I got my Gryphon in this week and recalibrated the speedometer for my tire size. I compared it with what my Escort Passport 9550i said my speed was and they are about 4-5 miles/hour different at 70. Passport is the higher speed of the two. Which one do I trust? Gryphon should be accurate because of the number crunching but the Passport uses GPS to determine speed. I would like to know if I have been speeding this whole time going off the Passport speed.

 

If the Gryphon is calibrated for the correct gear and tire size. I'd have to go with that over the other.

 

I haven't confirmed the gear. I will check on that. Thanks

 

There's been MANY posts in this forum on this subject. If you have a GPS, or a cop's radar gun, or if you do it the old-fashioned way like I did it at first with mile markers, and, if those numbers are different than what you are seeing on the Gryphon and the dash speedo, then I have to say the numbers you are putting into the Gryphon are wrong.

If you are really going faster than the speedos tell you, your tire size is too large. Reduce it. A 5 mph error at 70 mph is about 7%. reduce your tire size about 7%. (But, make sure your gear ratio is correct first).

- Jack

 

I checked my Gryphon with my GPS after installing, the Grypon and GPS showed the same speed but the dash speedo showed me to be 1 or 2 mph faster. I remember reading here or on PHP forums that the ford speedo's show 1 or 2 mph faster anyway. My stock f-250 shows about 2 mph faster than a GPS also.

 

Yup! You got this totally right!

- Jack

 

My 2004 speedo is showing about 2 mph faster than my Edge disply as well, looking more like a manufacturer error!

 

It's just the way Ford has calibrated the thing. If your Edge is showing speed correctly and if the dash speedo is 2 mph fast at approx 70, your odometer will be correct.

In my case, the 2 mph error is only about 1 mph in the 35-40 mph range.

- Jack

 

Ford is trying to help us avoid some speeding tickets maybe.

 

Lets just say that fords estimated error for a speedometer is +/- 1mph, or even 0.5 mph. That means they need to set it so that with the error, you aren't speeding. Could you imagine the backlash of Ford not considering this and 10000 people get speeding tickets because their speedometer was reading lower than it should. Just a thought at least.

 

Thats going to roll up extra miles what about my trade in value?

 

My new truck with stock tires appears to be right on. As your tires wear they become smaller and the displayed speed, and the error, increases. You figure a tire starts out with about 11/32 of tread, and you drive it down to about 3/32. The diameter decreases by 18/32, or 9/16 of an inch of of a 32 inch diameter. According to my math, that would be 1.5%. 1/64=.015625

A GPS will be the most accurate. It calculates speed based on distance and time.

 

Except, fitz - the odometer reading seems to be right on with the speedometer reading 2mph faster than actual. I've learned to just accept it. Maybe Ford IS trying to keep you from getting a speeding ticket!

- Jack