smaller tires better fuel economy?

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Derick Cardenas

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guys,



i changed tires from the stock 255x16 to 265x16 all terrain types. i noticed that i my ST eat up more fuel than before. it used to go 450km before a full tank 90liter now it only does a 400km run.



i was thinking to going back to a 255x16 tires or probably a 245 tires. any ideas?



derick
 
When speedometer reads 60mph (96.6km/h) actual speed will be 61.1mph (98.4km/h): 1.8% faster.
Click to expand...



The overall height difference is about 1/2 inch and you are traveling a little faster at 60mph. You didn't state if the tire is any wider, but with the all-terrain tire and slight height difference there is an overall weight differece which will result in more fuel used from a stand-still. You might not have noticed as much difference if you had used a street tire. I would think changing them is more expensive (unless you can for no penalty) than the extra cost in gas.
 
I would only go back down to 255/70/16's for the sake of safety. If ran mine from stock height with 255 and 265's and noticed more stability with the 265's. My mileage didn't go down that much but every truck/ driver is different. Now with the TT, shackle lift, BL, 285/75/16's that I've done I can notice a decrease in mileage but I at haven't recalibrated my speedo yet so not sure exactly what my true mileage is. If you do go back down to the 255's, look into do some upgrades ( air intake, TB, exhuast, etc.. I know when I change my intake and made the dual exhuast for mine it made a world of difference. Also I just cleaned out the TB, MAF, IAC, intake and used the Seafoam cleaner holy hell did that make a difference and I only did that yesterday but already makes a huge improvement to power/economy. Hopefully these ideas help.:D:banana::cool:
 
If exchanging the tires is not possible, you could order a electronic tuner that would allow you to change the tire diameter so your speedo would be back to "normal". You might find that your mileage is probably still about the same. I agree with Les and Jerry, more wieght and an inaccurate speedo can be very frustrating. :unsure:
 
When I bought mine it had 245/70/167 on it. and the speedometer was off the opposite way so thge trac was registering a lower speed that I was realy going.



When I put on the 265/75/16's I checked milegae using the mile posts on the interstate which in 100 mniles traveled, I actually now only registerd 95 miles not 100. So when I calculate mileage now, I add 5% to the miles traveled on that tank. When I do this, I am not noticing much of a difference if any at all. BUt since it had smaller tires on it before, I dont have anything to compare to like I owuld have had if it had 255's instead of the 245's.

 
These are a couple tire upsize/downsize calculators that quickly show speedometer variations and illustrate the visual differences.



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



http://www.1010tires.com/TireSizeCalculator.asp?action=submit
 
Might be more than 1.8%. On my old Trac I went from 235/70-16 tires to 265/75-16 and the difference was almost 10%. The 265's were almost 10% taller than the 235's, so I figured the speedometer was off by 10% and this was verified by a radar speed display sign at a toll booth that I use regularly. GPS will tell you the same thing. If I added 10% to the miles traveled when calculating mpg then it would come out about right, which was still less mpg than I got with everything stock.
 

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