Help, backspacing?

Hello all, I am in a hard stopping point right now. So, I am shopping for wheels and tires. But first off, 04 ST with a 3" body lift and a 4" suspension lift. I was looking at 20x10 with 37x12.50/20 tires. Having trouble figuring out backspacing for what I can fit. One shop told me 37s might be a bit much and should go for 35s. Also same shop said that 20x10s will fit with a -4 backspacing. This shop had tires but not a good selection of rims that I liked. Went to another shop and they suggested 20x9s because x10s would be too much. They also said that x9 rims would fit a x12.50 tire. They also agreed with -4 backspacing.



So I need some help... backspacing. What is the best for our truck? I thought about going with 0 only because from all the browsing I have done, I haven't found any rims with -4 offset.

I have 18x8.5 rims with 0 degree offset. They fit under the fenders, at the lip edge. Stock hieght and my tires are the same diameter as oem on the gen1 xlt rim. My tires have 9" tread width.

That might help you vizualize the correct offset for 9". 9" @ 0 offset would be .25" both sides of the rim.





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I love the look of those rims Eddie! What brand are those and where did you get them? Sorry for the unrelated post.

Agree Doug K. If Enkei made the RT-6 in 16" I would have bought them long ago. I believe they are now discontinued but may still be found if you search. Click "M" next to user name for profile. GL

Also, what is the hub bore of the ST?

So I think I found a set of rims that I like. I read online that the factory wheels are 16x7 with a hub bore of 70.3 and an offset of +12mm. The wheels I like are 20x9 with hub bore of 78 and an offset of -12mm. I used the link below to match things up and it looks like it will work. As for tires, my factory rims are on 265/75r16 and am going to upgrade to 35/12.50/20. The link doesn't use 35 tire size but the equal size of 35/12.50/20 is 318/68/20. I used 315/70/20 as my measurement and it looks like it will fit fine, except hang out past the fender by 1.9".



With the factory hub bore at 70.3 and the aftermarket wheel hub bore at 78, would that still work out? or does it have to be exactly the same or closer to?

Regardless of overall rim width, there isn't room for more than 4.5" of backspace at most and that's on a 10" wheel, 3.75" to 4.25" is better.

What does 3.75 to 4.25" equal per mm for offset?>



I haven't found any wheels with backspacing for -4 to -6. All that I have found is some 0, and a lot of -12mm. Of course there is a lot +mm but that just makes it goes under more. Have never had a problem shopping for wheels unlike I am for the ST.

The wheels i liked have a 4.5 backspacing. Would it work if i put .25 spacer in?

BD,

I cant answer for shure. To me backspacing is subject to the thickness of the rim bead edge. Backspaceing is measured to the putside edge. What works for me is rim width and mm of offset compared, to oem width and ofset. Offset is the bead seat.

I have used paper or cardboard cutouts of the oem rim widths and offset. VS, a cutout of the width and offset, of rim I want. I line them up on the bolt seat to help make up my mind.

Itmight sound hokey that way but after all the rims I have bought. I never made a bad choice of fitment.

Thanks for every ones help. I contacted SuperLift for more help. They suggested that if I go with a 20x9, not to go more than -12mm. They also suggested for backspacing to range between 3 & 3/8 and 4 1/2.



The only last question I have is... The Sport Trac hub bore is 70.3. The wheels I like have a hub bore of 78. I know you can't go smaller, but is 78 too much? I am pretty much set on these wheels with a 35/12.50/20 tire. I just want to make sure everything is correct.

Interesting.... Thank you.

I used a 4" backspace on my Gen 1 and it worked perfect.

The -12mm with 4.5 backspacing on 20x9s worked perfectly. In front, tires are out about 2" and rear is not out at all. Thanks for the help everyone.