Trying to install a bigger rim. Local shops aren't much help so...

1973 F100
2WD

Currently has 275/60R15 Tires. From what I understand, these trucks came with 215/75R15's from the factory.

I would like to install a set of 20" wheels.

The wheels I'm looking at have a 5 on 5.5 bolt pattern and a +25 mm offset.

My question is, if I buy the wheels above, which tire size would I have to get to make them fit? I believe it would be a 245/45R20, but I'm not 100%. Any help would be appreciated.

Thanks,

Jake

 

That is pretty close by my calculations. In 275/60R15, the 60 stands for 60% of 275, which is 165 mm. So you are adding roughly 2.5 inches on the radius of the rim. 45% of 245 is 110.4 mm. 165-110.4=54.75. 54.75/25.4 is 2.15551 inches (25.4mm=1 in).

So you are adding 2.5 inches on the rim radius and subtracting 2.15551 inches on the tire sidewall (roughly) so its pretty close.

 

wow. okay. I had to read your post 3 times to understand what was going on, but I think I go it. Roughly, I need to find a tire size that calculates to 2.5" less in sidewall size.

I can do that by subtracting the proposed tire size from the current tire size. Then divide by 25.4mm.

What about the offset on the wheel? What effect will that have on wheel fitment?

Thanks,

Jake

 

Make sure your are subtracting the 2 different ratios rather than the actual size. For example, you listed the size 275/60R15 and 245/45R20. You cant subtract 245 from 275 because those two numbers are your tread width in millimeters. you have the subtract the 60% of 275 from the 45% of 245 to get the sidewall height. That 60 in 275/60 is 60% of 275 meaning that your sidewall is 60% the size of your tread so 275x60% is 165 millimeters. So your sidewall is 165 millimeters tall. All these numbers are the measurements taken when the tire is properly inflated.

As for the offset im really not sure. i know all the ins and outs of tires but i know next to nothing about offsets lol. sorry

 

No worries. Thanks for all the info on the tires. I'll post this question in the wheel/tire section and see if someone can help me out with the offset.

Thanks again!

 

anyone have any info offsets? doing some research as I post this.

 

found some good info. thanks guys.