Larger tire calibration question
01-02-2012, 05:42 PM
#21
Senior Member
Thread Starter
I don't know what size they entered (sorry) but I put the garmin in the truck and it is spot on. Yes I went 275/60/20.
01-03-2012, 05:20 AM
#22
Grumpy Old Man
However the dealers IDS (integrated diagnostic system) requires a VIN to work. If your F-150 is not a Raptor, then your VIN probably won't allow IDS to calibrate the speedo for the LT315/70R17 size tire. But I'm not familiar with the newer version of the IDS. Way back when, a Ford Tech could use the IDs to calibrate for any revs/mile between 601 and 699. We need a Ford tech to explain the current limitations to us.
01-07-2012, 04:11 PM
#23
Senior Member
Thread Starter
I just wanted to give an update on my damaged wheels. The tire company ordered me four new wheels and installed them today. Life is good once again.
03-23-2012, 01:41 AM
#24
Deer Slayer
That Hypertech speedo calibrator works only on the 6.2L engine. No mention of the 3.5L EcoBoost, 3.7 V6, or 5.0L V8 engines.
Similar products are made by Pro Comp Accu Pro and SuperLift TruSpeed, but they won't work on 2011-up F-150 engines either.
Ford changed the software for speedo calibration around 2006 or so, and most hackers haven't yet figured out how to calibrate the speedo for other than stock-size tires.
So before you buy a speedo calibrator, be certain it's guaranteed to work with your current engine. If you find one, then please come back to this thread and inform us all.
Ford engineers don't like shade-tree mechanics changing to non-standard tire sizes, so they make it difficult to calibrate things when you do.
Here are the stock-size tires for 2012 models, listed from the shortest to the tallest. Most of these sizes are are applicable to earlier F-150s back to about 2009.
Tire size....... tire revs/mile
P255/65R17 = 691
P265/60R18 = 685
P235/75R17 = 674
LT245/75R17 = 658 (heavy duty payload pkg)
P265/70R17 = 654
P275/45R22 = 654 (Harley Davidson)
P275/55R20 = 652 (Platinum)
P275/65R18 = 648
Additional sizes used for the 2009 models include:
LT245/70R17 = 693
P235/70R17 = 681
The smaller the revs/mile, the taller the tire. The speedo/odo/tripmeter software uses the revs/mile parameter instead of tire diameter or radius because revs/mile is more accurate. So if you want the Ford dealer to be able to calibrate your speedo for new tires, be sure thay aren't taller than 648 revs/mile, nor shorter than 691 revs/mile.
The tire revs/mile is included in the specs for most major brands of tires.
Note that the popular 35" diameter has about 600 revs/mile. So if that's your tire choice, then the Ford dealer probably can't get closer than 648 revs/mile, which is still about 7% speedo error.
Similar products are made by Pro Comp Accu Pro and SuperLift TruSpeed, but they won't work on 2011-up F-150 engines either.
Ford changed the software for speedo calibration around 2006 or so, and most hackers haven't yet figured out how to calibrate the speedo for other than stock-size tires.
So before you buy a speedo calibrator, be certain it's guaranteed to work with your current engine. If you find one, then please come back to this thread and inform us all.
Ford engineers don't like shade-tree mechanics changing to non-standard tire sizes, so they make it difficult to calibrate things when you do.
Here are the stock-size tires for 2012 models, listed from the shortest to the tallest. Most of these sizes are are applicable to earlier F-150s back to about 2009.
Tire size....... tire revs/mile
P255/65R17 = 691
P265/60R18 = 685
P235/75R17 = 674
LT245/75R17 = 658 (heavy duty payload pkg)
P265/70R17 = 654
P275/45R22 = 654 (Harley Davidson)
P275/55R20 = 652 (Platinum)
P275/65R18 = 648
Additional sizes used for the 2009 models include:
LT245/70R17 = 693
P235/70R17 = 681
The smaller the revs/mile, the taller the tire. The speedo/odo/tripmeter software uses the revs/mile parameter instead of tire diameter or radius because revs/mile is more accurate. So if you want the Ford dealer to be able to calibrate your speedo for new tires, be sure thay aren't taller than 648 revs/mile, nor shorter than 691 revs/mile.
The tire revs/mile is included in the specs for most major brands of tires.
Note that the popular 35" diameter has about 600 revs/mile. So if that's your tire choice, then the Ford dealer probably can't get closer than 648 revs/mile, which is still about 7% speedo error.
03-23-2012, 09:55 AM
#25
Grumpy Old Man
The tire calculators all assume that a 275/65 tire is exactly 275 mm wide and that the profile is exactly 65 percent of the width when rolling down the road with a coupla thousand pounds on the tire. Most tire manufacturers measure the revs/mile at 45 MPH with a loaded vehicle. But most tire calculators assume the loaded rolling radius is the same as the static unloaded radius.
But real world tires don't match the sidewall size that closely, and the loaded rolling radius of the tire is nowhere near the unloaded static radius of that tire.
So if you want an accurate speedo, then use the manufacturer's revs/mile specs, not a generic tire calculator.
Last edited by smokeywren; 03-23-2012 at 01:05 PM.
03-23-2012, 10:46 AM
#26
Deer Slayer
No, my revs/mile specs are correct, per Ford and the tire manufacturers' websites. It's the generic tire calculators that are wrong.
The tire calculators all assume that a 275/65 tire is exactly 275 mm wide and that the profile is exactly 65 percent of the width when rolling down the road with a coupla thousand pounds on the tire. Most tire manufacturers measure the revs/mile at 45 MPH with a loaded vehicle. But most tire calculators assume the loaded rolling radius is the same as the static unloaded radius.
