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15x8 w/ 5" BS vs 4.5" BS (check my figures)

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msra_chevelle

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Discussion starter · #1 ·
So I've come to the conclusion that 15x8 will be the size to go on front and rear. Redrum has posted calculations of tire width so I thought I would do some figuring myself.

I was going to run the standard 4.5" backspacing which amounts to 0" offset. Tires were going to be 245/60-15 front and 275/60-15 rear. Since bigger wheels allow for more offset in the rear due to shock clearance, I thought why not see what a 15x8 with 5" backspacing or 1/2" offset would give me.

Assumptions:
245 = 09.64 section width
265 = 10.43 section width
275 = 10.82 section width
295 = 11.61 section width

Zero Offset
245 --> 4.820 & 4.820
275 --> 5.410 & 5.410

1/2" Offset
265 --> 4.715 & 5.715
295 --> 5.300 & 6.300

So with a 1/2" offset wheel I can now run a bigger tire with slightly more clearance at the fender lip. The tire will be pushed towards the center of the car but I have room there.

Why do I know there is more clearance to the inside you ask? Because there are plenty of people running 275/40's on 17x9.5 with 6" BS or 3/4" offset. If we calculate those numbers we equate to the following.

3/4" Offset:
275 --> 4.660 & 6.160

There are also people saying they run 295/50-15's with 5.5" BS or 0 offset with 15x10's. Most say you may need to roll the lip at this size with a 10" wheel while some say you'll be fine with stock lips. Those numbers would equate to the following.

0" Offset:
295 --> 5.800 & 5.800

So, what does all this tell me? I think I should run the 15x8's with 5" BS or 1/2" offset. What do you think? Does my arithmatic blow chunks?
 
Discussion starter · #2 ·
Oooh, one more calculation to add into the mix. KAA runs 17x11 with 6.375" BS or 3/8" Offset. His tires are 315/35-17 with an section width of 12.38 on the 11" rim. These numbers equate to the following.

3/8" Offset
315 --> 5.815 & 6.565

Both of the numbers are highlighted because this is an extreme size. Though I'm no expert with El Camino's. Do they have wider wheel wells than a Chevelle of the same year? Or my 69 Chevelle?
 
#5 ·
THe 295-50/15 is OK for height. BFG and others also make a 295-50/16 that gives you a 28" tall tire. The numbers get confusing easily. It is a motter of do you want 11" or 12" wide (section width ) and do you want 27" or 28" tall. With the '69 body, 28" tall tire seems to be a nice fit, these can even take a 29" tall tire with room left over.
 
#6 ·
If you go with the 295/50-15, I wouldn't recommend more offset. I have them on the back of my '70 Elky on 15x8's with 4.5" backspacing. I have plenty of clearance at the fender lip, but I did have some slight rubbing on the inner fender in hard cornering. Nothing a little massaging couldn't fix, but I wouldn't want them a 1/2" closer.
 
Discussion starter · #7 ·
As has been stated previously in other posts. Always measure your application and always chose the offset you feel is best. Jegs was extremely helpful with my change from 5" BS to 4.5" offset. I ordered the 5" BS on saturday and the 4.5" BS on sunday. Both orders arrived wednesday, and I refused the 5" BS per Jegs instruction. Needless to say, I should have stuck with the 5" BS. My car will be lower than most and both the front AND rear have proven to be problem areas with the 4.5" (zero offset) combonation. I have plenty of room between the frame and tire in the back and front. I will rub the upper outside fender on both the front and rear. Note that the first outside lip is not a problem. There is another rib just above the lip that sticks farther inside the wheel well area. This will be the problem area. It cannot be modified.

The tires I went with were 255/60-15 in front and 275/60-15 in rear. These things look damn huge. They look to fit the wheels perfectly. I'm also happy with the large diameter. The 50 series would have been too short. And the 295/50-15's in back would have been too damn big.

I do appreciate ALL reply's to my requests for info. They have ALL been helpful. I'm going to order the 5" BS again and see where things go. I will reply here with my findings.

These tires look huge!
 
#8 ·
Did you measure the backspacing on those 15x8's before mounting the tires?
The reason I ask that question is a pair of 15x8 wheels with 4.5" backspacing and 275/60/15 tires should easily fit your 69 Chevelle.
 
#9 ·
msra_chevelle said:
The 50 series would have been too short. And the 295/50-15's in back would have been too damn big.

!
Click to expand...

Did you mean to say 295/60-15's would have been too big? You mean too high or too wide? As long as the tire is centered properly, width would only really be noticed when looking at the rear of the car.
 
#11 ·
I wonder how much backspace can be run with 15" front wheels w/o chassis parts interference. My 17x9's have 5.25" and I can still run at least 6" of backspacing. That's with a 275/40 tire and tubular control arms.
 
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