Bumped!

 

In the 2008 JK brochure, it says an Unlimited on a 20 degree RTI ramp should get a 484 with the sways connected, and 644 disco'd.

With a 116" WB, a 644 means the JK go 74.7" up the 20 degree ramp.

That means the front tire was roughly 25.5" inches up w/o lifting the other 3 tires, etc.

That's supposed to be a stock LWB JK...stock shocks, etc.

To ramp 1,000 on the RTI ramp, the front tire would need to get 116" up the ramp, or get that front tire almost 40" high.

That's ~ another 15" of elevation.



Assuming that the total RTI scores are always a combination of the rear's ability to droop, plus the ramped tire's stuffage, and the front tire's droop....which comes down to the front axle's ability to rotate for opposite side stuff/droop....

To get one front tire up ~40", you'd need the front axle to be able to rotate another 7.5" in each direction to get the other 15" of height.

As the stock shock's (Front) come with 7.5" of TOTAL travel...(14.5- 22"), and can (At least in the brochure...) reach the 25.5" total tire height with that...the inboard location of the shock mount to axle length gives it a ratio of near 9" travel for 7.5" of shock travel, say ~ 1:1.3 - ish.

....so 7.5" of additional wheel travel would require roughly another 5 3/4" shock travel....or, 7.5" + 5.75" = 13.25" of shock travel? (To allow the front axle to rotate enough to have one side up 40", and the other side on the ground, next to the RTI ramp...w/o changing the rear travel...)

If we allow for some frame unlevelling/rear contribution to the above...we can probably let the frame tilt some more....but, I DO NOT know what degree of tilt the stock JK was at on the ramp in the brochure measurement....and where the COG would be the limiting factor, etc.

The front axle would still need to rotate enough to get one side 40" higher than the other, but getting say 2" of additional frame tilt to the drooped side would allow the front shocks to be ~ 2.6" shorter, or more like 11" travel, a 15 - 26" travel shock, a realistic product.

Even 1" more tilt would save ~ 1.3" of shock travel, still a 12" travel shock ( 15" - 27"), within available ranges.

So - It does mean that within your projected 27" droop range, an RTI Score of 1,000 should be reachable for a JK Unlimited.

Obviously, the SWB JK's would require far less modifiction to hit 1,000 on the RTI score.

The pics would provide a great way to visualize these limiting factors.

 

Pics?

Please?

 

I'll assume that an external link to my gallery is ok for this type of thing.

http://servicemms.smugmug.com/galler...12/1/249838681

I have about 3/4 of the pictures up with a brief description. Please post if there is a problem with the link. I'll add the rest of the pictures to the gallery shortly.

Mods if this is not ok, just tell me how to proceed.

 

This conversation hasn't ever been about a specific lift, but does anyone have a link to the shock specs for the OME lift?

I was a bit surprised to find a few things that needed to be addressed with only marginally longer shocks. None of them are a huge problem until you reach 27 inches of extension. Since the OME kit only includes shocks, bumpstop spacers, and shocks I have to wonder how close things are.

 

Wow!

Great Pics!

Saved thousands of words.



I can't wait to see the other 1/4 of them you didn't have a chance to upload yet.

I could not quite tell is some shots what the measurements were due to glare on the tape...

Also - I see you compressed the unconnected shocks and measured them (F/R) as Both getting down to 15"...but, I could not see a measurement of what they would compress to if the stock bumpstop was on, as in trail use, etc.....Or....if you were saying that the stock shocks DO go to full compression on the trail on full stuffage.

Your step by step break down of what limits droop at each phase was just perfect - you could do this for a magazine.



The points about the shell on the arm, the driveshaft droop relative to skid plate clearance and t-case clearance, etc....very interesting. Makes me wonder want a grinder/whiz wheel etc, might do for notching out a clearance area?

A pretensioner to force the ASB link to only fold one way, instead of leaving the option for the wrong way/hitting the steering cross over...possible?

I've seen a post where the disco'd ASB itself, it allowed to pivot UP out of the way, can puncture a sidewall...your pics illustrate the possibility of the linkage also being a culprit.

