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Rear Springs:165 progressive vs linear 140

I am currently running a 140lb spring and was curios as to what some of your thoughts were concerning the differences or +'s and -'s regarding each. I was thinking of switching to a progressive spring but wandered if i would lose some handling. Is a progressive 165 as aggressive as a linear 140 under load? These will be running on top of a bilstein adjustable and in a 4 banger.
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Old 02-27-2003, 07:37 PM
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Peter,

I don't know the answer to your question... sorry... maybe this will bump back to the top..

who did alignment for you. This is probably more noticeable and more important than the differences in the springs... If you change springs you'll likely have to re-allign... since there will be a small ride-height change........

I wouldn't think the difference would be too noticeable... but I have never actually tried the progressive springs either..

good luck
brant
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Old 02-28-2003, 06:30 AM
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I doubt that the progressive springs would make any difference on a car with a very old suspension design. If the price is the same then I'd give them a try, otherwise I'd save the $$$$$. Good luck.
Old 02-28-2003, 08:39 AM
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Brant, I got a couple of references for alignment shops. I think you guys said there was a place in boulder and that is where i was going to go till Mike up at Storz told me there was a place not far from my house that he recommends. They did a very good job. It is a Jim Paris Tire that has been doing porsches for years. Mike claims that he has used them for along time.
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Old 02-28-2003, 01:23 PM
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It would be my thought that the 165 p's and the 140's would give the same initial ride. However, there might be a performance enhancement from the 165p's in high speed manuvers.
Old 02-28-2003, 06:20 PM
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Progressive rate springs are wound in a manner that as loading occurs, the rate increases to a point where the body would cease to roll about it's center. In comparison to a standard rate spring, the ride would be softer, but as body roll occurs in a corner, the initial roll would probably be more severe that the standard rate. Depends on whether you're comfortable with the initial higher rate while rolling into a corner.

Just my $1.00 worth (inflation ya know)
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Old 02-28-2003, 07:28 PM
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Peter,

Rons pretty much right on. Since I have these on my 914, I would add a couple of things. One, with Bilteins, you can adjust the spring perch, so this allows you to pre-load the springs if so desired, decreasing the response of the spring load. Also, its not as though the initial unsprung load is that significantly different - certainly not softer than 140# springs. That leads to my final point. You will notice every bump in the road - more than you might already. I use mine for a daily driver and am willing to tolerate this, but some are not. It really pays dividends on these Arizona mountain roads though, when I'm right on the tail of 911's.

Enjoy,
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Old 03-01-2003, 08:04 AM
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Hi,

I am currently thinking about 165 progressive vs linear 140 for my car as well. After reading these postings I actually leaning more towards the 165 progressives. At the same time I will install the front sway bar that is already sitting in the garage.

Before it was mentioned that ...

Quote:
If you change springs you'll likely have to re-allign... since there will be a small ride-height change........
... I am confused! Assuming the alignment was correct beforewhy would changing spring and or shock change that (we are talking about the rear). Riding height can't be the reason for that?!

Patrick
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Old 03-01-2003, 08:24 AM
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A case could be made that the adjustment wouldn't change and a case could be made that it would. It would be my belief that the change would be insignificant.

For Change:
The wheel "in theory" travels in a vertical line about it's pivot point (inner mount of the trailing arm), but in actuality scribes an arc. The severity of this arc, in degree change would be aggravated by the length of the trailing arm length (center of piviot to center of wheel). The longer the arm, the less degree change for a given "vertical" movement.

The realtion of the piviot point to the ground plane is at a fixed height (at rest) with stock spring/shock height. The center of the wheel would also be fixed (at rest). If we envision that these points are parallel to the gound plane, the resultant angle would be 90 degrees. If one shortens the shock/spring, the pivot point would drop towards the horizontal ground plane, resulting in an angle between the pivot and center of the wheel, being decreased <90 degrees. Since the center of the wheel is now on the porition of the arc that decreases to zero, the wheel would have a tendency to move forward under suspension deflection, thereby possibly aggravating the (increasing) toe in of the rears.

The camber of the wheels could also be effected. The camber is set at a given ride height. The angle between the vertical wheel and the upper shock mount is fixed by the length. Lessening this length (lowering) would increase the camber (move the wheel centerline from vertical to less than vertical.)

Against change:
The deflection, due to superior kraut engineering, would be minimal as the design is truly engineered to move the wheel vertically(maintains maximum tire contact patch with road surface).

This does not apply to the front as the lower control arm moves in an arc. Lowering the front would definitely pull the ball joint inward (creating positive camber). The effective length of the arm (between the fixed frame mount and the ball joint would be shortened as the arm is no longer parallel to the ground, but on the part of the arc that decreases.

Also, the toe in would be effected as the length of the arm between the rack and the tie rod end would be shortened in the same manner - the tie rod end would be pulled in towards the rack as it deviates from the horizontal plane. Also creates "bump steer".

Whew! If you believe this, I have a bridge for sale.
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Old 03-01-2003, 08:00 PM
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I don't understaned.....
wouldn't changing the spring perch... actually just change the rear ride height..(and alignment).. instead of pre-loading the spring?

"with Bilteins, you can adjust the spring perch, so this allows you to pre-load the springs if so desired, decreasing the response of the spring load. "

b
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Old 03-02-2003, 06:26 AM
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Lowering the rear of the car will give you more negative camber, and more toe-in. This is due to the angle that the trailing arm meets its pivot. Try bending a paper clip into a 'T' shape, then bending the lower part of the 'T' to a 45-degree angle. Then bend the bottom of the T outward at a 90 degree angle to its former location. Rotate the clip around the two other arms and see what happens to the bent end.

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Old 03-02-2003, 07:03 AM
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Quote:
Originally posted by Dave at Pelican Parts
Lowering the rear of the car will give you more negative camber, and more toe-in. This is due to the angle that the trailing arm meets its pivot. Try bending a paper clip into a 'T' shape, then bending the lower part of the 'T' to a 45-degree angle. Then bend the bottom of the T outward at a 90 degree angle to its former location. Rotate the clip around the two other arms and see what happens to the bent end.

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Old 03-02-2003, 07:28 AM
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Quote:
I don't understaned..... wouldn't changing the spring perch... actually just change the rear ride height..(and alignment).. instead of pre-loading the spring?
Hmmm, the way I understand the whole deal is, that it would do both... While moving the spring perch some steps up it would raise the riding heights of the car while at the same time you could achieve a preload on the springs depending on how far you move the perches up.

In context with the alignment - after I read Ron Meier posting I have a better understanding what happens with the rear suspension while it is lowered. At the same time while lowering the riding heights - increasing the neg. chamber might be a nice side effect. Does anyone know the ratio here (like 10 mm change in riding high will result in X degree chamber change?

Thanks,

Patrick
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Old 03-02-2003, 01:13 PM
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I decided to go ahead and try the 165's. I'll keep the brand new 140's in case i don't like em as much. I am from the school of thought that I will want to have the new alignment rechecked. As a side note, Hey Brant, does your guy in Boulder have rear shims?
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Old 03-02-2003, 02:34 PM
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