Need help! Boss 338 fitment.

[RaceAGMC]

I know wheel fitment has been covered many times, but I have read threads and have gone dizzy trying to decipher everyone's setups and wheel fitments. So if someone could give me some help it would be awesome. I plan on running a 20x8.5 and 20x10.

My setup:

1970 SWB Fleetside
CPP disc brake conversion with NON modular 2-1/2" spindles
2" front spring
Stock 71 rear 5 lug axle
5" drop rear spring

I already have tires, I chose a common size that a lot of guys are running.
255/40/20 and 295/40/20

I plan on keeping my front fender wells. If I have to I can get the modular spindles, but would rather have a wheel that sets back in the wheel well with the spindle I already have but if its not an option with these wheels I can go to the modular ones.
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[lolife99]

What's your question?
Backspacing of the wheels?

[RaceAGMC]

Yeah. Back spacing/ offset. I'm so very confused, just don't want to make a $800 mistake.
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[lolife99]

20x8.5 (5.25" bs)
20x10 (5.5" bs)

[RaceAGMC]

What does that equate to as far as offset/et? They are trying to sell me +2. Is that correct?
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[BugzC10]

Here's a site you can plug in your tire and wheel specs...should be helpfull

http://www.rimsntires.com/specs.jsp
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[lolife99]

Originally Posted by RaceAGMC

What does that equate to as far as offset/et? They are trying to sell me +2. Is that correct?
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+2 for the fron or rear.
They are different.
If your wheel guy can't convert backspace to offset,... run.

Buy from this board member/vendor,... ksbrktracer.
http://67-72chevytrucks.com/vboard/s...d.php?t=585955

Look here in the Vendor Marketplace:
http://67-72chevytrucks.com/vboard/f...prune=-1&f=195

Here's an offset chart I use to understand backspacing,...

[lolife99]

You can see the fronts would be a +12 (only on a 8.5" wide wheel)
And the rear would be a 0 offset (only on a 10" wide wheel).

Boss actually calls their front 20x8.5 wheels a +14 offset,...

[RaceAGMC]

Saying both are +2.
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[RaceAGMC]

Originally Posted by lolife99

+2 for the fron or rear.
They are different.
If your wheel guy can't convert backspace to offset,... run.

Buy from this board member/vendor,... ksbrktracer.
http://67-72chevytrucks.com/vboard/s...d.php?t=585955

Look here in the Vendor Marketplace:
http://67-72chevytrucks.com/vboard/f...prune=-1&f=195

Here's an offset chart I use to understand backspacing,...

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I understand what you are saying about buying from board members, I do buy a lot of parts from board vendors, but I am getting a killer deal on the price of these wheels.

[lolife99]

Originally Posted by RaceAGMC

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I understand what you are saying about buying from board members, I do buy a lot of parts from board vendors, but I am getting a killer deal on the price of these wheels.

Have you priced them from the Vendor I mentioned?

Killer deal on wheels,... with the wrong backspacing,... are still the wrong wheel.

[RaceAGMC]

This is what they have for me. It shows +2 on front and rear. If this won't work, I can tell them what specs I need.




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[RaceAGMC]

Originally Posted by lolife99

Have you priced them from the Vendor I mentioned?

Killer deal on wheels,... with the wrong backspacing,... are still the wrong wheel.

I haven't but I will check with him.
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[magwakeenercew2jh]

I'm pretty sure that the reason there are so many questions on wheel (size, width and b/s) and tire size, is that there are soooo many combos. Too many.

You already have the tires. So, there's no question there. Seems like you have all the suspension set up...
I don't know from Jack about "modular spindles"....

You question seems to be about whether the Boss 338 8.5/10.0 20's will work, right?

Well, here's my set up....See how close it is to yours:

Boss 338 20's; 8.5/10.0
Tires are different 245/40's and 275/45's

Basically the frame and box are '71 Fleet Short
ECE 2.5" drop spindles
ECE 2" Springs in front
ECE 6" drop springs in back (no C-Notch)
Shock relocator kit including and KYB (or whatever they are called) shocks
ECE adjustable panhard bar (if that matters...it did to me for centering).


