NP300 "sag" issue - 5 link.

[DMM]

Hey all.

Notice a lot of people comment on the soft suspension of the np300 when towing.

Nissan have designed this specifically for ride rate control and also for brake force distribution systems. The other key issue with raised rear springs is the RC coupling and RC axis becomes further from loaded cog and enhances rear end lateral instability when loaded.

The np300 5 link runs up around 90% anti squat under towball load. Running taller or stiffer springs will upset the computers brake distribution and esc. Resulting issue under emergency braking will cause little rear brake bias when the rear lifts significantly under push (due to anti squat and towball weight + trailer load) bringing on potential jack knife and also increased stopping distance.

Food for thought.
Cheers.

 

[Cessa]

So with your analysus above, to compensate for the large sagging experienced when towing, i use a WDH and this works pretty well but i dont think its the cure due to the WDH's limitations.
Would air bag suspension be the answer?

 

[Martin'sD40]

Use heavier rated spring with air bags , polly or firestone , I'm running pollies 225psi , no more sag and is still a smooth ride

Marty

 

[Dion]

I'm running pollies 225psi

Is that all?


DMM - I don't envisage us staying long on your original topic; sorry! But I will try:

You have access to the NP300's CoG height? Sounds like you do very interesting work.

I think I'm most concerned that any anti- parameter changes significantly enough to comment on between RH and max towball load? What do you make it to be at RH?

More to your point about braking while towing though, I'm a little confused about the reference to anti-squat. For braking I'm better accustomed to thinking about rear axle anti-lift and I don't have an NP300 to go out and stare at for a bit!

Surely Nissan spent some prototype validation time on trailer tow limit handling; I'd call at-capacity towing one of the core usage scenarios for the vehicle.

 

[DMM]

Is that all?


DMM - I don't envisage us staying long on your original topic; sorry! But I will try:

You have access to the NP300's CoG height? Sounds like you do very interesting work.

I think I'm most concerned that any anti- parameter changes significantly enough to comment on between RH and max towball load? What do you make it to be at RH?

More to your point about braking while towing though, I'm a little confused about the reference to anti-squat. For braking I'm better accustomed to thinking about rear axle anti-lift and I don't have an NP300 to go out and stare at for a bit!

Surely Nissan spent some prototype validation time on trailer tow limit handling; I'd call at-capacity towing one of the core usage scenarios for the vehicle.

Hey Dion,

I don't have accurate specific COG, only Estimates.

My reference to braking while towing is in relation to lifted springs. Nissan calculated max towball load to sag the rear, as when breaking you are right, the rear will want to lift. This puts the rear back into normal ride height range - within the computers ESC values and parameters and also within the active break force range. The problem will arise if you run lifted and locked height suspension from factory height or higher, when emergency breaking the rear will lift even further, bringing less active brake load the the rear drums and ESC is also then out of its adaptable range.

RE AS (anti squat) the higher the suspension ride height from chassis to lowest trailing arm joint on the diff, the more the anti squat ratio decreases. The AS on solid axle 5 link is a direct relationship between the bottom arm angle and where that extends to intersect the Roll axis of the vehicle. 100% AS mean the theoretical line from bottom trailing arm angle will intercept the exact spot of the front RC height. 50% AS means the line intercepts essentially middle of the car. The more AS % the more resistant the rear end is to squatting under positive drive conditions and the more grip or friction weight is transferred to the wheel instead of being absorbed by the spring or shock.

 

[DMM]

Use heavier rated spring with air bags , polly or firestone , I'm running pollies 225psi , no more sag and is still a smooth ride

Marty

Hey Martin,

I agree with you, running heavy gauge spring set at normal heigh is the solution, or OEM springs with bags. Although if running a bag I would still want some squat when max load.

 

[Dion]

I don't have accurate specific COG, only Estimates.

Crankshaft CL is about the best I would get from an estimate.

My reference to braking while towing is in relation to lifted springs. Nissan calculated max towball load to sag the rear, as when breaking you are right, the rear will want to lift. This puts the rear back into normal ride height range - within the computers ESC values and parameters and also within the active break force range. The problem will arise if you run lifted and locked height suspension from factory height or higher, when emergency breaking the rear will lift even further, bringing less active brake load the the rear drums and ESC is also then out of its adaptable range.

