Suspension 101 Question

Submitted: Sunday, Feb 02, 2014 at 13:56
ThreadID: 106050 Views:1801 Replies:6 FollowUps:6
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I am interested in some perspectives on suspension. Over the past twelve or so years, I have driven a 105 Landcruiser, GU Patrol, 120 Prado and 2 x 150 Prados for a total of over 600 000 km through much of Australia. The only suspension modifications I have ever used have been the addition of variable rate coils in the rear of the Prados, because the Trackabout Safari camper we tow has a trailblaza on the drawbar and is a bit heavy.

I am about to take delivery of a D-Max LST to replace the current Prado.

I have read an awful lot on forums about the extensive suspension modifications and lifts that people make. Not ever having driven a significantly modified vehicle, I am simply ignorant of the practical benefits for driving and comfort. Like most 4W drivers, I enjoy getting off-road, but I don’t set out to test my vehicle to its limits. I'm unlikely to be doing much rock-hopping!

If I spent some money on the D-Max suspension, what would I notice to be different as a driver or a passenger? What are the benefits?
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Reply By: Nutta - Sunday, Feb 02, 2014 at 15:50

Sunday, Feb 02, 2014 at 15:50
With the dual cabs being longer at the rear theres a good chance you may need at least airbags or something for the Dmax with your camper on, especially if you start filling the tray up a bit.
AnswerID: 525639

Reply By: Ross M - Sunday, Feb 02, 2014 at 17:36

Sunday, Feb 02, 2014 at 17:36
If carrying a reasonable amount of weight in the tub and have a camper on the towbar, then it would tend to bottom, to the bump rubbers, when going through some dips when the vehicle weight is downward and the camper also pushes more with it's transfer of weight.

Going very slow not a problem, normal use you may/will bottom more easily without a lift.

A lift at the front only repositions the suspension at a lower level than normal but doesn't increase travel of the suspension. You still have to retain 1/3 of all possible movement as the downward movement from the "at rest" position, but that chassis higher position does allow some more absorption of bumps.

The lifting usually includes more capable shock absorbers and if chosen correctly they will also limit the for/aft pitching caused by the camper weight transfer on undulating roads.

Generally the shockers are matched to a vehicles normal use and outside that you may require more mass control. I don't know how good the new Dmax OE shocks are but the previous model was extremely poor in shock performance even brand new. More capable shocks are usually fitted to handle the movement..

The ride may be firmer and the rear also a little higher when empty but it can then bear the load and have a better ability to handle more rough action, not hardcore off road though.

Cheers
Ross M
AnswerID: 525651

Follow Up By: mike39 - Sunday, Feb 02, 2014 at 18:26

Sunday, Feb 02, 2014 at 18:26
Ross provides some good analysis, but one thing I have noticed about some of the modern ute/twincab etc. configurations is a certain propensity to chassis bending/failure under load conditions actually within the rated limits.
I have pics I have taken, the result is not good to look at.
mike
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Follow Up By: Ross M - Sunday, Feb 02, 2014 at 19:07

Sunday, Feb 02, 2014 at 19:07
G'day Mike
That is a good point and the earlier crop of all DC utes were a bit light in the chassis. The new Dmax has a stronger chassis than previous and is spring over and longer leaves as well.

Hopefully DMaximus isn't going to be pushing his luck though.
Cheers
Ross M
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Follow Up By: DMaximus - Tuesday, Feb 04, 2014 at 08:01

Tuesday, Feb 04, 2014 at 08:01
Thanks Fellas. Very helpful!
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Reply By: Hoyks - Sunday, Feb 02, 2014 at 19:42

Sunday, Feb 02, 2014 at 19:42
Springs carry the weight, shocks/dampers control the bounce. Keep this in mind when considering anything to do with suspension, there are a lot of beliefs about what magic shock absorbers can do, but all they really do is slow the springs extension so the vehicle doesn’t bounce all over the place. That said, a heavier spring carrying a heavy load will need a better damper than a standard spring with a light load. Getting them as a matched set for a particular application is a good idea. Some off the shelf dampers can be a bit too generic though, I looked at some and the application chart showed that fitted an F250 and a Feroza, same part number... WTF??

The modern dual cab is a study in compromise, it is built to take 1 ton, but still be reasonably comfortable when unladen. Unfortunately a production leaf spring struggles to perform both duties well. An aftermarket spring pack can be built to better suit your needs, but accept the fact that it will better suit one end of the scale than the other. Jack of all trades, master of none.

