Excursion speedometer 4 MPH off @ 75 MPH?
Thread Starter
|
Elder User
Joined: Jan 2007
Posts: 612
Likes: 0
Excursion speedometer 4 MPH off @ 75 MPH?
I am wondering if anyone noticed the speedometer on the Excursions is off? Because it appears mine is. At about 75 MPH my speedometer reads about 4 MPH fast. I know it reads fast because when the Speedometer says 80 MPH my GPS says 76 MPH. Well I don’t think the GPS is off because the speed display on the GPS matches up within 1 MPH to the speedometer on both my Jeep and my Toyota. I have stock tire size. Is there any way to adjust the speedometer? It does not appear to be constantly 4 MPH off. As I drive faster the speedometer reads increasingly faster then the GPS.
Posting Guru
Joined: Sep 2001
Posts: 1,539
Likes: 3
Even though they are rated as stock size tires, their rolling diameter may be different. Ive seen this especially in the tires built for sports cars. I have the same size tires on my camaro front and back. 275/50/17 but the goodyear eagl F1GSD3's are probably close to an inch taller then the same zied pirelli P-Zero Nero M+S On the front.
Go to your tire manufacturers website and you should be able to find the tires rolling diamater (i beleive thats the term? its how many inches it travels in exactly 1 rotation) and compare it to your stock tires rating. You may be surprised at the difference.
Go to your tire manufacturers website and you should be able to find the tires rolling diamater (i beleive thats the term? its how many inches it travels in exactly 1 rotation) and compare it to your stock tires rating. You may be surprised at the difference.
Tuned
Joined: Dec 2004
Posts: 357
Likes: 1
From: Washington DC
Originally Posted by SPL Tech
I am wondering if anyone noticed the speedometer on the Excursions is off?
It's not uncommon to have your speedo be a little off. Even certified poice car speedos can be off, they are just certified that they read x mph.
Fleet Mechanic
Joined: Mar 2004
Posts: 1,483
Likes: 1
From: SE PA
Mine is a couple off as well....reading higher than it should.
I installed a Scan Gauge and found that (after setting the SG up with my GPS) the truck's computer knows the right numbers, it's the dash speedo and odometer that are off.
I asked my tech about it, and frankly have been too busy to get back with him. He also said that the only speedos that are certified accurate are for Police cars. Interestly, he said that a speedo is like any other gauge that will be more accurate in certain parts of it's swing that others. So, while it may be more accurate in one speed zone....it can be worse than others.
Some say that there is a correction that can be made in the software.
A friend has an '05 SD that also reads high.
I installed a Scan Gauge and found that (after setting the SG up with my GPS) the truck's computer knows the right numbers, it's the dash speedo and odometer that are off.
I asked my tech about it, and frankly have been too busy to get back with him. He also said that the only speedos that are certified accurate are for Police cars. Interestly, he said that a speedo is like any other gauge that will be more accurate in certain parts of it's swing that others. So, while it may be more accurate in one speed zone....it can be worse than others.
Some say that there is a correction that can be made in the software.
A friend has an '05 SD that also reads high.
Post Fiend
Joined: Apr 2004
Posts: 5,158
Likes: 35
From: North of Salt Lake City
Everyone's speedo is likely to be off at some point in time. The diameter changes as the tire wears and can make a difference as much as 3% over the life of the tire. I just calculate my actual speed occasionally by using the mile markers on the side of the road. Set your speed to exactly 60 mph and mark the exact start time as you cross one mile marker and the exact stop time as you cross the mile marker at least three miles down the road. Remember high school math? Distance divided by time = speed. The actual formula is 3miles/180secondsX100X100. 60 Mph. When you know what your speed is vs. what the speedo is saying, you know that for today, your speedo is off by x% in all speed ranges. Piece of cake.
Elder User
Joined: Feb 2007
Posts: 855
Likes: 1
It seems everyone has hitmost of the reasons why speedo's are off. Tires are the biggest culprit always. I never even worry about it becuase I can never see what my speedo says since the top portion of my steering wheel is alwasy in the way. The only down flaw I do not like about my X, but then again that is because of my own driving preference.
Senior User
Joined: Oct 2006
Posts: 405
Likes: 0
From: Bremerton, Wa.
If your speedo is off,does that mean that your odometer is off too??? It seems to me that I remember a report not too long ago, on television (if it's to be believed) that several manufacturers were setting them so that the warranties ran out sooner..I don't think that I could really believe that,BUT it could be..If your speedo is four miles faster at speed,then how much sooner will you get to warranty mileage????
Trending Topics
Fleet Mechanic
Joined: Mar 2004
Posts: 1,483
Likes: 1
From: SE PA
bigdog...YES...your odometer would indeed read higher than it "really" is if the speedo is reading high. I figured mine to be 1 mile for every 100 or so.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
Junior User
Joined: Dec 2006
Posts: 93
Likes: 0
My understanding is that there is no adjustment it's a fixed setting in the computer and that the only way to change it is a device by Superlift called TruSpeed, about $200 it installs inline with the speed sensor and modifies the signal sent to the computer.
Junior User
Joined: Dec 2004
Posts: 82
Likes: 0
From: SW Chicago Burbs
Just a thought. I have access to a few different GPS systems. One of them is dead on with my spedo. The other one is about 2 MPH different than my spedo. This is the same on 2 different vehicles so it is making me believe the GPS is slightly off in the speed calculation.
Laughing Gas
Joined: Mar 2004
Posts: 751
Likes: 11
From: May Township, MN
All three of my Ford's speedo's are off. They all have larger than stock tires and all go faster than what the speedo reads. Tested them all with two different GPS's and the Microsoft navigation.
If your speedo says your going faster than you are you may be able to fix it by getting taller tires.
If your speedo says your going faster than you are you may be able to fix it by getting taller tires.