Recalibrating speedo for *2018* trucks
02-10-2019, 07:28 PM
#1
Senior Member
Thread Starter
Recalibrating speedo for *2018* trucks
As the title suggests, I'm looking for people who have recalibrated their speedometer after changing tire size, on a 2018 truck. I guess it would help to be 5.0, but I don't think that makes a difference.
So far, I can tell that I have two options: buy the overpriced Hypertech unit at $260 CAD, or use Forscan. The Hypertech product's shortcoming obviously is the price, but I've been told that the Forscan tire change method results in one of two DTCs, one of which can't be cleared via the PCM reinitialization process. If anyone with experience using these two methods to correct tire size on their 2018 truck could please chime in, that would be very much appreciated. The tire size in question would be 285/70R17; I'm a bit OCD about these things so I wouldn't settle for just letting the speedometer be 5 kph off.
I'm not tuned, so I wouldn't be using a tuner to do so, as easy as it would be. Thanks. If feedback is iffy on the viability of using the above methods on 2018 trucks, I'll just swallow my 33" aspirations and stay stock size for the tires.
So far, I can tell that I have two options: buy the overpriced Hypertech unit at $260 CAD, or use Forscan. The Hypertech product's shortcoming obviously is the price, but I've been told that the Forscan tire change method results in one of two DTCs, one of which can't be cleared via the PCM reinitialization process. If anyone with experience using these two methods to correct tire size on their 2018 truck could please chime in, that would be very much appreciated. The tire size in question would be 285/70R17; I'm a bit OCD about these things so I wouldn't settle for just letting the speedometer be 5 kph off.
I'm not tuned, so I wouldn't be using a tuner to do so, as easy as it would be. Thanks. If feedback is iffy on the viability of using the above methods on 2018 trucks, I'll just swallow my 33" aspirations and stay stock size for the tires.
02-10-2019, 07:54 PM
#2
I did mine with forscan. There is a guy on the forscan forum with a mustang that figured it all out. I had to reset two modules then it shows up right. I’ll see if I can find it again...
https://forscan.org/forum/viewtopic.php?f=13&t=2650
https://forscan.org/forum/viewtopic.php?f=13&t=2650
Last edited by kansasboy91; 02-10-2019 at 07:56 PM.
02-10-2019, 08:01 PM
#3
Senior Member
Don’t mean to hijack but your question is related since I have a 2018 5.0 also with larger tire upgrade. 285/65/20 or 34.5s. I’m off 4 mph.
Ive always wondered if the truck thinks I’m going 40mph when I’m actually doing 44mph, is my odometer getting behind also? My tuner arrives tomorrow so I planned on correcting it but have always wondered that if the truck thinks I’m going slower then I really am(based on tire revolutions) then it would also think I traveled less distance then I actually did, right?
If this is true then wouldn’t this “cheating” of the odometer add up quick if you take your engine drive hours and multiplied it by 4 to get the number of miles not reflected on the OD?
Ive always wondered if the truck thinks I’m going 40mph when I’m actually doing 44mph, is my odometer getting behind also? My tuner arrives tomorrow so I planned on correcting it but have always wondered that if the truck thinks I’m going slower then I really am(based on tire revolutions) then it would also think I traveled less distance then I actually did, right?
If this is true then wouldn’t this “cheating” of the odometer add up quick if you take your engine drive hours and multiplied it by 4 to get the number of miles not reflected on the OD?
02-10-2019, 10:46 PM
#4
First, you're not off by 4MPH. You're off by some percentage of the original speed. And yes, it does affect the odometer.
02-10-2019, 11:04 PM
#5
Senior Member
I only stated 4mph because every speed app I tried all show a speed 4mph greater then what my speedo says while driving. I understand how math wise I might be off by a percentage of the original speed but how does that completely negate the fact that percentage could equal out to 4mph in my case? Just trying to make sure I understand what your saying since you flat out said I’m not off 4mph despite that’s what everything I’ve used is showing me.
