Strut question for 74 super

[Eatoniashoprat]

Originally Posted by Humble

Sorry for the delay, my comp at home ate it's hard drive a couple weeks ago :P

I run the 200# springs up front because I had tried the 300# setup which was far too stiff. Wally runs 300# up front and seems to like it just fine. My street bug is 2280 w/ full tank and driver (and stereo ), and running anything less than 200# put the front on the bump stops in hard corners or more often if I took a passenger. It was so bad that even with 120# (a good bit stiffer than the normal maxx springs) I murdered the bump stops on both sides and blew the struts on both sides in the front. This was at the maximum ride height the maxx struts offered.

I haven't started adjusting the rear spring rates yet but I have a pile of springs to sort through. For coilovers I was looking at 500#-600# on the street bug, but I need to get a cup brace in the car before I can make the switch. TB wise I started with 23.5mm bars then 25.5mm bars but with the heavy alu case and sub box in the back I think I need a bit more. I've got single adjustable qa1's waiting to go on and that will make finding spring rates a bit easier.

I tend to go by feel and work my way back to find the hard numbers. I also push my bug harder daily than most, so I tune it to that level. What I consider soft, others might find jarring or vise versa. Admittedly, the feel I'm going for is the E46 M3 because I found it to be one of the best compromises between track and street.

Thanks Humble, that's good to know. I'm trying to figure it out close as I can since I don't have other springs or torsion bars to play with. Very few Porches around here to steal TB's from!

I just know right now the 71.5# max springs are waay too soft, loaded up with gear for a weekend, with no one in the car I can easily move the front bumper down an inch and hit the bump stops

Do you think its necessary to run the helper springs up front with the 200# springs? Also, have you test fitted the QA1 coil overs with the 2.5" springs in the rear to see if the springs physically fit in the trailing arm?

[Humble]

I'd suggest starting with the 200# springs in front and go from there. They might feel a little stiff without gear or a passenger but won't bottom out when you do.

Is it a helper or tender spring? A helper spring is usually very light (around 10#), easily compresses, and is only used to keep the main spring seated at full droop. A tender spring is a fair bit heavier and used to make a dual rate spring basically. A tender spring might be 50-70# and easily compress during high load but would smooth out the jarring ride of the main spring around town.

Now with my setup I put coil over sleeves on the maxx strut body and with a 10" spring I found I need a helper spring to keep the spring seated. Using a 10" spring also gave me a fair bit of ride height adjustment.

I haven't had a chance to fit the qa1 coilovers on the rear but it's a fairly simple affair. Just drill a 2nd 1/2" mounting hole higher in the cup, and locate the lower shock mount with spacers. For the top, drill out the upper mount to 1/2" (kafer brace too) and put the shock in place. I think sandeep but up some pics of the lower mounts for the qa1's.

[Eatoniashoprat]

Originally Posted by Humble

Is it a helper or tender spring? A helper spring is usually very light (around 10#), easily compresses, and is only used to keep the main spring seated at full droop. A tender spring is a fair bit heavier and used to make a dual rate spring basically. A tender spring might be 50-70# and easily compress during high load but would smooth out the jarring ride of the main spring around town.

I didn't realize the difference in terminology I thought they were called the same thing, my bad.

[Eatoniashoprat]

FYI, I did some calculations for something closer to Humbles setup (stiffer) to see what it looked like, this is what I found. Also, I made a little spreadsheet that I could email if someone wanted to check it out.

Front:
175lbs/in
CPM = 113

Rear:
Stock TB combined with 200lbs/in coilovers
CPM = 126

F/R CPM difference = 10.5%

[Humble]

Here's my street car setup w/ full tank and driver:

LF 488 RF 437
LR 691 RR 633

Front: 925lbs. 41.1%
Left: 1179lbs. 52.4%
Cross: 1128lbs. 50.2%

Total: 2249lbs.

I run the 200# up front and i'm not sure what the CPM would be but I'd like to match it and add 10% or so CPM on the rear. You might be in the same territory with the subie swap.

[Eatoniashoprat]

I think that's very close to my weight, I might be 50-60 pounds heavier but that's about it.

I went autocrossing for the first time last night and it was a blast, managed to turn some decent times but the front was on the bump stops the whole time and it understeered pretty bad unless you already had the back end coming around. It was a very tight course

For 200# here are the numbers from my spreadsheet. For the coil over with the torsion bar I'm just adding the wheel rates, hope that's the right way to do it. I'd take them with a big grain of salt but here they are anyway.

Front
200lbs/inch
121 CPM

Rear
stock TB
250 lb/inch coilover
134 CPM

10% difference

Rear w/944 TB
250 lbs/inch coil over
139 CPM

13.1% difference

[evilC]

Mike, Do you know what your damper rates are? Are you running a rear anti-roll bar? You might find that stiffer dampers plus a rear ar bar might dial out your initial understeer. Personally, I intend to set mine up as a soft(ish - 100lb/in front 944N/A rear) with stiff damping as most of the roads around here (that are used for Road rallys) are fairly bumpy and I don't like the thought of the front skipping across the bumps particularly under initial braking.

In all of this of course lies the variation of conditions/use/driving styles that will give wildly different results.

Clive