Speedometer Calibration Using Forscan
It's a Van Gogh
Joined: Feb 2010
Posts: 7,795
Likes: 1,326
From: Elk Grove, CA
Thread Starter
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Laughing Gas
Joined: Oct 2016
Posts: 1,072
Likes: 91
From: DFW, Texas
According to this website the RPM is 657.
None the less, its well worth the effort. Huge fan of Forscan!
Junior User
Joined: Nov 2019
Posts: 57
Likes: 0
Comparing to torque pro, snap on scanner my buddy has at his shop and another laptop one he has for the shop. They all agree with each other and the dash is off a little. About 100 rpm at 2k rpm. I remember reading somewhere it was adjustable on the back of the cluster but thought it would be nice to do it without removing it. Also the dash tach and speedo do not quite agree with my rpm mph gearing chart while the obd ones agree with the chart.
Can you compare at 1500, 2000, 2500 rpm? If it's off the same 100 rpm at all 3 then I doubt it's the CPS. If it were related to a sensor, it would be off a percent. Which would mean more than 100rpm at a higher rev and less than 100rom at less revs than 2k
More Turbo
Joined: Mar 2017
Posts: 571
Likes: 12
According to this website the RPM is 657.
It's a Van Gogh
Joined: Feb 2010
Posts: 7,795
Likes: 1,326
From: Elk Grove, CA
Yup, 295/75/16 Nitto Terra Grappler shows 604 RPM. That should be simple with Forscan. It gets tricky at less than 600 RPM where you need to inject final drive ratio, GPS speeds, etc into the equation.
The key is to look up the RPM for your specific tire on the specific tire manufacturer website to get the correct RPM.
Beyond all that once the tires are 3/4 worn the diameter and the RPM will be different. Accept that life in the real world is messy.
The key is to look up the RPM for your specific tire on the specific tire manufacturer website to get the correct RPM.
Beyond all that once the tires are 3/4 worn the diameter and the RPM will be different. Accept that life in the real world is messy.
More Turbo
Joined: Mar 2017
Posts: 571
Likes: 12
Yup, 295/75/16 Nitto Terra Grappler shows 604 RPM. That should be simple with Forscan. It gets tricky at less than 600 RPM where you need to inject final drive ratio, GPS speeds, etc into the equation.
The key is to look up the RPM for your specific tire on the specific tire manufacturer website to get the correct RPM.
Beyond all that once the tires are 3/4 worn the diameter and the RPM will be different. Accept that life in the real world is messy.
The key is to look up the RPM for your specific tire on the specific tire manufacturer website to get the correct RPM.
Beyond all that once the tires are 3/4 worn the diameter and the RPM will be different. Accept that life in the real world is messy.
More Turbo
Joined: Mar 2017
Posts: 571
Likes: 12
So I have everything running and I go to hit "Run Service Procedure" and I'm getting an error "Service procedure has been interrupted."
I have turned the truck off and back on with same results. Any idea what it could be? Possibly my obd2 connector not a true elm327? I'm able to read codes and what not with it on ForScan. Also in the configuration it says adapter eld327 v 1.5
Edit. Looks like I got it. Uninstalled newest version and installed older.
I have turned the truck off and back on with same results. Any idea what it could be? Possibly my obd2 connector not a true elm327? I'm able to read codes and what not with it on ForScan. Also in the configuration it says adapter eld327 v 1.5
Edit. Looks like I got it. Uninstalled newest version and installed older.
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Tuned
Joined: Jun 2003
Posts: 465
Likes: 53
From: Connecticut
Bump! Nice ot see this thread get some traction (har de har) since 2018. I'm still driving ym Excursion on 20" wheels and lovvin' it.
I'm trying to help a buddy with his Excursion on 37s, and dropping it to 600 (tone ring still at stock 120) is *just* not enough; the speedo is 2-3 mph too slow from 50 through 70. Any thoughts on where to put the settings to get me a tad closer? Manufacturer indicates 565 revs/mi.
