I've done the honorable thing and searched until my eyes are red and I have a migraine. My question just hasn't quite been answered by old posts in the 73-79 forums. However my searching did educate me on all kinds of other stuff...

I just found a sweet '76 Ford F250 4x4 with a 460 conversion. I had the same truck but with a 428? back in '88 and sold it to get married, and within a year I wanted it back. So almost 20 years later I got it and I'm very happy, but need to get some things the way I like them.

I intend to install a 4" Skyjacker lift (all four springs). In addition to the stock SJ kit I will probably lengthen the brake lines, replace the shackle bushings, replace all bolts, and maybe replace all tie rod and drag link bushings. No pitman arm is offered, so after I set it down I'll see how it runs and go from there (from posts herein, it appears that I'll be able to get around fine - I just may not like it much). The forum educated me on 'crossover', so maybe I'll go that route.

Did I cover the lift ok? Am I missing something?

I am considering these tire sizes, as this forum makes it clear they'll all fit fine:
315/75R16 (35x12.5) tires on 16x8 rims
315/70R17 (35x12.5) tires on 17x9 rims
37x12.5x17 tires on 17x9 rims
37x13.5x17 tires on 17x9 rims
I'd prefer, I think, to stay with 17x9 rims because it gives me good freedom to go up and down on tire sizes.

My question on rims is, what backspace/offset will work best on the '76? I've found rims that range from +2 to -12. I know this isn't a ton, but I don't want to screw this up since I plan to buy the set online. Do any of you with tire sizes close to mine remember your backspace/offset? I find most rims online show an offset number, not a backspace. I called Jack-It and they said a 4.5" backspace is good. I'm thinking a -6 to a -8 offset isn't much as far as stress on the bearings, and it allows the narrow 37x12.5 tires to poke out a smidge more. Would a -8 work well with both the 12.5 wide and 13.5 wide tire? In your experience, what is the minimum and maximum offset/backspace for a '76 highboy sporting these tires.

Sorry, this got long for just a couple questions. Thanks in advance for your patience and input. I'll get some pics in the gallery soon. I'm really proud of this truck - brings back good memories from 20 years ago.

 

Dang, dang, dang, I tried real hard not to even mention 'highboy' in that last post and sure as nothing there it is at the very end of the post, plain as day.

Sorry, after tons of hours surfing here, even I, proud as can be of my new truck, am sick of reading the 'highboy' questions.

 

I just did a quick search on the rims I currently run and the rims that were on my last truck. Here's what I found.

The one I'm driving now is a '76 F250, stock height, 37x12.5x16.5 Irok radials, 16.5x9.75 American Racing Outlaw II wheels with -14 offset, 4 7/8" backspace. The tires fit great with no problems, no rubbing, and no binding of any sort.

The last truck I had was a '73 F250, stock height, 315/75R16 Big O Big Foot X/t's, 16x8 American Racing Nitro wheels listed as 4 1/2" backspace, offset listed as 0. These tires fit the wheel well ok, but the tires rubbed on the springs at full lock.

Both wheel sizes are taken right from AR's site.

I don't know how much of a help this is, but at least you have one more piece of information.

 

Ok, your talk of offsets has me re-thinking what I thought I knew about backspacing, so I looked it up (thank you google,) and found this definition.

 

What I'm not understanding on that is that according to that definition, my 73 had 4 1/2" to mount, my '76 has 4 7/8". That means that the rims and therefore the tires on the '76 are closer to the springs than they were on the '73, yet they acted opposite of what you would think (the '73 rubbed, not the '76).

Only thing I can figure is that because the wheels on the '73 were only 8" wide, they must have caused the center of the tire to be pinched further in, therefore making the center of the sidewall stick out further. Sound right?

Edit - Ok, just looked at your chart and I think I'm more confused than ever.

 

its not my chart, I just found it, and plagiarized it for use here.

The best way I can explain it is... well, I am getting confused trying to explain it. I cant, but here is what I do. I normally buy used rims and tires, put one on to see if it fits correctly, if it does, I buy em. The tire shop can measure this stuff for you, and recommend the correct rims. When you buy, do not mount your tires until you are sure you want the rims. Once you mount them, you own them.

 

Your post cracked me up, I literally laughed out loud. That's pretty much the way I've always bought rims too.

Every time I go to a tire shop they're just as confused as me and so we end up trying sets on, kinda like shopping for shoes. The problem with the tire shops now is that they don't sell rims by size anymore, they sell them by application (what vehicle they're made for). All the new catalogs from the manufacturers tell the tire shop what size belongs on what vehicle, no thinking involved. When you have a 30 year old truck it just confuses them since it's never in the computer.

Just like looking for any other parts on an older vehicle, if they don't still have paper catalogs, and older guys to interpret them, a hunt for parts can be pretty frustrating.

 

Oh thanks so much. Great info from both of you. I was clear on definitions of offset and backspace, but the formula from Masterbeavis is what I longed for! I googled too but didn't notice this series with the conversions. Nice.

(backspacing is about equal to [Wheel Width / 2] + [Offset] + [about 1/4] )

That last conversion chart is great too. Thanks.

I used the above formula for both of ShamelessMT's rims and came up with:

9.75rims/2 = 4.875 + (-14mm offset= -.5512) = 4.3238 + .25 = 4.5738 backspace (AR claimed 4 7/8 backspace) Close enough?

8.0rims/2 = 4 + (0 offset) = 4 + .25 = 4.25 backspace (AR claimed 4.5 backspace) Confused on this one.

If we interpolate off the chart, both the 9.75" and 8" rims look about right for the claimed offset and backspace.

ShamelessMT: Thanks for the real-world examples and researching your rims. This helps alot. I'm thinking it wasn't the backspace that was a problem on the 8" rubbing issue for your '73. Maybe a smidge of 'sidewall bulge' and softer sidewalls, combined with tires that were just a bit wider than the 37's ? Who knows.

