good idea or bad idea

[cornflake]

just red this guys write up where he ditched his torsion bars for coil overs

good or bad idea

after looking through it looked very easy and this was on a bigger truck in the states




http://www.performancetrucks.net/forums ... hd-504605/

[Mattman]

If yoiu go to that effort and get a cert would you not be better off doing a SAS?

Torsion bars aren't the week point of IFS

[tweake]

i see he was doing it for ride quality.
certainly coil springs will be better than torsions.

you would have to be careful of how you do the mounts. i doubt you could just use stock shock mounting points. even stock A arm may not handle the different load location.

[diogenese]

I can't get my head around the reason for changing to coils, a torsion bar is just a coil spring straightened out, the physics are the same.

[lax2wlg]

Great idea IMO. Part of my long travel Nissan IFS plan is to convert to coil over shocks or possibly coil over linked air shocks, combined with a hydraulically operated in-cab quick disconnect sway bar (to match the roll center advantage that a solid axle offers).

The main benefits of coilovers as I see it are; easy ride height adjustability (and therefore alignment on an IFS vehicle), the ability to calculate & tune spring rate/shock valving based specifically on the application/intended use, rebuildability, packaging advantage, progressive spring rate and of course ride quality.

Would need a lot of research depending on the platform of the vehicle. Packaging could be a challenge unless tubular upper a-arms were used. If it was a Toyota, may need to consider beefing up the lower control arm (as the torsion spring pivots on the upper arm in that particular setup). I agree that beefing up the lower arm mounting location would need to be considered on any setup.

Shock mount would definately need to be reworked as it was never intended to support the weight of the vehicle.

The pros/cons of torsions as I see it are:

Pros: durable, adjustable
Cons: complicated for what they are, lots of parts/weight when you add up the the crossmember, adjuster keys, torque arms etc., poor packaging (on some applications they are exposed to rocks), they can sag when overextended (knocking it out of alignment), linear spring rate.

A less costly option if not going long travel and only needing normal stroke would be struts out of a later model Pajero or Toyota, which for all intents and purposes are a coil-over. Then you would need to devise a method of setting/adjusting ride height, and compensating for camber change if they sagged due to wear. Concentric cams would probably work here but IMO they arent the most durable thing in the world and can seize up with rust quite easily.

[derk]

only a yank would want to lift a 2wd truck

[Lchundy]

My opinion if it's a good idea depends on how much money you want to waste lol
Better off going solid axle
My 100 series is torsion bar front and it rides plush as in the front maybe it's just the shitty designed Yankee torsion bar set up.
Long travel ifs suspension doesn't exist and if it does cant see it being reliable unless it's a custom setup with the arms pivoting closer to the centre like a trophy truck.
But hey I'm no expert

[tweake]

I can't get my head around the reason for changing to coils, a torsion bar is just a coil spring straightened out, the physics are the same.

i don't think torsion bars has variable spring rate like you can do with coil springs.

[lax2wlg]

Yeah 99 percent of torsion bars seem like that.
Jim Connor Racing did a 2-stage torsion bar setup for Nissan vehicles in the 90s, the second bars were much shorter and therefore stiffer to prevent bottoming out at speed.


Also Nissan Motorsports did a dual rate bar the 720s


But IMO neither of these provide the advantages/tuning ability that coilovers offer.

Bolt on long travel IFS kits have been available for Toyotas for quite a few years now. The principle is to stretch the control arms 2-4 inches each side and maintain factory mounting positions. Obviously this increases track width and the rear would need to be widened too, but the increased track width obviously adds stability and offsets suspension lift to return the vehicle to factory specs. In the case of the Nissan you would stretch the arms and use axle halfshafts from a 300ZX turbo which are the same spline as V6 WD21s but 2 inches longer, retain factory DOJ CV joints, and relocate the tension rod and replace it with a conventional non binding bushing. This would allow for 11-12 inches of unrestricted travel. Then for matching the increased track width in the rear you could use a Patrol rear end or a C200 full float axle from an Atlas.

Alas I am going offtopic.

Regarding the original post - I definitely feel that in developing a custom IFS system, in order to maximise performance/tuneability/reliability, the torsion bars have to go in the bin.

[tweake]

thats really cool to see

[cornflake]

only a yank would want to lift a 2wd truck

a cupple pages in there was a guy that did it to a 4x4 and started to sell his own kits



but love the feed back on this

[Crash bandicoot]

only a yank would want to lift a 2wd truck

depends on the size of the v8 driving the rear wheels though inni't? after all trophy trucks are rear wheel drive.

also Josh the D22 navara shafts are also a tad under two inches longer then the D21/R20

[tweake]

i wonder if you could leave the torsions in and add coil overs. use the coil over to fine tune it and torsions take the bulk of the weight.

[De-Ranged]

i wonder if you could leave the torsions in and add coil overs. use the coil over to fine tune it and torsions take the bulk of the weight.

.