Lift wise, about all you will get is about 50mm as that is about all that is available without engineering approval and the D-max is well down the shopping list of those that want a ‘heavily modified’ vehicle.
AnswerID: 525660

Follow Up By: Hoyks - Sunday, Feb 02, 2014 at 19:47

Sunday, Feb 02, 2014 at 19:47
Oh, and airbags.
I wouldn't. They put load forces into the chassis in an area that the engineers never intended a load path to be. If it had coil springs, then go your hardest but not with the leaf spring.

The other thing is that the dual cab has the towing load applied to the bar well aft of the axle so this adds a hell of a lot of leverage and mechanical advantage to the whole equation.
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Follow Up By: DMaximus - Tuesday, Feb 04, 2014 at 08:04

Tuesday, Feb 04, 2014 at 08:04
Thanks very much Hoyks. It helps me!
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Reply By: splits - Monday, Feb 03, 2014 at 00:54

Monday, Feb 03, 2014 at 00:54
Dmaximus

Any changes to the suspension of a car may improve it in the area you want but it will also have an adverse affect on something else. A big problem with dual cabs is not the suspension design but the way people distribute the weight in them. Owners may pay close attention to keeping them under maximum weight when loading them but more often than not will end up with far too little on the five seats and far too much out the back, particularly behind the axle. If you want to take the car up to maximum weight and have it sitting level as its manufacturer intended then you are going to need the equivalent of four big rugby forwards plus the half back in the cabin.

There is any amount of suspension and vehicle handling information on the net but you will most likely need Einstein sitting beside you to help you understand it. For a general overview of vehicle handling and towing problems, it is hard to go past this articlehttp://www.caravanandmotorhomebooks.com/pdf/vehicle_dynamics_complete.pdf Note what he says about camper trailer tow ball weights. Many cars have been unnecessarily modified because of poor trailer design.

Another problem is air bags. Your steel springs are linear and will compress in direct proportion to the load. Your bump rubbers are exponential and will get progressively harder the more you compress them. Air bags are also exponential and can become like a rock by the time they are around 60 to 70% compressed. Slamming the overloaded rear end of a chassis down onto rapidly hardening air bags has caused a huge amount of chassis damage on rough roads.
AnswerID: 525675

Follow Up By: DMaximus - Tuesday, Feb 04, 2014 at 07:59

Tuesday, Feb 04, 2014 at 07:59
Many thanks Splits. Appreciate your reply.
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Reply By: Warren B - Monday, Feb 03, 2014 at 20:26

Monday, Feb 03, 2014 at 20:26
Hi mate, I have a 2011 D Max and have modified it, your post is very timely as I am thinking of altering mine. I have an IRONMAN suspension that was fitted by TJM in 2011 and right from the start was unhappy with it but put it down to the fact that I just got out of a modified 80 series. there were 3 levels, comfort, performance, and constant I were advised performance as our van is nearly 3 tonne and has a ball weight of 260kgs. Also lifted 50mm.
In the bush the ride is harder than I would like and no matter how hard I push it I cannot get the shockers to heat up. ( unlike my 80 the shockers got real hot )
I have moved the towbar to as close as possible to the car and it has eliminated a lot of the porposing with our heavy van.
givern the choice again i would choose comfort which is why I am going to replace the front IRONMAN shocks with the OE and see what happens. incidently the rep fobbed me of saying nitro gas shocks don't get hot. Would also suggest the lift it is worth it.
For what its worth the D Max continuely suprises.
Cheers Warren
AnswerID: 525717

Reply By: MAVERICK(WA) - Tuesday, Feb 04, 2014 at 12:26

Tuesday, Feb 04, 2014 at 12:26
If you are going to tow your camper and also load your tub you will need to do something to prevent the problems as outlined above re bottoming out etc. However Isuzu managed it (and it may have something to do with the extra length of the leaves) the DMax is as comfortable as it gets for a dual cab. I have fitted a 300kg OME front and rear and empty it still maintains a good level of comfort - not car comfort but good for what it is. When tripping around the place with a load it maintains good comfort and control when the gravel roads and tracks get corrugated and gnarly. So far I am happy with the DMax and hope to maintain that level of happiness for a few more years. rgds
Slow down and relax......

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