Based on what I've got so far, ShamelessMT's input and Jack-It's input, it looks like for a 17x9 rim I want a -8 to -12 offset to give something like a 4.5 to 4.75 backspace. I'm thinking I may stay on the cautious side and do a -12/4.5

And ya guys, I was chuckling too: Les Schwab said the same thing, "we just try rims on 'til it works". So I know better, but, for the size tires I'm looking at, LS is going to kill me in the pocket book. They just can't touch online prices for tires and rims. I guess the next question is, do I dare buy the tires and rims online and have them mounted and shipped ready to go when they arrive? Ugh. I think I know what Masterbeavis is gonna say. Never done it this way before, always Les Schwab, but I figured I'd give the online packages a whirl... I take that back. Back in, uh, '84 I bought a Cepek tire/wheel mount and balance combo by mail order and shipped them to Alaska for my FJ40 Landcruiser. I didn't have a clue then about backspace and just got lucky I guess.

K I'm gonna post this and see if I can find pics of the ShamelessMT '76. I probably have your pic downloaded on my pc already if you have them in the gallery. I've got a file crammed with pics and notes on lifts/tire size! Almost ready to do it.

Thanks again gentlemen.

 

ShamelessMT - Yep, found your truck in the gallery, and already had a pic downloaded. I was studying it last night in fact since it had the 37.5's on stock suspension. Now that I know your backspace, I got a better idea on the 12.5 stance.

I'm thinking you might even be able to handle 13.5 wide on the stock suspension - what's your opinion? Done anything else with your truck since those pics?
Uh, btw, you gotta understand I'm in Afghanistan right now so I can't just run down to the tire shop and figure this all out. I only have so much time in the states on leave, so I want to have all the parts sitting in the garage waiting for me and the boys to play with. Coming back in November for a few weeks and want to get it set up quick and get us out for hunting season. Otherwise I wouldn't be bothering you guys with this nonsense. Thanks again.

 

I would guess that you could fit 13.5" wide tires in the wheel wells, but you could very well end up with some tire rub at full lock. I don't think that you'll really have other tire rubbing issues, as I've flexed mine as far as it will go and haven't made contact with the sheet metal. It appears pretty tight though, so I'm actually going to buy a set of cut-out fender flares so that I can trim the wheel wells back a little.

I've done a lot to the truck since those pics, but nothing you could see. Matter of fact, today I'm putting a new(to me) instrument cluster with LED bulbs in. Last week was a backup light and a couple other small items. Couple of weekends ago it was a shaved door handle kit. Next weekend will be the window anti-rattle kit. It's always something around here.

Now back to the subject on hand... When you did the math, those numbers came out completely different than they are listed as. 4 7/8 is 4.875 and you got 4.5738 which is 4 9/16, not very close, and on the other wheel it was off .25 or 1/4. Once again, I don't know what the deal is with the sets of numbers. It seem to me that they're independent of reality...

As far as buying tires, the Iroks were bought from Big O. That is not an item they ever stock, but like you, I was looking to order them online. I knew that I was going to need someone to mount the tires when they came in so I went to Big O to find out what they charged for mounting/balancing and just to see what they would say for a tire price. To my great amazement, they were able to get their price to within $50 and that was to include a lifetime road hazard warranty. Furthermore if I bought the tires from them I got free mounting and balancing. I decided to go with them, as the cost difference really worked out to about $25 and they warrantied them, something no one will do online.

The big tire shops are realizing that they need to compete with the online companies and are getting more flexible on their own prices. I understand that you're in Afghanistan, so you can't really go work a deal with the local shop, but I thought I'd share that bit of info anyway.

 

I like that chart better than the formula. The chart is fuzzyer! I was thinkin' of getting way **** and expanding that chart to cover every millimeter. Not.

You know that's just the reason I've always liked the local Schwab shop. Hassle free on road hazard and rotations and flats and winter tire swaps and all that. Question is, what is that service worth to me???

I can actually make internet phone calls from here to get things rolling. I never came right out and asked the Schwab guys (only show in town) to try to get closer to my online package prices. Even their sale price on Toyo Open Country was just too high. I'll have to just come right out and challenge them to do better. Small town - they'll get mad at me for being a tightarse. If I went with them I'd probably do the Hankook RT03 MT or the Toyo Open Country MT on AR or Ultra rims. I do know their rim prices aren't really off too bad. I guess I need to do a bit more homework and make a call.

Thanks for redirecting my thoughts a bit.

Your 'little' projects are what I can't wait to get started on one of these days. Have fun with it. Shameless can you check yer PM?

 

When I play Charlie cheap **** or J.T. (Jew Tony) I tell them that I have found way better prices on the internet, however I recognize the importance of local businesses, and wish to do business with them because you can't get face to face service over a phone line, and when I have a real problem that needs fixing right now, it is nice to have somebody local and knowledgeable to deal with my problem. I have had better luck getting them to come down on their price that way, then throw in the "so and so online will do it for 40% less."

Papadawg, Yes you can get great prices online for tire and wheel packages, but I would check to see if there is refunds available if you have issues, not to mention paying shipping three times instead of once.

 

You fit 37"s on your stock 76? Dang! I haven't tried putting 37"s on mine but should they fit on all 76 4X4s?

 

if you plan on getting the 4" skyjacker lift kit, make sure you get the kit with the nitro shocks. i messed up and ordered the kit with hydros and only have the rear shocks since they dont make them for the front.

 

Sure, they'll fit on the F250's if you have good springs that haven't sagged too much. Usually though, I'd say that 35's are a safe bet, 37's are pushing it a little. Check out my gallery to see what it looks like.