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Tire/lift math --

Discussion in '80-Series Tech' started by erics_bruisers, Aug 22, 2003.

  1. erics_bruisers

    erics_bruisers

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    Hi all --

    So, I'm getting down to the numbers of my next upgrade -- the OME 861/650 springs with kit from Christo's --

    -- while I'm at it, I'll upgrade my tires to fill up the wheel-wells a bit better and make my 80 generally more capable, lest I ever move out of the rat-race and in to the country --

    -- for now, I have stock 275/70R16s and I was looking at MTR 305/70R16s or ATS 305/70R16s -- I am really tempted to go with the ATS's, because a majority of my miles are road miles (*gasp*) and I don't want to kill my mileage/quality of ride -- any comments on this?? ???

    -- For the total kit, I'm looking at an overall lift to my 80 of 3-1/3 inches -- I have to know that, since I may not be able to clear the garage door!!

    Here's how I did my math:

    Currently, my LTX 275/70R16s are 275*.7 mm ground to rim (192.5mm) -- converting that to inches, I get 192.5mm * .03937 = 7.57". This height, top and bottom of tire, is a total of 7.57*2, or 15.15" -- from there, I added the wheel height of 16" to get 31.15745" total height.

    Next, the proposed MTR or ATS 305/70R16s were figured in the same manner, with a total height of 32.81"

    So, the diffence in height between the two tires, mounted, is 1.65" -- and I divided that in half to measure the added height difference from the axle, yielding .82" additional height from the MTR/ATSs compared to the LTXs --

    -- finally, the OME kit of 2.5" height increase, adding the .82" tire difference, would give me a total of 3.32" additional vehicle height when everything was completed --

    -- I'm a total neophyte at this, so any insight you'd have to my attempt would help -- ::)

    THANKS!!

    eric

    Also, THANKS for YOUR OFFER to help do the install, Junk -- I WILL take you up on that!! I'll bring beers and lunch this time!!
     
  2. yomama

    yomama

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    Hey Eric, if you do happen to see Junk ::), remind him he was going to send Yomama his old boost gauge ;)

    As far as your math goes, it looks good to me, seems odd that you only get less then an inch by going from a 275 to a 305 ???. I would think it would be double that, but I am no accountant....

    Yomama
     
  3. landtank

    landtank SILVER Star

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    That's all well and good Eric, but I'll need to know the running tire pressure to properly calculate this for you.

    Actually I couldn't get through it :p, maybe somebody else can.
     
  4. shocker

    shocker

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    Do you mean your going with a 851/860 spring combo?

    Let's see, 275/25.4 X 70% = 7.58
    305/25.4 X 70% = 8.41

    8.41 - 7.58 = .83

    You really don't need to factor in anything else, since all your looking for is a difference from where you are now.

    So, looks like your math is right.

    I know I have a smaller garage, and I can juuuuuust fit in with 850/863 and 285's, but I don't have a factory roof rack either. Depending on how much your stock springs have sagged over the years, you may actually get a 3" - 3.5" lift, at least initially.

    Yes, the tire is almost 2 inches greater in diameter, but only the difference in radius determines the difference in height (how much tire below the hub).
     
  5. erics_bruisers

    erics_bruisers

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    shocker --

    would you go with the 850/863s over the 851/860s?? Same price -- I have no heavy mods -- would it lift me even higher??

    eric
     
  6. Junk

    Junk

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    Only two things you didn't factor is was the, usually, inflated measurements of the tires and the sag of your susp which can be worse than an aging wifes. I haven't found a tire yet that actually even comes close to what the mfg claims it to be.

    No problem. Just exchange that #6 for diet cokes and no pooch. Got enough sheet in my garage without any poochsheet :flipoff2: :D :D
     
  7. sleeoffroad

    sleeoffroad Supporting Vendor

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    [quote author=erics_bruiser link=board=2;threadid=4531;start=msg33993#msg33993 date=1061557207]
    So, I'm getting down to the numbers of my next upgrade -- the OME 861/650 springs with kit from Christo's --[/quote]

    Do you mean 851/860?
     
  8. shocker

    shocker

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    All I have is an ARB up front, no winch. Oh, and my fat arse.

    Honestly, I would go for the heavier springs. I had initially went with the low lift OME's about 1 1/2 years ago, then swapped to the ones I have now a few months back. Just like everything else, you'll tell yourself you're not going to go toooooooo extreme, then the next thing you know you're grabbing the sawzall with some Gene Wilder 'Frankenstein's Monster' look on your face. :D

    Really, though, it's basically like this: If you're planning on adding anything (i.e. bullbar, rear bumper/tire carrier, rear drawers, sliders, etc.), get the heavy springs. If your not planning on adding anything, you will be soon.

    By the way Eric, ben meaning to ask you, who's that in your avatar? Looks like Tom Waits.
     
