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

[The M]

In the rear...
Your spring length will depend what adapters and ride height adjusters you are using since they are different thicknesses. The stock spring pads are 5mm (0.20") each.

Stock springs are 8.75" long and compress just under 3 inches statically, at which point it moves into the 550lb/in region (progressive rate). So the total height of the stock spring + pads is: 8.75 + 0.20" + 0.20" = 9.15".

If you are running 550lb straight rate springs in back, they will compress just under 2.0 inches statically, so a 1.0 inch difference. At the wheel that translates to about a 1.4 inch difference. So if you wanted to maintain stock ride height, you would want a spring + adjuster height of 9.15" - 1.0" = 8.15". So you'll need to measure your spring adjuster minimum height and see what it is. I'm guessing it's probably .75" ish, meaning the longest spring you can run is a 8.15 - .75 = 7.4" or a 7" spring. If you want to lower it, then the 6" that you have sounds right. How low is it and what is your height adjuster set to?


In the front...
Are those 60mm ID Swift springs? They only have 4.1 inches of usable stroke and 4.5" max stroke. At 336lb/in, you are already using 2.5" just to hold up the car, meaning you only have 1.6" of travel before it starts to bind. Depending on your shock setup (bump travel avail) you might need to consider stiffer springs, longer springs (8 or 9 inch), and/or barrel springs.


At least, I think those numbers are right. I am going through this right now.

My rear has Ground Control weight jacks extended nearly all the way up but with the 6" springs it's still too low for me. Height was perfect with my previous track only setup of 900lb 6" springs but the 550 street springs just compress too much.

And yes, the fronts are 60mm Swifts. I guess I wasn't thinking clearly enough about how much the softer springs would compress, leaving barely enough spring remaining for dynamic travel.

The car height looks nice with the short springs but I'll get new ones to raise it to be more usable.

imageimage

[cobra]

IIRC I'm also 6", but I went with Eibach's "extreme travel" line of springs to have sufficient travel. They're basically barrel springs, so you can more compression without binding.
https://eibach.com/us/i-83-eibach-xt...me-travel.html
^ not my actual spring, just a link to a product in the line

At full compression, if I didn't have a bump stop (metal on metal), I'd be 2mm more compressed than the springs allow for. But, I do run a bump stop, and it should never get compressed to less than 2mm, so I should be in range at all times. There has been zero evidence of any coil bind, so reality seems to back up the theory.

All that said, I'm going through that because I want the spring above the tire, because I like to run ET35 tires on track. If you're an ET25 person, just run a longer spring. :P

Hmm... even with the XT springs, a 6" 350lb version only has 4.1" of travel. How much bump travel do you have and what rate are you running?

Also, random question.... anyone know what the maximum wheel width and offset is allowed to fit a 2.25" spring next to the tire/wheel?

[The M]

Thanks for all the responses guys. It's great to not have to reinvent the wheel so I can hopefully order the right length this time.

[Obioban]

Hmm, seems to be available only in 2.5" diameter. Bah.

They work fine on 65mm perches, as well. I switched over to Ohlins perches for just that reason.

[maupineda]

Perches and adapters are easy and cheap to source.

[elbert]

IIRC I'm also 6", but I went with Eibach's "extreme travel" line of springs to have sufficient travel. They're basically barrel springs, so you can more compression without binding.
https://eibach.com/us/i-83-eibach-xt...me-travel.html
^ not my actual spring, just a link to a product in the line

Hmm, seems to be available only in 2.5" diameter. Bah.

[Obioban]

Just curious; what spring lengths do you have? I'm asking because I have 336lb 6" Swifts up front and had to run them so far up the strut threads that I'm now getting spring bind.

Also, I have 550lb 6" in the rear (swapped from my old front track setup) and it's too low I think. I need to order new ones and want to get your info first...

IIRC I'm also 6", but I went with Eibach's "extreme travel" line of springs to have sufficient travel. They're basically barrel springs, so you can more compression without binding.
https://eibach.com/us/i-83-eibach-xt...me-travel.html
^ not my actual spring, just a link to a product in the line

At full compression, if I didn't have a bump stop (metal on metal), I'd be 2mm more compressed than the springs allow for. But, I do run a bump stop, and it should never get compressed to less than 2mm, so I should be in range at all times. There has been zero evidence of any coil bind, so reality seems to back up the theory.

