Gas mileage on a '78?!!

purple horse · 03-06-2000, 06:23 PM

I have a '78 mustang II with a four cylinder, 3 speed automatic. the tire size is 155/80 R 13. my current gas mileage is about 10 miles per gallon. will bigger tires make my mileage better? Are these tires too small for this car? These are the same size tires as they were when I bought the car. Will a 215/70 R 14 or 185/ 75 R 14 be better or worse?

Quik 64 1/2 · 03-06-2000, 09:34 PM

Going to a taller tire or bigger rim (15") will change your gear ratio slightly making it get taller. For example: I just went from 275 by 60 on the rear to 245/60. Now instead of 60 mph @3000rpm, I am now at 55mph @3000rpm. You must also take into consideration that wider (not taller) tires create more friction with the road causing fewer miles per gallon. Just take all these factors into consideration before making your decision. There's not much you can do with 13" rims as far as tires so I would suggest going up to 15" if possible

k.s. · 03-07-2000, 12:40 AM

sounds like there is something wrong with your car.how does it run at idle aand while cruising,does it have any power?

muncie · 03-09-2000, 01:07 AM

... last thing i'd look for , would be a tire size improvement here... check the oil & see if it doesnt come up 95 octane....*shudders*

03-06-2000, 06:23 PM	#1
purple horse Registered Member Join Date: Apr 1999 Location: sterling co. usa Posts: 27	Gas mileage on a '78?!! I have a '78 mustang II with a four cylinder, 3 speed automatic. the tire size is 155/80 R 13. my current gas mileage is about 10 miles per gallon. will bigger tires make my mileage better? Are these tires too small for this car? These are the same size tires as they were when I bought the car. Will a 215/70 R 14 or 185/ 75 R 14 be better or worse?

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03-06-2000, 09:34 PM	#2
Quik 64 1/2 Registered Member Join Date: Feb 2000 Location: Tampa Florida Posts: 50	Going to a taller tire or bigger rim (15") will change your gear ratio slightly making it get taller. For example: I just went from 275 by 60 on the rear to 245/60. Now instead of 60 mph @3000rpm, I am now at 55mph @3000rpm. You must also take into consideration that wider (not taller) tires create more friction with the road causing fewer miles per gallon. Just take all these factors into consideration before making your decision. There's not much you can do with 13" rims as far as tires so I would suggest going up to 15" if possible

03-07-2000, 12:40 AM	#3
k.s. Registered Member Join Date: Sep 1999 Location: rowlett tx,usa Posts: 18	sounds like there is something wrong with your car.how does it run at idle aand while cruising,does it have any power?

03-09-2000, 01:07 AM	#4
muncie Registered Member Join Date: Dec 1999 Location: walton ind usa Posts: 15	... last thing i'd look for , would be a tire size improvement here... check the oil & see if it doesnt come up 95 octane....shudders