4 link headaches

[DaveB]

I have been playing with the four link calculators and reading pirate till my head aches. I am trying to come up with a good design for the four link system that I want to put on the commando project I am building. Using measurements from the commando that limit what will fit I can get a fully triangulated design that has good anti squat, roll axis angle, and instance center but the roll axis is too low. From what I read the roll axis should be within three inches of the center of gravity. I can move the roll axis up by raising the upper links but I can only go so far. I can get all of the numbers to come out pretty good but in order to do it I have to take out most of the triangulation. I would imagine that this would require a panhard bar to be road worthy. I have attached the spreadsheets for anyone who wants to look at them and give me some pointers. I have also noticed that the unsprung mass numbers make a difference but have guessed as to what they are. The front is a d44 and the rear is a d60 semifloater, any ideas on weight ?

Also I can't find anything that helps with the front link design. I have found a three link with panhard spread sheet for a rear setup that I have tried but I'm not sure if it is giving me valid information.

 

[BenHanksRacing1]

Well you opened a can of worms by asking every Keyboard Crawler on here to put in there 2cents. Be careful what you hear on the interweb everyone is a pro and no ones wrong! If you have some time go read Dave Cole's (Time to go Faster) on Pirate4x4 its way more stuff then you will ever need to know and its right. There is no magic formula that takes in everything about your rig just use your brain you'll get it!

 

[bryson]

...every Keyboard Crawler...Be careful what you hear on the interweb...There is no magic formula...

Calculators are good for a general idea, and headaches. But when it comes down to it, you still have to make it fit on your rig.

 

[Shawn]

Quit being an engineer and over analyzing everything. There are just a few basic guidelines to follow.

 

[DaveB]

Quit being an engineer and over analyzing everything. There are just a few basic guidelines to follow.

It is hard to overcome all of that training I had in school.

 

[DaveB]

Well you opened a can of worms by asking every Keyboard Crawler on here to put in there 2cents. Be careful what you hear on the interweb everyone is a pro and no ones wrong! If you have some time go read Dave Cole's (Time to go Faster) on Pirate4x4 its way more stuff then you will ever need to know and its right. There is no magic formula that takes in everything about your rig just use your brain you'll get it!

I'll go look that one up. There are so many posts on Pirate and you are right everyone has different ideas. I'll see what I can come up with. If I show up at your shop with some drawings to make sure I don't screw it up, what will it cost me ?

 

[Goose]

I was in the same boat as you a few months ago, I read info untill my brain started to bleed.
the biggest thing for me was to understand what I wanted my suspension to do & how to acompilish that. From there I needed to figure out my limitations on my stock chassis.
then I had to figure out what copromises I was willing to make.
on a stock frame theres usually no way to build it exactly the way that you want it.
If you have a basic understanding youl be fine, good luck.

 

[LT.]

I was in the same boat as you a few months ago, I read info untill my brain started to bleed.
the biggest thing for me was to understand what I wanted my suspension to do & how to acompilish that. From there I needed to figure out my limitations on my stock chassis.
then I had to figure out what copromises I was willing to make.
on a stock frame theres usually no way to build it exactly the way that you want it.
If you have a basic understanding youl be fine, good luck.

This is the best advise I have seen yet. I also was in the same boat a few months ago. Again, if you can come up with a perfect set up it will not fit your chassis. There are always going to be compromises. You will end up moving the uppers somewhere where you did not want them. The lowers may end up being shorter then you wanted. Heck, even your axle separation is going to change from what you were wanting. This is why it is kind of fun using an existing chassis instead of a buggy chassis.

LT.

 

[BenHanksRacing1]

It wont cost anything! Everyones right you can't do it perfect so you need to compromise come in and check out what we have in the shop. There are about 12 Jeeps in here that have links and all of them are different.

 

[GOAT]

pm sent

 

[DaveB]

It wont cost anything! Everyones right you can't do it perfect so you need to compromise come in and check out what we have in the shop. There are about 12 Jeeps in here that have links and all of them are different.

Thanks, I'll stop on by once I have something that I think might work.

 

[DaveB]

pm sent

I'm not seeing one, hopefully my inbox isn't full.

 

[rondo]

Dave, after meeting you and talking to you about 4 links once i realized if i took you to my family reunion you'd be smarter than all of my kin put together! But i have to agree with Shawn, don't over analyze it. just build it and drive it. Wheeling is even more fun than building. Well except for my neighbor chuck who's been building his TJ for 2 years. It's as beautiful as the space shuttle but hasn't been wheeled. Good luck with your project.

 

[reddman]

I would bring your AS down if you can. I like it low, it reduces the likelyhood of axle hop as you go through traction changes under torque application.

I think you have plenty of triangulation in that design.

A stock 60 front, 70 rear, and 14B rear each weigh in around 550#. I would estimate your axles to weigh in around 400# each, fully assembled, maybe a little less. Don't forget to add the weight of your tires, wheels, half of each suspension link, coils springs, trusses/brackets, etc. to the unsprung weight too.

Both link calculators work for front and rear, the important numbers are all the same. The only real differences are that what it calls Anti Squat will actually be Anti Dive, and it still means the same thing, and that the links will swap tension for compression and visa versa.

 

[DaveB]

Thanks for the comments everyone. I have been making small changes to the spread sheets to improve the numbers. I have also put in placements that will fit the frame. I am planning to build some adjustability into the uppers to dial in the anti squat. The main issue I am having now is roll center axis height. The full double triangulation has the roll center about 7-8 inches below the cog line. Most things I have read say to get it to within 3 inches to keep the rig from being too tippy. Will something like an anti-rock bar help me here ? This rig needs to be useable on the street as it will be driven to the trails.