All that said, I'm going through that because I want the spring above the tire, because I like to run ET35 tires on track. If you're an ET25 person, just run a longer spring. :P

[cobra]

Just curious; what spring lengths do you have? I'm asking because I have 336lb 6" Swifts up front and had to run them so far up the strut threads that I'm now getting spring bind.

Also, I have 550lb 6" in the rear (swapped from my old front track setup) and it's too low I think. I need to order new ones and want to get your info first...

In the rear...
Your spring length will depend what adapters and ride height adjusters you are using since they are different thicknesses. The stock spring pads are 5mm (0.20") each.

Stock springs are 8.75" long and compress just under 3 inches statically, at which point it moves into the 550lb/in region (progressive rate). So the total height of the stock spring + pads is: 8.75 + 0.20" + 0.20" = 9.15".

If you are running 550lb straight rate springs in back, they will compress just under 2.0 inches statically, so a 1.0 inch difference. At the wheel that translates to about a 1.4 inch difference. So if you wanted to maintain stock ride height, you would want a spring + adjuster height of 9.15" - 1.0" = 8.15". So you'll need to measure your spring adjuster minimum height and see what it is. I'm guessing it's probably .75" ish, meaning the longest spring you can run is a 8.15 - .75 = 7.4" or a 7" spring. If you want to lower it, then the 6" that you have sounds right. How low is it and what is your height adjuster set to?


In the front...
Are those 60mm ID Swift springs? They only have 4.1 inches of usable stroke and 4.5" max stroke. At 336lb/in, you are already using 2.5" just to hold up the car, meaning you only have 1.6" of travel before it starts to bind. Depending on your shock setup (bump travel avail) you might need to consider stiffer springs, longer springs (8 or 9 inch), and/or barrel springs.


At least, I think those numbers are right. I am going through this right now.

[duracellttu]

Just curious; what spring lengths do you have? I'm asking because I have 336lb 6" Swifts up front and had to run them so far up the strut threads that I'm now getting spring bind.

Also, I have 550lb 6" in the rear (swapped from my old front track setup) and it's too low I think. I need to order new ones and want to get your info first...

I’m using 7” Swift 336# springs in the front. If you have adjustable coil overs you might be able to get to a decent ride height, but getting a longer spring will help out if you run out of adjustment travel.

[The M]

Neutral FRC is ~75. Those a look a bit oversteer biased to me.

I ended up in the middle of you’re range— ~362 up front, ~675 in the rear.

Just curious; what spring lengths do you have? I'm asking because I have 336lb 6" Swifts up front and had to run them so far up the strut threads that I'm now getting spring bind.

Also, I have 550lb 6" in the rear (swapped from my old front track setup) and it's too low I think. I need to order new ones and want to get your info first...

[r4dr]

If a larger tire were to increase front grip (I don't think so, but for the sake of discussion), that would give you more oversteer, so you'd want a higher FRC-- not lower. Higher FRC is more underdersteer biased, lower FRC is more oversteer biased.

I run square on track, staggered on the street. It's neutral on track and... honestly, no idea on the street. PS4Ss are grippy enough that I don't find myself exceeding them on the street.

Oh yeah, had my numbers backwards. Makes sense.

[Obioban]

Turner front sway would be at the medium setting in the above scenario.

Raising the bounce ratio frequency would settle the car sooner? What is a little higher?


Thanks,

Jesse

The bounce ratio basically determines the speed at while the front and rear of the car settle as the same time.

This section of the spreadsheet lets you calculate at what speed the front and rear settle at the same time:



Inputs are in blue.

So, with an 80mph target speed (front and rear settling at the same time, and a 2.2hz rear, you'd need a 1.14 bounce frequency ratio-- which it's showing would come with a 1.93hz front setup, in that example.

So, choose your target speed, and ratio accordingly.

But, 1.01 bounce frequency with 2.20 rear settles evenly front and rear at 350mph

[D-O]

Turner front sway would be at the medium setting in the above scenario.

Raising the bounce ratio frequency would settle the car sooner? What is a little higher?


Thanks,

Jesse

[Obioban]

I tried to target 75% FRC with my front sway (only adjustable one) in it's middle position-- so I could dial in exactly to taste using the sway's adjustments, instead of having to replace parts.

... and if possible, I'd suggest trying to get the Bounce ratio a little higher.

[D-O]

Closer to neutral, with adjustment both ways on the front bar.



Jesse