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Hillbilly RTI question

Discussion in 'The Garage' started by 84_Chevy_K10, Jul 5, 2004.

  1. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Yesterday I was messing around in my front yard with a tree and managed to get my left front tire 42" from the ground when measured at the center of the hub without lifting a rear tire. I was checking out my clearances and stuff because I wanted to know if I could get the tires to touch the floorboards (learned I certainly can, it is my bumpstop for up travel. /forums/images/graemlins/rotfl.gif

    My question is, when you measure RTI based with a forklift, how do you figure your score? I am assuming I should have measured from the bottom of the tire to the ground, but all the info says that from the hub to the end of the ramp is how it is measured when you do it on a ramp.

    Since I didn't measure the bottom of the tire to the ground I have no idea what that number is.

    RTI for 42" and 119" into the calculators generates an RTI of 1032 which seems a little bit reaching. Just guessing and removing 16" from that 42 and factoring the wheelbase would put me at around 600 which would be rather sad.

    So, which is it? 1031, or 600?

    These are both factored on a 20* ramp of course.

    So, distance tire from the ground, or hub?
     
  2. RustBuket

    RustBuket 1/2 ton status

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    Distance travelled up ramp / wheelbase x 1000 = RTI

    So really its kinda like figuring out a percent except using 1000 instead. So if you go farther up the ramp than your wheelbase length then you get over 1000.

    So if you measured to your hub then just subtract half your tire which you say is 16". So, you could use Sin Cos and Tan properties to figure out what it would be. So if you have a scientific calculator handy you can figure out what your length up the ramp would be.

    Sin20* = 24"/H (H being the hypotenuse or the distance travelled up the ramp.)
     
  3. ben427

    ben427 1/2 ton status

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    but your supposed to measure from the bottom of the tire not the hub right??
     
  4. RustBuket

    RustBuket 1/2 ton status

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    Ok so I busted out the old Scientific Calculator and figured it out for you. So assuming your tires are 32" tall you have 16" from the hub to the bottom of the tire. So therefore, we subtact that from the total height measured to the hub of 42". We're left with 24". So I did a sketch and made a right triangle (like an RTI ramp) and made the one angle 20* and the side was 24". So using the properties of Sin (Opposite over hypotenuse) I can figure out the length travelled up the ramp(hypotenuse).

    - Sin20* = 24/H

    - .342 = 24/H

    - .342H = 24

    - H = 70.175" travelled up the 20* ramp. Using the RTI formula and assuming you have a 105" wheelbase (70" / 105 = (.667)x1000

    RTI = 667

    Tell me if you think I messed up somewhere. /forums/images/graemlins/peace.gif
     
  5. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    My calcs give me a score of 550 figuring half of your tire diameter not 16". Your profile says 38.5's so I went with 19.25" lower than the 42". Threw all that into autocad and it says you traveled 65.528" up a 20 degree ramp. Rounded that to 65.5" and then used the formula stated above. Those figures still aren't exact though.
     
  6. 84_Chevy_K10

    84_Chevy_K10 Banned

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    /forums/images/graemlins/thinking.gif I wonder how the hell fourwheeler magazine got a stock K5 to ramp nearly 700 and my rig can only manage 550.

    I suppose I'll have to run it up a ramp to find out.

    I guess I'll have to re-do it and measure from the bottom of the tire if I want to do it the hillbilly way.

    Damn, if it's this hard to score 500-600, really envy those that score 1000 on a 30* ramp!
     
  7. 84gmcjimmy

    84gmcjimmy 1 ton status

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    at the top truck 2003, toby got 1200 on there TRI ramp /forums/images/graemlins/yikes.gif
     
  8. 84_Chevy_K10

    84_Chevy_K10 Banned

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    [ QUOTE ]
    at the top truck 2003, toby got 1200 on there TRI ramp /forums/images/graemlins/yikes.gif

    [/ QUOTE ]

    I know, I've definitely got some serious work to do. I've got to do something about rear shock mounts to start with.

    It's amazing to see such a pathetic number with all the mods to my suspension (moved shackle hangers, 7" long shackles, ford towers, shackle flip, 12.5" travel gabrials).

    Just seems pathetic for all the work I've done if you ask me.
     
  9. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    I think something is binding up on you. Do you have a swaybar in the front?
     
  10. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Nope, no sway bar. The left front shock was 2" from being closed but the tires were against the floor boards so no more compression there. The right side up front was drooped until the shock was completely done with travel. The rear left I had about one more inch of shock down travel before I was done and the right rear was stuffed into the fenderwell about 1" from hitting the wheel tubs.

    I don't understand what could be binding, it's all moving around, just not enough. /forums/images/graemlins/rotfl.gif

    I'll have to get some pics.
     
  11. willyswanter

    willyswanter 1/2 ton status GMOTM Winner

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    With as flexy as my truck is I can only get a max of about 700 due to my wheelbase... I would have to have a tire like 11 feet in the air to score a 1000 with a 170" wheelbase /forums/images/graemlins/smirk.gif /forums/images/graemlins/rotfl.gif
     
  12. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    I suppose alot of it has to do with wheelbase as willyswanter has pointed out. Just comparatively speaking, I had a pickup bodied blazer frame with an out of the box 4" superlift kit and that was about if for suspension mods and that would hit 800 something. Short wheel base though. I didn't do much else to it.
     
  13. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I did the forklift RTI with my truck a few months ago when I had my hard top off (but before I cut the steel half cab off) and got a solid 45" under the rear tire (at the center of the tread) with the other three tires all still on the ground. My front shocks were maxed, and my rears were very close to maxed.

    107" wheelbase.

    That would be 131.57" up a 20 degree ramp and an RTI of 1229.

    I'm hoping my truck gets a little more rigid with the addition of a cage. I could be happy with much less body flex, and RTI numbers aren't all that useful on the trail.

    Rene
     
  14. miniwally

    miniwally 1/2 ton status Premium Member

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    The only thing a RTI number is for is comparing manhood sizes.
    The ramp however is an extremly valuable tool for checking clearances, travel, and as Tim has discovered remounting the shocks to a better location to achieve a good amount of wheel travel.
    Travel really is not everything, Becks buggy picks tires up all the time where Stephen and I don't. I haven't seen yet where this really hurts him but it does look somewhat more prone to a rollover in some situations.
     
  15. 84_Chevy_K10

    84_Chevy_K10 Banned

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    That's basically what I was doing, checking tire clearance, shock mounts, etc. I had the measuring tape out to measure for bumpstops that I'm planning on installing and while I was at it, I figured I'd tape the tire.

    With lockers, you're right, travel certainly isn't everything. You don't always need to keep every tire on the ground to continue moving forward. /forums/images/graemlins/thumb.gif
     
  16. MR4WD

    MR4WD 1/2 ton status

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    I ramp 1200 on 20 degrees with leafs at all 4 corners, minimal frame flex and 109" wheelbase.
     

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