stock tire diameter?
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Senior Member
Joined: Mar 2003
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From: Sacramento
stock tire diameter?
Anyone know the diameter of a set of stock tires/wheels on a standard late model F150 pickup?
I am thinking Supercab XL, but just looking for a basic number.
I am thinking Supercab XL, but just looking for a basic number.
Technical Article Contributor
Joined: Jun 2002
Posts: 10,511
Likes: 10
From: Under the flightpath of old ORD 22R
I just did the calculations on the stock 255/70-R16 when upgrading to the 285/60-R18s.
The diameter of the 255/70-R16 is 30.06"
The cir = 94.39"
This makes the Revs/mi 670.90.
?In case you are looking at an upgrade on the 16s like others have posted, the 265/75-R16 is 31.65". I am not commenting on if you should mount a 265 on a 16x7 wheel, just the daimeter. I did this to try to answer the question of will a 265/75-R16 fit on a 4x2 ( yes it does, the 285/60-R18s are 31.46", which is actually 667 Revs/mi, vs the Tirerack info of 641 Revs/mi ).
I think I did my math correctly, I checked it twice, and came up with the same answer (be it right or wrong ?? ).
The quick math in case it is not a 255/70/16, is 25.4mm to the inch, use your tread width in mm x the % of side wall, times 2 ( both sides of the tire ) and add in your wheel size ( 16 or 17 ).
In case you want the forumula for Cir that is C=2PiR ( 2*3.14*radius ).
12" to the foot of course, and there is 5280' per mile to get Revs/Mi.
Hope I got all that correct, if not post back and tell me what I screwed the pooch on.
Let me know if I need to dig up my "feels like" formula for before and after for axle ratios.
The diameter of the 255/70-R16 is 30.06"
The cir = 94.39"
This makes the Revs/mi 670.90.
?In case you are looking at an upgrade on the 16s like others have posted, the 265/75-R16 is 31.65". I am not commenting on if you should mount a 265 on a 16x7 wheel, just the daimeter. I did this to try to answer the question of will a 265/75-R16 fit on a 4x2 ( yes it does, the 285/60-R18s are 31.46", which is actually 667 Revs/mi, vs the Tirerack info of 641 Revs/mi ).
I think I did my math correctly, I checked it twice, and came up with the same answer (be it right or wrong ?? ).
The quick math in case it is not a 255/70/16, is 25.4mm to the inch, use your tread width in mm x the % of side wall, times 2 ( both sides of the tire ) and add in your wheel size ( 16 or 17 ).
In case you want the forumula for Cir that is C=2PiR ( 2*3.14*radius ).
12" to the foot of course, and there is 5280' per mile to get Revs/Mi.
Hope I got all that correct, if not post back and tell me what I screwed the pooch on.
Let me know if I need to dig up my "feels like" formula for before and after for axle ratios.
Thread Starter
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Senior Member
Joined: Mar 2003
Posts: 208
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From: Sacramento
Wow, lots of information!
I received my truck with Falken 265/60/18's mounted on AFX 18x8" wheels. I asked the question in order to determine whether or not these were taller, shorter or almost the same diameter.
I think my answer is embedded here somewhere. Thanks!
Sacto
I received my truck with Falken 265/60/18's mounted on AFX 18x8" wheels. I asked the question in order to determine whether or not these were taller, shorter or almost the same diameter.
I think my answer is embedded here somewhere. Thanks!
Sacto
Technical Article Contributor
Joined: Jun 2002
Posts: 10,511
Likes: 10
From: Under the flightpath of old ORD 22R
Sacto,
Did you look to see what the door tag had for the tire size.
Don't ask me why it took until today to realize that the stock tire size is always there...my brain did not engage.
If you post the stock tire size from the door jamb, that could get you the stock diameter, radius, which can give you the cir, which in turn you can figure out how much the speedo is off by due to the revs/mi.
When I went 255/70-R16 to 285/60-R18 I was about 3 mph off, which actually took my speedo from reading 3 mph under to at par. I checked this against a few speed trailers and so far it holds true to 45 mph. I don't know why I was reading low before, that is the way it came from Ford.
Just a quick calc:
235/70-R16 is:
D= 28.95"
R=14.475"
Cir=90.903" or 7.58'
Revs/mi=696
265/60-R18:
D=30.52"
R=15.26"
Cir=95.83" or 7.99'
Revs/mi=660
Now you got the data for 255/70-R16 or 235/70-R16 along with your current size.
With Rev per mile is is easy to calc what the speedo is off by.
*Slightly* more involved for what the rear end feels like vs what the actual ratio is.
Good luck
Steve
Did you look to see what the door tag had for the tire size.
Don't ask me why it took until today to realize that the stock tire size is always there...my brain did not engage.
If you post the stock tire size from the door jamb, that could get you the stock diameter, radius, which can give you the cir, which in turn you can figure out how much the speedo is off by due to the revs/mi.
When I went 255/70-R16 to 285/60-R18 I was about 3 mph off, which actually took my speedo from reading 3 mph under to at par. I checked this against a few speed trailers and so far it holds true to 45 mph. I don't know why I was reading low before, that is the way it came from Ford.
Just a quick calc:
235/70-R16 is:
D= 28.95"
R=14.475"
Cir=90.903" or 7.58'
Revs/mi=696
265/60-R18:
D=30.52"
R=15.26"
Cir=95.83" or 7.99'
Revs/mi=660
Now you got the data for 255/70-R16 or 235/70-R16 along with your current size.
With Rev per mile is is easy to calc what the speedo is off by.
*Slightly* more involved for what the rear end feels like vs what the actual ratio is.
Good luck
Steve
Last edited by SSCULLY; Jun 20, 2003 at 10:54 AM.
Thread Starter
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Senior Member
Joined: Mar 2003
Posts: 208
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From: Sacramento
THANKS!!!
The REASON I asked this was due to my suspicion that this tire/wheel combo actually lifted my truck up a little bit. Now, as I consider the next size of tires I will get, all of this info is GREAT.
Later-
Sacto
The REASON I asked this was due to my suspicion that this tire/wheel combo actually lifted my truck up a little bit. Now, as I consider the next size of tires I will get, all of this info is GREAT.
Later-
Sacto