Soooo.....The REAL QUESTION is about the Boss 338 b/s. On my mfg date, they came in one b/s only for the 20's. I had to use spacers to get the rears out away from the bed side of wheel well.

I chose to go with 1" spacers. Good ones. At the time, the b/s Boss was selling was something like 5.23" for the rear. If you dug around on the forum, you would see that Boss came
out with different b/s more recently than my buy. The complaint on those was that they seemed to have added material to get a smaller (in inches) b/s and it did not create a deeper rim
on the outside....(the polished surface in mine).

I have no idea what the 8.5 x 20's b/s is. They are all they had at the time, too.

Subsequent to that first fit, I bought some 1.5" spacers for the back and moved the 1" spacers to the front. That's only because I wanted mine to be "closer" to the outside wheel well...
...wider stance...Different than what you are after, I take.

So, I'll look for pics. But it won't really matter.

You already have the tires. And, you want to buy Boss wheels. So, if there's any choice in b/s, and, like someone else stated, the folks you're buying them from can't tell by your stats,
either run or buy the wheels. There's no science. It is often a guess. About fit...And we're not even getting into the art of the wheel/stance ratio yet.

Like I said, there are as many questions as there are trucks on the road. Just buy the wheels and take a shot. If they fit, you'll be surprised how much you like them once you pay out the bucks.

The first three pics are when she first came home from the shop after I laid under her for three plus years. The one with me leaning on her has a minor P/S (turn signal elimination to see
if I wanna go with the 67-70 front bumper).

The last one is yesterday after I prepped for taking her to the paint man.

Point is, the first three are with the 1" spacers in the back and none up front. The last one is with 1.5" and 1" spacers, rear and front, resp.

Hope this helps.

[lolife99]

Originally Posted by magwakeenercew2jh

I'm pretty sure that the reason there are so many questions on wheel (size, width and b/s) and tire size, is that there are soooo many combos. Too many.

You already have the tires. So, there's no question there. Seems like you have all the suspension set up...
I don't know from Jack about "modular spindles"....

You question seems to be about whether the Boss 338 8.5/10.0 20's will work, right?

Well, here's my set up....See how close it is to yours:

Boss 338 20's; 8.5/10.0
Tires are different 245/40's and 275/45's

Basically the frame and box are '71 Fleet Short
ECE 2.5" drop spindles
ECE 2" Springs in front
ECE 6" drop springs in back (no C-Notch)
Shock relocator kit including and KYB (or whatever they are called) shocks
ECE adjustable panhard bar (if that matters...it did to me for centering).


Soooo.....The REAL QUESTION is about the Boss 338 b/s. On my mfg date, they came in one b/s only for the 20's. I had to use spacers to get the rears out away from the bed side of wheel well.

I chose to go with 1" spacers. Good ones. At the time, the b/s Boss was selling was something like 5.23" for the rear. If you dug around on the forum, you would see that Boss came
out with different b/s more recently than my buy. The complaint on those was that they seemed to have added material to get a smaller (in inches) b/s and it did not create a deeper rim
on the outside....(the polished surface in mine).

I have no idea what the 8.5 x 20's b/s is. They are all they had at the time, too.

Subsequent to that first fit, I bought some 1.5" spacers for the back and moved the 1" spacers to the front. That's only because I wanted mine to be "closer" to the outside wheel well...
...wider stance...Different than what you are after, I take.

So, I'll look for pics. But it won't really matter.

You already have the tires. And, you want to buy Boss wheels. So, if there's any choice in b/s, and, like someone else stated, the folks you're buying them from can't tell by your stats,
either run or buy the wheels. There's no science. It is often a guess. About fit...And we're not even getting into the art of the wheel/stance ratio yet.

Like I said, there are as many questions as there are trucks on the road. Just buy the wheels and take a shot. If they fit, you'll be surprised how much you like them once you pay out the bucks.

The first three pics are when she first came home from the shop after I laid under her for three plus years. The one with me leaning on her has a minor P/S (turn signal elimination to see
if I wanna go with the 67-70 front bumper).

The last one is yesterday after I prepped for taking her to the paint man.

