Strut question for 74 super

[Eatoniashoprat]

Thanks Clive this has really helped a lot.

If I input my weight into the calculations this is what I get:

100lb/in front
CPM 85

170lb/in rear wheel rate (23.5mm)
CPM 95

~10% difference.

If I go higher rate in the front I'd have to go coilovers or even bigger TB otherwise the CPM's become very close.

Have a good weekend! Have a cold one for the germanlook forum (I may have several)

Mike

[Eatoniashoprat]

I think I just found an error on the Eibach springs worksheet page.

In step 2 it shows WR = C/MR^2 (assuming no ACF)

But I'm pretty sure it should be WR = C*MR^2

Otherwise your wheel rates would be higher than your spring rates since the motion ration is less than 1.

'Tip2' on that page also contradicts 'step 2'.

[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.

[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%