I agree that any change from the standard springs has every potential to make the calibration ineffectual. However I think I would focus most on the impact of changes to the front RH and spring rate on the EBD calibration.

I think the standard rule still dominates - when towing heavy, the car will not save you from a poorly configured trailer brake setup or ham-fistedness. ESC, EBD or none - same story.

RE AS (anti squat) the higher the suspension ride height from chassis to lowest trailing arm joint on the diff, the more the anti squat ratio decreases. The AS on solid axle 5 link is a direct relationship between the bottom arm angle and where that extends to intersect the Roll axis of the vehicle. 100% AS mean the theoretical line from bottom trailing arm angle will intercept the exact spot of the front RC height. 50% AS means the line intercepts essentially middle of the car. The more AS % the more resistant the rear end is to squatting under positive drive conditions and the more grip or friction weight is transferred to the wheel instead of being absorbed by the spring or shock.

I'm familiar with anti-squat but not with how it relates to braking, is what I meant.

*roll axis not involved in pitch behaviour

*instantaneous centre, not RC

Front RC height (which should say front instantaneous centre) is not part of the equation as you have mentioned... but CoG height certainly is.

It doesn't so much get absorbed by the spring, but with 100% (or more!) anti-squat you do score a slightly longer moment arm to the CoG, so you'll get more instantaneous weight transfer and notionally more grip. In practice though, design for a low-ish anti-squat and then focus on some better suspension parameters.

 

[DMM]

Crankshaft CL is about the best I would get from an estimate.



I agree that any change from the standard springs has every potential to make the calibration ineffectual. However I think I would focus most on the impact of changes to the front RH and spring rate on the EBD calibration.

I think the standard rule still dominates - when towing heavy, the car will not save you from a poorly configured trailer brake setup or ham-fistedness. ESC, EBD or none - same story.



I'm familiar with anti-squat but not with how it relates to braking, is what I meant.

*roll axis not involved in pitch behaviour

*instantaneous centre, not RC

Front RC height (which should say front instantaneous centre) is not part of the equation as you have mentioned... but CoG height certainly is.

It doesn't so much get absorbed by the spring, but with 100% (or more!) anti-squat you do score a slightly longer moment arm to the CoG, so you'll get more instantaneous weight transfer and notionally more grip. In practice though, design for a low-ish anti-squat and then focus on some better suspension parameters.

Hi Dion,

just FYI roll axis has a large effect on pitch behaviour. If cog is even throughout the car, but roll axis is slanted, the roll coupling force is then different at each end. Pitch effort and weight transfer is then relative to a percentage of the difference between cog and rc - which will then give you a load bias on either compression or extension.

 

[Martin'sD40]

DDM , that should have read 25PSI not(225psi) LOL Doh , I'm using std springs with polly air bags a@25psi she sits stable and true suspension is a little firmer much like the D40 did but still rides well

Dion - man are you on the weed or what LOL

Marty

 

[ryzan]

The D23 runs a physical distribution valve over the rear axle to control front-rear brake bias depending on load which is a pretty basic unit. So provided that this is adjusted to suit raised spring height, there should be little to no impact on abs, ebd etc. anyway. Abs and ebd aren't overly technical from an operational point of view and are pretty flexible (to a certain degree of course) when it comes to things like ride height, tyre size etc.

You'd probably be suprised how little work the rear drums do when unladen. Rather underbraked from factory to avoid them locking up in the wet as it's safer to have a higher front bias.

 

[indio2010]

does anyone know how much it costs to put air bags in? i carry a load of about 500kgs in the tub and i worry it will wreck the suspension

 

[Bakes]

does anyone know how much it costs to put air bags in? i carry a load of about 500kgs in the tub and i worry it will wreck the suspension

It cost around the $400 mark for the airbags with the High Pressure sleeves and about an hour of your time to install.

 

[Stelianos]

500kgs is not a weight to worry about, at least in leaf spring suspension.