Point is, the first three are with the 1" spacers in the back and none up front. The last one is with 1.5" and 1" spacers, rear and front, resp.

Hope this helps.

Lots of good info,... but if you don't include the backspace numbers,... there is nothing to compare to.

The OP asked what would work with his truck.
I gave the answer I would use if it was my truck and it had the same 71-72 width rearend.
Trying to make the OP's wheel guy's wheels choices fit,... is not for me to decide.
Good luck with your purchase.

[RaceAGMC]

Originally Posted by lolife99

Yes.
Those are MY wheels.
+2 on a 20x10 is a 6.225" BS.
TOO MUCH!
You need a 5.5" backspace on your 20x10's.

Thanks. And 5.25 for the fronts as well?
Glad I asked for help before I picked up wheels and had them mounted up.

What do those backspace numbers convert to in offset so I can tell them to et me the correct fitting wheels.
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[Andy4639]

This is what I have on the front.
I have a 1/4" spacer on the back wheels so the tire want scrub. The fronts I shaved just enough off the hub for the cap to fit without sticking.
Sorry they had already threw the back boxes away when I thought to take pictures of them.

[RaceAGMC]

I stopped by the shop today and measured the back spacing on the wheels they have for me. The fronts are 4-3/4, so ill have them swap those out for 5-1/4". The rear is at 5-1/2" that's what I want correct.

Thanks Andy, btw I met u at the C-10 cruise in, I like your truck, congrats on he long haul.
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[lolife99]

Originally Posted by RaceAGMC

Thanks. And 5.25 for the fronts as well?
Glad I asked for help before I picked up wheels and had them mounted up.

What do those backspace numbers convert to in offset so I can tell them to et me the correct fitting wheels.
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You need:
+14mm for the front 20x8.5
0 offset for the rear 20x10

EDIT:
I guess being sick all weekend has messed up my brain.
My 6.225" BS 20x10's have a +20mm offset.

Glad you got it figured out.
Just make sure you get the +14mm offest 20x8.5's and you will be fine.

[ksbrktracer]

[QUOTE=RaceAGMC;6139035]I stopped by the shop today and measured the back spacing on the wheels they have for me. The fronts are 4-3/4, so ill have them swap those out for 5-1/4". The rear is at 5-1/2" that's what I want correct.

]

Pm with pricing sent per request ...... Hopefully I can help you out .

[Andy4639]

Originally Posted by RaceAGMC

I stopped by the shop today and measured the back spacing on the wheels they have for me. The fronts are 4-3/4, so ill have them swap those out for 5-1/4". The rear is at 5-1/2" that's what I want correct.

Thanks Andy, btw I met u at the C-10 cruise in, I like your truck, congrats on he long haul.
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Cool. Sorry I meet so many people in so few days it was really hard trying to remember everyones names. Good deal on the wheels they should look good on the truck.

[RaceAGMC]

Well guys for anyone wondering, I installed my front wheels today. They have 5.25" backspace and I'm running a 255/40/20, with that setup i still had to remove my inner fenders to get the clearence I needed to not rub. Looks like to run my inner fenders I will have to pick up some CPP modular spindles.
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[lolife99]

Originally Posted by RaceAGMC

Well guys for anyone wondering, I installed my front wheels today. They have 5.25" backspace and I'm running a 255/40/20, with that setup i still had to remove my inner fenders to get the clearence I needed to not rub. Looks like to run my inner fenders I will have to pick up some CPP modular spindles.
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They rub the fender lip?
Or the inner fender?

[magwakeenercew2jh]

Hummmm.

My 245 40's didn't rub (before or after the 1" spacers) with ECE 2.5" drop spindles and ECE 2" drop springs.
I'm pretty sure the b/s is the same...can't be positive of that. But I'd bet on it.

I guess, all other things considered, that difference in the tire made the difference.

Pics and "rubbing data" sure might be helpful for others, Race.

[RaceAGMC]

Originally Posted by lolife99

They rub the fender lip?
Or the inner fender?

Inner fender. After I removed them I was in the clear. I would still like them more, esp if I decided to go lower. Plus if they are tucked in a lil more I can prob run the inner fenders again.
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