This is a good idea

Reduce the size of the torsion bar... don't reduce your pre-load this will have a negative effect from your shocks effectively over damping the suspension meaning the wheels won't follow ground contours on rebound (reducing grip)
Add in a coil or air spring... this would depend on your intended use of the vehicle, the coil will increase your rate at the point it takes up giving you a dual rate but the bonus is it won't change its rate if you push it (race), the air bag will create a rising rate as it compresses catch is if you work it had it heats the air inside, changing spring rate till it cools off

Another bonus with the torsion bar is weight placement and possible weight saving
a coil over system needs structure in the chassis up at mid level to hold the weight of the truck where the top of the coilover is, where as the torsion bar is all down at chassis level and already has a strong structure in place to attach to... the chassis so there is room for weight savings
Just for the books I have seen an offroad racing buggy chassis that was setup to run torsion bars.... was told its brother competed well

Oh and just saying... just because a coil over has two or more springs doesn't necessarily mean its got a dual rate lol there is alot more to this sort of setup to gain the dual rate

[lax2wlg]

Yeah I am by no means a suspension expert.. really I am just sharing my personal preferences and specific plans for future modifications. That is a good point about the need for vertical structure when considering coilovers.. possibly this is one of the reasons manufacturers have used torsion bars in mass produced setups for such a long time?

I am interested in what else is needed to gain a dual rate or two stage torsion bar setup.

Interestingly, there was a company in South Africa that did a non adjustable strut/coilover helper spring conversion for the Nissan D21/WD chassis in the 90s. ie the torsion bars were retained and this was used as a helper.

They claimed that it was useful for preventing nose dive under braking and preventing sag due to winch bars etc etc
Personally I have considered this and I dont think it is a path I would like to go down. As I see it, this system is introducing new forces to the upper arm and upper balljoint by asking them to support a portion of the vehicles weight, rather than just act as an index for the knuckle. I have noticed that the lower BJ on the Nissan ie the load bearing one is about double the size of the upper. So I see the upper BJ wearing out far quicker. Also, it is too complicated for my liking. IMO the benefit of the coilover/torsion bar delete is to simplify the spring system by reducing the number of parts.

I have definately considered mounting the spring/shock to the tubular upper arm, though. But first I would upgrade the upper balljoint to something with much more bearing surface area. Humvee upper BJs look like a good option here. A lot of ATVs and of course the t-bar Toyota IFS mount their spring on the upper arm, from what I have researched it is an acceptable method. If not, please advise. This would make access CV joints etc much easier.

[Checkerhead]

Very interesting stuff Lax and De-ranged. Good info.

I could be wrong (wouldn't be a first) but I think both of those torsion set ups you posted (Lax) would be dual rate. From a coil perspective all that is required for a daul rate system is for one (the softer) spring to reach coil bind, and then your rate is just what ever the rate of the unbound spring is. On normal (fox king etc) coil overs this is achieved by having a ring that stops the slider (between the two springs) from continuing up. Thus from that point on the rate is just that of the lower spring again.

Both those torsions pictured seem to have an "intermediate stopper" thing that bottoms out, thus only the front half of the torsion would be active, thus changing the effective rate.

Interesting thread. Thanks guys.

[De-Ranged]

There is nothing wrong with what you plan but you will find it snowballing out of control

The biggest issue is going to be cert.... thanks to some cheaply made american tube arms that were crap the rules for tube arms are extreme, check with your certifier if your buying a kit they may have already gone through the tec commity and be accepted otherwise you'll have to submit them (takes a couple of months and somewhere around $150 from memory)

Next you may have to upgrade the mounts at the chassis as these are originally designed to take just an indexing load, I'm not familiar with the Humvee BJ's but if they have a different mount to the spindle trust me you don't want to go down this path lol cost in machining to get it to fit and back to the tec comity again
There is also a possible issue with the spindle not being designed to take the load on the top BJ so the mount for it maybe too light (not familiar with Nissan IFS stuff sorry) from experiance I would guess its good enough due to it being 4wd it should be stout enough

As for the SA option.... its not that bad an option
Your right the top BJ will wear faster as its now taking a load but that load is minor remember your lower arm is still taking the lion share of the suspension load, the other thing to consider is as it wears it is wearing out the top of the joint not the bottom so there is little safety risk (the bottom one has to be that size due to it holding the weight of the vehicle on the lips and side of the BJ instead of the top of the ball and cup)
I would guess its a motorcycle coilover as that would be about the right weight for a helper, has its own damper so it isn't just an extra spring working harder on the factory dampers
They have even made there mount that sits on the upper wishbone large enough it spreads the load out to the outer vertical rib
The only thing I don't like is the bolt through on the chassis for the hoop but I can understand the need for this as a bolt on kit

The catch is this isn't a dual (ramping rate) suspension setup, but with the right coilover and spring setup it could be

My opinion would be adapt this design.... stick with there bolt on plate upper wishbone mount as this makes cert a whole lot easier, cut up into the inner guard so you can fit a ultralite buggy coilover and run a slidder that bottoms out to the body it may mean you have to mount the shock so its not using all its travel but you'll get an increase in standard spring rate to help the torsion bar (offset weight from a winch bumper or give it a bit of lift) and when the slider bottoms on the shock body you can increase you spring rate

[lax2wlg]

Thank you very much for the feedback, I appreciate the insight.
Re; off the shelf long arm kits, unfortunately there is nothing available that suits the WD21 chassis. Total chaos do a kit for the WD22 Navara\Xterra, but the mounting system for the a arms is different, and therefore would not be compatible.

I am starting to think that fabricating new extended upper a arms would be a good idea - or more accurately having new ones made by a fab expert such as yourself - with a built in provision for the coilover mount.

Totally agree re; strengthening the mounting location for the upper a arm, I am thinking something along the lines of a new spindle made from 4140 or similar, with bolt on L brackets to support it. Unfortunately the brackets would have to be bolt on to allow rebushing etc. Example below, ie the red Rancho arms in the middle


Will keep you updated as plans develop. No doubt I will have more questions. Thanks again.