[ryanjorunner]

After the inglorious failure of the last thread I decided to throw together my own calculator to share with the community.

https://docs.google.com/spreadsheets...it?usp=sharing

You should be able to download it then make edits.

So far it includes a bounce frequency/ratio calculator that can tell you if a set of springs/coilovers you're considering are an appropriate match for your car.

For more info on this subject check out section 3 of this research article:
https://www.ijera.com/papers/vol9no3...3036064%20.pdf

I've started compiling a list of OE/Aftermarket springs and coilovers to compare using this method and I'd like continue populating it.

If you know the rates or can take the measurements of a set of springs/coilovers to calculate them using the calculator in the top right of the excel please do and post your findings.

P.S.
Feel free to share this calculator as you like.

[ryanjorunner]

Update: Added a bunch of calculated rates for eibach pro kit springs and a lot of KW and Bilstein coilovers. Though, the Bilsteins seem to use a helper section on the rears that throws off the rate calculation. I'll have to do some research on how to account for that.

[Neuner]

For dual spring systems, the total rate = (RATE 1 x RATE 2) / (RATE 1 + RATE 2) until the tender spring bottoms. You can calculate spring travel for both (load / rate = deflection) & switch over to just one when the other reaches its block height (= Number of coils - 0.25) x wire dia).

examples here -> https://eibach.com/us/p-108-eibach-e...tem-guide.html

edit: selfishly (& for the benefit of F31 owners), could you make the corner weights &/or total weights + weight distribution modifiable? Or copy to a new tab which uses the weights from the C&D test sheet please?

Edit 2: C&D test sheet -> https://drive.google.com/file/d/1M82...ew?usp=sharing

[ryanjorunner]

Thanks I'll check that out.

You should be able to edit the whole document if you download it.

[exE36M3]

FaRKle! - consistent with what you've seen?

[andino]

B14s spring rates are 399/565 lbs/in and they are most def in the pitch range. Not sure where you got the data but I don't think the data for b14s is accurate.

[ryanjorunner]

Originally Posted by andino

B14s spring rates are 399/565 lbs/in and they are most def in the pitch range. Not sure where you got the data but I don't think the data for b14s is accurate.

399/565 are the #s i've seen floating around the forums as well, but i haven't seen a source so I found the certification sheet from Bilstein for my car.

It lists the front spring part # as E4-FD1-Y226B00 with these dimensions:

Wire dia: 12mm
# coils: 6.7
Coil OD: 121- 95mm (I took an average of these ->108mm which is an assumption and source of error but can't lead to the rate being off by 1/2. If the full spring was 95mm OD it would still only be 303 lb/in.)

So I plugged those numbers into the spring rate calculator and got 196 lb/in.

I was just about to shoot off an email to Bilstein to try to verify.

[FaRKle!]

Originally Posted by ryanjorunner

399/565 are the #s i've seen floating around the forums as well, but i haven't seen a source so I found the certification sheet from Bilstein for my car.

It lists the front spring part # as E4-FD1-Y226B00 with these dimensions:

Wire dia: 12mm
# coils: 6.7
Coil OD: 121- 95mm (I took an average of these ->108mm which is an assumption and source of error but can't lead to the rate being off by 1/2. If the full spring was 95mm OD it would still only be 303 lb/in.)

So I plugged those numbers into the spring rate calculator and got 196 lb/in.

I was just about to shoot off an email to Bilstein to try to verify.

There's a difference between physical coils, and "active coils." TUV documents only ever specify physical coils. Additionally, the springs are dual rate, so when the low-rate is bound, it's out of play and the number of active coils changes.

Also, as you've found out, making assumptions about coil diameter leads to HUGE errors.

IIRC Andino's data comes straight from Bilstein themselves, and I've seen other communications where Bilstein has said the same thing about this kit.

[ryanjorunner]

Yeah, I'm concerned about the # of active coils as well. I can't tell if the pictures on each mfg site are of our actual springs or just some generic coilover so I didn't try to figure out active coils that way.

