new tires=bad gas mileage

-
R

rippedvinyl

Member
Joined
Aug 3, 2010
Messages
24
Reaction score
0
Location
hull
I have a /6 72 4 door Dart. I went from 195/70/14 cheapo tires, to 225/70/14 decent tread tires. I figured I would loose a little in gas mileage, but I've lost 2 miles to the gallon, with alot of drag when the car should be coasting. I'm 90% sure the tires will be returned, but I was just wondering if this has happened to anyone else? And if it's possible to remedy.
 
going to a 225 is wider... so more rubber on road... also a 225 is taller and might of changed your gearing some. a taller tire with make a motor work harder
 
racerkilla said:
going to a 225 is wider... so more rubber on road... also a 225 is taller and might of changed your gearing some. a taller tire with make a motor work harder
Click to expand...


X2

Your speedO may be a little off too going with a taller tire so you could be going a little faster than you think you are.
 
I'm pretty much just going with the same flow of traffic that I always do. The drag is the main issue. It just doesn't glide the way it used to. I'm just surprised that I lost 30 miles on a full 14 gallon tank.
 
I haven't checked yet. It's only been a few days since I got them. I assume they are at the correct pressure since they were just installed.
 
I would check them. You never know. Also if you have steel wheels and they don't clean around the beed they will leck on you. Ask me how I know. LOL any way just some thing to check on.
 
rippedvinyl said:
I'm just surprised that I lost 30 miles on a full 14 gallon tank.
Click to expand...
that's about a 15% change in tire height, so it's about a 15% change in you speedometer too. If you normally get 250 miles to a tank and this time you got (an indicated) 220, you're pretty much bang on.
If you normally get 300 and you got an indicated 270, your mileage is actually better...
 
@ 95teetee: You may be right, I will monitor it tonight on my commute. It's 28mi, if my speedo says something closer to 30 you may be on to something.

@Burntorange70: How would I clean/check the bead at this point?
 
rippedvinyl said:
@ 95teetee: You may be right, I will monitor it tonight on my commute. It's 28mi, if my speedo says something closer to 30 you may be on to something.

@Burntorange70: How would I clean/check the bead at this point?
Click to expand...


He is right your odometer is going to be off now too.

I would just keep an eye on the pis and if you got to keep filling them every day or two you need to take the tire off to clean them. Mix some soap and water in to a spray bottle and spray it on the bead. If you see bubbles your in trouble. Mabby take it back to the place that put them on. You need a tire machen to brake the bead down. Then use and angle grinder with a sanding disc in it to clean the rust up.
 
Since the taller tires actually reduce the gear ratio, like going from a 3.23 to a 2.94, it can hurt mileage in stop-n-go traffic because the engine torque isn't working as efficiently with less overall gear. You may also be pushing down on the pedal more to get it going like it use to. The taller tires also make the car sit higher, hurting aerodynamics, but that may be insignificant at lower speeds.

But the lower speedometer/odometer readings may make the most difference in your figuring. Your odometer would read LESS mileage because the taller tires would make less rotations driving the same distance, so the odometer would reflect fewer miles.
 
Locomotion said:
Since the taller tires actually reduce the gear ratio, like going from a 3.23 to a 2.94, it can hurt mileage in stop-n-go traffic because the engine torque isn't working as efficiently with less overall gear. You may also be pushing down on the pedal more to get it going like it use to. The taller tires also make the car sit higher, hurting aerodynamics, but that may be insignificant at lower speeds.

But the lower speedometer/odometer readings may make the most difference in your figuring. Your odometer would read LESS mileage because the taller tires would make less rotations driving the same distance, so the odometer would reflect fewer miles.
Click to expand...



Yes. I do have to push down harder on the gas to get the same results I used to. And you're right LESS miles on the odometer.
 
Mileage is exact. Looks like I'll be returning these tires that look great on my car, but horrible in my wallet
 
you can return used tires? they are going to put on your old ones???? what made you go with a non stock tire size, thats a 26.2" tall tire thats the size i have on my 68 RR
 

Attachments

  • 68 RR 383 4-speed (43) (640x480).jpg
    114.2 KB · Views: 285
EL5DEMON340 said:
you can return used tires? they are going to put on your old ones???? what made you go with a non stock tire size, thats a 26.2" tall tire thats the size i have on my 68 RR
Click to expand...



I have 30 days to try out the tires, if I don't like them I can exchange. What made me go with that tire size? Lots of tread for commuting 60 miles round trip in New England>
 
If you calculate the percentage of difference between smaller diamater and larger diameter you may be getting close to the same mileage. But the smaller diamater will get you the better gas mileage.
 
rippedvinyl said:
It just doesn't glide the way it used to.
Click to expand...

I noticed the same thing when I went from skinny 13"ers to wider, taller 14's. If anyone remembers the gas crisis in 1973, the car makers put skinnier tires on some of the new cars to help gas mileage.
 
Best gas mileage regardless of tire size comes from increasing tire pressure. Increases tire pressure will decrease tire drag and rolling resistance. Look up your tire inflation data for your car as compared with the max rating on the sidewall of the tire and go for a compromise somewhere between the 2. If the ride becomes too harsh, decrease pressure slightly until you find a nice comfort band with mileage you can live with.
I think someone had a pressure graph or formula posted to figure this stuff out pretty close. I run all my cars about 8# higher than auto mfg. reccommended pressure.
 
Update:

I returned the tires, and put some michelin 205/70/14's on. I'm back to my average of 18mpg, up from 16mpg.
 
In any case you should :
Inflate your tires to whatever they say say 35 psi cold.
Find a 10 or more mile stretch of highway with mile markers.
Note your mileage on your odometer
Drive to the tenth mile and check your odometer.

if it is far off calculate the percentage difference, pull your odometer gear out of your trans and go get one that is the correct number.

Example :
If your are 10 percent high on your odo You read 11 miles after driving 10 miles.
Your gear is 10% too small and you need to get one %10 larger.

If your are 10 percent low on your odo You read 9.1 miles after driving 10 miles.
Your gear is 10% too large and you need to get one %10 smaller.

Replace your gear and retest
Or you can go to a speedo shop if you can find one.
 
Why is it important to check my odometer?

My commute to work is 27.2 miles on google maps, and from door to door in the dart it's 27.2 miles. Regardless of what tire size was on the vehicle it was always 27.2.
 
You must log in or register to reply here.
-

Back
Top