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RTI questions

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by CK5, Oct 16, 2000.

  1. CK5

    CK5 In my underwear Administrator Premium Member GMOTM Winner Author

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    Got a question about the rti ramps, do you measure from the end of the ramp or the ground according to the 25 degree angle? The reason I ask is it makes a big differance in the score, the ramp I used was a little over 2" high at the very begining, they have the begining of the ramp cut off, I think because it is a trailer as well. I have no idea how they do this at any of the events.

    [​IMG]
    5,000 Pounds of American Rolling Steel
     
  2. keith

    keith 1/2 ton status

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    Good Question. I want to build a ramp. I saw one that was easy to make just need some good measurements.
     
  3. tom

    tom 1/2 ton status

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    Good question. I assumed the RTI was the height gain of the wheel on the ramp divided by the wheelbase. That would make the index independent of the ramp angle and any other ramp feature. Apparently, that's not the way it is done. How is it measured?
     
  4. Brian 89KBlazer

    Brian 89KBlazer 1/2 ton status

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    Use a straight edge and project back to the ground where the ramp would end if it extended to the ground and measure from there.

    Hope this helps
    Brian
    89KBlazer
     
  5. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    When my truck got ramped they used a straight edge to project back to the ground.
    I think my shocks are the limiting factor on my truck. No sway bar it ramped a hair under 800 on a 20 degree ramp (I think it was 20 degree, I never asked [​IMG])

    Rene

    [​IMG]
     
  6. 6.2Blazer

    6.2Blazer 1/2 ton status

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    You need to measure to the ground following the line as if the 25 degree ramp extended clear down (was not cut off). If you simply measure to the end of the cut-off ramp, it does not take into account that 2" of vertical height.

    Doing some quick calculations, if the end of the ramp was 2" off of the ground and you measured to the end of the ramp, you are losing almost 5" in your measurement and results in almost a 50 point difference in RTI on a K5.
     
  7. Shawn

    Shawn 1/2 ton status Premium Member Author

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    Here's a pic of the ramp Steve is talking about.

    [​IMG]

    6.2 is right, 5" is the amount you loose if you measure from the ramp.

    RTI= Distance up the ramp / 106.5

    Shawn
    87 K5
    http://www.off-road.com/chevy
     
  8. Emmettology 101

    Emmettology 101 3/4 ton status

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    So what is the formula for us who do not have acces to a ramp and use a forklift?

    The last time I measured I could lift my drivers side front tire in the air 30" beofre the backk tire would come up.

    I think someone calculated that for me beofre and it came out to be about 823 on a 20 degree ramp.

    How do you figure this out?

    i dont have access to that forklift anymore, but I wish I did since I have done a few more things and would like to test it out again! :)

    Mike [​IMG]
    See <font color=green>EMMETT</font color=green> -&gt; http://emmett.coloradok5.com
     
  9. Shawn

    Shawn 1/2 ton status Premium Member Author

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    This is a previous post from 6.2Blazer:

    *******************************
    Here is a simple formula to calculate RTI if you know how far a tire can be lifted off the ground (such as lifting a tire with a forklift).
    This ONLY works with the 106.5" wheelbase of the K5 ('73-'91) and assuming a 20 degree ramp.
    Measure from the bottom of the lifted tire to the ground.
    Multiply that number by 27.456 and you have the RTI if it was on a 20 degree ramp.
    Example:
    Bottom of tire is 36" off ground, 36 x 27.456 = 988 RTI
    Bottom of tire is 18" off ground, 18 x 27.456 = 494 RTI.......etc, etc.
    ****************************************

    BTW- To get a 25 degree score, divide the score above by 1.236666.

    Shawn
    87 K5
    http://www.off-road.com/chevy
     
  10. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    The ramp that I have been using they took a yard stick while it was sitting on a level concrete floor layed on the ramp slid it down till it hit the floor and then painted a mark at 10 inches from the ground. Then they measure from the 10 inch mark to the wheel and add 10 inches to the measurment to get the travel number.
    The reason they did that was so if it's sitting on dirt at the event they had a good base line to start from and to account for the drop off like the ramp Shawn posted. Mine does a 752 on that ramp and it was at the 25deg angle (this ramp is adjustable 20, 25,30. I'm proud to say in my 62 family club that I have only seen 5 other trucks beat my 752. One was a Jeep with the warn coilover one was a Jeep TJ with about $10k in upgrades and one was a very custom Bronco with air suspension that maxed the 25 and comes close on the 30 to doing the same. The last one I haven't seen ramp but my guess is he would beat me. His Jeep flexes up pretty good.

    Diging it in the dirt with my K5's
    Grim-Reaper
    http://grimsk5s.coloradok5.com/
     
  11. Brady

    Brady 1/2 ton status

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    I haven't ramped mine yet but just guessing I think it would max a 20degree and do allright on a 25 degree ramp.There are a couple of ramps around here but I never have the blazer near them.Need to drive over and hit one just to see what it will do.I can put the drivers front up on a rock and have the blinker lense above my eyes and I am 5'10".This is only a 2.5" rancho lift with 33"s on it so it does flex!!.I run 12" travel shocks in the rear and use every in of them.Going to do the ford mounts in front now.Brady

    '73Beautiful Disaster
     
  12. Emmettology 101

    Emmettology 101 3/4 ton status

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