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Calculating Tire Size

 
  #16  
Old 01-05-2011, 05:26 PM
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2610 is the unloaded (i.e. perfectly round) circumference.

Tires are not perfectly round. When loaded, they squish (anywhere from 2-5%). This reduces the effective diameter.

Thus you need to reduce the unloaded diameter by multiplying the unloaded diameter by .98, .97, or .96, etc. as a starting point. Then you need to confirm/verify with a known speed (i.e., GPS) or distance (Google maps) and adjust based on the percentage of your error.

 

Last edited by shotgunz; 01-05-2011 at 05:29 PM.
  #17  
Old 01-06-2011, 12:21 PM
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Originally Posted by shotgunz View Post
2610 is the unloaded (i.e. perfectly round) circumference.

Tires are not perfectly round. When loaded, they squish (anywhere from 2-5%). This reduces the effective diameter.

Thus you need to reduce the unloaded diameter by multiplying the unloaded diameter by .98, .97, or .96, etc. as a starting point. Then you need to confirm/verify with a known speed (i.e., GPS) or distance (Google maps) and adjust based on the percentage of your error.

i did the .97 squish and my gauges show about 2 mph higher than my programmer. should i go more squish or less squish. lol
 
  #18  
Old 01-06-2011, 12:36 PM
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Originally Posted by ridinonmoto17s View Post
i did the .97 squish and my gauges show about 2 mph higher than my programmer. should i go more squish or less squish. lol
The truck speedometer will always be about 2 mph faster than the digital readout. Ford builds them that way. Get you digital readout calibrated to a GPS to make sure you have it correct.
 
  #19  
Old 01-06-2011, 12:47 PM
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ok. but if i leave it the way it is now should i go by my gauges or the programmer. its an edge evolution.
 
  #20  
Old 01-06-2011, 12:57 PM
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Originally Posted by ridinonmoto17s View Post
ok. but if i leave it the way it is now should i go by my gauges or the programmer. its an edge evolution.
Yes, but how do you know it's dead on? The digital could still be off.
 
  #21  
Old 01-06-2011, 01:02 PM
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lol i'll just have the cop in my town use his radar to check it. i can get by with warnings by saying the tires have my gauges off, the cop just says have it flashed and heres your free pass be glad im in a good mood. lol works about 95% of the time. and we took my gf's g6 on a trip and took the garmin and the garmin always read 3-4 mph lower than her gauges and its bone stock with the same tires it came with from the factory. so maybe i shouldnt rely on my gps
 
  #22  
Old 01-06-2011, 01:13 PM
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I would bet the gps is correct and the car speedo is off. I would set the Edge to match the Garmin, then ask the cop to check it for you.
 
  #23  
Old 01-27-2011, 06:10 AM
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hi shotgunz,
thanks for providing the tire size calculator. i will really help many users at this forum.
you did really a good job.
Thanks


9xm live tv
 

Last edited by Bothom; 10-01-2012 at 10:45 AM.
  #24  
Old 01-28-2011, 05:49 PM
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Here is imo the best tire size calculator I have found. Let's u put in stock size and compare up to 3 prospective sizes. Check it out.
www.1010tires.com
 
  #25  
Old 01-28-2011, 06:00 PM
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  #26  
Old 02-11-2011, 06:12 AM
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Originally Posted by shotgunz View Post
2610 is the unloaded (i.e. perfectly round) circumference.

Tires are not perfectly round. When loaded, they squish (anywhere from 2-5%). This reduces the effective diameter.

Thus you need to reduce the unloaded diameter by multiplying the unloaded diameter by .98, .97, or .96, etc. as a starting point. Then you need to confirm/verify with a known speed (i.e., GPS) or distance (Google maps) and adjust based on the percentage of your error.


Can someone tell me what nimber they are using for 295/70/18 Trail Grapps. I had my truck broken into and my GPS unit stolen. My cell phone has a GPS unit, but it doesnt have and odometer.

Thanks
 
  #27  
Old 02-11-2011, 06:43 AM
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Should be between 2597 (5% squish) and 2652 (3% squish).

You can also use Google Maps for accurate distances...
 
  #28  
Old 02-14-2011, 10:58 AM
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Originally Posted by gilsnuxs View Post
Can someone tell me what nimber they are using for 295/70/18 Trail Grapps. I had my truck broken into and my GPS unit stolen. My cell phone has a GPS unit, but it doesnt have and odometer.

Thanks
I am running 2651 at 45psi.
 
  #29  
Old 02-18-2011, 11:32 AM
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ok i have a question. i have stock 20" rims on my f150. current tires i have right now are 275/55/20. i want to go bigger. would i be able to put a 35x12.5x20 tire on these rims?
 
  #30  
Old 02-18-2011, 12:04 PM
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Originally Posted by mattp868 View Post
ok i have a question. i have stock 20" rims on my f150. current tires i have right now are 275/55/20. i want to go bigger. would i be able to put a 35x12.5x20 tire on these rims?
Your question would best be asked in a new thread in the Wheel and Tire forum.. It is a little off subject in this thread, plus may not be seen by many.
 

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