Will 17x8 rims on 6.5 8 lug bolt pattern with a 4.5 backspace work on the rear of a 51 f3?
I know there is a lot of discussion on wheels but the more I read, the more confused I become. Sorry gang.

 

I doubt anybody has first hand experience doing this. So my response will be just based on what the charts and books show, and on my own stock wheel and tire measurements.

Your stock 17" widowmakers are Budd #49380. They are 5.5" wide and have 9/16" positive offset. Also called dish. Standard backspacing charts like the one below show that a 5.5" wheel with no offset (remember yours have 9/16") will have a backspace of 3.25". You are wanting to go with an 8" wheel so you'd be looking at 4.5" of backspace. You're adding 2.5" overall width or 1.25" on each side for the wheels alone. Below are the backspace chart and a chart showing offset calculations.




So now you need to figure out if you have room in the rear wheel wells. The below F-3 chart shows that you have 62" rear track width. According to one of my manuals a stock 7.50 x 17" tire has a section tire width of about 8.5" (I confirmed that on one of my tires). The F-3 chart shows there is about 48.5" between inner wheel wells and 70.25" between lower outer fender lips. The chart doesn't tell the space available at the top of the rear fender arch. I went out and put a tape on one of my two wheel drive trucks that has stock wheels and tires and get about 2.5" between tire and upper fender arch. That same approximate of 2.5" is available between the stock tire and the inner fender well.

So you are wanting to add in wheel width alone 1.25" on each side of the wheel mounting surface. You've not said what tires you want to use, but it's a safe bet any tire to fit that rim would rub on both the inner fender well and outer fender upper lip. So I don't think this will work for you. Stu

 

Thanks Stu.
I am just beginning my journey on my F3 and am learning as I go along so I really appreciate the quick and complete answers to my questions. I know the simple answer for my problem is to replace the rear end with the Dana 60 rear differential but I don't know if I have the skills to do that. I have seen it said that it should be a simple bolt on switch with no modifications. Is that correct?
Thanks
Bill

 

I've not done it either, but have read here many times that it's a bolt in job. IIRC the '67 to '71 is simply a bolt in, and that the '72 is straight forward too but has to be modified in small ways. On that I don't remember specifics. Later years went with a wider axle on the F-250, but I think I remember hearing that F-350 flat beds used the narrower axle too in later years. Others please clean up anything I've not said fully or correctly. Stu