New tires and size - JeepForum.com
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post #1 of 18 Old 08-14-2019, 08:47 AM Thread Starter
oaks3
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New tires and size

I have a very stock 1979 cj 7. It has 31 x 10.5 x15 tires on it. A friends gave me a set of black rims and tires that are 33 x 12.5 x 15. Would putting this new ones be possible? Will I need to buy anything extra to make this happen? I am not savvy to anything like this so this is why I ask. By putting these on, Will it mess anything thing up? Thank you in advance!

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post #2 of 18 Old 08-14-2019, 09:09 AM
bob4703
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To use the 33s you will need to lift your Jeep. The larger tires will affect the gearing also and thus your performance will suffer.

Keep then wheels and trade the tires for more 31s.
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post #3 of 18 Old 08-14-2019, 10:37 AM
Hurricane4
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I run BFGoodrich All Terrain T/A 31x10.50R15 tires on stock suspension.

These tires don't rub and look like they fit the Jeep.

FYI - Overall diameter of these tires is 30.5 inches.

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Jeeps I Have Owned in Year Order:
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post #4 of 18 Old 08-14-2019, 10:45 AM Thread Starter
oaks3
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Quote:
Originally Posted by bob4703 View Post
To use the 33s you will need to lift your Jeep. The larger tires will affect the gearing also and thus your performance will suffer.

Keep then wheels and trade the tires for more 31s.
Hi bob, thanks for the response! I have 31’s on my Jeep right now. I could just switch the tires and put on the new rims?
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post #5 of 18 Old 08-14-2019, 12:25 PM
Hurricane4
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What size wheels do you have now with the 31s mounted on them?

Currently I am using 15X8 white spoke with my 31x10.50R15 tires.

"The unbelievable we can do immediately . . . the impossible just takes a little longer."
My College Accounting Professor

"Success is not final. Failure is not fatal. It is the courage to continue that counts"
Winston Churchill

Jeeps I Have Owned in Year Order:
'61 CJ5, '63 CJ6, '78 CJ5, '79 CJ5 (Current), '79 CJ7 & '86 CJ7.
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post #6 of 18 Old 08-14-2019, 01:01 PM Thread Starter
oaks3
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Quote:
Originally Posted by Hurricane4 View Post
What size wheels do you have now with the 31s mounted on them?

Currently I am using 15X8 white spoke with my 31x10.50R15 tires.
Hurricane, I have no idea. They came with the Jeep when I got it.
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post #7 of 18 Old 08-14-2019, 05:00 PM
Hurricane4
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OK - There should be stamped - imprinted on the backside of the wheel the size - something like 15 X 8 JJ

You will find this on the rear rim portion - probably need to do some major cleaning to find it.

FYI - If you are interested in new lug nuts and locking lug nuts - here is what I purchased:

https://www.summitracing.com/parts/mcg-74043
McGard Lug Nuts 74043 - Qty: 2 ( Have some extra )
Lug Nuts, Marine, Conical Seat, Standard, 1/2 in. x 20 RH, Steel, Chrome, Set of 10

https://www.summitracing.com/parts/mcg-74041
McGard Wheel Locks 74041 - Qty: 2 ( Have extra and get two removal sockets )
Lug Nuts, Wheel Locks, Standard Locking, Conical Seat, 1/2 in. x 20 RH, Steel, Chrome, Set of 4
Special key tool included

"The unbelievable we can do immediately . . . the impossible just takes a little longer."
My College Accounting Professor

"Success is not final. Failure is not fatal. It is the courage to continue that counts"
Winston Churchill

Jeeps I Have Owned in Year Order:
'61 CJ5, '63 CJ6, '78 CJ5, '79 CJ5 (Current), '79 CJ7 & '86 CJ7.
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post #8 of 18 Old 08-14-2019, 09:35 PM Thread Starter
oaks3
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Quote:
Originally Posted by Hurricane4 View Post
OK - There should be stamped - imprinted on the backside of the wheel the size - something like 15 X 8 JJ

You will find this on the rear rim portion - probably need to do some major cleaning to find it.

FYI - If you are interested in new lug nuts and locking lug nuts - here is what I purchased:

http://www.summitracing.com/parts/mcg-74043
McGard Lug Nuts 74043 - Qty: 2 ( Have some extra )
Lug Nuts, Marine, Conical Seat, Standard, 1/2 in. x 20 RH, Steel, Chrome, Set of 10

http://www.summitracing.com/parts/mcg-74041
McGard Wheel Locks 74041 - Qty: 2 ( Have extra and get two removal sockets )
Lug Nuts, Wheel Locks, Standard Locking, Conical Seat, 1/2 in. x 20 RH, Steel, Chrome, Set of 4
Special key tool included
Those new ones say 15 x 7 j5
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post #9 of 18 Old 08-14-2019, 10:14 PM
BagusJeep
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The new ones are only 7" wide. The tyre is 12.5" wide. The minimum rim width recommended for this size is 8.5".

If you want to use the 7" rims I would suggest reducing the width to 10.5". Plenty of good tyres 31" to 33" diameter which are 10.5" wide and fit those rims.

The other thing to check is backspace. The mounting face of the wheel relative to the centre line of the wheel. 3.75" is common on CJs. If it has similar backspace to the old wheels, you are OK.

