[ryanjorunner]

In the miata world I used to use a calculator to understand the ride quality and handling characteristics that different spring rate and swaybar adjustments would make. This was pretty common practice for track/autocrossers.

I'd like to do the same for my f30. Does anyone have any info on the details needed specific to this chassis? Mainly need suspension motion ratios for front and rear. This can be measured at home but I'm hoping someone has already done that hard work. I can ballpark the various weights need.

I'm also finding it surprising difficult to find info on oem spring rates and swaybars. If anybody knows what oem spring rates for the various versions of the f30 are that would be helpful. I'm specifically looking for 340i base suspension RWD AT, but all variations would be useful for comparison.

Even more surprising is a lot of coilovers don't readily list the spring rates they ship with. Just the drop range like that's the only important piece of info you need!

If we can compile a list of this info we could use a calculator to make much more informed decisions for suspension setups on this chassis.

[FaRKle!]

Are you working with Shaikh on a project for your F3x?

I have virtually all of the information you're asking for and have posted things here and there. I measured/acquired that info to make my own calculators for ride height, ride frequency, and flat ride. But there's some proprietary info in there that I'm not willing to release.

Front motion ratio is 0.96. The rear damper motion ratio is 0.84, and the spring motion ratio is 0.59.

As for spring rates, there are too many to list, and it varies within model due to options (weight). Unloaded, base suspensions are around 1.2Hz front ride freq, M-Sport about 1.33Hz front, and M-Perf in the 1.5-1.55Hz front range. Flat ride ratios tend to be about 10%, with exception of the F32 at around 4%.

There are NO coilovers I've seen aside from Ohlins R&T that have flat ride (and those only have it for a 6cyl engine RWD F30/32 vehicles). The spring rates for Bilstein, and all of the BC-type coilovers are posted, and some KWs. Nothing really "all-in-one" though that's public.

[ryanjorunner]

Originally Posted by FaRKle!

I have virtually all of the information you're asking for and have posted things here and there. I measured/acquired that info to make my own calculators for ride height, ride frequency, and flat ride. But there's some proprietary info in there that I'm not willing to release.

Front motion ratio is 0.96. The rear damper motion ratio is 0.84, and the damper motion ratio is 0.59.

How about stock (340i base sus) sway bar dimensions? I understand they're not a popular upgrade due to install complexity but we need to know the stock dimensions to understand their influence on FRC%.

Originally Posted by FaRKle!

There are NO coilovers I've seen aside from Ohlins R&T that have flat ride (and those only have it for a 6cyl engine RWD F30/32 vehicles). The spring rates for Bilstein, and all of the BC-type coilovers are posted, and some KWs. Nothing really "all-in-one" though that's public.

That's why I'm reluctant to buy off the shelf coilovers without checking the math first.

I'll update the OP with the data I find. Thanks!

[FaRKle!]

Originally Posted by ryanjorunner

How about stock (340i base sus) sway bar dimensions? I understand they're not a popular upgrade due to install complexity but we need to know the stock dimensions to understand their influence on FRC%.

For sway bar dimensions I recommend looking at the TUV documentation that H&R and Eibach put out for theirs. It'll give you the appropriate lever arm lengths to use in modelling.

[ryanjorunner]

Took some Swaybar measurements today. These are pretty rough taken with a plum drop from the swaybar/endlink interface.

16 340i Base Sus Swaybars:
Front: 900mm wide (Endlink Mounting Hole), 260mm elbow, 25mm diameter 21.2 ID according to REAL OEM
Rear: 1250mm wide(Endlink Mounting Hole), 180mm elbow (assumed same as eibach), 12mm diameter solid

[ryanjorunner]

As FaRKle! mentioned Ohlins may be the only option that maintains flat ride characteristics, though it seems KW Street Comfort is borderline.

From here I'd love to find spring rates for other OEM springs such as m-sport and M-performance, or other chasis/drivetrain configs.

[andino]

I'm not home at the moment but if you haven't gotten OE swaybar measurements by the of SIP in CA, I'll get some for the rear RSB. I have an OE 328i xdrive wagon sway in my storage shed. I'm still running an OE front bar so I won't be able to get measurements for that.

