Larger tires and speedometer/odometer variation

**Boxman7481** · 10-22-2009, 09:43 PM

With larger than stock tires installed on my Colorado the speedometer is 4-5 MPG less than actual at speeds of 65-75 MPG (checked with GPS).

How does this affect the odometer? Am I putting more miles on my truck than actual??

**daweinah** · 10-23-2009, 03:50 AM

Hmm, your wheels have a larger circumference, so they are traveling further per every rotation of the wheel, so I think your odometer would actually read less?

EDIT: So yes, if your wheel circumference got 10% longer, you will have traveled 110 miles when your odometer says you've been 100. Would probably throw off your DIC readings too. Wonder if that can be adjusted..?

**Thundare** · 10-23-2009, 04:45 AM

Yes this can be done by changing the gear in i think the transfer case to match the size of your new tires.

**XS ive** · 10-23-2009, 01:28 PM

I believe you can also modify the ECU to compensate for larger tires by changing shift points as well as speedo/odo readings??

**canislupis69** · 10-23-2009, 05:50 PM

You can adjust for the tire size (and gear size if you ever change gears) with a hand held tuner. I used a hand held tuner to adjust my speedo for my 35 inch tires and my gear change from 3.73 to 4.56. I used a garmin and kept adjusting with the hand held until my speed was dialed in perfect.