Rim size suggestions please?

[GMJimmy]

I have a 68 SWB FS with 2-1/2" drop spindles and disc brakes and the rear axle is out of a 1972 C10 with drum brakes. It presently has 15X8" 5X5 bolt steel Chevy rally wheels on it front and back. Tires on the front are 245-60-15 and on the back are 275-60-15.

My rally's have a 4.25" back space so I was hoping to find something similar. I'm looking at some Rocket Igniter Gray wheels for it but I can't get the same back spacing on a 15X8" so I'm looking at the 15x8 with a 3.75" back space for the rear and a 15X7" with a 4.25" back space for the front. I was going to put the 15X8's front and back but am afraid the 3.75" back space will cause front tire clearance issues???

I have searched quite a bit here but can't find any specific do's and don't for these trucks in regards to wheel size. Any help would be appreciated.
Thanks
Jim

[Mike C]

Zero offset rims are usually a good choice for these trucks. Wheel width is measured between the bead seats and not overall width. So an 8" rim with zero offset is usually 9" wide so 4.5" backspacing. Backspacing IS measured from the edge of the rim to the WMS (wheel mounting surface).

This may be some advice you are not interested in hearing....

Ditch the 15's. They just don't give you many options in terms of tire IMO. After contemplating rims for my '69 short step, 17's was the conclusion I reached that would be best for ride, handling, load as well as looks. And nearly 2 years later, there may be more options in 18's. IMO, 20's are just absurd, but hey, just my opinion.

My truck also has 2 1/2" drop spindles in the front and 2" springs. Rear is a DJM leaf flip for about 7" drop. I have a wider 5 lug rear from a '72 leaf truck also still on drums.

17x8 with 4.5" backspacing in front with 235 55 17 for 27" overall diameter. 17x9 rear with 5" backspacing and 275 55 17 for 29" OD. It looks like you are going to try and keep the tires you have but get new rims? Once again, MO, but you will be much happier if you go up in rim size and can keep a taller tire with the same sidewall or less.

[GMJimmy]

Mike
Thanks for the reply and suggestions. You're right about me wanting to keep my existing tires but I'm not completely set on that. I could probably sell them as a set easier than just the rims but wanted to save some money as the tires have only about 600 miles on them. I'm going to take your advice and look at going with a 16" or 17" wheel. What brand of wheels do you have?
Jim

[Mike C]

Mine are Summit Legend wheels. I think they are no longer under the Summit name but the Vision Legend name. The 17x8 are $125 in gunmetal on the Summit Racing website. The 15x8 are only $85, but IMO, the 17's really help nail the look.

[schroederchevelle]

My question is what kind of backspacing do you need if the wheels are offset? Is that why some have around 3.75" backspacing?
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[GMJimmy]

Originally Posted by schroederchevelle

My question is what kind of backspacing do you need if the wheels are offset? Is that why some have around 3.75" backspacing?
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Offset and backspacing are kind of the same but not. For example the same rim can have a 4.25 inch back space and a -6mm offset. Back spacing is measured from the back edge of the rim to the mounting flange. Offset is measured from the center of the wheel between the beads to the mounting flange and is expressed in a positive or negative reading. It really depends on how the manufacturer measures his and how he publishes it. This should be standardized as it can get confusing.

[schroederchevelle]

That makes sense. I'm just trying to get things sorted out way ahead of time. My project probably won't be done for a couple years, but thinking about it keeps me busy. I like the looks of 17 inch wheels on these pickups. However, I think I want to stay with 15s just for the fact that I can get white letter tires, and I like the look of the taller sidewalls. Things might change before I get around to ordering wheels and tires, but for now that's what I'm thinking. Another question you might be able to answer is if I install 2.5" drop spindles, how much will the back need to be dropped to get it to sit close to level? What's the easiest way to do so?

[Mike C]

Typically the rear is 2"-3" more than the front. On my truck the front is 4.5" (spindles plus 2" springs) and the flip kit in the rear netted 7" for a 4.5"/7" drop or 2.5" more in the back. I split the difference. But doing a leaf flip gets you what it gets you. You have a lot more control with a coil truck.

[schroederchevelle]

I don't want to drop it too much and I think a leaf flip would take more out than I would want. If I could just drop it a couple inches I think I would be happy. Do the lowering shackles DJM sells work at all?
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[Robznob11]

Originally Posted by schroederchevelle

My question is what kind of backspacing do you need if the wheels are offset? Is that why some have around 3.75" backspacing?
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I think that you are correct sir... If you have a 8" rim with only 3.75 bs. I think your tires will be closed to flush with the edge of your fender. With your current drop maybe no problems because you would have to hit a hard dip or bump to make contact. But if you go more you will definitely have issues. I have 15x8 with 4 1/2 bs and 255/60/15. I have a 3" body drop and 2 1/2 spindle with a 1 1/2 drop spring. That's 7 total. They will tuck while straight but if I hit a bump when I turn they will rub. You will notice your troubles when you turn. I'm fixen to go a little smaller.

[GMJimmy]

So getting back to my question? I was going to put the 15X8's front and back but am afraid the 3.75" back space will cause front tire clearance issues??? Does anybody have these on their swb fleetside?

[Robznob11]

In short if you only have 2 1/2 drop spindle s you should be fine with 3.75 bs. If you go to the 4.25 bs you will likely have to clearance the channels on the lower a arm. It's easy tho....if buying new the deeper bs is a better option in my .02

[GMJimmy]

Originally Posted by Robznob11

In short if you only have 2 1/2 drop spindle s you should be fine with 3.75 bs. If you go to the 4.25 bs you will likely have to clearance the channels on the lower a arm. It's easy tho....if buying new the deeper bs is a better option in my .02

Thanks for the reply. I already have 15X8 GM rally wheels all the way around with a 4.25" BS. I really want to put Rocket Igniters on it but they are only available in a 15X8 5X5 with a 3.75" BS or a 16X8 with a 4.5"BS. I'd like to use the 15" tires I have but am afraid the 3.75" BS will cause fender interference on the back. Not to concerned about a 3.75" BS on the front. The 16X8's with a 4.5" BS may not clear the lower control arms so I think the only choice here is to go with a 15X7 with a 4.25" BS all the way around but wanted the 8" rims???

[Robznob11]

Well if it helps any I am running 12" wide rims on back with 6.5 bs. The rear on the 67 is 1" narrower than the 70 up. Even so I have a 5.5 front dish and it clears with a ballooned sidewall. So I bet the 8" you want would work.

[Mike C]

I used the ECE shackles on my 70 GMC C2500. You can get an inch or so that way. 1 1/2" if you trim the bed support.

I would do 2 1/2" spindle in front and 4" spring in the rear. Springs are expensive, but right way to do it.