But that is not the end of the story, your 31" tyres are the largest you can put on a stock CJ without compromising other aspects. It can get expensive to do it properly. There are reasons why Bagusjeep has 31" tyres, mostly poverty.

When you move to a larger diameter tyre you will need to lift the Jeep to get them under the rear without touching the wheelboxes and lips. 4" lift over stock will safely clear them, those 33" tyres will not fit within the wheelbox.

The front tyres are wider so they will probably touch the leaf springs on full lock, which is really bad. There are adjustable bump stops on the spindles so you can dial this out, but the turning circle will be wider. If too bad, you can either get a rim with more backspacing or fit wheel spacers to push the tyre out from the frame. A 1 1/2" spacer will net a good reduction in turning circle and widen the stance, but you should extend the wheelarch flares as well so no rocks are thrown up.

So to fit those free tyres you will need new rims, a 4" suspension lift, maybe wheelspacers and wheelarch extensions. And when you find the 33" tyres are making it sluggish, a regear of both axles.

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1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
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post #10 of 18 Old 08-14-2019, 10:28 PM
Hurricane4
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I agree with BagusJeep - a 7 inch wide wheel is too narrow for a 12.5 inch wide tire.

As BagusJeep stated larger diameter and wider tires affect many items on your CJ.

"The unbelievable we can do immediately . . . the impossible just takes a little longer."
My College Accounting Professor

"Success is not final. Failure is not fatal. It is the courage to continue that counts"
Winston Churchill

Jeeps I Have Owned in Year Order:
'61 CJ5, '63 CJ6, '78 CJ5, '79 CJ5 (Current), '79 CJ7 & '86 CJ7.
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post #11 of 18 Old 08-14-2019, 11:43 PM Thread Starter
oaks3
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Quote:
Originally Posted by BagusJeep View Post
The new ones are only 7" wide. The tyre is 12.5" wide. The minimum rim width recommended for this size is 8.5".

If you want to use the 7" rims I would suggest reducing the width to 10.5". Plenty of good tyres 31" to 33" diameter which are 10.5" wide and fit those rims.

The other thing to check is backspace. The mounting face of the wheel relative to the centre line of the wheel. 3.75" is common on CJs. If it has similar backspace to the old wheels, you are OK.

But that is not the end of the story, your 31" tyres are the largest you can put on a stock CJ without compromising other aspects. It can get expensive to do it properly. There are reasons why Bagusjeep has 31" tyres, mostly poverty.

When you move to a larger diameter tyre you will need to lift the Jeep to get them under the rear without touching the wheelboxes and lips. 4" lift over stock will safely clear them, those 33" tyres will not fit within the wheelbox.

The front tyres are wider so they will probably touch the leaf springs on full lock, which is really bad. There are adjustable bump stops on the spindles so you can dial this out, but the turning circle will be wider. If too bad, you can either get a rim with more backspacing or fit wheel spacers to push the tyre out from the frame. A 1 1/2" spacer will net a good reduction in turning circle and widen the stance, but you should extend the wheelarch flares as well so no rocks are thrown up.

So to fit those free tyres you will need new rims, a 4" suspension lift, maybe wheelspacers and wheelarch extensions. And when you find the 33" tyres are making it sluggish, a regear of both axles.
Quote:
Originally Posted by Hurricane4 View Post
I agree with BagusJeep - a 7 inch wide wheel is too narrow for a 12.5 inch wide tire.

As BagusJeep stated larger diameter and wider tires affect many items on your CJ.
I appreciate you bother very much! Is it possible to for the 31 10.5 15 tires on the rims that have the 33’s on them?
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post #12 of 18 Old 08-15-2019, 12:24 AM
Hurricane4
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Rim width range should be something like this for a 31 X 10.50 X 15 tire:


Rim Width Range (Min/Max)
7" - 9"

"The unbelievable we can do immediately . . . the impossible just takes a little longer."
My College Accounting Professor

"Success is not final. Failure is not fatal. It is the courage to continue that counts"
Winston Churchill

Jeeps I Have Owned in Year Order:
'61 CJ5, '63 CJ6, '78 CJ5, '79 CJ5 (Current), '79 CJ7 & '86 CJ7.
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post #13 of 18 Old 08-15-2019, 03:24 AM
BagusJeep
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As Hurricane just said, yes. ^

BagusJeep lives in Bali.

1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE
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post #14 of 18 Old 08-15-2019, 08:41 AM Thread Starter
oaks3
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Quote:
Originally Posted by Hurricane4 View Post
Rim width range should be something like this for a 31 X 10.50 X 15 tire:


Rim Width Range (Min/Max)
7" - 9"
Quote:
Originally Posted by BagusJeep View Post
As Hurricane just said, yes. ^
You two human are great. Thank you for your help and answering my questions. I don’t really know a lot about this type of thing, so thank you! I received this as a gift from my mother in law when my father in law passed away. It say for 12 years. The original owner sold it to him for $1,200 because he needed to bury his dad when he passed away. Literally this thing say in a barn until I picked it up.
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post #15 of 18 Old 08-15-2019, 04:05 PM
Axhammer
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Backspacing is the relationship of the WMS to the outer edge of the inside of the wheel. The relationship of the WMS to the wheel centerline is Offset. See diagrams attached.
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