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Mad Scientist
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Topic # 198973 29-Jul-2016 21:49
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Hi I've got a Subaru barely 20,000ks (IMPORT - please don't ask me to use warranty). Just noticed that - when fully loaded, the rear end sags, ie cannot see top of the tyre. Let's assume There's nothing wrong with the car or suspension, as it's stock and new, and that it is a load issue, the suspension wasn't built with carrying people and their things in mind.

 

What is the best way to fix this and maintain suspension performance? I know the cheapest way - fit stiffer springs. That means the shock and damper will be the same set up. 

 

Now if the stiffer springs maintain the car ride height when loaded, surely that "should" mean the shock and dampers would be working better than if the car was sagged?


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  Reply # 1601113 29-Jul-2016 22:53
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Lots of car's seem to be fitted with far too soft suspension for common loading (particularly rear)

 

Being near the bump stops is not to good, ride comfort goes out the window, extra shock loads are transmitted through the car, and independent rear suspension, your camber becomes way too much.

 

I think their are three bits to this:

 

  • People typically test drive cars with the boot empty (and often less than full occupant load). Setting the suspension for this load condition will give better ride, and hence encourage buyers compared to cars with over stiff rear end's. (I learnt to drive in a ute with springs to suit something like a 1 tonne payload. ride was nasty when empty).
  • Spring's soften with use, and shock absorbers wear with use. As cars age they sink lower when loaded compared to new car's
  • Some cars here are delivered with JDM spec suspension (i.e. previous gen Mitsubishi outlander, NZ and japan get coil-overs, rest of the world gets coil with separate shock absorbed). I guess this is to make things easier with the large volume of used imports. I would guess that Japanese loading exceptions are generally lower than ours.

Cheapest possibilities (bit cludgey, don't know if they are legal here)

 

  • Fit spacers to existing springs
  • For non coil-over setups: Install firestone coil rite or similar airbag inside coil spring:

 

     

  • Fit spring spacers

 

 

 

Mid Range

 

  • Swap out for stiffer springs

 

 

High End

 

  • Swap out for adjustable coil-overs
  • Get passive load leveling suspension (like what is fitted to Subaru outback)
  • Get some kind adjustable air suspension (some holden commodores have an tire style air valve in the boot so the driver can manually add more air if they expect a heavy load, and reduce the pressure for a normal load). Luxury vehicles often have built in compressors which will automatically level your load. (Note the latter systems are notorious for failing on older luxury vehicles)

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  Reply # 1601204 30-Jul-2016 09:06
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Fascinating post there Scott3. @op what kind of load are you expecting it to carry? E.g. 5 adults and luggage? 




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  Reply # 1601207 30-Jul-2016 09:27
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not that much to be honest I'll try to estimate

 

2 adults = 140kg

 

3 kids = 70kg

 

3 carseats = 30kg

 

2 suit cases = 40kg

 

roofbox + skis + ski gear = 80kg

 

random stuff = 40kg

 

est above kerb weight = 400kg




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  Reply # 1601208 30-Jul-2016 09:29
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if 5 adults would be say 75x5 = 375kg so I'm not that overboard with stuff. that's a pretty good sag with not much!


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  Reply # 1601227 30-Jul-2016 10:03
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It's always a trade off. The manufacturer has chosen a spring rate - suspension hardness for a sweet spot based on the estimated load that most of that model will carry most of the time.

 

The simplest fix is to put in 'hard' aftermarket springs. But your car will ride like a truck when lightly loaded. And not handle as well.

 

Scott3 has covered most of the options. It really depends on how much money you're willing to spend for those few times you have a heavy load in the back.

As far as I'm aware it's legal to fit most of those things, the NZTA rules around it kick in mainly when you change the ride height of your vehicle.
It doesn't mean it's completely safe though. The engineers have included the factory suspension rates into the performance graphs in your vehicle's computer for abs, traction control etc.
They've also set a limit to the weight that can safely be carried on your car's rear suspension. You'll see that on your glovebox tire tag or in your owner's manual.
As long as you don't exceed this you'll be relatively safe - just be aware of the extra weight, drive to conditions.

 

I've recently put aftermarket suspension and larger wheels onto a friends vehicle. He wanted improved off road performance.
They exceeded the allowed changes, required an engineering inspection, certification and a compliance plate. It was expensive.
And I'm convinced it's turned his vehicle into a dog.
For a marginal improvement the few times he takes it offroad he's sacrificed road noise, handling, ride quality and a degree of safety during the 90% of time it's on the road.

