Topic: 30x9.5 15 & mpg

[g2tj06]

My jeep is a stock 2006, 2.4l with 6spd.  It has 30k.

I went from the stock 215/75/15 to Cooper Discoverer ATR 30x9.5 15's. 

Ive noticed my mileage has dropped off at least 2 maybe 3 mpg.  I didnt think it was going to be a big enough change in size to make a much noticeable difference but I guess I was wrong.  This is with me making a adjustment for the bigger tires. 

Is this about the norm and is it worth recalibrating the speedo.?

[jagular7]

You went to a taller and longer circumference tire. It takes more energy to get it rolling. It takes more distance to make it go completely around from a point on the tread. You will see a slight decline in mpg for city driving as you stop/start. However, you should see a slight increase in highway mpg as you don't use as much fuel to get a longer distance. The larger tire acts as an overdrive on the highway. But again, it all depends on the terrain (hills, mountains, flat) of the roads, if there is any wind, tail or head, and overall weight you carry.

[Dylan]

Try bumping your tire pressure up, doing so will reduce your rolling resistance and help milage.  If you go this route, be sure to watch your tire wear pattern... if they start wearing excessively in the middle then drop the pressure back down.

[Jeffy]

My jeep is a stock 2006, 2.4l with 6spd.  It has 30k.

I went from the stock 215/75/15 to Cooper Discoverer ATR 30x9.5 15's. 

Ive noticed my mileage has dropped off at least 2 maybe 3 mpg.  I didnt think it was going to be a big enough change in size to make a much noticeable difference but I guess I was wrong.  This is with me making a adjustment for the bigger tires. 

Is this about the norm and is it worth recalibrating the speedo.?

Recalibrating your speedometer.  You're not getting accurate mileage numbers.  Your speedometer is slow and so is your odometer.

[sharpxmen]

Recalibrating your speedometer.  You're not getting accurate mileage numbers.  Your speedometer is slow and so is your odometer.

x2
that can throw off your mpg by the same amount (if your speedo/odo is off by 7% that's by how much your mpg results will be off, so for 15mpg you're actually at 16mpg)

[g2tj06]

I know my odometer is off.  I have been adding right around 6% to my trip odometer at fill ups. 

I am still down about 3mpg.   

I will start checking pressure more often to be sure it stays consistent.  I know this can cause a fluctuation in mpg.

[Jeffy]

I know my odometer is off.  I have been adding right around 6% to my trip odometer at fill ups. 

I am still down about 3mpg.   

I will start checking pressure more often to be sure it stays consistent.  I know this can cause a fluctuation in mpg.

The speedometer isn't used just for speed and mileage.  It's used to fine tune your air/fuel maps.

[YoungJeeper]

The speedometer isn't used just for speed and mileage.  It's used to fine tune your air/fuel maps.

Really!? Is that for both the auto and manual? That's awesome! about how much difference will it make? (besides no longer having to add 10%) 

[Jeffy]

Really!? Is that for both the auto and manual? That's awesome! about how much difference will it make? (besides no longer having to add 10%) 

Both.  Since the new gear is around $20, it's well worth it to fix.  See the FAQ for details.

[aka-justin]

Good to know, I'm running 31's :)

[g2tj06]

thanks for all the replies

I will order the gear and replace it since the tires affect not only the speedometer/odometer but also the air/fuel mixture.

And on the going back to old size, not really worth it for difference in mpg I would gain back.  It would take me 16 months to make back the difference to pay for a new set of tires in the old size.

The new tires have grown on me and I didnt buy the jeep for mpg's anyway.  Just wondered if that about the norm. 

[Torch_Ind]

thanks for all the replies

The new tires have grown on me and I didnt buy the jeep for mpg's anyway.  Just wondered if that about the norm.  

I was going to ask why you got a jeep if you were worried about mpg's in the first place lol.  

for long trips and mpg's is a factor we hop in my g/f's honda civic hatch 2door with a little 1.6L and got for miles and miles for 20$ lol  even then the mpg's don't bug me I would take the jeep but she complains about the extra cash spent for nothing lol especially if it's nice out and we can go top down!!