The split-pivot design has always intrigued me, never ridin it! Your computer rendering looks sweet! Are you gonna be building a ridable bike for your project. Oh and the XJ 3 link looks like it worked good, and sounds like it drives great!
Thanks John. I cant take full credit for the rendering, it has been a group effort. We just ran one of the pieces on the CNC mill today. We used high-density foam and it will be the mold for our carbon fiber layup.
The ultimate plan is to have a rideable bike in the end, but time will tell.
I weighed the jeep this past week. 3990# empty with a full tank of gas. I expect 4500-4700ish loaded down? With 2 people in it, we were at 2320# in the front, and 1980# in the rear. Once I'm loaded down, it will make for a pretty equal front/rear split.
I've been doing a lot of research on the 3 link lately. I downloaded Triaged's link calculator and finally ran the numbers.
Center of gravity approximated as the top of the bell housing - I hope to calculate my true center of gravity soon)
The reason I haven't run these numbers before is because there were some basic parameters that I was building the 3 link to, and ultimately it boiled down to putting things where they fit while best following the basic 3 link guidelines. I built the track bar as long as I could, I got 8.25" vertical separation at the axle, pushed the axle side lowers out as far as I could horizontally, brought the frame side lowers in horizontally to where it would clear the frame rails at bump, tucked the lowers up as far as I could, and put the frame side upper as far up as I could without it intruding into the passenger side floor space. The above numbers are what I ended up with.
The roll axis angle makes me very happy (I am very close to no over or under steer), the roll center height seems fair to me (still researching optimal height), but the anti-dive (shown as anti-squat) is not cutting it.
For those of you that are not familiar with the details of suspension design, anti-dive directly relates to the amount of brake dive you experience under braking. The value defines the dispersion of the rotational forces of the wheel/rotor into the suspension links and the springs/shocks. At 100% anti dive, the suspension links are taking 100% of the braking forces, while the springs take 0%. As a result, the front end does not 'dive' at all, because the forces being placed into the control arms is combating the forces that would normally cause the suspension to compress. At over 100% anti-dive, the rotational forces from the brakes are translated through the suspension links in such a way that the suspension links push the body up and away from the wheels/axle. This causes the front end to actually lift when you hit the brakes. Anti-dive values less than 100% allow the springs/shocks to take some of the load. I.E. at 70% anti-dive, the control arms take 70% of the load, while the springs and shocks take 30%.
Disclaimer - that is my understanding. Please correct me if I'm wrong.
Excessive anti-dive can often lead to the tires being more prone to skipping/skidding when you are on the brakes. This can be bad on the road, and also when trying to feather the brakes to let you slowly drop down a ledge or rock.
Anywho, I'm at 102.69%. I drove around town with my roommate and had him watch the upper control arm through the hole in the floor as I slammed on the brakes and he confirmed that the control arm did not move up or down at all, with a very small chance that it actually moved down minimally (front end lifting) as I slammed on the brakes.
The options I have to lower the % anti-dive is to lower the frame side lower mounts, raise the lower axle side mounts, lower the axle side upper link location on its mount, or raise the frame side upper mount. Changing either of the lower mounts would be too much work, and I am very happy with the amount of vertical separation I have at the axle, so I will be raising the frame side upper mount 4", with adjustability every inch. This allows me to adjust the anti-dive from 102.69% down to 90.04%, 77.32%, 64.52%, and 51.63%, respectively from the bottom hole to the top hole.
From what I have gathered, 60-70% anti-dive is a fair number for rock crawling. I have nothing to back it up as that is based off of personal opinions, but I'm building adjustability into it this go-round so I can do my own testing to find what I like best.
Anyway, is what I'm doing overkill and most likely unneccesary? Most likely. But I am enjoying the hell out of it, and I didn't spend all this time building it just to settle.
I had to pull the crossmember out anyways due to some clearance issues (tcase to crossmember) and because the seal between the transmission and transfer case is leaking (thanks to the clocking ring). While its out, I'll be rebuilding that upper mount.
I hope you guys find this tech interesting and useful. Also, please correct me if I am misunderstanding something or spreading bad info. And if you have already been through all of this before, let me know what worked for you.
