Effect of ACE/SLS (D2a) on shockies

**bidds** · 10th January 2012, 09:05 PM

Hi there,

The earlier D2's had multiple shock absorber specifications for each permutation of coil/air/ACE suspension, both front and rear. The D2a has a single specification shock for all. On the UK webshops, the D2a shock is about twice the price of the earlier versions.

Questions:
How did they manage to get one shock to do the job of four? Is there something special about this D2a shock (as might be indicated by it's price)? I know the panhard rod on the D2a is shorter than the D2 and I think the sway bars are thicker for non-ACE vehicles - are there other suspension/geometry changes that allow the single shock specification?
Were the original multiple specifications really all the same?
Or did they just get lazy &/or cheap?

Going futher...

More questions:
I think I'm pretty happy with the differences between airbag and coil springs where the airbags have a progressive rate as they compress. Also, in rebound the air bags will want to keep expanding and is only controlled by the shock; the coils will tend to control themselves more. All told this should mean a shock valved for air has less compression damping and heaps of rebound damping, compared to that for coil spring. Is this basically correct?

The effect of ACE on shock valving is something I don't really understand. My guess is that the ACE helps improve the steering response and roll in corners, which should allow the shocks to have much less low speed/initial compression damping. Is this correct or is there more going on?

Would the air-rear/coil-front design of an SLS D2a introduce any special requirements on the front shocks? I'm guessing that if the rear shocks are controlling the air bags well, the front end really wouldn't have any different shockie requirements to a vehicle with a coil sprung rear end.

Any information to help me understand this stuff is greatly appreciated!

**benji** · 12th January 2012, 08:04 PM

I was reading the shock part numbers the other day, and it's got me confused too.

I don't own a D2 (my cousin does) but i've got all the manuals and have read them all, so here's my take.

Aparently the shorter panhard rod resulted in less bump steer - I don't know how, but...

The swaybars on the ACE vehicles are a lot thicker, almost 1 inch in diameter at the front, though front and back are different sizes.

I too have always felt a steel spring controls it's rebound a bit better than air bag (just a seat of ya pants kinda feel), so, yes, maybe airbag shockers have more rebound valving, although some air springs are linear in their compression due to the shape of the bottom piston (front RRC).

My take on the ACE would be that you would be able to run less rebound valving (as i've read this is what controlls sway - althou not necessarily body roll). I know in my cousins D2 over speed humps his shocks have a lot less rebound valving than my p38.

I wonder if someone would have a dynograph (if thats the word) of the shockers?

**Slunnie** · 12th January 2012, 08:15 PM

Thats it, the SLS shock will probably have less damping on compression. I'm not sure why an ACE shock, if anything I would have expected a stiffer very low speed valving on the dyno curve, but that would make for a very jittery ride so I cant imaging LR doing that. The dyno curve would typically be linear, the values would be really interesting though.

**bidds** · 13th January 2012, 08:21 AM

If we're saying that less rebound damping is required (due to presence of ACE) to control sway I think that holds up: My rear shocks appear to have lost the plot with rebound and while it pogos a on bumps while going straight along the highway, turn in and cornering are still well controlled.

So what does less rebound damping mean - slow speed or high speed? Or should that be a position based thing, given that an SLS/ACE equipped vehicle should be riding at the same height regardless of load (within reason of course).

And with all these changed requirements from a conventional suspension - how did LR go from shocks that account for each configuration to a single spec that does it all? I do know the springs in the D2a are of a different steel composition to the D2; there's the different panhard rod length; and I think the sway bars on the non-ACE D2a are thicker than the D2. Also, would piston design in the rear airbags also impact rebound characteristics to be more like steel springs (although I'm not aware of any difference in airbag spec between D2 and D2a)?

Perhaps this all means that ultimately they've made the conventional suspension of the D2a behave much more like an ACE/SLS system, allowing a single shock spec? Or is there a shock design that somehow adapts for various suspension behaviours?

**gusthedog** · 13th January 2012, 09:26 AM

Im not as 'technical' as some of the other blokes (and ladies) on the forum, but I've recently replaced all my suspension in my D2 (not D2a). I have ace and sls - I went for the Old Man Emu kit, simply because I have a mate who used to work for ARB and could get me a good deal. I have 30mm plus springs in the front with 'comfort' shocks and new dunlop airbags in the back with a lift block and 'standard' shocks. To be honest, they are excellent. The ride is fantastic, comfortable and seems to work well off road. I could look up part numbers for you if you like but I seem to recall that they were the same rear shocks as for the 'coil spring' discos. I dont really know about low speed valving and all that stuff. I'm more concerned with comfort, longevity and a good deal using stuff that was at least designed in Australia.

**Graeme** · 13th January 2012, 09:37 AM

I suspect that LR decided it didn't want to keep carrying all the different shocks for the D2 vehicles as it was already planning the D3 before the D2a was released, so changed to a compromise/general purpose D2 shock.

**bidds** · 13th January 2012, 12:10 PM

That's my primary suspicion too (LR being 'cheap'). However it doesn't explain the much greater expense of the D2a shock over the D2 shocks. And the fact that they bothered making so many changes to the D2a over the D2 may indicate that they were still intent on improving the vehicle despite it's soon demise.

In any case all the technical q's I've been asking are because I don't believe I need to have a terrible ride to go with the great handling of my ACE/SLS D2a. I've ridden in many trucks and cars that manage to combine the two. While I read about and experienced that many are happy with the HD spring/OME I'm keeping the original springs and ride height, so they're out.
I'm also trying to decide what's worth buying after I've already spent $1500 on shocks (not including fitting or any other components) and totally hate them. And these are supposed to have been the best on the market, specially tuned to my vehicle. I do feel I've been Group Thinked into believing they were the best, even after I didn't like the same brand on my RRC - stupid me.

After this thread and some in depth discussion with two suspension shops, I've now decided that for me, a super high quality, pure oil shock (no gas) will give me the supple ride with control, along with the ability to keep going over endless corrugations (planning a few of the classic outback trips) and improved adjustability.

While I appreciate that Fox and Bilstein do some amazing off road racing shocks and they would probably be very very good, I don't want a gas shock and I want something I can just bolt up with zero modification.

So I'm going with Koni HT Raids. They cost an amazing amount but the inbuilt hydraulic bump stops for both compression and rebound, 3yr/unlimited kms warranty, including if dinged, pure oil construction all add up to something that I figure is good value. After I've spent a bit of time with them, I'll post up my experience - fingers crossed!

cheers

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