[Neuner]

good thread, here's Car and Driver's test sheet for a 2014 328ix F31. note corner weights and CG.

https://drive.google.com/file/d/1M82...ew?usp=sharing

[brigade24]

When I corner balanced my car, it was 3,714lbs with me (158lbs) in it. I'm Xdrive so there is no way your 3700lbs +160lbs if you're RWD. This is going to affect your spring rate calculation a little bit so its important to factor that in.

[ryanjorunner]

Originally Posted by brigade24

When I corner balanced my car, it was 3,714lbs with me (158lbs) in it. I'm Xdrive so there is no way your 3700lbs +160lbs if you're RWD. This is going to affect your spring rate calculation a little bit so its important to factor that in.

You're right. Its hard to find someone with my exact setup that has posted a corner balance. I just found jalkster's thread He corner ballanced a 340i rwd AT. I'll drop the curb weight to match his so 3621lbs + driver.

The other thing that is going to throw off the calc when comparing to stock is that most people that are installing coilovers and corner balancing probably dropped the front more than the rear to get some nice forward rake/reduce understeer/reduce wheel gap or whatever. That'll affect the F/R weight dist compared to stock.

[brigade24]

Originally Posted by ryanjorunner

Your right. Its hard to find someone with my exact setup that has posted a corner balance. I just found jalkster's thread He corner ballanced a 340i rwd AT. I'll drop the curb weight to match his so 3621lbs + driver.

The other thing that is going to throw off the calc when comparing to stock is that most people that are installing coilovers and corner balancing probably dropped the front more than the rear to get some nice forward rake/reduce understeer/reduce wheel gap or whatever. That'll affect the F/R weight dist compared to stock.

yes that's an issue so the numbers will be different because of the variety of reasons for lowering. I believe my numbers were LF: 1000 lbs; RF: 1002lbs; LR: 891lbs and RR: 890lbs. So note the 3714 i mentioned earlier was with the sway bars connected...as you can see, im much closer to 3800lbs once the bars are disconnected. My objective was the get to 50-50 weight distribution from L-R for autox.

[FaRKle!]

One thing you need to be careful about when doing calcs is using sprung weight vs curb weight. To do this you'll need to look up the weights of all of the unsprung mass and subtract that from the curb weight. RealOEM has the information, but the decimal places aren't always in the right spot. There are other sources out there you can use to verify the weight/decimal place. Some of the component weights vary by model too (such as drive axles, luckily their contribution is pretty small though).

Using the published curb weight (from BMW NA, not EU), published weight distribution (from BMW NA, not EU), and subtracting unsprung weight are components I used in my own calculator. KW SC doesn't have flat ride in my calculator by about 2%.

For front sway bars BMW has variable thickness ones. Typically the arms are thicker than the center "main straight" portion. For thickness you should use the OD of the "main straight" section since that's where the torsion loading is. Everything else is just a lever arm to transfer force to that "main straight" section. Note that RWD vehicle front sway bars have thicker ODs than xDrive bars, however the lever arms are longer than xDrive bars.

[ryanjorunner]

Originally Posted by FaRKle!

For front sway bars BMW has variable thickness ones. Typically the arms are thicker than the center "main straight" portion. For thickness you should use the OD of the "main straight" section since that's where the torsion loading is. Everything else is just a lever arm to transfer force to that "main straight" section. Note that RWD vehicle front sway bars have thicker ODs than xDrive bars, however the lever arms are longer than xDrive bars.

I was just about to ask about this. I see realoem and other forum posts show the front bar as 25/21.1mm or 25/22.2mm. I was assuming these were OD/ID of a hollow bar. meaning the M-sport bar is actually thinner walled and less stiff. Are you saying the bar is 25mm at the ends (which is what I measured) and 21.1 or 22.2mm in the middle? Is it solid? So many questions!

[FaRKle!]

Originally Posted by ryanjorunner

I wonder if the difference is your 328xi wagon vs a 340i sedan's weight dist. Or I could just have the spring rates wrong. Like I said its hard to find published info so the rates I have were from some forum post, so I'm not claiming perfect accuracy there.

Right now I'd say the there's still a decent amount of error possible in the calcs mostly coming from curb weight and weight dist uncertainty. However if I just use stock as a baseline I can get an idea of the magnitude of changes of different springs and whether they reduce, maintain, or increase f/r bounce freq ratio.[/quote]

This isn't the case since I've done the work for all the F3x US models, not just the F31 .

