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      05-18-2020, 12:59 AM   #1
FaRKle!
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F3x Chassis Suspension Frequency Calculator, By FCM & FaRKle!

Shaikh at Fat Cat Motorsports convinced me to work with him on some suspension calculators for this BMW community. Our first version of a suspension calculator is out, and can be downloaded from the Fat Cat Motorsports' site (direct download link).

This V1 calculator allows users to see what frequencies BMW factory and BMW aftermarket suspension configurations produce across the F30, 31, 32, 34, and 36 chassis. Additionally there's a "custom setup" output where users can enter whatever spring rates they like, and use either preset weight/weight distribution values or enter their own. I also included aftermarket suspension options that I had in my database for reference.

Expect more versions of the calculator in the future with expanded feature sets (such as sway bars and roll couple).


Last edited by FaRKle!; 05-18-2020 at 11:23 PM..
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      05-18-2020, 03:27 PM   #2
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Very Cool! Thanks for the effort!
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      05-18-2020, 03:48 PM   #3
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Update on KW non street comfort V1/V2/V3?
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      05-18-2020, 06:49 PM   #4
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Quote:
Originally Posted by nickf30 View Post
Update on KW non street comfort V1/V2/V3?
You can email KW to find out the spring rate info for those coils. They'll be different based on body style on f3x. Then you can plug those numbers in to figure out if they're what you're looking for.
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      05-21-2020, 11:02 AM   #5
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Thanks for this FaRKle! After reading many threads on the forums, I'm a bit lost on suspension upgrade options for my 2017 340i m sport (rwd/non adaptive). I'm looking for some drop (at least an inch over m sport), while maintaining comfort, performance, and a flat ride. Am i asking for too much? I'm open to coils or spring/strut combo, but having trouble finding spring rates on KWs and H&R springs since they're progressive. Based on your calculator, Ohlin's seem to be the best option for my purpose? I mostly engage in spirited street driving, but id like to open up the option to track the car several times a year. Could you guys help point me in the directionin the best options out there for my platform? It seems like majority are upgrading xDrive with adaptive from what I'm seeing.
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      05-21-2020, 11:58 AM   #6
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What a great contribution to F3x community. Thank you.
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      05-21-2020, 03:08 PM   #7
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A very big thank you.
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      05-21-2020, 04:16 PM   #8
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Quote:
Originally Posted by nadefade View Post
I'm looking for some drop (at least an inch over m sport), while maintaining comfort, performance, and a flat ride. Am i asking for too much? I'm open to coils or spring/strut combo

I mostly engage in spirited street driving, but id like to open up the option to track the car several times a year.
You'll probably want coilovers wanting a drop that much. There are a couple of options depending on your budget.

If you're looking to spend under $2k, you might want to look at one of the semi-custom options where you can spec your own spring rates like BC or Fortune Auto. I'm not sure how much they'll let you specify the damping you want though.

If you're going to be spending above $2k, It's pretty difficult to beat going with FCM on a full custom setup built off of either a Bilstein B14 or H&R Street performance set as a donors. Since you're in the Bay Area, FCM is local to you too.
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      05-21-2020, 06:12 PM   #9
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This is great! thanks Farkle!

BC is limited with damping they will do...whomever will have to do some persuading to get what they are looking for and even then they may not do it.
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      05-22-2020, 12:19 AM   #10
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Thanks for the responses! Are BC/Fortune decent quality options? I imagine they are entry level based on price point only. I've heard the BC name more than Fortune though
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      05-22-2020, 10:58 AM   #11
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Quote:
Originally Posted by nadefade View Post
Thanks for the responses! Are BC/Fortune decent quality options? I imagine they are entry level based on price point only. I've heard the BC name more than Fortune though
BC/Fortune is an entry level coilovers to me. Why it is recommended because they offer different spring rate on there coilovers or you can get a compatible spring to go along with them.
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      05-22-2020, 10:29 PM   #12
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So if you get stiffer springs in the rear on any of the BC, or FA and the like, are you really doing yourself any benefit if the shock isn't valved to match?
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      05-23-2020, 12:03 AM   #13
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Quote:
Originally Posted by Logicoeur View Post
So if you get stiffer springs in the rear on any of the BC, or FA and the like, are you really doing yourself any benefit if the shock isn't valved to match?
It depends on your use case. If you're really just DDing the car, then yes, because the ride should be smoother. If you're running it in HPDEs, then probably not since you'll be underdamped. That said, you can still have fun with it, as andino can attest to after doing so on his B14s. Of course it's possible to put something on there that'll make it horribly underdamped, and then you can end up with a similar vague sensation as the OE suspension, but it still won't be as bad since the stiffer springs don't travel as much.
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      05-23-2020, 12:41 AM   #14
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Couldn't you adjust the damper settings to match the selected spring rates if the company doesn't custom tune to your selection? Also, is there anyone running BC/Fortune cools with custom 4K/14K springs (or similar)? I'm curious on how the ride feels compared to something more mid/high tier

Edit: 4K/14K
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      05-23-2020, 12:51 AM   #15
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Quote:
Originally Posted by nadefade View Post
Couldn't you adjust the damper settings to match the selected spring rates if the company doesn't custom tune to your selection? Also, is there anyone running BC/Fortune cools with custom 4K/12K springs (or similar)? I'm curious on how the ride feels compared to something more mid/high tier
To begin with BC default spring rate is 9k front and 11k rear. So if your target is 4k front and 12k rear... the rear would be in range of default damper setting....only the front will be over damp from going 9k to 4k . The question is will damper set to the lowest is going to be ok... as I heard alot of BC owner still set there adjustment on the high side.
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      05-27-2020, 06:00 PM   #16
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This is awesome. Thank you for sharing with the community.

