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Not knowing the exact corner weights of the car or even the front to rear weight distribution, I played with the calculator linked above: Spring Rates & Suspension Frequencies - Plus Calculator! — DRTuned Racing

55/45 weight distribution, 4000 pound vehicle, gives 2200 pounds front axle 1800 rear axle, or 1100 front corner 900 rear corner, motion ratio 0.9, frequency 1.5

Front springs should be ~300lb/in and rears about 250lb/in (not accounting for cargo)
Would you use curb weight or gross weight for the calculation if you were the car manufacturer?

 

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Curb weight is empty and gross weight is fully loaded with passengers and cargo, right? I think manufacturers optimize the suspension for the car being essentially empty except for the driver, since that's how test drives are taken, how car reviews and tests are done, and most people use their cars that way. That's why if you're someone that regularly tows or carries heavy stuff like a built kitchen in the back of your Outback, you probably need stiffer springs in the back.

But pickup truck suspensions are designed with cargo in mind, even though they are driven empty most of the time.
 
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Not knowing the exact corner weights of the car or even the front to rear weight distribution, I played with the calculator linked above: Spring Rates & Suspension Frequencies - Plus Calculator! — DRTuned Racing

55/45 weight distribution, 4000 pound vehicle, gives 2200 pounds front axle 1800 rear axle, or 1100 front corner 900 rear corner, motion ratio 0.9, frequency 1.5

Front springs should be ~300lb/in and rears about 250lb/in (not accounting for cargo)
For current gen5, 3.6r touring, i measure with 6k springs with no load
The front (driver - passenger) 426kg - 377kg
The rear (driver - passenger) 338kg - 287kg

The combined weight is less than the book bc some components are not carried by the suspension (unsprung weight)

The rear motion ratio is about 0.8 so 225lb(4k) front and 250(4.5k) rear gives ~ 1.5hz frequency which is close. I currently have 5k springs front and rear (280lbs) and it handles well but can be harsh empty. With 600lbs added weight, the car rides a lot better. Thats why im trying to go with lower rate springs. Shock valving is also another key. Im hopeing the flatout has better valving than bc.
 

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It’s interesting to note that more often than not passenger cars are setup with higher rear suspension frequency, since this helps bumps in the road to be absorbed “in synch” by the front and rear suspension and has the effect of smoothing out the ride quality.


The rear ride frequency must be greater than the front. This is due to the fact that there is time delay between hitting an obstacle by front and rear wheels. The rule that the rear suspension should have a higher spring rate (higher ride or natural frequency) rationalized the observation that vehicle bounce is less annoying as a ride motion than pitch. The time lag between front and rear wheels during hitting an obstacle can be calculated using following expression:

T= L/V where L is the wheelbase and V is velocity of vehicle.

To minimize pitching tendency of vehicle one must plot the front vs rear ride frequencies in an amplitude vs time graph by considering the time lag. By performing various iterations of frequencies one can identify which two frequencies matches early so that there will be only bounce motion. The graph looks like as follows.


View attachment 528570

I was interested in this too. Though in order to do so, for 5k front, the rear will need to be 7.5k or 8k and that can be really rough ride unloaded. Maybe if the 4k(225) works out, ill try 6k(335) rear springs.
The OP did say 300lbs rear did create a rough ride unloaded. Options options...hmm
 

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Wow the driver's side sure weighs a lot more - is that with the driver in the car?
 

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I'm wondering about the motion ratio - I'm reading that Macpherson struts motion ratio is close to unity 1:1 - I chose 0.9 just from thinking that since the spring is inboard it's less than unity.
 
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Johnny, do you have the black lock to ring to attach the endlink for the front given you jave the 5th gen like i do. If you do, itll be another to adjust endlinks location in addition to adjustables.
The 6th gen guy has endlink adjustment point welded on the the lower mount body
Yeah, the question is, I haven't tried the sophisticated method Jim is describing and attached the links to the most natural position when the car was lifted. Is that how do mechanics install links? I assumed so. Otherwise they'd have to jack up the control arm each time.