02-10-2019, 11:12 PM
#6
Senior Member
Thread Starter
I did mine with forscan. There is a guy on the forscan forum with a mustang that figured it all out. I had to reset two modules then it shows up right. I’ll see if I can find it again...
https://forscan.org/forum/viewtopic.php?f=13&t=2650
https://forscan.org/forum/viewtopic.php?f=13&t=2650
There's a spreadsheet tool for F150 Forscan usage that calculates the values you need for speedo recalibration. It's around here somewhere. But that's not I'm worried about; I'm sure it's an easy process as is all the other Forscan tweaks I've done. But I'm not willing to make the jump then have to drive around with a wrench icon that no one can fix because it just happens to be the one code that the relearn doesn't cover. That's my worry.
Don’t mean to hijack but your question is related since I have a 2018 5.0 also with larger tire upgrade. 285/65/20 or 34.5s. I’m off 4 mph.
Ive always wondered if the truck thinks I’m going 40mph when I’m actually doing 44mph, is my odometer getting behind also? My tuner arrives tomorrow so I planned on correcting it but have always wondered that if the truck thinks I’m going slower then I really am(based on tire revolutions) then it would also think I traveled less distance then I actually did, right?
If this is true then wouldn’t this “cheating” of the odometer add up quick if you take your engine drive hours and multiplied it by 4 to get the number of miles not reflected on the OD?
Ive always wondered if the truck thinks I’m going 40mph when I’m actually doing 44mph, is my odometer getting behind also? My tuner arrives tomorrow so I planned on correcting it but have always wondered that if the truck thinks I’m going slower then I really am(based on tire revolutions) then it would also think I traveled less distance then I actually did, right?
If this is true then wouldn’t this “cheating” of the odometer add up quick if you take your engine drive hours and multiplied it by 4 to get the number of miles not reflected on the OD?
Now, back to the topic of recalibration please.
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02-10-2019, 11:31 PM
#8
Senior Member
I would be curious to know which one of the DTCs showed up when you made the changes. Supposedly, the PCM relearn doesnt fix all the potential codes, but this also begs the question of whether there is a pattern as to which trucks throw which codes, which is why I asked specifically for feedback about 2018s, which is what I have.
There's a spreadsheet tool for F150 Forscan usage that calculates the values you need for speedo recalibration. It's around here somewhere. But that's not I'm worried about; I'm sure it's an easy process as is all the other Forscan tweaks I've done. But I'm not willing to make the jump then have to drive around with a wrench icon that no one can fix because it just happens to be the one code that the relearn doesn't cover. That's my worry.
It's not off by 4mph. Say you go from 265/70R16 to 265/75R16, your speedo is always off by about 3%. It is the same percentage difference regardless of speed, but obviously at different speeds there will be a varying discrepancy measured in mph, say less than 2kph at low speeds but closer to 5kph on the highway. That 3% is taken from the difference in circumference or revs/mile, which you can find on tiresize.com for example. You would also take your mileage since the new tires, and multiply it by 1.03 (assuming it's exactly 3% for example) to find your actual mileage (more or less, it won't be perfectly exact due to the dynamics of a tire that's actually in motion).
Now, back to the topic of recalibration please.
There's a spreadsheet tool for F150 Forscan usage that calculates the values you need for speedo recalibration. It's around here somewhere. But that's not I'm worried about; I'm sure it's an easy process as is all the other Forscan tweaks I've done. But I'm not willing to make the jump then have to drive around with a wrench icon that no one can fix because it just happens to be the one code that the relearn doesn't cover. That's my worry.
It's not off by 4mph. Say you go from 265/70R16 to 265/75R16, your speedo is always off by about 3%. It is the same percentage difference regardless of speed, but obviously at different speeds there will be a varying discrepancy measured in mph, say less than 2kph at low speeds but closer to 5kph on the highway. That 3% is taken from the difference in circumference or revs/mile, which you can find on tiresize.com for example. You would also take your mileage since the new tires, and multiply it by 1.03 (assuming it's exactly 3% for example) to find your actual mileage (more or less, it won't be perfectly exact due to the dynamics of a tire that's actually in motion).
Now, back to the topic of recalibration please.
I went from stock to these day 1. I believe stocks are 275/55/20s but can’t remmeber. It’s going to be more then 3% using your example sizes to percentage. Should have it tuned right by tomorrow.
