Tire Diameter and fuel data

**buckeyesalt** · 07-23-2009, 09:40 PM

Have a 2005 Chevy Suburban 3/4, 4x4, 8.1L. C ame with 245-75-r16 tires. I came across a good buy on some 265-75-r16 tires. I know they will alter my mechanical speedometer reading but what about the driver data provided by the computer such as: mpg and miles remaining until empty? Will they mess that up to?
If so, how can I restore its accuracy and still use the larger tires?

**Mean_Green_95** · 07-23-2009, 09:55 PM

you will have to get a hand held programmer and change the tire diameter that is set in the computer.

**bill190** · 07-24-2009, 12:32 AM

Actually the newer the vehicle, the more things which rely on vehicle speed and the speed of the tires.

Like a factory radio stereo will increase the volume with the speed of the vehicle.

NAV units use this for keeping track of where you are in tunnels or where no GPS signals can be received.

ABS uses differences in tire speeds for diagnostics and when to apply brakes.

Of course speedometer/odometer.

Traction control uses this information to determine if a wheel is slipping.

The engine computer uses this information along with the computer controlling the transmission.

**tlperry68** · 07-24-2009, 12:53 AM

I've talked about this to the dealer with my truck. I put on 285 / 75 / 18 and I was told they had to flash the computer. After they looked into it there is no current GM "computer code language" for the year truck I have. So my computer still thinks I have the stock tires on. Now it says I get 13.5 MPG but I know its off a bit, I sould be around 16 to 18 for the average.

**5speedsilverado** · 07-24-2009, 03:20 PM

its not a big difference, i wouldn't worry about it, i made that switch on my truck, and the speedometer says 60 and im going 62, so its not worth it to me

**SOUTHERN_FREEDOM1861** · 07-24-2009, 03:32 PM

My speedo was off by 2 mph and still got 21 mpg on the interstate after installing 265-75-16s mudders on my 98 4x4 surburban.

**silveradotrailblazer** · 07-24-2009, 06:39 PM

The stock ecm will adjust up to 10% increase in the size. The factory understands some people change to a slightly larger tire so the built this into there ecm programs.