FCM E46 M3 Ride Harmonizer suspension spreadsheet - aka Flatride !!!

[Obioban]

Question, whom here has messed with the spring rates on the Eibach coil overs? Were there any limitations?

Thanks

I had them on the wagon, but didn’t bother— the shocks just felt like junk. Replaced them with Koni yellows and was much happier.

[Chas3n]

Question, whom here has messed with the spring rates on the Eibach coil overs? Were there any limitations?

Thanks

[Gearhead55]

Hey guys. I was active on the M3forum.net before it died under the same username, just signed up here.

I have been running a flat ride set up with MCS 1wnr dampers on the street for a while now and just did my first track day with the set up last Sunday. I had been very happy with the set up on the street and in the canyons. Even with track-car-stiff springs rates the ride was reasonable on the streets. Now I am again impressed after tracking it. The car had tons of grip, minimal body roll, and it managed track surface imperfections and undulations much better than my previous Bilstein PSS set up. The predictability gave me much more confidence and allowed me to put down very consistent times and beat my PB even though it had been more than a year since my last track day. The only "downside" to the set up is the front end dive under braking, which I honestly don't mind that much because it allows for deliberate weight transfer. If it was a dedicated track car I might consider a stiffer front spring.

As it sits I am running 448/840 swift springs with a 30mm whiteline front bar on the middle setting, stock rear bar. I think that puts me at 1.05 R/F and 77.8% FRC. I will be switching to the softer front bar setting before my next track day, as I wouldn't mind it being biased more towards oversteer. If that isn't enough I may convert the rear to a true-coilover and pick a rate for a higher R/F.

[e46m3_06]

Ahh darn I realize now he actually put his measured motion ratio in the spreadsheet at the bottom. He's using .938F and .7R. I suppose the only difference could the angle of the struts/shocks but that's not a large factor considering a degree or two.It's hard to see how people get such different measurements though.

[maupineda]

the factor is .88 F and .45 R. this is derived from a motion ratio of .94F and 0.67R

[e46m3_06]

I don't seem to be running out of bump travel per the tie wraps but it's close.
I worked backwards through the spreadsheet and it looks like when i set the weight distr. to 50/50 and enter the same spring rates front and rear I get a wheel rate to spring rate ratio of .88 front and .49 rear. From what I've read the rear's are a bit high but the front is really low. Some sites say .98 F and .44 R. I used 3415 pound car. i coulda made a mistake but the rates are close enough that I'm assuming I didn't.

[e46m3_06]

Hmm it seems with a 650 spring and GC Konis and a lightened car that it wouldn't have much chance of bottoming out. Also it doesn't seem like the oversteer is such an instantaneous event like a bump stop collision. But I can try the ziptie test this weekend to verify. The GC dampers only have a rebound adjustment and I haven't really experienced much change with adjustments. I don't know what spring rate the dampers were built to accommodate since I'm not the original builder and GC can't seem to provide the data with the info I can supply. That could be an issue as well so I'm starting to think about changing dampers.

[Obioban]

Well I really like the idea of this spreadsheet but its not mapping to what I feel on the track. My car with driver is about 3100(fully stripped with roll cage). I'm using 650/650 springs, rear in stock location, and GC front ARB with no rear bar at all. According to this spreadsheet I should be understeering like mad. I've been considering reducing the rear springs cause I get a bit of oversteer after a while although its fairly neutral at the start of the day and session. My FRC should be 86.8% which would be way too much understeer. I'm still way faster than a street car but looking to get a better as some cars in my class seem to be out cornering me. Any ideas?

Perhaps you’re running out of bump travel, and your rear bump stops are engaging first, ramping up the rear rate and causing oversteer? Could be too little travel, could be too much rebound causing the rear to jack down.

[e46m3_06]

Well I really like the idea of this spreadsheet but its not mapping to what I feel on the track. My car with driver is about 3100(fully stripped with roll cage). I'm using 650/650 springs, rear in stock location, and GC front ARB with no rear bar at all. According to this spreadsheet I should be understeering like mad. I've been considering reducing the rear springs cause I get a bit of oversteer after a while although its fairly neutral at the start of the day and session. My FRC should be 86.8% which would be way too much understeer. I'm still way faster than a street car but looking to get a better as some cars in my class seem to be out cornering me. Any ideas?

