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Suspension tuning?

The thread on skid pad performance triggered a more general question. For many of us, our teeners are a collection of parts from other cars, other fanatics. How do I know my suspension parts are optimal, or at the very least compatible?

For example, I'm running 200lb rear springs (recommended by an "expert" to hold up a 3.2 / 901 combo), the torsion bars on the front are whatever is stock on the Carrera front suspension I snagged, "original" front sway bar (19mm) 'cause it's adjustable, and Bilstein sports all around.

Any tips on what to look out for when the beast hits the track for its first D/E next week? Any tips on potential tweaks?
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Old 03-06-2002, 07:03 AM
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The original front sway bar is not adjustable. If you have an adjustable one, or if you have a 19mm bar, it is aftermarket. Probably Weltmeister, they're one of the most popular brands, especially for the adjustable bars.

200# springs are pretty heavy. I wish I knew what diameter the stock 3.2 Carrera torsion bars were... I'm guessing (wild guess) that you'll be close to oversteering on the balance. With all the power of the 3.2, and stiff rear springs, I recommend being very careful with the throttle, particularly at first. If you can find an autoX befoore your DE event, I suggest you go run that to see what the balance of the car is and how it reacts.

--DD
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Old 03-06-2002, 08:38 AM
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200 lb springs?
I would expect to see the back end trying to pass the front
This is just a WAG and you're going to have to find out for your self what is going on here. The 911 t-bars are the unknown here.
I *think* they are 21 mm, but am not sure. The balance may be better than I suppose.

Pick a nice safe corner, get a hole in traffic and go for it.

If your front sway bar is adjustable, I would set it to a very stiff position in hopes of dialing in a bit of understeer (or dailing out some oversteer).

At some point, it might be advisable to put some 140-160 lb springs at the back. The stock 6er springs were somewhere in the 100 lb range. Your 3.2L is maybe 60-80 lbs heavier than the 2.0L, 6.
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Old 03-06-2002, 08:44 AM
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That set up really should not be too bad for a high speed DE event. I'm running 22mm front bars with #200, or #250 rear spring and a light weight 4 cylinder motor over the back.....
We have stripped the rear of all unnecessary weight including rear fiber glass bumper, no muffler, no muffler shielding, etc.....

The car is very neutral, very forgiving... it did help to go from the 19mm bar to the 23mm, but it will work well still with the 19. Play with the front roll bar.... I'm guessing you will need to go to a stiff setting......

It all depends upon the track, and mix of low-speed versus high-speed corners.

have fun.
brant
Old 03-06-2002, 10:34 AM
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Would it be a good idea to have an LSD w/ those stiff springs in the back...to maybe give it some more traction and/or remove the rear sway bar? I'm asking because I have no clue (my setups is totally different for my 2.0)...any suggestions.
Thanks,
Nathan
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Old 03-06-2002, 10:58 AM
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Yee-ha, thanks guys, glad I asked this question! I have enough opportunities to embarrass myself to be tryin "auto ballet" in front of all those 996's.

Brant, 200 #'ers w/ 22mm torsions sounds mega-stiff; you got any pot-holes out where you live???

So Dave, what's *your* opinion on rear spring rate? JP sez 140-160, you guys list a 140 and a 165 progressive. Any recommendations? I'm looking for a street / DE compromise that will keep a 3.2 off the lawn at Lime Rock. Stock 911 torsion bars are 19mm, tho I have no idea what that translates to in terms of spring rate. My 19mm front sway bar is adjustable (4 settings), when I said "original" I meant "was on the car when I bought it".

Is the goal to balance spring rates, front to rear? Guess I gotta go buy me a "Suspension Tuning for Idiots" book; any recommendations?
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Old 03-06-2002, 11:04 AM
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The LSD and rear bar go hand in hand..... For DE the consensus is to disconnect the rear bar if you do not have some type of rear diff....

The differential comes into play some where around 140-150 hp.. On a big six I would want one. On a stock 4 its not necessary.. I'm running a locked rear differential (read cheapo) on my track only car and noticed very minimal improvements....

This is a track only car with a cage.... plenty chassis stiffening.... additionally were running at 2141 lbs, so its quite heavy as race cars go. I think the heavy spring rates are necessary with the stiff chassis and high weight.

Definitely try to balance your front and rear rates..... 914s are very balanced cars... my car was miserable on the street (too stiff) but even with rough tracks there are times when the #200 rear springs aren inadequate...... thus the #250s come into use at times.........

