do bigger tires throw off your speedometer? - F150online Forums



do bigger tires throw off your speedometer?

Reply
 
 
  #1  
Old 03-01-2011, 03:46 PM
Member
Thread Starter
 
Join Date: Feb 2011
Posts: 63
do bigger tires throw off your speedometer?

i just upsized from a 31" tire to a 33" tire. anyone know how bad this will throw off my speedometer? or is there a way i can calculate it myself?
Reply With Quote
  #2  
Old 03-01-2011, 03:58 PM
Senior Member
 
Join Date: Jun 2008
Location: Indianapolis, IN
Posts: 1,874
Use this to put in your full size of each tire

Tire Size Calc
Reply With Quote
  #3  
Old 03-01-2011, 05:58 PM
Senior Member
 
Join Date: Apr 2007
Location: Ohio
Posts: 517
a mile or 2 at the most..increases with speed
Reply With Quote
  #4  
Old 03-02-2011, 12:15 AM
Member
 
Join Date: Jun 2009
Location: Trenton Il.
Posts: 69
It should be about 3 mph difference.
Reply With Quote
  #5  
Old 03-02-2011, 12:58 AM
Member
 
Join Date: Oct 2006
Location: Mission Viejo, California
Posts: 63
*not trying to hijack* but i think, hopefully, the op would like the answer to this also,
Is the speed reference taken before the differentials? Would changing the gears "fix" the spedo?
Reply With Quote
  #6  
Old 03-02-2011, 01:39 PM
Senior Member
 
Join Date: Sep 2001
Location: cairo,ga
Posts: 28,202
The OP didn't give any info on his truck, so we can't answer how to fix his speedo calibration. If he has a 99 or newer F-150, he can recalibrate with one of the aftermarket computer tuners.
In theory, you could recalibrate the speedo by changing the gears in the differentials but that would depend on what gears are available. The gears he needs may not be available for his truck.
Reply With Quote
  #7  
Old 03-04-2011, 11:05 PM
Member
 
Join Date: Dec 2008
Location: melbourne, fl
Posts: 63
the dealer can also recalibrate your computer, or you can just use a hand held gps and take ride and see what the difference is at various different speeds.
Reply With Quote
  #8  
Old 03-04-2011, 11:29 PM
Senior Member
 
Join Date: Sep 2009
Location: Mechanicsville
Posts: 803
i had 255/70/16's on my truck and put 295/75/16's and at 70 mph its about 11mph off....yes ELEVEN.....if i put cruise on 64 its actually doing 75.....my Garmin GPS says about 77 but its a little off i think
Reply With Quote
  #9  
Old 03-04-2011, 11:55 PM
Patman's Avatar
Global Moderator &
Senior Member
 
Join Date: Aug 2005
Location: DFW
Posts: 19,997
people that say its off by X mph are not giving accurate description.

its would be off by a percentage. If your 31" tires are factory, then the 33s would be 93% of the 31s. so if you are actually doing 20, the display would show 20x.93=18.6 If you're doing 75 the gauge would read 75x.93=69.75. So at 20 its off by 1mph, and at 75 its off by 5.

So its really inaccurate to say "its off by 2mph"
Reply With Quote
  #10  
Old 03-05-2011, 11:31 PM
Senior Member
 
Join Date: Sep 2009
Location: Mechanicsville
Posts: 803
Yeah its definitely going to increase with speed but at the only place it really matters, (highway), mine is off by atleast ten.... around town doing 30-45 its off anywhere from 4-6mph but thats not a huge deal cuz you dont really look at ur speedo to much around town anyway
Reply With Quote
  #11  
Old 03-06-2011, 03:41 AM
Senior Member
 
Join Date: May 2009
Location: Kelowna BC
Posts: 1,083
Mines around 16% off which isn't too big of a deal around where I live I just go by what my speedo says and haven't got been stopped.
Reply With Quote
  #12  
Old 03-11-2011, 09:00 AM
Member
 
Join Date: Feb 2011
Location: Newark, Ohio
Posts: 14
Thanks for the link!
Reply With Quote
  #13  
Old 03-12-2011, 11:24 AM
Senior Member
 
Join Date: Feb 2006
Location: Windsor, Ont.
Posts: 3,762
Example, going from 265/70/17 to 285/70/17 Goodyears actually brought my speedo closer to the actual mph, speedo says 69, gps says 70. That's going basically what you're asking, 31 to a 33 inch tire.
Reply With Quote
 
 
Reply

Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Reignheavytruck
V8 Engines
6
08-03-2015 07:07 PM
Rebel Off Road
2009 - 2014 F-150
0
07-23-2015 02:35 PM
Rebel Off Road
2015 - 2016 F-150
0
07-23-2015 02:23 PM


Thread Tools
Search this Thread

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are Off



All times are GMT -4. The time now is 03:41 AM.