Is this a simple mathematical formula?
I'm trying to help a buddy with his Excursion on 37s, and dropping it to 600 (tone ring still at stock 120) is *just* not enough; the speedo is 2-3 mph too slow from 50 through 70. Any thoughts on where to put the settings to get me a tad closer? Manufacturer indicates 565 revs/mi.
Is this a simple mathematical formula?
Tuned
Joined: Jun 2003
Posts: 465
Likes: 53
From: Connecticut
Answer is: very close.
Speedo was still 2-3mph slow at a setting of 600rev/mi with 37x13.50R17LT Toyos, who say they're 565 rev/mi. I took 565/600=0.941667, times 120 tone ring = 113 tone ring and set it to that. Speedo was now roughly 2-3 mph too fast. Increased the rev/mi from 600 to 615 -- nailed it.
Now, does anyone know if changing that tone ring will affect ABS activation? I'm presuming that refers to the number of teeth on the ABS rings at the wheels.
Speedo was still 2-3mph slow at a setting of 600rev/mi with 37x13.50R17LT Toyos, who say they're 565 rev/mi. I took 565/600=0.941667, times 120 tone ring = 113 tone ring and set it to that. Speedo was now roughly 2-3 mph too fast. Increased the rev/mi from 600 to 615 -- nailed it.
Now, does anyone know if changing that tone ring will affect ABS activation? I'm presuming that refers to the number of teeth on the ABS rings at the wheels.
Junior User
Joined: Dec 2018
Posts: 64
Likes: 0
From: Louisville
New to the wizardry of FORScan, but loving it so far. Still dialing in specs, so naturally Wheels/tires on the list. I have 20” wheels on my 2000 F250 CC.
”The 275/65R20 Goodyear Wrangler AT/S has a diameter of 34.1", a width of 11", mounts on a 20" rim and has 609 revolutions per mile. It weighs 60 lbs, has a max load of 3750 lbs, a maximum air pressure of 80 psi, a tread depth of 16/32" and should be used on a rim width of 7.5-9.5"
I’ll be putting that in the computer today. Thanks for the great video and other tire info.
”The 275/65R20 Goodyear Wrangler AT/S has a diameter of 34.1", a width of 11", mounts on a 20" rim and has 609 revolutions per mile. It weighs 60 lbs, has a max load of 3750 lbs, a maximum air pressure of 80 psi, a tread depth of 16/32" and should be used on a rim width of 7.5-9.5"
I’ll be putting that in the computer today. Thanks for the great video and other tire info.
Fleet Mechanic
Joined: Sep 2011
Posts: 1,613
Likes: 106
From: Albuquerque
Just fixed my speedometer , Forsscan showed 649, 657 was what the website called for, messed around and at 670 speedometer was dead on with my gps!
Thanks for the write up here guys, as always you all are a wealth of infomation!
Thanks for the write up here guys, as always you all are a wealth of infomation!
Cargo Master
Joined: Jan 2009
Posts: 2,800
Likes: 31
From: OKC, OK
I finally got this done. I only posted that I needed to do it in January. Actually I have needed to do it since 2009 when I bought the truck. I already had an OBDlink MX for Torque so that is what I used for the bluetooth connection.
The interwebs said the revs for my 35 x 11.5/20 was 598. I set it at 600 and that was a little to far. I think I need to try 605. When speedo says 70 GPS says 68. However my computer died on the test drive and it was 11 pm and I wanted to go to bed. Close enough for my trip to Colorado tomorrow. I will take the laptop and (maybe) adjust it some more.
Thanks for the wrote up!!
The interwebs said the revs for my 35 x 11.5/20 was 598. I set it at 600 and that was a little to far. I think I need to try 605. When speedo says 70 GPS says 68. However my computer died on the test drive and it was 11 pm and I wanted to go to bed. Close enough for my trip to Colorado tomorrow. I will take the laptop and (maybe) adjust it some more.
Thanks for the wrote up!!