It all becomes very miniscule at the limit..... sounds like your biased towards street so keep it liveable..... You may want to corner balance your car and check your rear weight with that big lump-o-six and all of the associated oil lines and tank.... I'll stand by my estimate that your #200 lb springs are not too far off.... Like JP said, find out how big your fronts are... if there from a late model car they are likely 20 - 21 mm already...

brant
Old 03-06-2002, 11:38 AM
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The goal isn't necessarily to balance the spring rates. The goal is to balance the way the car handles--you want to be able to get it to oversteer or understeer when you want it to. The roll stiffness is a major contributor--and the roll stiffness is affected not only by the torsion bars and the springs, but also by the sway bars if any... Ugh.

I like the way my car handles with 140# springs in the back, stock torsion bars up front, and the 19mm adjustable sway bar. Some people have told me that the car will be great that way, some that it will oversteer a lot that way. I like it, though I think I need to adjust the front bar a bit stiffer...

If I'm correct, the stock torsion bars are on the order of 17mm. Torsion bar spring rate goes up with the fourth power of diameter, so [digs out calculator] you have about 1.6x stock rate up front. You've got about 1.4x the rate of the 140s in the back... Hmmm... It might actually work out pretty well!

You're gonna have to try it and see. That's the way suspension mods work a lot of the time. If you're lucky, someone else has done the same thing before and can give you an idea of how it works.

--DD
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Old 03-06-2002, 01:53 PM
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I can't add much to what the other guys said on the spring rate topic. You do need to eventually pin-down what front t-bars you've got in the car and decide if they're 'optimal' for you.

If you plan to do serious track driving in the car, you may wish to keep the 200 rears and go with a larger front swaybar and/or t-bars if the car seems to oversteer a lot.

Also don't forget that you have some leeway in fine tuning via tire pressures. If it oversteers a bit, try decreasing the rear pressure or increasing the front a pound or two.

Lastly, correctly setting up the ride height, alignment and corner balance is crucial. Just having the right parts does not do the trick: the whole 'system' has to be dialed-in.
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Old 03-06-2002, 08:25 PM
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Sleepdoc,

The setup I have is somewhat similar in my 3.2. I have 180 rear springs and 23mm bars upfront with new bushings all the way around. Also, I have a 22 mm sway bar that is non-adj and is the type that goes under the master cyclinder.

The car is very neutral in the turns. Of course I can always make a mistake w/the throttle and have the rear end come around.
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Old 03-07-2002, 03:15 AM
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Guys, thanks for all the great advice and experience. Looks like I'm gonna just have to follow JP's advice and calibrate the seat of my pants, so to speak. I'm in the newbie run group, so I'll have an instructor to help keep me in line.

I do indeed have 19 mm torsions up front along with the 19mm anti-roll bar, and the car has been lowered, cornered, and aligned by folks who know what they're doing. I'll crank the a-roll bar to its stiffer setting and see what happens.

One more question - do tires (or car) give you any warning when they are about to break loose, or is your first clue the change of view? My tires are treaded types (Kumho ecsta 712), not slicks.
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Old 03-07-2002, 05:36 AM
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John -

Are you running both days up at Lime Rock? I didn't register for this DE (it would help if I put all of the parts together), but I was planning on being there to provide some moral support to some friends.

Unfortunately, I just found out that I can't be there on Friday. However, I will definitely be there on Saturday. If you are going to be there, I will look for the guy with the yellow 6.

Paul
Old 03-07-2002, 05:49 AM
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Sled wrote:

>One more question - do tires (or car) give you any warning >when they are about to break loose, or is your first clue the >change of view? My tires are treaded types (Kumho ecsta 712), >not slicks.

I can only speak from my own experience here.
I *suppose* that much depends on suspension/ tire set-up.
In my own case, the answer is no warning. One does, with some practice, learn to feel when the g- loads have build to the point
of slippage. IMO, the key here is to know (or learn) what is going to happen and how to correct for it.

I threw in another 70-80 hp (2.4L to 2.7L) into the back end of my car and ,with no futher mods to, went to play AX.
It had been "skitish" with the hard street rubber, but now was nearly undrivable. It was/is set up "loose" (great NASCAR term),
and when the back end departed, there was no catching it.
Lurid tank slappers, followed by a spin (that takes up a lot of space !!). I sez to myself:"Well...this sux. Now what, dummy".

More grip would seem like a good solution, but more at the rear than at the front. Kumho Victor Racers in 225 X50 in the rear and 205 X 50 at the front. Them butt ugly flares just sorta' came with the package. The nice thing here is that these tires are catchable.
I haven't spun it since I put them on, but we're not always going in the direction the car is pointing It is predictable, however.

Looking at the wear pattern of the tires, I'm only using 2/3 of the tread. Now I need more negative camber. I'm working on that.
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Old 03-07-2002, 08:20 AM
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Paul, assuming I don't break anything, or run out of changes of underwear, I'll be there both days. Surprisingly, there have been multiple yellow teeners at LRP DE events, my car number is #914, strangely enough...
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Old 03-07-2002, 09:03 AM
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