H-arm vs Trailing arm

[fabr]

Having never needed to consider using a trailing arm rear suspension before I'd never put any thought into one till tonight. DAMN there's a  lot of 1/2 shaft plunge with those things!  Sooooo,that clinched it for me.I'm going to go double H-arms. Any pitfalls I should look out for?

[Engineer]

Not to change your mind, but I thought that at first to.  There are two things that reduce the plunge more than you might think.  If you use semi-trailing arms, the arm swings in a bit of an arc, looking from the rear.  Looking from the side, when the wheel is in full droop it should be positioned straight below the tranny output.  When the tire moves upward, it swings back, behind the tranny output.  I haven't put a pencil to it, but these factors make the plunge less than it may first appear.

If I may ask, what kind of driveshafts do you plan to run?  930, U-joints, etc.

With the H-arms, do you plan to have any rake, and have you thought about it's affect under acceleration, and braking?

[fabr]

You are correct about the semis of course.I've done quite a bit of research about them really but haven't put it into cad before.I really hate plunge of any kind.
  930 shafts are the plan at this time.Don't like uj shafts and have heard all the pros and cons.For now I'll stick to cv's unless I have a travel issue and am forced into uj shafts.
  Yes I've considered the accel/braking things out also but had not considered using rake on the rear. What are your thoughts on all these points?

[Engineer]

Hmmm.  Haven't really thought about it, thought you may have done research.  With no rake on the rear arms, they should be neutral with respect to acc/dec.  The though of no rake on a long travel setup leaves me a bit queasy.  Trailing arms, and 5-links have the equivalent of rake because there,...... well trailing.    and generally at a down in the rear attitude at ride heigth.

[fabr]

The car dsrace built for enemy is an h-arm design and I don't think it has rake.It was pretty dark and several beers into the night when I saw it tho. LOL! It seems to handle well. Maybe he'll chime in here with his thoughts. My thoughts are that rake is in general overrated on cars with larger tires.The bigger the wheel the less rake MAY be desirable front or rear. On smaller buggies with atv size tires I see the advantage of rake.

[Engineer]

I think you are absolutely right with regard to tire size.

Is that Enemy's car that had videos posted on here?  Yellow with aluminum panels?

[fabr]

Yes that was it

[fabr]

The car I'm building has no rake in front.Might be a mistake but time will tell.This won't be the last car I do.

[Engineer]

Like you said tire size does as much as rake.  What are you running front and rear?  I never could see Enemy's suspension in the vids, but it seemed to work fine.  Mabey DSrace will chime in tomorrow with some pics.

[fabr]

I'm using 31's.I pm'd ds about chiming in.He likely will would be my guess.

[Enemy]

Like you said tire size does as much as rake.  What are you running front and rear?  I never could see Enemy's suspension in the vids, but it seemed to work fine.  Mabey DSrace will chime in tomorrow with some pics.

I can chime in with the only pic of the rear I can find on this POS laptop of mine at work....That's about all I'm good for...
DS will have to give you the specs of the meterial, I can't keep that kinda stuff crammed in my little noggin..

Found another..
And yes, remove calipers, hold them over yer head, and have helper pump the pedal to bleed, (brake fluid is excellent hair conditioner!) but it works...

[Yummi]

That looks pretty beefy.  Assuming it is done right on the build, what could the down side be? 

[dsrace]

Not to change your mind, but I thought that at first to.  There are two things that reduce the plunge more than you might think.  If you use semi-trailing arms, the arm swings in a bit of an arc, looking from the rear.  Looking from the side, when the wheel is in full droop it should be positioned straight below the tranny output.  When the tire moves upward, it swings back, behind the tranny output.  I haven't put a pencil to it, but these factors make the plunge less than it may first appear.

If I may ask, what kind of driveshafts do you plan to run?  930, U-joints, etc.

With the H-arms, do you plan to have any rake, and have you thought about it's affect under acceleration, and braking?

this is a good idea, one that vw designed into there cars back in the 60's I think. if you look at a stock torsion housing the pivot points are offset to that of the outers and it does minimize plunge but it also creates a camber curve ( similar to the swing axle just not as extreme) , not for the best either. this is why so many companies use the dual pivot trailing arm but then your back to the long spline cv axles or long spline uj's axles. if you go back a while in time and look at the early long travel and even some modern day companies you'll see a lot of 5 link rear end designs but then they came out with the dual pivot training arms I mean trailing arms, this design was cheaper and faster to build and install. not to meantion the consumer could no longer tune the suspension and screw it up because they didn't know what they were doing.

[dsrace]

I'm using 31's.I pm'd ds about chiming in.He likely will would be my guess.

 

I did get the pm but had alot to do today but of course I will chime in on this one.

I am not personally a fan of training arms, they limit the suspension in a # of ways but are tried and true in design as well as cheap and easy to install where as a multi link takes alot more time, design work and money but it is fully tunable and yes you do still have that rake that engineer was referring to, this is why I have been reading the post about the third link by I think rick s. I really like the thought behind it but I am not sold on it just yet. enemy more than I have been testing this dual h-arm design to some pretty extreme points. I have seen some weak points that have only come out because of few crooked landings but that was after about 55 - 60 jumps in about 5 months on dirt and then sand- enemy am I right or off a bit ( on the #'s not my rocker ). the tabs on the rear suspension/ engine cradle have to all be gusseted tabs unlike a multi link set up. in the pics enemy posted the lower control arms ( h arms ) are 1 1/2" od 1" id just to make sure they handled the loads of the rail as well as the shock. you also need to take into consideration that the h-arms are driving the rail by the suspension cradle rather than the side of the rail as in a multi link or by the frame right below the seat. I have seen 2 rails with training arms tear the frame about 2" or so in front of the weld on the inside pivot point. when this happened the rail collapsed and did some pretty good damage. one of the rails was a jackson sand car that was using a built air cooled ( vw ) engine, I have no idea on how hard he was with the rail before it broke or in the past. dunebound 69 was there on that trip he saw this one as well. I will have to go check on some #'s and then I will post a little more on how I would build the next one, for air time and not so smooth landings.

also you will notice in the pic. enemy's and my instruction manual standing under the rail

[fabr]

Would it not be practical to move the front mount forward on top and bottom arm to near the vertical plane that a trailing arm normally attaches to so it more directly transfers the loads of accel and decel and lessens loads on the rear portion of the cradle?