Looking forward to the rest!

 

I don't have a tape picture of the bump stops on the plates. I was running out of time because it was 13 degrees outside and my heater quit. As you can see the Jeep was a slushy salty mess, and it was turning into an ice rink in my garage when the temps fell into the teens.

When you pull the coils in the front and jack the axle to the stops, you can get the shock compressed to less than 15 1/2 inches as the vehicle is lifted off the stands. That only leaves 1/2 inch for additional compression on hard impacts. I slammed a few times on the stops on a sand dune trip last year. I see no physical evidence that the shock took the impact, but wow it is close. My guess is they even count on the compression of the rubber mounting hardware on the shock!

So far I learned:

Don't use shocks over 15 inches compressed without modified bump stops.
Don't use front shocks over 1 inch longer than stock without longer ASB links.
Don't use rear shocks over 1 inch longer without moving the rear brake lines.
Don't use rear shocks over 1 inch longer in the rear without fixing the e-brake cables.

I have run into issues where the various makeup of parts from each Jeep means that my numbers may not apply in every case. However, it seems that DCX really did try to get articulation from the factory. Or at least they maximized articulation with what they had. Things are pretty close and need to be checked after any modifications. I have no proof, but I suspect that things need to be very carefully checked with the "minimal lift, minimal parts, minimal cost" lift kits that come with new shocks. If the shocks are longer than stock then there are some things to be addressed.

I think that grinding the front edge of the skid for the front driveshaft would work for a bit of articulation. My numbers need a little more research in this department. There are two things of concern in addition to the skid. One is the extended length of the shaft at that much droop on the driver's side. With the boot on the splines I can easily tell how close it is to maxed out without pulling the shaft. The other is the proximity of the boot and clamp to the trans pan and case. In my tests with everything disconnected, I can't get the shaft to touch but I have seen pictures that show shaft and trans damage in this area. As long as this was taken into consideration when an aftermarket shaft was designed an aftermarket shaft could solve the entire problem. The point you need all of this is just about where you need control arms as well. The bushing shell on the arm is wide enough to touch the brackets as the axle falls lower.

All the pictures I have are up, I'm not sure if they were all there when you viewed the gallery or not. Anything with a blurry tape is either shown in another picture or in the text. I had to throw out a few pictures because I left the camera on and the lens fogged up.

 

So, i read this entire thread, and now that im a little better educated, how do i determine what lift for my 4 door rubicon will give a 1000 on an RTI ramp. Will a FT 3" ultimate do this ???

 

Well, a 116" WB Unlimited would have to go up the 20 degree RTI ramp 116" to score a 1000.

The sin of 20 degrees is 0.342, so if the hypotenuse is 116", that means the opposite is the tire height of roughly 40".

So - you need to be able to get one front tire 40" higher, while keeping the other three tires on the ground.

A stock JK Unlimited RTI's about 644 disco'd...according to Jeep.

That's 74.7" up the ramp.....you need to get another 41.3" up the ramp to reach a RTI score of 1,000.

__________________

If you make it to 1,000 -

With your front axle having the upper tire resting at 40", and the other front tire on the ground by the ramp....that puts the front axle at an angle of about 40.25 degrees....

....as you'd have a roughly 61.9" track as your hypotenuse, and 40" as your opposite, making your adjacent about 47.24" (The space to the side of the ramp where your drooped tire is on the ground.....Adding spacers lengthens the track, lessens the angle, etc...but this is the concept...)


So - all that means you need to be able to lift the front tire up another 15" or so higher....to ramp a RTI of 1,000.



So - you either add 15" of droop (Hard to add that much droop)....or, split the difference between the two axles and frame...allow the ramped tire to have as much uptravel as possible....and allow the truck to rise as the tire climbs the ramp....so you can lean the frame over more to get the axle over to a 40 degree tilt, etc.

Hope that helps.

 

holy crap teej...sounds complicated. Break it down in Bo terms for me lol. So, how hard is that to achieve with a 3" lift ?? Could you get a 1000 with your set up?? arent you running teraflex 3" lift