Motocross247365

So I bought a 2014 F150 FX4 5.0 V8 and I've been having issues with my speedometer being off anywhere between 5 and 10 mph and I've done some research and have found out bigger tires can cause that problem the truck came with LT275/65R20's on it but I can't seem to find a straight answer if these are the oem rim/tires or aftermarket and if so what would you guys recommend I do to fix the speedo?

yanki01

275/55/20 was the stock tire size so the tires you have are bigger than stock. to fix the speedo you can try via forscan.

kbrock

I don't know what wheels you have to say if they're OEM or not, but that tire size is not what comes with the truck. The FX4s with the 20" wheel option came with 275/55r20, not 275/65r20. That would certainly change the speedo, it's a difference of over 2".

You can easily fix it yourself with Forscan if you do some research on it

Edit: yanki beat me to it haha

Motocross247365

Thanks yanki and kbrock that is exactly what I needed!!!

16IngotFX4

Your factory size is listed on the door jamb of the driver door.

At 60mph you should only be about 4mph inaccurate.
At 80mph it's only off 5.5mph.
If your off by 10mph that's quite inaccurate.

Trio

Buy the correct size tires when your current ones wear out, or resell the current ones on CL or FB if they still have most of their tread. As others have said above, your current tires are MUCH bugger than stock, and are the cause of much or most of your speedo issues.

jhanna

exactly, your speed (and odometer) will be off a percentage, rather than a fixed amount.

if you use the link below, to compare the door jamb size to your current size. Look at the circumference difference as a percentage.

https://tiresize.com/comparison/

When I went with a different size tire on my truck, I was only off .5-.6%. Which equates to 1/4mph at 50mph.