 

Looks cool though. And he's happy as a clam..




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  Reply # 1601302 30-Jul-2016 12:05
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Understood. But it's always going to be loaded when performance is needed. Surely the shock and dampers won't be operating at optimum when it looks like a plane taking off. It's not like I'm taking it to track days when it will be fully unloaded.


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  Reply # 1601330 30-Jul-2016 13:06
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You can look at Progressive rate springs - They are pretty standard rated with light loads but when you load them up e.g. sharp corner the travel gets to the stiffer section of spring and the car holds.

 

This is from a cornering/performance point of view but I would imagine it would be similar effect for a static load


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  Reply # 1601336 30-Jul-2016 13:28
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What you're describing is perfectly normal for a passenger car. If it's not a regular thing I would say crank up the sounds and just carry on. If it is a regular thing I would suggest you need to consider a vehicle more suited to the task.




Always be yourself, unless you can be Batman, then always be the Batman





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  Reply # 1601338 30-Jul-2016 13:33
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Yogi02:

 

You can look at Progressive rate springs - They are pretty standard rated with light loads but when you load them up e.g. sharp corner the travel gets to the stiffer section of spring and the car holds.

 

This is from a cornering/performance point of view but I would imagine it would be similar effect for a static load

 

 

Excellent.


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  Reply # 1601404 30-Jul-2016 17:38
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Are you sure 100% sure that the suspension is stock?





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  Reply # 1601407 30-Jul-2016 17:48
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The inside-coil airbags are/were road legal in NZ when I used to install them. "Fully Equipped" used to sell them, by their hundreds for Mitsi Challengers for govt departments/company lease vehicles. They actually work quite well too! Improve sag and cornering. Plus they're adjustable.

 

 

 

Most stock coils are progressive these days. 

 

I'd be totally agreeing with @scuwp

 

 

 

 

 

Or buy a big car with self-levelling suspension. tongue-out




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  Reply # 1601409 30-Jul-2016 18:01
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blakamin:

 

The inside-coil airbags are/were road legal in NZ when I used to install them. "Fully Equipped" used to sell them, by their hundreds for Mitsi Challengers for govt departments/company lease vehicles. They actually work quite well too! Improve sag and cornering. Plus they're adjustable.

 

 

 

Most stock coils are progressive these days. 

 

I'd be totally agreeing with @scuwp

 

 

 

 

 

Or buy a big car with self-levelling suspension. tongue-out

 

 

Big car = poor handling ... this thing is like driving a rocketship on rails. The mechanical grip is insane. Made it up a frozen ski field on performance summer tyres without any wheelspin!




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  Reply # 1601411 30-Jul-2016 18:03
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 Oh talking about big car I do have a van which also made it up the ski field fine :)


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  Reply # 1601414 30-Jul-2016 18:17
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joker97:

 

 

 

Big car = poor handling ... this thing is like driving a rocketship on rails. The mechanical grip is insane. Made it up a frozen ski field on performance summer tyres without any wheelspin!

 

 

Nooo...Doesn't have to be! Look at Big Mercs and my 7series... mad handling. I add 100kg of weight everytime I fill up with fuel, but you'd never know! Computers, DSC, and SLS are awesome! (I have no idea what DSC does, but I can carry 2.1 ton around a corner with minimal body roll and only wheelspin when I turn some other 3 letter acronym off)

 

 

 

I'm just being a fanboi now anyway. But you knew that :D


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  Reply # 1601422 30-Jul-2016 18:58
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scuwp: What you're describing is perfectly normal for a passenger car. If it's not a regular thing I would say crank up the sounds and just carry on. If it is a regular thing I would suggest you need to consider a vehicle more suited to the task.

 

What kind of Subaru?

 

I have self leveling rear suspension in mine (Outback), however I bought it to handle lots of crap in the boot and a small caravan. Just had engine pulled for new headgaskets and clutch, even with warranty not much change for $2,700 including excess. It has 150k, K's on it though.

 

The springs in yours sound really soft. Is it just a small Impreza hatch?

 

I wouldn't say 400kg is a big ask.

 

If it looks really nose up that can really effect braking and steering in an emergency.


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