speedometer question

This has been bugging me for a while now an can't seem to find the answer.I have a 08 TRD offroad double cab,I've had this since almost new,everything is stock but my speedo is off about 3 MPH slower than my actual speed..My question is: since the Offroad came with 16" wheels an the Sport came with 17",is that unique to the Offroad or is it just my vehicle??

 

Get 265/75/16 tires....

Im even with gps now

 

Yep, this^^^. Mine is dead nuts with the GPS, too.

 

Mine is about 3 off as well on a completely stock truck. Not like I follow the speed limit anways

 

It has 265/70 16 tires on it,that was the original size I believe ..

 

Not what was recommended by posters above...........

 

Within 3 mph is about as close as you can ask for. There are so many variables that exact readouts are impossible. Before GPS we never knew and were happy.

My 07 was always about 3 mph slow compared to my GPS with stock tires, 265/70/16. When I went up to 1" taller 265/75/16's the speedo matched the GPS perfectly, at first. But as the tires wore down they became smaller in diameter. By the time I replaced them the speedo was off again by about 3 mph.

Many guys never consider that as their tires wear down they are essentially 1 size smaller than they were when new by the time they replace them. The odometer and speedometer will vary somewhat as they wear. When Toyota, or anyone else builds them they don't know exactly what size will end up on each truck and even if they did it will still vary over time.

My son is an electrician and usually commutes 40-60 miles one way to various construction sites. When his company completes one project he is assigned a new location. Each project lasts several months. He came to me a couple of years ago and pointed out that for the last 3 months he had been driving exactly 100 miles round trip each day. But suddenly the same drive was only 95 miles. I pointed out that he had recently put new tires on his car. Even though they were the same size, they were 5% larger in diameter than the old tires and effecting both his speedometer and odometer by that much.

 

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My truck has been 5 mph off since I bought it from my gps and my buddies gps. So know if I drive the limit (big if) I no that I'm under or I drive 5-10 over anyway.

 

It's really not that big of a deal,but I have 3 vehicles an this is the only one like it, an it's been consistent ,regardless of the tire wear. I have an 04 TRD an its spot on with the GPS but it has the 265/75-16 tires..I thought maybe it was just "a thing" with 05-12 TRD offroads,since a lot of the other models came with 17"rims...

 

Mine was 3 MPH off with the stock tires too. When I put 32s on it it was perfect.

 

Story (urban legend?) floating around 10 years ago was manufacturers deliberately "programmed" speedometers to read 2-3 mph high (reduce complaints about getting speeding tickets), but didn't do odometers the same way. My 09 with new tires was like this (speedometer reading high), but odometer was extremely accurate, less than 1% difference compared to mile markers or GPS. For those who have gone to 265/75/16 tires, your odometer most likely has more error if speedo has less. And, as mentioned above, error will change on both speedo and odo as tires wear. Only solution I know is to compare every 10,000 miles or so to gps or mile markers if you are really that paranoid about accuracy, either for mph or mpg or both.

In the old days, you swapped a gear in the transmission to adjust the cable drive to the dashboard for speedo/odo. Now it's part of the electronics.

 

My 2011 TRD offroad w/285/75_16 tires is 1 mph off at 65mph...

 

I use to travel extensively for my business and I have rented many types of cars. I have found that most car speedometers show 2 MPH faster than are actually going. For example most Toyota's show 40 but your actually going 38. Fords typically show 2-3 MPH faster than actual. This provides a tolerance for speedometer error. Most laws around the world give tolerances such that a speedometer will never show a speed that exceeds the speed limit.

 

The Off-Roads come with 265/70R16's and the Sports come with 265/65R17's, which is as near as makes no difference the same size. Bump up the tire sidewall ratio on either wheel size by 5% (75 on 16's and 70 on 17's) and it evens out the speedometer but throws off the odometer.

 

I have the Michelin M+S 245/75/R16 on my 2010 stock access cab and I am always about 4mph behind GPS...