Here are the parts needed to take into account for unsprung weight.

Originally Posted by ryanjorunner

I was just about to ask about this. I see realoem and other forum posts show the front bar as 25/21.1mm or 25/22.2mm. I was assuming these were OD/ID of a hollow bar. meaning the M-sport bar is actually thinner walled and less stiff. Are you saying the bar is 25mm at the ends (which is what I measured) and 21.1 or 22.2mm in the middle? Is it solid? So many questions!

No way is that OD/ID. That'd be a ridiculously weak bar. That's the OD for the thicker lever arm part and then thinner main straight section. All the OE bars are solid.

[ryanjorunner]

Originally Posted by FaRKle!

No way is that OD/ID. That'd be a ridiculously weak bar. That's the OD for the thicker lever arm part and then thinner main straight section. All the OE bars are solid.

Modeling stiffness for a 21.2mm solid bar and a 25mm OD/ 21.2mm ID bar is actually pretty close. But, after looking at some pictures of factory bars it looks like you're right so I updated the calc for that

I'd still really like to see m-sport spring rates for comparison if anybody knows what they are.

[andino]

All the OE springs weights are slightly different based on suspension package (m-sport, base), engine, and body style.

[ryanjorunner]

Yeah, I've heard. I'm particularly looking for 340i 8at Rwd m-sport, but I'd take anything really. I'd like to have a complete list but I can't find much of anything about OEM m sport spring rates.

[ShaikhJalalAhmad]

User 'ryanjorunner',

You are altering my copyrighted work without permission. You have removed the copyright from the document on my website, which is also copyrighted. I created the spreadsheet as a public benefit for use on my website. You are NOT authorized to publish derivative works based on my intellectual property.

You need to cease and desist publishing this derivative work of my copyright, or at a minimum I will ask the forum owner to assist in removing your posts. Further remedy may be available to me via legal action if you do not comply.

Shaikh Jalal Ahmad

[ShaikhJalalAhmad]

To the fine folk of F30Post forum,

This isn't how I would have intended to introduce myself, but I was compelled into action. I've been working with Andrew and a few other F3x owners for some time. As you already know, 'FaRKle!' (Andrew) is very well-informed and has studied / analyzed the F3x chassis and variations more than anyone I know.

I'm working with him to create a free online spreadsheet of the Ride Harmony spreadsheet for anyone to use on my business website. While I appreciate the enthusiasm to create better analytics for different suspensions, it is NOT acceptable to copy, alter, and publish my own original copyrighted work.

This is the first time someone has blatantly attempted to knock off this spreadsheet, which took me significant time and expense to gather information and refine to the point it is now. I don't want to begin pulling spreadsheets off my website, but I'll appreciate the community's support in reporting copyright violations like this.

I have taken legal action in the past to defend my intellectual property and I prefer to not go down that route again.

Shaikh

[ShaikhJalalAhmad]

A reminder of the Terms of Service and the section pertaining to Intellectual Property:

=

[ryanjorunner]

Originally Posted by ShaikhJalalAhmad

User 'ryanjorunner',

You are altering my copyrighted work without permission. You have removed the copyright from the document on my website, which is also copyrighted. I created the spreadsheet as a public benefit for use on my website. You are NOT authorized to publish derivative works based on my intellectual property.

You need to cease and desist publishing this derivative work of my copyright, or at a minimum I will ask the forum owner to assist in removing your posts. Further remedy may be available to me via legal action if you do not comply.

Shaikh Jalal Ahmad

I removed all reference to your IP, though the original link I posted took you to your publicly available nc Miata calculator with copyright clearly visible on your website.

Not trying to step on your toes here. You made a useful calc and made it publicly available, I plugged in different #s into the calc and shared it.

[Neuner]

LOL @ putting a spreadsheet (based on standard formulas that itself attempts to reverse engineer a car manufacturer's IP) in the public domain and claiming copyright!

Shaikh, are you suggesting you own the calculations and concepts for roll center, roll couple, spring rates, ride frequency, and shock damping? Are Bill and Doug Milliken aware of this?