But real world tires don't match the sidewall size that closely, and the loaded rolling radius of the tire is nowhere near the unloaded static radius of that tire.
So if you want an accurate speedo, then use the manufacturer's revs/mile specs, not a generic tire calculator.
The tire calculators all assume that a 275/65 tire is exactly 275 mm wide and that the profile is exactly 65 percent of the width when rolling down the road with a coupla thousand pounds on the tire. Most tire manufacturers measure the revs/mile at 45 MPH with a loaded vehicle. But most tire calculators assume the loaded rolling radius is the same as the static unloaded radius.
But real world tires don't match the sidewall size that closely, and the loaded rolling radius of the tire is nowhere near the unloaded static radius of that tire.
So if you want an accurate speedo, then use the manufacturer's revs/mile specs, not a generic tire calculator.
03-23-2012, 10:54 AM
#27
Deer Slayer
And SmokeyWren here is the official Ford manual on the subject..Scroll down to page #4 and note where it states
Note:
Note:
Calculate revolutions per mile by dividing 63360 inches/mile (5280 feet/mile x 12 inches/foot) by the measured circumference of your tire (in inches).
Here is the link to the entire manual so you can brush up on your info
http://www.fordracingparts.com/calib...structions.pdf
Here is the link to the entire manual so you can brush up on your info
http://www.fordracingparts.com/calib...structions.pdf
03-23-2012, 11:07 AM
#28
Senior Member
A "generic" tire calcualtor? It is called simple math my friend not a "generic" calculator.. They all use the same equation and numbers to get rev/mile. And while carrying a load may affect those number slightly why would ford say "hey lets do our rev/mile test at 45mph with x-amount of load in the back" rather than just going by the mathematical equation that has been used for years and is the standard in the industry. Sorry my friend but you are wrong unless you can prove to me and show me exactly where you got your numbers from.
Just an observation my friend.....
Not only do you come across in your threads/posts as a hand-wringing and always worried/fearful individual, but for someone who is always seeking help, you come across as a real unappreciative a**-hole in your responses to those who have been on this board for some time, and are trying to offer you help and advice! Again, just my observation.
Next, just for the record, I have had a 2" leveling kit and nice big 35" Toyos on my truck for nearly 3 years now, w/o changing anything in the computer settings and only checking the alignment each year; and my truck runs fantastic in all respects!!!
03-23-2012, 11:32 AM
#29
Deer Slayer
Just an observation my friend.....
Not only do you come across in your threads/posts as a hand-wringing and always worried/fearful individual, but for someone who is always seeking help, you come across as a real unappreciative a**-hole in your responses to those who have been on this board for some time, and are trying to offer you help and advice! Again, just my observation.
Next, just for the record, I have had a 2" leveling kit and nice big 35" Toyos on my truck for nearly 3 years now, w/o changing anything in the computer settings and only checking the alignment each year; and my truck runs fantastic in all respects!!!
Not only do you come across in your threads/posts as a hand-wringing and always worried/fearful individual, but for someone who is always seeking help, you come across as a real unappreciative a**-hole in your responses to those who have been on this board for some time, and are trying to offer you help and advice! Again, just my observation.
Next, just for the record, I have had a 2" leveling kit and nice big 35" Toyos on my truck for nearly 3 years now, w/o changing anything in the computer settings and only checking the alignment each year; and my truck runs fantastic in all respects!!!
03-23-2012, 11:51 AM
#30
I think everyone needs to relax a bit.
It's tough to figure people out on forums. It misses sarcasm and inflection that would otherwise make statements acceptable.
There are so many variables in tire size and speed calculations that it's impossible to be accurate without actual measurements from the actual tire in question. Even manufacturers' numbers can be off. Also, what happens when a tire wears? The diameter is smaller and now your speedo will be off again. Most, if not all, cars have optimistic speedo reading for liability reasons. Ususally it's 5mph @60mph. One of the reasons for this is so consumers can't blame the auto manufacturers if they get a ticket. I've noticed my speedo read correctly on my 4runner when I went from the stock 31" to a 32" tire. I'm currently going from a 32" to a 33" on my F150 and I'm guessing I'll have similar results. If it's off too much, I'll buy a tuner that can also fix the wheel size.
It's nice to be accurate but it rarely works out in the real world when it comes to cars and trucks. You can get really close but w/o exact actual measurements, you can't say one person is wrong if they're close. Be a little flexible with your expectations and you'll rarely be disappointed.
Group hug?
It's tough to figure people out on forums. It misses sarcasm and inflection that would otherwise make statements acceptable.
There are so many variables in tire size and speed calculations that it's impossible to be accurate without actual measurements from the actual tire in question. Even manufacturers' numbers can be off. Also, what happens when a tire wears? The diameter is smaller and now your speedo will be off again. Most, if not all, cars have optimistic speedo reading for liability reasons. Ususally it's 5mph @60mph. One of the reasons for this is so consumers can't blame the auto manufacturers if they get a ticket. I've noticed my speedo read correctly on my 4runner when I went from the stock 31" to a 32" tire. I'm currently going from a 32" to a 33" on my F150 and I'm guessing I'll have similar results. If it's off too much, I'll buy a tuner that can also fix the wheel size.
It's nice to be accurate but it rarely works out in the real world when it comes to cars and trucks. You can get really close but w/o exact actual measurements, you can't say one person is wrong if they're close. Be a little flexible with your expectations and you'll rarely be disappointed.
Group hug?