If anyone has a good source for any particular spring rate I'm happy to update the spreadsheet, I was just trying to avoid plugging in #s with no source or method of measurement given.

I guess I was also trying to give Bilstein and KW the benefit of the doubt that they wouldn't sell coilovers with such horribly mismatched spring rates for our cars.

[ryanjorunner]

BTW its basically the same story for KW and Eibach so take those rates with a grain of salt as well. I'm Happy to adjust those values for verified spring rates.

[ryanjorunner]

Quick response from Bilstein but not the best news

[ryanjorunner]

And B16 Comfort rates:



Spread sheet updated...

[andino]

Originally Posted by ryanjorunner

399/565 are the #s i've seen floating around the forums as well, but i haven't seen a source so I found the certification sheet from Bilstein for my car.

It lists the front spring part # as E4-FD1-Y226B00 with these dimensions:

Wire dia: 12mm
# coils: 6.7
Coil OD: 121- 95mm (I took an average of these ->108mm which is an assumption and source of error but can't lead to the rate being off by 1/2. If the full spring was 95mm OD it would still only be 303 lb/in.)

So I plugged those numbers into the spring rate calculator and got 196 lb/in.

I was just about to shoot off an email to Bilstein to try to verify.

I emailed bilstein for the data last year when I was specing my suspension out. Probably why those numbers are floating around because Farkie and I have done some legwork to figure out our suspension setups.

I forget which PN is rwd and which is xdrive but the rates and things are same regardless so it doesn't particularly matter unless you're buying for your car. The specs are identical across f3x/f2x regardless because Bilstein is lazy af.

(photo 1) 47-207233 old part number new part number 47-264625
(photo 2) 47-217522 old part number, new part number 47-264632

edit: oh I didn't scroll LOL.

[ryanjorunner]

Now double verified. haha.

[Gen13 F36]

This thing is giving me a headache.

Sorry what do I need to calculate for, is it just spring rate?

I'm interested on Tein flex z coilovers with EDFC for my car. According to their advertisement sheet it springs are F: 6kg/mm and 10.6kg/mm

That's about 336 lbs/in and 594 lbs/in.

[ryanjorunner]

Originally Posted by Gen13 F36

This thing is giving me a headache.

Sorry what do I need to calculate for, is it just spring rate?

I'm interested on Tein flex z coilovers with EDFC for my car. According to their advertisement sheet it springs are F: 6kg/mm and 10.6kg/mm

That's about 336 lbs/in and 594 lbs/in.

Assuming they're going on an f36 that has similar curb weight and F/R weight dist to the default f30 340i you just need to plug those spring rates into the appropriate green cells.

For those rates It spits out a bounce ratio of .83 which is well into the pitch range. That means those spring rates on not well suited to that car.

[andino]

Originally Posted by Gen13 F36

This thing is giving me a headache.

Sorry what do I need to calculate for, is it just spring rate?

I'm interested on Tein flex z coilovers with EDFC for my car. According to their advertisement sheet it springs are F: 6kg/mm and 10.6kg/mm

That's about 336 lbs/in and 594 lbs/in.

Most coilovers out of the box have spring rates that aren't really optimized for the chassis. They tend to push a more pitch ratio because that style tends to be more "sporty" feeling to end users. What ends up happening is the rear end tends to trail behind the front (good steering input feel due to the higher front ride freq) but this tends to make it easy for the chassis to get upset on more textured surfaces. Also this setup also lends itself that see-saw motion pitchiness that comes with really textured roads. When your car has flat ride (where the rear rate is a higher frequency than the front), the car will settle quicker and also the rear will follow the front end around corners better.

That's like a really high level of what the bounce freq ratio is for. This is purely for spring rates only but doesn't take into account bump stop stiffness/engagement or sway bars yet. There's lot of info on this stuff by Farkie as well as on youtube from Fat Cat Motorsports who really goes into depth. I'd recommend checking all the resources out if you want to understand how it all fits together.

