the taller tire would register less mileage on the odometer?

Mike

 

[Red Regal T]

No, I didn't Mike. Do you think it would make that kind of difference? Sounds like a lot with an inch an a half taller tire.

 

[VIN7]

Well, not that much difference but some. There is a % diff of about 5.6% between 27.5 and 26 diameter, which would be about 1 mpg difference. Accuracy in height measuement may affect that difference. What are the tire sizes? Maybe one has a wider contact patch and more resistance?

Mike

 

[Black Car]

Hi John,
Yes it will make a big difference. Your speedometer wll be reading say 65 and you will actually be doing 70 or better. I don't have the formular but my guess is 3-4 mpg.
Do you have a measured highway or road in your area?
Using highway markers will get you close if you use 10 or more miles as a test run.
If you have a speedometer shop in your area would be the best option.

Gary

 

[gnXfan]

The revs a mile are interesting.

http://www.miata.net/garage/tirecalc.html

 

[Red Regal T]

Well, for sure my gas mileage dropped when I put on the 295-50 16s. They are 10 1/2" wide and 27 1/2" tall. I had to take them off because when I put the hooker catback system on my car, I couldnt get the tires back on because they hit the tailpipe. I put my 255-50 16s back on and then realized I was getting great mileage. I think you guys are right. No matter what, it feels better to get good mpg. Kind of like when you buy a car and the odometer says 60,000 miles but everybody but you knows it has 160,000 on it.