Speedometer/Odometer incorrect

I have a standard, 5 Lug Regular Cab running stock tires. I have always felt that I was going slower than it was stating and I now have possible proof.

Running 70 mph with the cruise on, my GPS "every time" states I'm going 65 mph. Now I thought as most of you are thinking that the GPS probably is at error. Last week I picked up my wifes new '08 Honda Civic with a digital odometer. Every time I put her car at 70 mph with cruise on the same GPS locks in at 70 mph. Why would my Taco at 70 mph display 65 every time on the GPS while the new Civc constantly shows it right on. I truely believe the Taco is displaying incorrect speed and mileage.

This means that not only am I not going as fast as I select - but the odometer is racking up mileage faster than true mileage shortening the tme between maintenance/warranty from the odometer readings point of view.

When these stock tires wear out I am planning on putting on 16" rims with 215/70/16 vise the stock 215/70/15's. Adding in looks with better looking rims/tires plus should bring the odometer reading closer to true.

Just thought others might find this true with their taco as well.

 

I haven't checked the odometer for acuracy but I will whe I get back from this trip. Maybe it's old school thinking but odometers and speedometers use to work in unisen (spelling) off each other. Maybe it's not the case with the taco's - as I said I'll check it out when I get back home.