U-Joint angles/rear suspension geometry?

[DJDIRTWORKS]

I know there's lotsa smart poeple here so I have a question for ya'll.
Now I know there's been a lot of discussion on rear 3/4-link geometry, but I have possibly a slightly different spin on it.
To give a little background, all of my link experience so far has been with race-style suspensions where my biggest concerns are not too much squat, fairly consistant PINION angle and minium driveline plunge to create a durable drive line while keeping the vehicle's hanleing reasonable. This has never been too difficult, and if I plot out the instant center and anti-squat lines they seem reasonable.

Now, I doing something a little different. My current project is a 4-wheel drive, live axles front and rear. This will be a prerunner/trail runner/minor rockcrawler/street driven 4-seater with a short(in the 100" area) wheelbase. Now I know an all around vehicle is much harder to build than a specific purpose one, and that comprimises will abound in it's design, and I've just required that this vehicle do an awful lot( maybe I should try to make it fly, too, huh!!)

So my problem is, the short wheelbase coupled with the long travel suspension mandates a C.V. style driveline, which in turn mandates that the rear U-JOINT(not pinion) angle stay pretty constant.

Easy, right? Except that the geometry of the links created by this causes terrible looking instant-center and anti-squat lines.

So has anybody had any experience with something like this? While this is not a hard-core rockcrawling machine, it will see some climbing duties, and I'm a little fearful that if it squats too much when climbing, it'll want to transfer too much weight to the rear and flop over.

If i set up the geometry close to what I consider normal, the rear driveline angles get so far out of whack that I'm sure this thing would be like a paint shaker on the road, where it also needs to be driveable.

thanks in advance for any input anyone has!

Oh yeah, bonus question: the same problem exsists in the front, except now it's anti-dive. Any thoughts on that??

Thanks,
DJ

[phorensic]

I would surf the pirate4x4.com forums for a good long while. Search, search, and then search some more. There are many topics on that forum about links and crawling. The current generation of competition level buggies are using traditional 3/4 links with desert-level travel. FWIW: Most link systems I've seen on crawlers replace the upper links with a panhard bar. This might help you a bit: http://digital-addiction.net/images/91626-4linkCAD.xls

[WannaB-class5]

I can't agree more. Pirate is a great source for this stuff. if you can't find what you need and start a new post, one thing you need to know is there are MANY cocky people who don't like new or "dumb" questions. deal with there crap and you will end up with amazing info.

[FABRICATOR]

By your own prediction, it will be fair all around and really good at nothing.

[WannaB-class5]

I talked to the pirate guys and there answer was swaybars. At least to the specific part about too much squat when climbing. The expensive TT style bars are great. This is all from pirate and not me so take it as second hand.

Pahl McAllister

[ntsqd]

Hum, how are sway bars going to help when both sides of the same axle compress?

[phorensic]

Yeah, I fail to see how anti-sway bars will help his anti-squat and pinion angle change issues.

[WoodyW]

That's why the Pirates are over there and we're over here...

[ntsqd]

That's why the Pirates are over there and we're over here...
Good point, and also why I call that place "POoR"

[DJDIRTWORKS]

Well, I didn't want to say anything about the sway-bar theory, but seeing as you mentioned it.....

Oh well. Hey thanks anyways for trying to help, I really do appreaciate it!

-DJ

[Stephen]

I was able to keep the angles reasonable in the last couple linked vehicles we put together and it seems like the trick is making the upper links pretty long. On my front, the upper is longer than the 2 lowers. At that point I was able to mess with the AS numbers and still keep the pinion mostly in line with the driveshaft. You won't get it perfect so get ready for.....guess what.....one more compromise.
In general you're going to run into more problems with more AS% than less. More makes the vehicle raise up under power which can send you over. It also tends to make it ride rough under power can give you a lot of bounce as you gain and lose traction. Keep it moderate and you'll be OK. There are some pics of my K5 and my brother's tube buggy on our company website in the custom rigs and "our travels" section. They might be worth a look. It's www.offroaddesign.com

[DJDIRTWORKS]

Stephen, thanks for the input. I had previously visited your website after seeing your blazer in one of the off-road mags. I really like your blazer-it looks like you guys have put a lot of time and thought into it. Very interesting steering, by the way.

any idea of how much u-joint you get at full droop? That,s where my biggest problem is, but the u-joint angle is also changing too much in the area just below the ride height zone. What do you find accecptable or way too much? 5, 10, 15 degrees?

Your rear links- the uppers don,t appear to be longer than the lowers, right?

The front doesn't concern me quite as much right now, except that it's a packaging night mare. My main concern is to make sure that it's road manners aren't so bad as to make it unsafe to drive, while still giving it good off-road handling traits.

Thanks so much for the input, at least I know someone else went through the same issues that I'm having.

By the way, long, long ago I used to live in Cripple Creek and Woodland Park as well as waaaay out in the woods in a log cabin in a then fledgling sub-division in Divide County. I bet none of that looks the same now. When I lived in Cripple Creek, it was very small and seemed to barely be surviving(Iremember they had a curfew, and at curfew time every night there was a big steam whistle they blew somewhere that you could hear for miles) last I heard it's a thriving indian casino town. Hard to imagine.