Deciding tire size

Discussion in 'Flat Fender Tech' started by Wenaha, Feb 11, 2016.

  1. Feb 11, 2016
    Wenaha

    Wenaha Member

    West Coast
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    I'm rebuilding/restoring my old CJ2A.

    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
     
  2. Feb 12, 2016
    47v6

    47v6 junk wrecker! Sponsor

    Washington DC.
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    For a stock 2A its not about the height but more about the width. The ross gear does not like a wide tire, in fact you will get a work out and be pretty unhappy with wide tires. Also your turning radius will suffer with wider tires. Personally I would go with the tallest narrowest tire i could find. The buckshot mudders always looked awesome to me, but I am sure the ride quality would be marginal at best on road. One way to make the steering effort easier is to use a V6 or ,I think, an m-38a1 ross box which are larger than the 2a and require a lot less effort to steer while being a direct bolt in.
     
  3. Feb 12, 2016
    Wenaha

    Wenaha Member

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    Chris -- granted - narrow is better. I have run 9.50/29/15 Interco Swampers on 7" rims and the Jeep had NO trouble at all - it originally had wide gum balltires which were a beast to drive. I am thinking that the 235 with a tread width of 7.5" would be a breeze. I already checked the front geometry and do expect to run 1" spacers with the 6" wide rims (backspacing about 4.25") on the front to avoid frame rub.

    I am wondering if 31.5" is too tall? I don't want to go bigger.
     
  4. Feb 12, 2016
    47v6

    47v6 junk wrecker! Sponsor

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    From my experience, and I think yours too, you will be happy with a 31.5 inch tall tire. I think NDT's were about 31" tall.

    I bet those Interco swampers looked awesome.
     
  5. Feb 12, 2016
    Mike C

    Mike C Member

    Austin, TX
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    I think they are steering you in the right direction. I have 215 75 15 on my MB and am looking at going to 215 85 15 Swampers. The 6.0 x 16 NDT's are about 28" tall. The 7.00 are about 30" tall and the 7.5 31" in my experience so the 235 85 16 should be a good fit.
     
  6. Feb 12, 2016
    garage gnome

    garage gnome Rust polisher Sponsor

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    I'm going to go with 6.50x16 super tractions from Walcks on Ted. They have a super swamper type tread and are 30" tall.
     
  7. Feb 13, 2016
    oldtime

    oldtime oldtime

    St. Charles,...
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    The Ross system vs tire width is the main concern.
    But 2.35 x 16" is not overly wide concerning tread width for use with a Ross system.

    The 31.5 tall will be a problem concerning front tire / spring interference.
    Using offset wheel spacers should proved the needed clearance.

    The 31.5 x16 will be a slight problem concerning rear tire / inner wheel house interference.
    Again...using offset wheel spacers should proved the needed clearance.

    No other problems should be encountered.

    Changing to a lower geared Ross box yields both positive and negative effects.
    A lower ratio Ross box reduces steering effort but it also proportionately increases the steer wheel free motion.
     
  8. Feb 13, 2016
    oldtime

    oldtime oldtime

    St. Charles,...
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    Repost from the 2A forum.......

    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.
    [​IMG]
     
  9. Feb 14, 2016
    shaun

    shaun Member

    ohio, Beavercreek
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    what would be a good daily driver tire on my CJ5? i have 32X11.5x15 on there now, but thinking all terrain tires for daily driver, let it be known i do live in Ohio. but thought about 31x8x15. Whats your opinion
     
  10. Feb 15, 2016
    Patrick

    Patrick Super Moderator Staff Member Sponsor

    Los Alamos, NM
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    I think the 215/85R16 is a fine size for a flatty. Here's mine, on 5" wheels with 1" wheel spacers. 215/85R16 Hankook Dynapro MT[​IMG]
     
  11. Feb 15, 2016
    oldtime

    oldtime oldtime

    St. Charles,...
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    IMHO the 2 best choices for a CJ with Ross steering are the 6.50 x 16 " STA Super Traxion's or the 215/85R16 Hankook Dynapro MT's. in case you prefer radials.
    Not real sure about the best tires for use with 15" wheels.
    Just whatever is relatively narrow tread and near to 31" actual tire diameter.
     
  12. Feb 15, 2016
    shaun

    shaun Member

    ohio, Beavercreek
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    so a 32 or 31X8X15 would be sufficient? I don't need to go up in rim sizes but looking for what a good width would be. I was thinking of saving my MT which are 32 X 11.5 X 15 but I may get AT tires for that and sell the tires, they are in great shape. but I need to get a new rim, I only have 4 and want the 5th wheel. but deciding what size width i want, that I can take on and off road. but more of a daily summer ride than off road.
     
  13. Feb 15, 2016
    oldtime

    oldtime oldtime

    St. Charles,...
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    With a manual Ross system keep the tread width under 7 " wide.
    The narrower the better.
    8" tread will be hard to steer if aired down below 20 psi.
    "Hard to steer", implies increased wear (decreased service life) on the Ross steering components.
     
  14. Feb 15, 2016
    ojgrsoi

    ojgrsoi Retired. Sponsor

    The Colony, TX
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    Fully agree with "Hard to steer."
     
  15. Feb 16, 2016
    shaun

    shaun Member

    ohio, Beavercreek
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    I'll be running Saginaw PS with Disc up front. I think 11.5 MT may be overkill for daily drive. Maybe good for off road/sand dunes with 10psi but daily drive I won't air down. Still think 8 in width is good
     

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