Hey guys I Am running the Xcal 2 with vmp tunes. I told justin what size tires I was running and he plugged them into the tune, but when I use my gps system it will say I am doing 60mph when my truck says I am doing 62-63mph. Is there anyway to correct this with this tuner or is this something I will have to do through VMP?

 

Yes you can change it. Go into the "Optional Paramaters" menu, and go to the Revs per Mile submenu then. Since your speedo is running a little fast, your will want to reduce the revs per mile. Say its 620 right now, try 610 or 605 or something and see what it does. You will have to play with it a bit.


A lot of vehicles speedometers actually read a couple MPH fast from the factory.

 

How do you get to the revs per mile parameter? When i go optional parameters mine pops up with "spark" and i have to pick something...

 

My speedo also runs a couple of mph faster. Speedo will be on something like 30 mph, but my scanguage II will say I'm doing 28. I haven't tried adjusting the tire rev though.

 

thanks man, i'll have to try that

 

If you read posts from Bill Cohron at PHP, you'll find he says Ford sets the speedometer to show about 2mph faster than what you are actually doing. What you are seeing is normal.

If you change the tire rev so your scanguage reads differently, the truck's speedo will still read 1-2mph faster.

- Jack

 

... so Ford is the reason for that speeding ticket... wish i could blame it on them!

 

In actuality your going slower then what the speedo reads so ford is saving you from a ticket

 

I have 35" tires. At 605 RPM, I'm only off by about 1/2 MPH.

 

haha oh yeah.... duh

 

If I remember correctly, the revolution per mile (RPM) is based on a tires speed at 40 mph. As the speed increases the tire will distort, and have a tendancy to grow which will give you an inaccurate reading.

 

Part of what you say has to be correct - the tire radius has to increase with increased speed, but the speedometer reading doesn't seem to really match that.

In my truck, using a hiking GPS, I've got the Gryphon programmer I've installed showing the correct speed no matter how fast I drive (up to 80mph). It gets its information from the PCM, which gets its input from a rotation sensor on the rear axle (I think). The truck's speedo reads about 1mph high in the 40mph range and about 2mph high in the 75mph range. So, the dashboard speedo seems to be "overcompensating" for tire expansion.

However, the truck's odometer seems to be correct in spite of all of this.

Doesn't make a lot of sense, but that's the way it is.

(And Fifty150 - are you a 1/2 mph slow or fast when stopped at a light? )

- Jack

 

My truck spedo was right on and matched my GPS before I installed my VMP tunes. After the tunes at 70mph my spedo is reading 4mph fast. At 35 it is reading 3mh fast. I'd like to get mine resolved as well.