[Obioban]

I checked off #1 on this list. Which was easily the best weight mod you could do on the car.

On the old forum we had a weight / weight reduction thread. Any chance you have approximate weight savings associated with this list? Might be worth starting a separate thread on this again.

1) ~45 lbs
2) 59 lbs
3) ~50 lbs
4) ~45-50 lbs... mostly wire

[Johnvu]

I have had experience with two set ups: 8k front and 14k rear, oem front sway and no rear sway Ratio: 1.01, and FRC: 70ish. I took the car to the track on this setup and it felt pretty good, but there was a good amount of body roll.

I just recently changed out toa tuner front sway bar at full stiff and oem rear sway. Bounce Ratio: 1.01 and FRC 75.4 (with the sway bars) . I did a shakedown run with some friends on some fun country roads and I have to say that there was a pretty huge difference. The car feels way more responsive/ sharper on turn in, which took some getting used to. The car definitely felt like it was more predictable as well.

All in all, I really love the flat ride calculator. The ride is still pretty damn comfortable and it doesn't bounce around like the some other cars I've been in. My only regret on my current set up is not using this calculator before ordering my coilovers.

When I upgrade my fortune's from 500s to 510s, I am going to up the rear springs rates. With that being said, Is there a good target for the bounce ratio? 5%, 10%, or 15?

[duracellttu]

My car is ~300# lighter than stock. ~200# of that comes from 4 mods:
1) cf roof
2) fixed back seats (cobra nogaros— still leather/heated and allow back seat access)
3) lithium ion battery/battery cable delete
4) light weight stereo/stock stereo harness delete

The other 100# is the result of many small 1-5 lb changes.

I could easily knock another 50# off with a lighter than stock muffler and back seat delete, but ruining the civility/practicality isn’t worth it to me.

I checked off #1 on this list. Which was easily the best weight mod you could do on the car.

On the old forum we had a weight / weight reduction thread. Any chance you have approximate weight savings associated with this list? Might be worth starting a separate thread on this again.

[Will]

My car is ~300# lighter than stock. ~200# of that comes from 4 mods:
1) cf roof
2) fixed back seats (cobra nogaros— still leather/heated and allow back seat access)
3) lithium ion battery/battery cable delete
4) light weight stereo/stock stereo harness delete

The other 100# is the result of many small 1-5 lb changes.

I could easily knock another 50# off with a lighter than stock muffler and back seat delete, but ruining the civility/practicality isn’t worth it to me.

What was the contribution of #4 (the light weight stereo/stock stereo harness delete)? I know you had a thread on the old m3f, but I forgot the specific number(s). Thanks.

[Obioban]

Wow, yeah that is gutted! Looks great! Now I don't feel so bad hahaha. I basically have a full stock interior. Removing the sunroof and going with a slicktop CF roof definitely helped though.

My car is ~300# lighter than stock. ~200# of that comes from 4 mods:
1) cf roof
2) fixed back seats (cobra nogaros— still leather/heated and allow back seat access)
3) lithium ion battery/battery cable delete
4) light weight stereo/stock stereo harness delete

The other 100# is the result of many small 1-5 lb changes.

I could easily knock another 50# off with a lighter than stock muffler and back seat delete, but ruining the civility/practicality isn’t worth it to me.

[duracellttu]

Oh, I don’t currently have the GC front bar. I am running the Turner bar on full stiff with a stock rear bar. I had the same thinking has Ian and I’m happy to hear that if I decide I want to raise my FRC after an upcoming event that my plan will play out just the way I thought it would. The car feels pretty damn great at present but I’m curious what it’ll be like on the track.

As as far as weight reduction goes, you shouldn’t feel bad. My cars diet has been substantial since it’s a track car. The only things behind my buckets are a half cage, rear glass and my suspension reservoirs. I deleted the sunroof (AJ Hartman panel, the only true cf option) and plenty of other things. Hell, I even had the parcel shelf chopped out when the cage went in to help offset the jungle gym a touch. Saved like 13-15lbs, I forget which.

This photo was taken just after picking it up from the fabricators

Wow, yeah that is gutted! Looks great! Now I don't feel so bad hahaha. I basically have a full stock interior. Removing the sunroof and going with a slicktop CF roof definitely helped though.