What about adding the M3 spring rates to the table for a reference point given I am sure the question of the rate comes up frequently and there are those of us running them on our cars?
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      05-27-2020, 06:36 PM   #17
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Quote:
Originally Posted by nadefade View Post
Couldn't you adjust the damper settings to match the selected spring rates if the company doesn't custom tune to your selection? Also, is there anyone running BC/Fortune cools with custom 4K/14K springs (or similar)? I'm curious on how the ride feels compared to something more mid/high tier

Edit: 4K/14K
i ran 6k/18k with the BC springs. I ran this setup for a year and I really liked it! the car felt balanced and was comfortable on the street. Even while competing, I would just stiffen up the dampers and send it...for dual duty setup I was content.

I upgraded to 7k/20k swift springs and my BCs are on the softest setting when driving on the street. when i put in the swifts, the car's height increased in the back even though it was the same length of spring as the BCs i removed. For what I am doing, the rates are almost bang on! my car feels alive. but for a predominantly street machine, those rates might be a bit much. 6k/18k using a good quality spring I think would be ideal. my car is xdrive so that had an impact on my numbers when the spring rates were calculated. RWD can go stiffer in the front and softer in the rear, how much depends on weight/application/preferences.
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      05-27-2020, 06:52 PM   #18
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Quote:
Originally Posted by Logicoeur View Post
So if you get stiffer springs in the rear on any of the BC, or FA and the like, are you really doing yourself any benefit if the shock isn't valved to match?
yes is the short answer since a stiffer spring will support the weight under load...its just that the valving may not support the constant loading and unloading of the weight. The oil is also a factor here albeit may not be noticeable. The benefit comes from the handling dynamics. by stiffening up the rear, you effectively increase front end grip which is important if you're xdrive since I would imagine that you would want to avoid understeering particularly in a hard transition when you need that front end to stick.

loosening and stiffening sway bars had the same effect when I tested it.
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      05-27-2020, 10:18 PM   #19
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Thanks for the feedback!
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      05-28-2020, 12:52 AM   #20
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Quote:
Originally Posted by brigade24 View Post
i ran 6k/18k with the BC springs. I ran this setup for a year and I really liked it! the car felt balanced and was comfortable on the street. Even while competing, I would just stiffen up the dampers and send it...for dual duty setup I was content.

I upgraded to 7k/20k swift springs and my BCs are on the softest setting when driving on the street. when i put in the swifts, the car's height increased in the back even though it was the same length of spring as the BCs i removed. For what I am doing, the rates are almost bang on! my car feels alive. but for a predominantly street machine, those rates might be a bit much. 6k/18k using a good quality spring I think would be ideal. my car is xdrive so that had an impact on my numbers when the spring rates were calculated. RWD can go stiffer in the front and softer in the rear, how much depends on weight/application/preferences.
I got RWD... and i plug in all the numbers for my car F36 on that calculator, it's the same as your xDrive rear spring rate need to be stiffer, at least 3x stiffer than the front. Example 4k/12k
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      05-28-2020, 03:29 PM   #21
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Quote:
Originally Posted by Gen13 F36 View Post
I got RWD... and i plug in all the numbers for my car F36 on that calculator, it's the same as your xDrive rear spring rate need to be stiffer, at least 3x stiffer than the front. Example 4k/12k
The calculator should get you close to establish a baseline. You can fine tune based on feel or application. Having said that, there is a weight difference between RWD and Xdrive cars so I would have never thought you would end up with the same numbers as me.

One reason why you may be getting the same numbers is because the mounting location of the suspension for both types of vehicles is the same. those suspension mounting locations is the information used to calculate motion ratios and hence, spring rates. the other part of that calculation is weight so again, not sure how you are getting the same numbers. You know what, I will plug in my numbers and post back with the results.

You don't have power going to your front wheels so going stiffer upfront is less likely to induce understeer than with an xdrive. for example, there is a gentlemen on here who is RWD and regularly does HPDEs, he is on 8k/16k setup and is very pleased with it.
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      05-28-2020, 04:34 PM   #22
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Quote:
Originally Posted by brigade24 View Post
The calculator should get you close to establish a baseline. You can fine tune based on feel or application. Having said that, there is a weight difference between RWD and Xdrive cars so I would have never thought you would end up with the same numbers as me.

One reason why you may be getting the same numbers is because the mounting location of the suspension for both types of vehicles is the same. those suspension mounting locations is the information used to calculate motion ratios and hence, spring rates. the other part of that calculation is weight so again, not sure how you are getting the same numbers. You know what, I will plug in my numbers and post back with the results.

You don't have power going to your front wheels so going stiffer upfront is less likely to induce understeer than with an xdrive. for example, there is a gentlemen on here who is RWD and regularly does HPDEs, he is on 8k/16k setup and is very pleased with it.
I'm not saying the numbers 100% the same with xdrive and my RWD F36. I think the front /rear weight bias contributes to the unusually closed numbers for a flat ride setup. There are still difference.

I could be wrong with my argument. Anyway I'll try to get a 4k/12k spring rate for mine but it will be awhile when I'm going to replace my suspension, probably end of this year or early next year.
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