(400 x1.1) / 0.45 = 977.xxxx
/.randy
Agreed, my new motion ratio takes the 400lbs/in spring and makes the wheel rate 440lbs/in. My previous springs was a 750lb/in bee-hive spring which resulted in a 338lb/in wheel rate with a 600lb/in spring in the front.
I've finished three weekends and six races with them, and have been very satisfied. I'm in the get in the car and drive it stage at this point, and really need to fill in my note book with some testing. As I've just finished in the top 50% in points in STU and three races at three seperate majors weekends, I'm qualified for the Runoffs at Laguna Seca.
Tony and Joe are fab and set up wizzards, I'm very satisfied with their work on my car. I also had some cage work and replaced the pedal box with a Tilton firewall mount, which resulted in much better modulation and less flat spots (although I've still managed to flat spot, it was much harder to do and easier to get out of it). As a side benefit, the clutch is much quicker so I'm on the gas more.
Last edited by Z3racer701; 05-19-2014 at 04:39 PM.
I think he is saying it would take a 977# spring to replicate a 440# wheel rate which would be close but not quite there.
Now in E92 M3 ZCP -- Absolute beast
My observation was in part based on fact I've heard numbers ranging from .42 to .45 conversion rates which are premised on a formula of a factor squared. As such, it doesn't take much to move the needle a little here or there but the point is on point. I guess I'm going to re-read that STU build thread for the reinforcement to allow for the coilover since our units are already threaded.
Now in E92 M3 ZCP -- Absolute beast
The wheel rate quoted is about right for using the stock shock mount point on the control arm. I would assume the top mount is tied into the cage.
/.randy
My orginal motive when replying to this thread was to post this link that I'd found useful to why the rear wheel rate to spring rate would be ~0.45:
http://www.e30m3project.com/e30m3per.../eff_rate2.htm
Now that's the curious thing, because I had Tony install the coil-overs, and he could have welded in any sort of reinforcement, like he did for the firewall mount tilton pedals, but he didn't. He used the rectangular clevis to mount the top heim joint and bolted through the two stock bolt holes. It doesn't even cover all of the round opening in the body, only about the outer 2/3's of it. I'm using 2.25" spring and they rub the rubberized body schultz. It's a tight fit but seems to work well.
The rear down tubes are about 2-3 inches away and mount on the panel at the top of the trunk. I also had Tony add a cross bar from the passengers side of the hoop to the bottom of the drivers side down tube. There are pictures of each added bar.
Last edited by Z3racer701; 05-19-2014 at 10:21 PM.
I'd keep on an eye on your shock towers then. Most people who converted to true rear coilovers tend to implement some reinforcement to prevent mushrooming. I kinda wondered how you did that and I didn't remember it. That cross bar must be his solution to the issue.
Last edited by z3papa; 05-19-2014 at 10:31 PM.
Now in E92 M3 ZCP -- Absolute beast
Spent the day in the garage changing springs, cleaning the camber plates and re adjusting the end links on the sway bar. I have noticed the following before but now it has gotten into my brain.
I have my rear strut mounts mounted the way most people said to do it, with the bolts facing down. From the factory the mount was inside the car and the bolts were facing up. Seemed like a good idea at the time as it made it very easy to install and remove the shocks without having to struggle inside the car. Now as I am adjusting my rear ride height I again notice that at full droop there is no pre load on the springs. Now I could turn the adjusters and add pre load but then my ride height gets too high. As it is now I am at 22 3/4 when measured per the manual, only 1/2 below factory setting of 23.15 inches. So it seems to me I am wasting about 1/2 inch or more of my shock stroke and if I put the mounts inside the car I would benefit from more shock control. As it is now I leave my rear shock full soft or I get loose, this method of mounting the rear shock mounts may be a cause.
14045302260_eece6f4f88_b.jpg
Last edited by jbrannon7; 05-20-2014 at 03:14 PM.
I think your rear shocks are worn and are sagging/coming down further than if they were fresh. I know since mine were just refreshed, and in order to bolt them up, I need to put pre-load on the springs with a jack and that is at 22 1/4" with a 500# rear spring. Before, I could physically compress or decompress the shock with force to get it to bolt up at any number of heights.
Now in E92 M3 ZCP -- Absolute beast
What rear spring are you running? Length? Mine are 650 lb 5.5", so they are very short. If I ran longer, softer springs then I would have some pre load. I don't see how shock wear could make the shocks droop further than when they were new, and I did notice this when they were new, just never thought a lot about it. According to the AST tech, there are no internal bump stops.
Last edited by jbrannon7; 05-20-2014 at 05:39 PM.
I'm running 5.5" 600# rear springs but have my shock mounted the same way you have it mounted.
Last edited by z3papa; 05-20-2014 at 10:24 PM.
Now in E92 M3 ZCP -- Absolute beast
Do yours look like this a full droop?
14233844071_6991fa5def_b.jpg
Last edited by jbrannon7; 05-21-2014 at 09:12 AM.
Bump.
Christmas present time...what springs should we be putting in the rear these days? Did you guys find a magic combination?
600? 700?
Maybe santa will bring me some.
Want to post some info as Scott and I have been discussing this for a little while.
I'm running TC Kline DAs with their recommended spring rates - 400F and 500R. I have the rear shocks turned all the way up to keep the back end from sagging excessively while turning or accelerating.
I'm going with Ground Control SAs this time around. Their recommended rates are 440F and 660R. Having driven this setup I can confirm it is way, way better.
I just ordered 600# springs for the rear of the TCK car to match the 400# fronts. I'll report back once they're installed.
I ended the season with 500F/700R no rear bar and have a multitude of other spring pairs with rates including 600F, 650R and 750R, if I am correct. On top of that, I have access to many other spring rate pairs from a shared library. I will be in a position to sell the leftovers once my car sells or the AST coil over sells since I'd like to give the buyer their choice of rates.
Now in E92 M3 ZCP -- Absolute beast
I'm running 350 rear 750 front with rear coilovers, with a rear bar
Similar discussion about spring / wheel rates here
http://www.bimmerforums.com/forum/sh...of-development
So to those running 600-700# springs, for those of us running 500# or less, are 600-700 extremely jarring/harsh/bad on normal roads or do they seem OK for weekend drives and back roads while making the car handle more predictably at autocross/track events?
Sounds like 600+ is the way to go and the only thing stopping me is not knowing if they make the car too hash to enjoy on the street.
While the 100# increments sound like large changes, these effective rates show the jumps aren't really that much. If that's the case, maybe there isn't much to worry about by upgrading to 600-700# springs.
I drove Asim's car with 440/660 springs and didn't find it too jarring. FWIW I'm running 550/672 on my M3 (AST 4100) and it's not jarring at all. That said, the ASTs are miles better than any Koni based suspension I've run.
Scott, I think some of it depends on your shocks. I am running 750 rear with AST monotubes and the rear is very compliant, in fact I think the rear springs are not firm enough for the shocks which I now have set full soft. If I go any firmer on the rear shock rebound setting the car gets very loose. No rear sway bar and new trailing arm bushings. I have 525 on the front and that can be jarring.
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