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Deciding tire size

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Mike S View Drop Down
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    Posted: 12 Feb. 2016 at 12:38am
My 2A has new (stock) suspension. it is more or less complete and sitting on jack stands. The center of the axle to the inside of the fender/wheel well measures:

Front - 20-1/2"

Rear - 25"

I have a set of 16 X 6  older Jeep rims. I would like to go with IROK NDs in 235/85/16 that have a spec of 31.4" overall diameter. I am wondering if these will be too big, or not? I know that most tire diameter specs are larger than actual - actual is often a inch or more smaller.

Thanks for your comments.

M
'47 CJ2A -- #114542
Warn FF D41 rear
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11" drum brakes
Dual master cylinder
T90C Transmission
16 X 6 Jeep truck wheels
Cooper STT Pro tires
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windyhill View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote windyhill Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb. 2016 at 2:46am
Those should work nicely, might have to bump up to 1" super lift springs. 
'48 CJ2A
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Joe Friday View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joe Friday Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb. 2016 at 4:15am
At that diameter using the original wheels you will scrub the frame at the front and rear of the front tires significantly on hard turns
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Mark W. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark W. Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb. 2016 at 5:11am
Joe couldn't Mike just lengthen the stop bolts on the Knuckles to keep from rubbing? Granted he will be loosing a small amount of his turning radius. But better that then tearing up tires and frame paint.
Chug A Lug
1948 2A Body Customized
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Late 50's 134L 9.25"clutch T90A D18 (1.25") D44/30 flanged E-Locker D25 5.38 Since 1962
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oldtime View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldtime Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb. 2016 at 3:41pm
Rear wheel house opening is 31".
That pretty well indicates the optimum tire diameter.
 
Radials tend to have rounded shoulders so that will somewhat reduce the amount of leaf spring contact at full steer.
 
That said with Ross steering the narrower the tire; the better the steering.
I suggest 215 85 16 as being the optimum radial tire size on Willys CJ's with Ross systems.
Plus the 215 designation will better fit your narrow rims.
 
I'm currently running STA 6.50 x 16" on 4.5" Kelsey Hayes rims.
These tire tend to run tall and wide for their size designation.
They are 30.5" tall and 6" wide across the tread.
With Rzeppa front axle shafts I get a full 29* steering angle.
Other front axle shafts produce less steering angle than Rzeppa's.
Spicer axle shafts provide 27-1/2* and Bendix only provide 23* angle.
 
The 6.50 x 16 STA tires just begin to rub the springs at 29* angle..
That combination provides maximum tire diameter at minimum turn radius
Other front axle shafts produce less steering angle than Rzeppa's.
 
If you look past the lower zerk you can see how 29* steer angle allows The STA tire to barely touch upon the front leaf spring.

 
Currently building my final F-134 powered 3B .
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Joe Friday View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joe Friday Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb. 2016 at 5:51pm
Yes, I have grooves in the edge of the tread on some of my tires from scraping the zerk fittings.

Ken is right, the 215/85 is really the biggest without mods.
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Mike S View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike S Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb. 2016 at 6:52pm
I did look at the front steering angles to check for interference. I believe that a 1" spacer on the front will get me clear of trouble without moving the stops on the steering. I doubt I need spacers on the rear. 

I do want something taller than standard and aggressive but relatively narrow. The springs i have are new Crown units and stiff. I can't imagine enough weight in the jeep to get full articulation.

Tire specs:
SIZEINTERCO NUMBERWEIGHTTREAD PLYSIDE PLYSKID DEPTHTREAD WIDTHO.D.
235/85R16LTIND-10 NEW5010220.2/327.631.7

'47 CJ2A -- #114542
Warn FF D41 rear
Lock-Right locker
11" drum brakes
Dual master cylinder
T90C Transmission
16 X 6 Jeep truck wheels
Cooper STT Pro tires
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Joe Friday View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joe Friday Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb. 2016 at 7:26pm
A half inch spacer in the front would be enough. but a half in the rear would likely cause you to snag the body on full articulation. Those specs show a 20/32" tread depth which is pretty good, and a 10 ply rating (load range E, 80 PSI) with an actual sidewall of 2 plies of polyester.

I'd be surprised if you ever ran over 24 psi in them. For offroad 10-12 psi will probably be the sweet spot.

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