33 or 35 inch tires with my set up ??!!?? - JeepForum.com

 
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post #1 of 13 Old 05-02-2011, 11:24 AM Thread Starter
DonAltman3
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33 or 35 inch tires with my set up ??!!??

Here the situation..
I have a 1990 YJ
I have a 4 inch pro comp lift.
The jeep currently has 35 inch thornbirds on 15x10 inch micky thompson wheels.

The jeep looks awesome.

I went an ordered some of the 35 inch goodyear mtr with kevlars about 3 months ago.. they were on back order and finally came in last week.

However I have been contemplating on perhaps dropping down to 33 inch tires.


The jeep has a 258 with an automatic transmission.
I crawled under it to find out what gear ratio in the back but the tag is gone.


As it is the jeep doesn't have much torque... however once rolling pretty good it has plenty of go. I can live with it as this isn't a hot rod but im curious if I will notice anything dropping just one size smaller tire.

I wonder if the jeep would look gimpy with the smaller tires on it.

Do automatics have a standard rear end.. that I could figure out the ratio..
or are they as varied as the standard shift jeeps?

Also what is my idle shift point.. it seems like my jeep my be shifting a bit premature... again could this have anything to do with tires size and would changing them help or hender this?

I'm just running over some of this in my head and looking for a few ideas..

the 35's really set my jeep off.. and they are only a few dollars more than the 33 inch tires.

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post #2 of 13 Old 05-02-2011, 11:35 AM
Destr0
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If you already have the 35s, why worry about it if you are fine the way it drives. To figure out the gear ratio you can jack up the rear end and sping a tire- count one revolution of the tire and see how many times the DS spins. Mark the DS with a piece of tape or something will make it a lot easier.

Count the number of times the DS spins- this will be your gear ratio, i.e. if the DS spins a hair over 3X for one wheel revolution, you have 3.07 gears. With an auto this is probably what you have, but I am not very well versed on the older YJs so go count. :-)

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1981 CJ7 SBC 350
2005 KJ Libertyt 4x4 CRD w/ 2.5" Frankenlift DD
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post #3 of 13 Old 05-02-2011, 11:52 AM Thread Starter
DonAltman3
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Gear ratio is said to be 3.54 so I am going to go with that.

I have 35's on it that are worn out.. I ordered some new 35 inch tires but haven't paid for them or put them on yet...
I was wondering if 33's will give me enough power or possible fuel savings to sway me into buying them over the 35's which I think will probably look a little better.....


I am wondering if the 33's would give me any more "power" I highly doubt anything noticable with only one tire size but just curious.


Are 35 with the 3.54 gear ration acceptable in most people eyes or would I be told to do a re-gear?

I think the jeep might have some shift point issues as it seems to shift to early and too quickly.. this could also be adding to my "lack of power"
feeling I am trying to possibly blame on the tires... although 35's are big and probably do rob alot of power..

I am just trying to think of all angles before I shell out this much cash on a new set of rubber.
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post #4 of 13 Old 05-02-2011, 12:08 PM
Destr0
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OK, your question makes a lot more sense now! :-)

33 to 35 may only seem like one size, but the difference in rolling mass can be quite a lot. You will almost certainly see more power with 3.55 gears if you drop down to 33s. Your shift points may be a little closer to what they should be. Will it be dramatic? Probably not, but you will certainly be able to tell a difference.

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1981 CJ7 SBC 350
2005 KJ Libertyt 4x4 CRD w/ 2.5" Frankenlift DD
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post #5 of 13 Old 05-02-2011, 12:21 PM Thread Starter
DonAltman3
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Alright for my next question.. I went outside with a ruler and laid it ontop of my current worn out thornbird then stuck a tape down to the pavement..
even though this tire is a 35 it's physical height is only 32.5 inches tall.
Is this becuase its so dang worn there is actually that much difference?
Would this tire be that close to the hieght of a new 33... and would a new 35 actually be 35 inchs tall?

AGHHHHH...

Something tells me I am going to go back with the 35's and try to fiddle with the shift points.. if I even can..
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post #6 of 13 Old 05-02-2011, 12:27 PM
Destr0
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Wow, I have a set of 31s that measure 32" tall...

My BFG 35s measure to 34.75" tall, and that is at only 20 PSI...

Most 33" tires will measure somewhere between 32 and 34" tall so you will probably not notice much difference switching down to 33s from what you currently are running.

1994 Jeep YJ off road toy
1981 CJ7 SBC 350
2005 KJ Libertyt 4x4 CRD w/ 2.5" Frankenlift DD
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post #7 of 13 Old 05-02-2011, 12:36 PM Thread Starter
DonAltman3
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thats kinda of what I am afraid of.. I am thinking that the 35 might actually be 35 inches and it would effectivly be 3 inches taller than what I am now...


I never felt severaly underpowered but it is kinda slow from a start.. once im rolling though I zip around pretty good and have no problems going interstate speed (70 plus)
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post #8 of 13 Old 05-02-2011, 12:57 PM
Destr0
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I had the same problem with starting from a stop on my YJ on 35s (2.5 w/ AX5). What I did was re-gear, although my re-gear was also fueled by me finding an 8.8 out of an XJ with 4.56 gears and tru-track LSD.

Regearing would help more than dropping to 33s- 4.10 would be the best gear ratio while staying on the cheap as they can be found (D30) in YJ and XJs.

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1981 CJ7 SBC 350
2005 KJ Libertyt 4x4 CRD w/ 2.5" Frankenlift DD
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post #9 of 13 Old 06-13-2011, 02:44 PM Thread Starter
DonAltman3
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I put the wrangler 35's on it and it made a night and day difference in take off handeling... everything..

The thornbirds looked cool but boy they are horrible.
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post #10 of 13 Old 06-13-2011, 03:03 PM
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FWIW, I have a 1990 YJ with a 258 and it came stock with 3:07 gears.

I have 4:10 now, with 35s and it goes ok but 4:56 or 4:88 would be better

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post #11 of 13 Old 06-13-2011, 06:36 PM
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Quote:
Originally Posted by DonAltman3 View Post
I put the wrangler 35's on it and it made a night and day difference in take off handeling... everything..

The thornbirds looked cool but boy they are horrible.
I don't know why Interco made that tire for so long. All show and no go.
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post #12 of 13 Old 06-13-2011, 07:02 PM
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Ever thought of doing the 4.0 head swap instead? It's an easy 20HP, probably more, and you get better mileage out of it.

-Noltz
'91 Frankenheep YJ. 4.0, 4" BDS, Richmond 8.8, Titan 12k, 35" KM2's, rust.
'88 YJ, 4.2/4.0 head, +4˝" & shackles, BFG 33's (sold)
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post #13 of 13 Old 06-13-2011, 09:50 PM
jeepnbrett
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Its hard to answer your question because there is no "right" answer. But I can tell you that you will notice a big difference between 33's and 35's with 3.55 gears. I run 33's with 4.11's and a 4.0 auto. 60mph it revs about 2700-2800 rpm. Most will agree that 3.55's are way too high for 35's. Bottom line is if you are happy with it the way it is, RUN IT!!!

Brett

4.0, AT, 3.5 Fabtech, 1" SRS, 1" BL, 35x13.50x15 Toyo MT's, HP30, TJ shafts, Lockrite, 8.8, Power Trax No Slip, 4.11's, Warn bumpers, W8274, SYE, and a bunch of other stuff....
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