285's and Gas Mileage

[canadianchevy]

For anyone who has changed their tire size to 285's, what has it done for your gas mileage. I was told once that every tire size I move up, will drop my RPM (at 60 MPH) by 100. This in turn should give me better gas mileage.

What has happened in the real world. Do 285's improve or decrease your gas mileage. Also is your truck a 5.3, 6.0, or diesel. I have a 2002 1500HD 4*4 with the 6.0.

Thanks

Darren

[RyanbabZ71]

5.3 ext cab Z71.  Have had the tires for over 20K miles.  I seen no major decrease or increase in mpg.  I once calculated it to be about +/- 0.3 mpg (this was after 10K on the firestones (265s) and 10K on the 285s)

[NV5600]

I dropped immediately from around 16 to 14.6-14.8. Keep in mind, the odometer does not give you credit for every mile now since the tires are rotating somewhat slower to maintain the same MPH as before due to the larger circumference. That in itself doesn't account for much of the drop. I used the HPPIII to compensate for the larger tires and 93 octane tuning. That got me back to 15.5 mpg. I then added the FIPK and am now a tick over 16.5. Now I get the larger tires, no ping, better fuel mileage and much more satisfying performance with 0-60 time around 7.75

[Redapple]

Unless you update the computer for the new tire size you really don't have a way to calculate the mileage difference. It should however not be a very large difference. You would need to compensate all of your milage readings by 3.7%. For example:

If your odo showed 250 miles when you fill up you need to add 3.7% more miles or 250(displayed miles) * 1.037 = 259.025(actual miles) Then do your fuel milage calculation.

 

So when you are traveling at a displayed 60MPH you are acutally travelling at 62.2MPH

 

The difference in tire revolutions per mile would go from 637RPM to 614RPM.

 

Here is a good link:

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

 

I hope this helps.

Bill

[Curtis Loew]

Even though I compensated for the larger diameter with my HPPIII, when I went to BFG AT 285's, my mileage dropped over 1 mpg.  What displeased me the more, inspite of my 410 gears, was the loss of acceleration.  Well at least they look cool.

[2000LTZ71]

I've had my Yokohama 285's now for about 6000 miles and find my average in town mileage to be around 15.2 mpg. I'm very pleased with that considering I only got 12 mpg with my dodge and that only had 265's on it. My truck has the 5.3 with 3.73 gears