scanguage 2 shows different mph then speedo

So i got a scanguage 2 for christmas, and its all hooked up. I also am running 285-70-17 tires on my truck so i know my speedo is gonna be off.

But at highway speeds say when my speedo says im going 70 mph my scanguage says im only going 67 mph. I thought it was supposed to be the other way around since i have bigger tires. So which one is right, if any? I dont want to pass a cop when my speedo says 70, and im actually going faster. Thanks

 

My SG says im +2 mph at 65 and up its the the same as my GPS though...

 

did you adjust the scangauge for % difference in tire size?

 

My scangage and gps say the same thing, which is different than my speedo. I go with the scangage speed - it goes off the engine speed. Speedo's can be off a certain percentage yet still fall under acceptable settings per the dealers. Go with the scangage speed. My speedo will say I'm doing 65 and the scangage will say 61/62.

 

no. how do i do that? i didnt even know you could do that haha

 

it tells you how to do it step by step in the manual

 

you got it backwards.

Bigger tire, means you're going faster than indicated.
Smaller tires means you're going slower than indicated.

With the bigger tires, you have longer tread surface area. So for the same rotation, you go farther. Which means faster.

 

By default The speedo is 2-3 mph off. GPS tells me i am going slower than my speedo says. I even called a buddy i was taking a road trip with and asked how fast we were going. He said 72, when my speedo said 75.

 

which is why i am asking. I know when my speedo says 70 im actually going about 73 or 74. Thats why i dont understand why my scanguage is telling me the other way

 

lol i actually misread your numbers.

 

its all good. i guess i gotta recalibrate it to the tire size i have.

 

Which page is it on??

 

Don't alwayst trust what the speedometer says.

My truck is completely stock.

My Scangauge shows 2mph less than the speedo on my dash. My GPS & my scangauge match.

The scangauge is pulling the data directly off the computer and is accurate. The needle on the speedometer (on the dash) is not calibrated properly to visually show you the actual mph from the computer data.

 

but is the scanguage still pulling the correct info and speed even tho i have bigger tires then stock? Prolly not, but im not sure, thats why i thought its weird that my scanguage would still be saying 2 mph less then my speedo, even with the bigger size tire.

 

You need to get a GPS and test it.

With larger tires, the data in the computer is wrong. So until you test it via GPS, you really don't know how far off it is.

 

a little late, but page 17

 

Found it.Starts at the very bottom of pg.16.
Thanks.+1

 

The PCM reports the speed of the vehicle by calculating the driveshaft speed vs a formula that factors in tire size and gearing. This is the number that is reported by the scangauge. Your speedometer is set up to indicated a higher number than the actual reported by the PCM. All tacomas are like this. THAT IS WHY THE NUMBERS ARE DIFFERENT. Now go read the manual that came with your scangauge, borrow a GPS, and go for a drive. Adjust the speed offset to match the GPS. The speedometer is not that far off after larger tires are added.
All the scangauge does is gives you an un-filtered view of what the PCM reports.
PCM = Powertrain Control Module

 

I use the my GPS & scanguage for the more accurate speed... Speedos are usually a little off.