285's and speedometer

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Apr 14, 2009 | 10:02 PM

Gmcbuffalo

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Mountain Pass

Joined: Feb 2007

Posts: 159

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From: Wilsonville, OR

285's and speedometer

I have 285 tires on now and the speedometer is right on, which is wasn't when I had the 265's.
Is there any other reason to have the PCM board reprogramed for the 285 tires?

GregM

Apr 14, 2009 | 10:10 PM

pbr man

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Joined: Nov 2005

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From: North Idaho

My speedometer is right on with 285's, but the miles are off about 5%. The speedometer checked out with GPS and the miles were checked on a 100 mile stretch of freeway and it only recorded 95 miles for 100 traveled. I don't think it is worth reprograming for that.

Apr 15, 2009 | 01:18 AM

officer131

Posting Guru

Joined: Dec 2007

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From: Metro Detroit, MI.

not worth it in my opinion. Might mention it if you sell it

Apr 15, 2009 | 06:32 AM

st8yd

Tuned

Joined: Oct 2008

Posts: 302

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From: central fl

Mine's right on w/285's

Apr 15, 2009 | 07:46 AM

fordboy67

Cargo Master

Joined: Dec 2007

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From: Minnesota

Mine is about 1MPH off with 285s, never checked the distance, have to do that on next road trip.

Apr 15, 2009 | 11:01 PM

Gmcbuffalo

Thread Starter

Mountain Pass

Joined: Feb 2007

Posts: 159

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From: Wilsonville, OR

I thought that the tire size had something to do with transmission shift points?
More reason to believe that this rig was built for 285's.

GregM

Apr 16, 2009 | 08:42 AM

BostonX73

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Joined: Jan 2008

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I know my speedo is off with the 265s according to the GPS. never thought to check the mileage though. I ran it through the tire calculator and figured out it's thinking I have 285s - so they are sitting in the driveway now waiting to get installed.