speedo changes

[Chris Brown 2]

i ordered my tires and i got a warning that changing from 255/65/16's to 265/75/16's the speedometer wouldnt work properly.

say the speedo reads 60 mph, how fast would i actually be going? faster or slower than the speedo reads?



is there a simple fix for this that doesnt cost any money or no?:blink:

 

[Steve Krusich]

Go to http://www.discountpartcenter.com/tirecalc.html



It will calculate the speedo effect of your tire change.



Steve

 

[Hal S]

It's a very simple process to recalibrate the programable parameters, but you will need access to some sort of scan tool, or buddy up to your local Ford dealer.

You would be amazed just what you can get with a box of donuts.

 

[Matthew W]

With larger diameter tires, you will be going faster than the speedometer indicates ... assuming that the speedometer was correct before the tire change (which is rarely the case). What I would recommend before going thru any type of re-calibration process is to go by one of the speed warning radar trailers that the police set out in problem zones ... compare what it displays to what your speedometer indicates ... if within a couple of MPH, I wouldn't worry about it (but keep it in mind when passing a police vehicle ... and if it is only a few MPH off, it will not do any mechanical damage.

 

[Chad Merry]

Your speedo will be off by about 5 mph. So if your speedo says 65 your actually doing 70.

 

[Jake Levin]

you're speedo will be off by a percentage, not a hard number. It's based on how far you go in 1 revolution of your tire and how many revolutions your tire makes in a set amount of time. If your speedo say 30, you might only be off 2-3 miles per hour (really going 32-33), but at 60 you might be off 4-6 and at 90 you might really be going 96-100.

 

[Aaron Yarbough]

jlevin is correct, your speedometer will be off by a percentage not a hard number.......

 

[Chad Merry]

The hard number is based from a percentage, it is just rounded to 5. Do the math and you will see the percentage difference between the 2 tires. That number at 65mph would equal 5 mph. I used 65 mph since that is what 99.9% of the tire manufactures use to determine the amount of revolutions per mile.

 

[Aaron Yarbough]

Chad, not tryin to bust your chops but speed is not a factor in determining the # of tire revolutions per mile. It's a function of distance, not speed. It's a simple calculation which is the circumference of the tire divided by 5,280 ft. That yields the number of revolutions it takes a tire to go 1 mile.

 

[Matthew W]

Just FYI ... your speedometer is probably wrong from the factory - up to a few MPH. I have noticed that with numerous Fords, including both of my Tracs ... when I switched to 265/75/16's from stock 255/70/16's, my speedometer actually became MORE accurate !!

 

[Chris Brown 2]

awsome, thanks guys

 

[Hal S]

Too bad you don't live closer, I could do that for you in just a few min.