  9. Junk

    Junk

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    [quote author=yomama link=board=2;threadid=4531;start=msg34001#msg34001 date=1061559036]
    if you do happen to see Junk ::), remind him he was going to send Yomama his old boost gauge ;)[/quote]
    :flipoff2: LOL - didn't forget yomamma. Cleaned out some junk and set up the tig this week. Will get it out to ya. Got to, uh, wipe my [​IMG] with it first. :flipoff2:
     
  10. erics_bruisers

    erics_bruisers

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    [quote author=sleeoffroad link=board=2;threadid=4531;start=msg34020#msg34020 date=1061563548]
    Do you mean 851/860?

    [/quote]

    oops, I did, Christo -- I think I'll just go with the 850/863s for S&G --

    and shocker, my avatar is Miles Davis -- isn't Tom Waits white??

    :D
     
  11. shocker

    shocker

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    Yes, but I thought it was a chalk & charcoal or lead pencil sketch. Now that I look at it closer, I can see that it's not.

    Kind of Blue, Kind of Blue.........

    Nevermind the drunk man behind the curtains!!!! :D
     
  12. sleeoffroad

    sleeoffroad Supporting Vendor

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    [quote author=erics_bruiser link=board=2;threadid=4531;start=msg34027#msg34027 date=1061563891]
    oops, I did, Christo -- I think I'll just go with the 850/863s for S&G --

    and shocker, my avatar is Miles Davis -- isn't Tom Waits white??

    :D
    [/quote]

    If you go with that, and you don't have weight in the back or front you are going to get more than 2.5" in the back.
     
  13. erics_bruisers

    erics_bruisers

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    [quote author=sleeoffroad link=board=2;threadid=4531;start=msg34030#msg34030 date=1061564332]
    If you go with that, and you don't have weight in the back or front you are going to get more than 2.5" in the back.
    [/quote]

    I just spoke with someone in your shop (not sure who it was) and they mentioned the same thing, telling me I'll get odd vibrations at that height --

    -- so you would suggest the 851/860s then, right??

    THANKS!

    eric
     
  14. sleeoffroad

    sleeoffroad Supporting Vendor

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    Call us conservative, but we never recommend the 850/863 for a stock truck. It was not designed to go on a stock truck and you can get vibrations and the caster correction can not bring the caster back to stock.

    See http://www.sleeoffroad.com/technical/tz_35.htm
     
  15. cruiserdan

    cruiserdan SupportingVendor Emeritus Supporting Vendor Moderator

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    Christo,

    About how much additional weight does it take for the 850/863 combo to make sence? Additionally, about how much more grunt does the 864 have over the 863. I mentioned a test I did with 864's in another thread and I'm thinking I need 863's to do what I need as the 864's were WAY UP THERE.


    Dan.
     
  16. sleeoffroad

    sleeoffroad Supporting Vendor

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    [quote author=cruiserdan link=board=2;threadid=4531;start=msg34043#msg34043 date=1061566359]
    Christo,

    About how much additional weight does it take for the 850/863 combo to make sence? Additionally, about how much more grunt does the 864 have over the 863. I mentioned a test I did with 864's in another thread and I'm thinking I need 863's to do what I need as the 864's were WAY UP THERE.


    Dan.
    [/quote]

    You can run 850's with just a ARB bull bar. Slight vibrations sometimes from the front drive-shaft and caster is a little low.

    if you run 851's with a bar and winch, the nose feels to soft.

    You can use 863's in the rear without any additional weight. Little hard and the truck will be raked.

    I ran 863's in my blue truck. Had 44 gallon aux tank, TJM bumper with tire carrier and aux carrier with toolbox and CO2 tank. Initially it was fine, but after 3 years of wheeling the springs softened up and when loaded with full gas tank and camping stuff etc, the back was to soft in winding roads. When I sold the truck, I pulled the 863's and 1.5" spacers and installed 864's without spacers. They height was the same but it handled a lot better.

    Does this help.
     
  17. cruiserdan

    cruiserdan SupportingVendor Emeritus Supporting Vendor Moderator

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    Thanks Christo.

    If gas is about 7 lbs a gallon that makes it about 300 lbs plus the tare weight of the tank. that's about what the tongue weight of my boat trailer is. If I understand correctly, the 864 lifted yours about 1.5 inches over the 863 with the same load? When you say the back was "soft" later in the life of the springs did it "sag" as well? If I read between the lines it appears I should broom my old Downeys and do the 850/863

    My current curb weight (less boat) is 3200 lbs ft/ 2840 lbs rear.

    What say you, Meistro Christo?
     
  18. Beowulf

    Beowulf

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    Eric,

    A while back, a guy on the 80sCool list did his OME install in his garage. He sent a message to the list a few hours later that his truck was stuck in the garage and too tall to get out.

    Just an FYI. :D

    -B-
     
  19. cruiserdan

    cruiserdan SupportingVendor Emeritus Supporting Vendor Moderator

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  20. erics_bruisers

    erics_bruisers

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    haha -- that's good stuff, beo -- my neighbors already think i'm odd enough, saying, "why don't you ever drive that car"??