Question re Suspension setup

[FNQGU]

Gents,

I've got what I thought was a pretty reasonable suspension set up, but now think it might need a bit of tuning perhaps. After a recent trip on gravel at speeds around 80-85kph we hit a couple of stretches where the road has like long drawn out undulations in it. Before I knew it the truck started to get a real wallowing feel and almost uncontrolled bouncing which affected the steering of course, and with a trailer behind me, it could have gotten nasty. Bloody awful things, and the only way to manage them was of course to slow right down, which I did.

Is this something others have experienced?

Are my springs perhaps too soft (standard 2" Lovells constant rated springs)?

Or are my shocks possibly not right for the setup? I have the Koni 88 series for a 2" lift and have generally been very happy with them.

[threedogs]

when towing are you level? were the front springs rated to hold the 6.5 chev?
if shocks are knackered try some Koni on each corner to control your ride adjustable and rebuildable

[Stropp]

also what tyre pressure are you running on the car and trailer??

[BigRAWesty]

Tough call as you have extra weight and without knowing road conditions its made harder.

Quick test for your shocks is to bounce the car on each corner and once released it should settle after 1 rebound, (so release on the down push, it will recoil up and settle On the down, not bounce again.)

Are your shocks adjustable?

[FNQGU]

Vehicle is set up nice and level. Oh, I also have airbags in the rears which would have been fairly firm at the time.

The Springs were actually installed by Brunswick Diesel, so hopefully they know enough about weights and suspension. I asked for the Koni 88 series shocks but didn't touch on the springs, just went with what they put in.

Re the Koni's, I actually intended to get the 90 series Raid shocks, but Brunswick put the 88's in, which were a fair bit cheaper, so I decided to run with it. They were even trying to say the 88's were over-kill but I had just come out of driving a well set-up Sahara that ran Koni 90 Raids, and it was an awesome ride.

[MudRunnerTD]

You might also have found the sweat spot between undulations. So if your travelling at the right speed for the undulations you hit the next one just as the suspensions finished the previous, this can make for a really smooth entry into the next one, great exit but a messy entrance into the third.

I did this on the beach one night in the GQ, by the third undulation I launched at least 3m into the air and missed the next undulation completely!! On reflection that was as scary as hell! Blast at the time! Lucky landing.

Travel at the speed the road dictates. When you slowed to say 60kmh how did it handle the conditions.

[FNQGU]

Tyre pressure at the time was 28psi. Truck and Trailer.

Shocks are pretty much new still, have only done around 12000klms on them.

When I slowed to 60-ish, it was fine, so it may well have just been a freak 'sweet spot' as you call it. I certainly felt like I was about to get launched and it all happened pretty quickly. I did notice that smooth entry feel for the second one too. On the way back out I was ready for it and there were no dramas going slower.

[threedogs]

how old is this suspension package, type of driving done??

[MudRunnerTD]

Tyre pressure at the time was 28psi. Truck and Trailer.

Shocks are pretty much new still, have only done around 12000klms on them.

When I slowed to 60-ish, it was fine, so it may well have just been a freak 'sweet spot' as you call it. I certainly felt like I was about to get launched and it all happened pretty quickly. I did notice that smooth entry feel for the second one too. On the way back out I was ready for it and there were no dramas going slower.

Kind of like being on a swing mate, the 3rd push is the big one! Yeah with a trailer on the third one would have been getting pretty messy so it would have happened very quickly for sure. Form you other comments I don't think you have anything to worry about, learn from it, you will recognise that particular road condition next time for sure ;)

[BillsGU]

Sometimes incorrect towball weight will do that. By rule of thumb you should have about 10% of your trailer's weight on the towball. If you have too little the trailer has a tendancy to "lift" the back of your vehicle and too much weight will "lift" the front of your vehicle. Either situation will cause problems with steering and handling - especially on rough, undulating roads.

[FNQGU]

TD - suspension is near new.

Westy, I just did your little bounce test on the truck and all good there too. No obvious inclination to bounce.

Bill, good points. And once the undulations took over, I noticed that having a trailer on made things worse. Although I've never weighed the trailer weight on the tow ball, I think it will be at about the right mark. Heavy stuff like the fuel and water drums stay over the axle, or just a fraction in front to be exact. Lighter stuff in the front of the boat and back of the boat. This setup has done some horrible roads in the past and always served me well.

Mudrunner, I think you are right. I'll lock the experience away for the future reference. It was just bugging me in the back of my mind since coming back from that trip, so I thought it was worth throwing out there for comments, and to be sure I wasn't missing anything.

[threedogs]

it may have been just the way the trailer was loaded. maybe