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Motorsports & Track Forum
From Auto-X to Trackday to Racing and Professional Motorsports this is the place to discuss making BMWs fast

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Old 09-11-2009, 02:49 PM   #1
SpeedDemon
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Question Springs Rates for my new ASTs?

I'm trying to decide which spring rates to go with on my new ASTs.

I'm sure that I want to go with a 650lb/in rear spring, but I'm just trying to decide what to get for the front. I'm thinking of either a 450lb/in or a 500lb/in front spring.

My confusion comes from the fact that Vorshlag is telling me to go with a 550#/in front spring and RRT is telling me to go with a 400#/in front spring

Thanks for any help and just wondering if I can get some more opinions from experiences.
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Old 09-11-2009, 03:13 PM   #2
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Some info on what you do with your car would be helpful. For a street car, 400-450 is just fine.
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Old 09-11-2009, 03:16 PM   #3
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I'm more concerned about ratio between the front and rear spring rates since I've already decided that I want a 650# rear.

I'm going to be using the car for lapping days and a small amount of autocross. I'll probably do about 12 HPDE/Lapping days a year. I drive the car on the street regularly but have a high tolerance for a stiff ride. I just want to get the most neutral handling out of the car and still maintain a crisp turn-in.
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Old 09-11-2009, 05:11 PM   #4
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I would go with what Vorshlag is recommending. Im sure they asked what you will using the car for and how much your car weighs.

iwsti.com forum has suspension calculator thread that might help.
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Old 09-11-2009, 05:41 PM   #5
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I think I'm really leaning towards a 500# front and a 650# rear spring unless someone here tells me that I'm going down the wrong path.
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Old 09-11-2009, 07:32 PM   #6
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iwsti.com forum has suspension calculator thread that might help.
I followed that link, and I'm not sure what you're referring to. Can you be more specific or provide a direct link to the thread/post you're talking about.
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Old 09-12-2009, 09:07 AM   #7
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I'd ask RRT for the reasons why they recommend 400/650 over a 550/650 setup. Then I'd ask Vorshlag why they recommend 550/650 over 400/650. Compare answers and see how they fit in with your goals for the car.

Also remember that you need to consider more than just spring rates. I would imagine that if you went 400/650 you might want to ditch the rear anti-sway bar completely.
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Old 09-12-2009, 03:20 PM   #8
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For track use, I'd go 600 fronts.
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Old 09-12-2009, 03:36 PM   #9
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After, PM'ing vaio and talking with Vorshlag, I'm settled now on going with 550#f/650#r

I'll post a review up in a few weeks after I get it on the car.
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Old 09-12-2009, 04:37 PM   #10
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I'm sure you'll be happy with that setup.
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Old 09-16-2009, 01:27 PM   #11
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if you go 550, make sure to pick up a 30mm bar.

I've just been through a whole season of troubleshooting front end push on my AST 4200's with 550 fronts and a 27mm bar. Switching to 650's and setting the bar at full stiff finally prevented the car from being in the bumpstops up front and got rid of the push.

650/650 should work pretty well with H&R bars, I'm running 650/550 right now and it's working pretty decently. (basically just swapped my springs front to back from what I originally ordered)
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Old 09-22-2009, 02:42 AM   #12
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if you go 550, make sure to pick up a 30mm bar.

I've just been through a whole season of troubleshooting front end push on my AST 4200's with 550 fronts and a 27mm bar. Switching to 650's and setting the bar at full stiff finally prevented the car from being in the bumpstops up front and got rid of the push.

650/650 should work pretty well with H&R bars, I'm running 650/550 right now and it's working pretty decently. (basically just swapped my springs front to back from what I originally ordered)
Hey Murph,

So the source of your push was bottoming in front? Do you still think the diff make cause some push?

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Old 09-22-2009, 07:59 AM   #13
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So the source of your push was bottoming in front? Do you still think the diff make cause some push?
I can definitely still get push if I'm already at the limit of front tire traction and get on the gas, but that's my fault, not the diff's. =] If I'm under that limit, I can feel the diff bring me around the corner nicely.

When the front end was in the bumpstops I was convinced I needed more rear end rotation, as the front end was already fairly soft. (and generally the way to fix push is to soften the front end) So I was doing all kinds of things that are against the norm for a BMW, like running almost no rear toe in and less rear camber and jacking up the rear ride height. Now I'm having to undo all of that, to get the rear end to behave, because the front is sticking much better.

When Basham did well in '05 he was using 500/500, but he was also using a 30mm front bar and 25mm rear bar. I'm using more spring and less bar, but I think I'm headed towards around the same overall roll stiffness.
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Old 09-22-2009, 01:44 PM   #14
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Quote:
Originally Posted by murph1379 View Post
if you go 550, make sure to pick up a 30mm bar.

I've just been through a whole season of troubleshooting front end push on my AST 4200's with 550 fronts and a 27mm bar. Switching to 650's and setting the bar at full stiff finally prevented the car from being in the bumpstops up front and got rid of the push.

650/650 should work pretty well with H&R bars, I'm running 650/550 right now and it's working pretty decently. (basically just swapped my springs front to back from what I originally ordered)
What is/was your rear bar setup?
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Old 09-22-2009, 01:58 PM   #15
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I use the H&R non-M bars, so 27/21, full stiff all around.

I think the H&R M bar fits up front, which is 30mm, but not the rear one.

RD were the bars Basham was using, 30/25.

I think the Hotchkiss bars are 30/25 also, and will fit non-M.

I like the H&R's for the teflon coating on the bushings, which make them nice and quiet.

I'm still trying to dial everything in using 650/550, but I may try 650/650 as well. 650/780 was too much.
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Old 09-22-2009, 02:37 PM   #16
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Did you ever try softening the rear bar?
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Old 09-22-2009, 02:46 PM   #17
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I've not, though mostly due to being lazy, it's easier to swap springs! (provided you have some lying around, which I did) Also the bar setting isn't going to make a huge change in wheel rate, maybe 50 lbs? I'm going to worry about the rear bar when I'm closer to having everything else dialed in. Right now, if anything the rear springs are too soft, so having a bit of extra bar is good.
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Old 09-26-2009, 11:22 AM   #18
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Originally Posted by murph1379 View Post
I use the H&R non-M bars, so 27/21, full stiff all around.

I think the H&R M bar fits up front, which is 30mm, but not the rear one.

RD were the bars Basham was using, 30/25.

I think the Hotchkis bars are 30/25 also, and will fit non-M.

I like the H&R's for the teflon coating on the bushings, which make them nice and quiet.
Two things...

The Hotchkis bars are hollow which makes them pretty different from the other manufacturers IIRC. Also, I've had the Hotchkis bars on my car now for 10 months and they are still really quiet.
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Old 09-26-2009, 04:17 PM   #19
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To me 400F/650R sounds like a BIG difference in the rate. I'm not an expert though.

I have 550F/700R as per GC
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Old 10-07-2009, 12:39 AM   #20
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For those interested, I ended up going with 550/650 and am very happy with the setup! I'm probably done going to the track for this season, but if I feel that I less understeer next season, I'll just swap out the rear 650 for a 700 or 750.

ASTs are incredible. I've had Konis, Bilsteins, and KWs now on various E46/E36s that I've had and these are by far the best!!!
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