dreamr
Explorer Addict
- Joined
- October 5, 2003
- Messages
- 3,636
- Reaction score
- 13
- City, State
- Lynnwood WA
- Year, Model & Trim Level
- 99 XL / 4x4 / 4.0 ohv
I have actually tested quite extensively with a GPS to figure my true speed after upgrading tires but not the speedo gear.
I went from stock 225/75's to 30x9.5's.
What I found was that saying I am a certain MPH off is not accurate. In reality it is a percentile rather than a Number.
With that change I was approximately 9 percent off. Meaning at 30 I was doing 32-33 At 70 I was really doing 77.
With a tuner or chip Wayne or Doug would be able to correct this for you if your PCM has the appropriate files in it for adjustment. Some do, Some don't. I assume there must be a certain model year when that became possible, but I do not know which.
I went from stock 225/75's to 30x9.5's.
What I found was that saying I am a certain MPH off is not accurate. In reality it is a percentile rather than a Number.
With that change I was approximately 9 percent off. Meaning at 30 I was doing 32-33 At 70 I was really doing 77.
With a tuner or chip Wayne or Doug would be able to correct this for you if your PCM has the appropriate files in it for adjustment. Some do, Some don't. I assume there must be a certain model year when that became possible, but I do not know which.