GPS compare to speedometer

T

Toyboomer

New member
Just took my 06 Sport out and checked the speedometer with my GPS. From 35 mph to 80 I checked each 5 mph increment and it was exact.

This is the main reason I am sticking with the original tire size of 265-65-17 as I get rid of the Dunlop AT20s and replace with Revos of same size - just don't like to have an inaccurate speedo.

According to the software the Big-O tire dealer had comparing the effects of different tire sizes on the speedometer, if I were to install a 70 series tire it would change the accuracy by 3.5%. At 70 mph on the speedo you would be doing about 67.5 actual mph. Maybe not that bad for a lot of people but I like to know exactly how fast I'm going, esp. if I'm pushing the posted speeds.
 
Register to hide this ad
I'd be curious to hear how you think the ride and mpg changes when you switch to the Revos. I'm planning on switching from the Dunflops to either stock-size Revos or Pirelli Scorpions.
 
GPS and speedo

Pips - I'll post the info. on the Revos. Should be here this week. Only have 900 miles on the truck but have been tracking the MPG since 300 mi. - will check it before installing the Revos. My guess is the Revos may get a little less than the AT20 as they are shipped on the vehicle primarily to meet fuel standards. The Scorpion ATR sounds like a good tire also.

The way I look at the stock size is that the Sport already has an upgraded tire from the SR5 and the weight, etc. (less the X-REAS) is the same. The 06 Sport stock tire size is the same as my wife's 04 Limited so I don't feel like I'm giving up anything. I realize some people have reasons for a larger tire.
 
Toyboomer said:
Just took my 06 Sport out and checked the speedometer with my GPS. From 35 mph to 80 I checked each 5 mph increment and it was exact.

...if I were to install a 70 series tire it would change the accuracy by 3.5%. At 70 mph on the speedo you would be doing about 67.5 actual mph...
Click to expand...

Glad to hear it's exact.
As for your statement, don't you have it backwards? Upsizing the tire means that for each revolution you are travelling 3.5% further. Therefore at 70 on the speedo you're actually doing 72.5?
 
GPS and speedo

You have a point but I think there are two separate issues: how far you travel and how the speedo is calibrated. From some previous posts on tires, and from the tire dealer software, it was my understanding that the actual speed is less than indicated on the speedo with the larger tire. I remember thinking at the time that it was a good thing, insofar as law enforcement and being pulled over, that you would error on actually going slower than your speedo indicated.

I don't understand exactly how the speedometer is calibrated but I think it might not be a correct assumtion to say you are going 3.5% further, and if you are, does that answer the speedo question of going 72.5 actual mph when indicated is 70 mph. There is the other issue of tire revolutions. Just not sure how fewer tire revolutons per mile correlates to the speedo. This is a good question and perhaps others can chime in as well to answer this.
 
pipspeak said:
I'd be curious to hear how you think the ride and mpg changes when you switch to the Revos. I'm planning on switching from the Dunflops to either stock-size Revos or Pirelli Scorpions.
Click to expand...


I switched to the revos after about 7k on the dunflops and three trips to tahoe in the snow and ice...

I really dont notice much of a mpg change to be honest. The road noise is minimal, and the ride is nice and stiff. I hate mushy shocks, makes you feel like you are sailing more than driving.

I kept with the stock tire size.
 
After lots of 100 mile odometer comparisons, and speedo comparisons, I have concluded: BFG A/T KOs 265-70-17 tires yield a 6.6% understatement of distance. At highway speeds the speedo reads about 2 to 3 mph low. I used a Garmin 176C to check this out.
 
Re: Re: GPS compare to speedometer

Kmvreter said:
Glad to hear it's exact.
As for your statement, don't you have it backwards? Upsizing the tire means that for each revolution you are travelling 3.5% further. Therefore at 70 on the speedo you're actually doing 72.5?
Click to expand...

I Agree:iagree:

I have upsized the tires on the last 3 vehicles I owned. Each one show a increase in speed verses the speedo. Other words they were going faster than indicated by the speedo. It is a straight percentage. The plus side is your odometer will rack up 3.5% less miles than actually traveled. This does a couple things for you...

1. It slightly extends your warranty period since at 60000 on the odometer you actually traveled 62100 miles. (Assuming you change the tires out at delivery)

2. It may slightly help your resale value since it indicates less miles.

So as the original owner it is a plus, if you are buying it used with larger tires you must assume it actually has more miles than indicated.

If you do an oil change every 5k you actually traveled 5175miles.
 
I just completed a 2400 mile trip. My odometer was only off 8 miles compared to my Garmin gps after 2400 miles. This is with stock size tires.
 
You must log in or register to reply here.

Members online

Total: 282 (members: 3, guests: 279)

Forum statistics

Threads
278,306
Messages
3,554,045
Members
248,016
Latest member
Advally Service

Share this page

Trending content

Back
Top