I have a 2015 F150 with 18in wheels, I am wanting to buy a set of 20in takeoffs, will the larger wheels affect my speedometer?

Thanks ahead of time for any and all replies.

 

Short answer is NO. What can and will affect the speedometer is the overall diameter of your tire, it doesn't matter if the wheel size is 17, 18, 20 or 22". There is a handy tire rim calculator under the Tools dropdown at the top of the forum page that can help you calculate the overall diameter differences. You can then use forscan to enter the new values to have your speedo read correctly.

 

Larger tire diameter will, rim size will not.

So have the tire folks set you up with the proper size and you'll be perfect.

For example, my truck came factory with 275/55-20 but somebody replaced them with another factory wheel, 275/65-18 and are the same diameter. If the two sizes I mentioned are what you are dealing with (if the takeoffs have tires mounted) you'll be fine.

Otherwise, calculate the percent different between tire size. That percentage is how much your speedometer and odometer are off. For example, people with level kits install a tire about 6% larger. That means their distance traveled is reading 6% too little, and speedometer is 6% slower. So it's off 6% of 15mph and it is also off 6% of 75mph (which is a different end results). Speedometer is never "off by 2mph" except for at one specific speed.


Edit: Hilld answered before I finished reading/composing.

 

As it was mentioned it all depends what the tires size is not the wheel size. With that said. if your truck is a 2WD the stock tire is 265/60R18 which equals to 30.5X10.4. If its a 4X4 the stock tire is a 275/65R18 which equals 32.0X10.8. Trucks that come with 20"(2WD & 4X4) come with 275/55R20 which equals 32X10.8. So if your truck is a 4X4 then swapping to a 20" take off wheel with stock size tires will not change your speedo at all because they are both the same overall size. If your truck is 2WD yes it will affect the speedo but you can correct that with a custom tune or Forscan.

Wayne

 

The tires on my 2015 4x4 are 275/65R18 the ones I want to buy are 275/55R20. And yes I am buying the tires already mounted.

My 65Rs are the same size as the 55Rs?

 

Yes, the center number is the % for the aspect, larger wheel needs a smaller % to be the same.

 

Yes 275/65R18 is the same size as a 275/55R20

Wayne

 

Following

 

See my previous post above.

You are doing the exact opposite of what is on my truck. Same rules apply.

 

Looks great! What kind of level did you use? Is the rear stock height. I keep going back and forth between 1.75" and 2" of lift with the 5100's. I'm also going to be adding an AAL. When you're trying to get a specific set up it's hard to find a photo of the exact same.