[Gen13 F36]

Originally Posted by andino

Most coilovers out of the box have spring rates that aren't really optimized for the chassis. They tend to push a more pitch ratio because that style tends to be more "sporty" feeling to end users. What ends up happening is the rear end tends to trail behind the front (good steering input feel due to the higher front ride freq) but this tends to make it easy for the chassis to get upset on more textured surfaces. Also this setup also lends itself that see-saw motion pitchiness that comes with really textured roads. When your car has flat ride (where the rear rate is a higher frequency than the front), the car will settle quicker and also the rear will follow the front end around corners better.

That's like a really high level of what the bounce freq ratio is for. This is purely for spring rates only but doesn't take into account bump stop stiffness/engagement or sway bars yet. There's lot of info on this stuff by Farkie as well as on youtube from Fat Cat Motorsports who really goes into depth. I'd recommend checking all the resources out if you want to understand how it all fits together.

I understand just the basic. Personally I'm just trying to get a coilovers for my car that is affordable that just an improvement to the stock m-sport suspension.

Like everyone paying attention to this thread... ideal suspension is going to cost more because there is no out the box coilovers will pass this calculator. I am just trying to decide on a coilovers that is close enough to the ideal numbers.

[FaRKle!]

Originally Posted by Gen13 F36

This thing is giving me a headache.

Originally Posted by Neuner

edit: selfishly (& for the benefit of F31 owners), could you make the corner weights &/or total weights + weight distribution modifiable? Or copy to a new tab which uses the weights from the C&D test sheet please?

Originally Posted by exE36M3

FaRKle! - consistent with what you've seen?

Coming soon... Selectable stock vehicle options, sheets for F30/31/32/34/36 chassis, and reference data that only I've compiled (and spent many hours doing so).


When I'm done and this is released it'll be available for download for free from the Fat Cat Motorsports' site.

[ryanjorunner]

Originally Posted by Gen13 F36

I understand just the basic. Personally I'm just trying to get a coilovers for my car that is affordable that just an improvement to the stock m-sport suspension.

Like everyone paying attention to this thread... ideal suspension is going to cost more because there is no out the box coilovers will pass this calculator. I am just trying to decide on a coilovers that is close enough to the ideal numbers.

Word.
Right now the only viable options in my mind are in no particular order:

M-performance (nice mild upgrade but no adjustment)
Ohlins R&T (still not ideal ratio and spring rates are too high for me)
KW Street comfort with lighter 2039 front spring and 1 step heavier rear (still looking into feasibility)
Hit up our newly introduced forum member Shaikh from Fatcatmotorsports for some modified Bilsteins + custom spring rates

[andino]

Originally Posted by ryanjorunner

Word.
Right now the only viable options in my mind are in no particular order:

M-performance (nice mild upgrade but no adjustment)
Ohlins R&T (still not ideal ratio and spring rates are too high for me)
KW Street comfort with lighter 2039 front spring and 1 step heavier rear (still looking into feasibility)
Hit up our newly introduced forum member Shaikh from Fatcatmotorsports for some modified Bilsteins + custom spring rates

Fwiw, I'm planning to go the FCM route. I picked up a donor set of b14s for my car last year and have been testing 280/1000# springs on my car. Gives me a 12% bounce ratio for my n20 xdrive wagon. I think I've settled on this combo and will have the dampers tuned by FCM at some point this year.

[Gen13 F36]

Originally Posted by andino

Fwiw, I'm planning to go the FCM route. I picked up a donor set of b14s for my car last year and have been testing 280/1000# springs on my car. Gives me a 12% bounce ratio for my n20 xdrive wagon. I think I've settled on this combo and will have the dampers tuned by FCM at some point this year.

Your talking coilovers right. How would this go if say 280/1000 springs on a B8 shocks. Spring/shocks setup.... I guess the calculation would be the same.... right.

Seeing your getting all this separate .... can you give a ballpark cost you spending if this are new parts.