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Curb weight is empty and gross weight is fully loaded with passengers and cargo, right? I think manufacturers optimize the suspension for the car being essentially empty except for the driver, since that's how test drives are taken, how car reviews and tests are done, and most people use their cars that way. That's why if you're someone that regularly tows or carries heavy stuff like a built kitchen in the back of your Outback, you probably need stiffer springs in the back.

But pickup truck suspensions are designed with cargo in mind, even though they are driven empty most of the time.
Curb weight in Europe is all oils, 75% fuel tank and 75Kg driver. US Curb weight is without the driver I think. Gross is maximum permitted load.
Your explanation makes sense, I'd assume it is how it is done.
 

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For current gen5, 3.6r touring, i measure with 6k springs with no load
The front (driver - passenger) 426kg - 377kg
The rear (driver - passenger) 338kg - 287kg

The combined weight is less than the book bc some components are not carried by the suspension (unsprung weight)

The rear motion ratio is about 0.8 so 225lb(4k) front and 250(4.5k) rear gives ~ 1.5hz frequency which is close. I currently have 5k springs front and rear (300lbs) and it handles well but can be harsh empty. With 600lbs added weight, the car rides a lot better. Thats why im trying to go with lower rate springs. Shock valving is also another key. Im hopeing the flatout has better valving than bc.
Good point on un/sprung weight. I'm doing a big roadtrip soon and one fat family member asked me to give her a ride. So I'll feel better about my 350lbs springs being put to use. Yes, the ride is stiff, I have no idea why Flatout sent me 350lbs springs when I asked them to configure the coilovers for maximum comfort, I should've checked and know exactly what I'm ordering.
I'm tempted to order new Eibach springs, 225lb(4k) front and 250(4.5k) rear.
The calculation works with the weights you provided and motion ratios: 0.95 Front, 0.79 Rear.
The only factor we haven't changed in the calculation is frequency, stayed 1.5 for both.
 

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attached the links to the most natural position when the car was lifted.
I'm not sure what you mean by natural position because a sway bar is free to swing up and down. I see that you can clamp the top of the end-link at whatever height you want on the strut body?

@Jim_jm looks like his are clamped much lower than yours:




Also the motion ratio in the front might be different than the motion ratio in the rear.
 

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I'm not sure what you mean by natural position because a sway bar is free to swing up and down. I see that you can clamp the top of the end-link at whatever height you want on the strut body?

@Jim_jm looks like his are clamped much lower than yours:




Also the motion ratio in the front might be different than the motion ratio in the rear.
Yep, this was with the stock end links and the swaybar itself is pointed up more than normal, but you can't see it here. Since I've put adjustable links on, the ends of the swaybar are almost parallel to the ground now and I've positioned the black bracket a bit higher on the shock body than is shown here. As long as the swaybar is positioned correctly and the angle where the link and swaybar connect is 90 deg or slightly more, it may not make a big difference where the black bracket is positioned. Obviously, a lower position allows for a shorter end link and maybe less flex overall?
 

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The lower part of the sway bar to which you attach the bottom part of the endlink is parallel to the ground.
That felt the most natural to me. How did @Jim_jm positioned the clamp so low I have no idea :) But it looks like it was the time when it gave him clunking before he switched to the adjustable type. Because I would think the endlink would pull the sway bar very high with wheels on the ground.
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Also the motion ratio in the front might be different than the motion ratio in the rear.
What are the correct motion ratios then? Are we able to agree on the right values? I'm willing to experiment and order new springs in the name of science but want to do it correctly the first time (this time).
 

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Since this thread is actually about the Gen 6 and not the Gen 5, how different is your front sway bar than the Gen 6? Ours clamps below the frame channel not above it, but aside from that it looks very similar.
 

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What are the correct motion ratios then? Are we able to agree on the right values? I'm willing to experiment and order new springs in the name of science but want to do it correctly the first time (this time).
I honestly don't know what they are or how to accurately determine it. I've done a cursory search of the internet and it's just not that straightforward.
 

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So if he sees 1.21:1 do we take the reciprocal to get 0.826446280992 motion ratio? For the front, one of the linked articles says this:

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1.5 seems like a taut/firm/sporty frequency and 1.0 a soft ride - my guess is that the stock outback is closer to 1 than anything. We can reverse engineer using the known weight and spring rate to find the stock frequency.
 
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