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      11-20-2019, 01:06 PM   #23
PeanuKeeyes
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This is a great thread, although I am having some difficulty comprehending the math! - I have a 228i M sport package that came with H&R 1" drop springs, and while it looks great, it is extremely impractical for where I live. I have also read on here that lowering the car in the 1" + zone can be brutal on the stock shocks so I'm eager to bring it back to stock height.

having a guy send me over some used OEM springs out of a M240i with sport package/adaptive suspension. (hoping it's basically all the same components on both cars)

Anyone have some spring rates for 228i m sport springs vs 235i/240i? -- is the heavier front end of the i6 version going to mean my 228i will be a bit higher in the front when I put those springs in or will it be negligible?
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      11-20-2019, 01:47 PM   #24
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Quote:
Originally Posted by PeanuKeeyes View Post
This is a great thread, although I am having some difficulty comprehending the math! - I have a 228i M sport package that came with H&R 1" drop springs, and while it looks great, it is extremely impractical for where I live. I have also read on here that lowering the car in the 1" + zone can be brutal on the stock shocks so I'm eager to bring it back to stock height.

having a guy send me over some used OEM springs out of a M240i with sport package/adaptive suspension. (hoping it's basically all the same components on both cars)

Anyone have some spring rates for 228i m sport springs vs 235i/240i? -- is the heavier front end of the i6 version going to mean my 228i will be a bit higher in the front when I put those springs in or will it be negligible?
The M240i has different springs than the 228i M-Sport, both front and rear. The M240i's springs are quite a bit stiffer by like 50% in the front and 30% in the rear.
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      11-20-2019, 04:36 PM   #25
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Quote:
Originally Posted by FaRKle! View Post
The M240i has different springs than the 228i M-Sport, both front and rear. The M240i's springs are quite a bit stiffer by like 50% in the front and 30% in the rear.

Ok, good to know! Not too worried about the stiffness, (unless there are consequences to the shocks that I’m missing?) — mostly wondering if the front end will sit noticeably taller as a result.
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      11-20-2019, 07:32 PM   #26
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Quote:
Originally Posted by FaRKle! View Post
I'm kind of surprised Eibach would be stating their specs in imperial measurements. Eibach also has TUV documentation on their site with drawings, dimensions, cycling data, and spring rates (in N/mm). Here's one of their documents I used when looking at springs.
They do both, it depends on how you search but they allow for metric and and imperial from.what i recall in both dimensions and compression.
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      11-21-2019, 08:54 AM   #27
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Quote:
Originally Posted by XutvJet View Post
Are people actually testing the springs on a bench or simply running calcs on the coil diameter and number?

Reason I ask is 185 in/lb for the fronts and 415 in/lb for the rears seems off for a 3,400-3,500 lb. RWD performance car. The front rate seems too low and the rear too high.
The thing everyone is missing in this thread is motion ratio. The effectiveness of the spring is completely dependent on how far from the wheel it sits.

In the front, BMW uses a mcpherson strut with a true coilover design. The spring and strut travel about 93% the distance that the wheel does. Meaning, for every inch the wheel travel up or downthe spring only moves about .93". Meaning, a 130lb spring is actually only as effective as a 120lb spring.

In the rear, BMW is using a multi-link "HA-5" suspension. BMW has been using this design since the E8x/E9x generation (2006 or 2007+?). Small revisions have been made to the arms and geometry over the years (F series and now G series) but not much has changed whereas the E36 and E46 have significantly different rear-ends.

The rear uses a divorced spring. Meaning, the spring is mounted separately from the strut. The rear strut sits further from the spindle than the McPherson front strut. In the front, the strut is literally mounted IN the spindle which is why the motion ratio is close to 1:1 up front. In the rear, it sits at about .72? Meaning, for every inch the wheel travel the strut travels .72". Further, the spring sits even more in-board. The motion ratio of the spring is somewhere between .3-.4. Meaning the rear springs are effectively 1/3 as effective as their rating. A 400lb rear spring provides pretty much the same effective wheel rate as a 130lb spring up front. And like being pointed out by others, the general rule of thumb is to keep the rear spring rate 10% higher than the front. This maintains a "flat" ride as teh rear needs to react quicker to bumps than the front in order to keep the car from pitching and bouncing. It's a lot more complicated than "10%" but you can do your own research on flat ride.

This is all conceptual information I am providing based on fairly close numbers to reality. Just based off what I know about the E8x. The new F and G series rear multi-link will have very similar spring rates and motion ratios as I noted above. Street models will come in around 100/300 and performance variants usually run closer to 200/600 with stiffer sway bars. Effective spring frequency is like 1.1hz for a base model and 1.5-1.7hz for the more performance oriented models. There are countless part numbers for springs because of small package variations. The biggest differences though will be coupes vs sedans vs verts. Verts carry more weight over the rear wheels due to the roof so the rear spring rates will be higher than a coupe.

Like others are mentioning, BMW uses bump stops as "spring supporters." In the front, you should expect to find a 3" bump stop. In the rear, you will have less struts travel and therefore a slightly smaller bump stop closer to 2". Again, this is because of the rear struts lower motion ratio. The rear strut doesn't need as much travel to achieve the same rear wheel travel as the front. The bump stops themselves have effective spring rates close to 800lb+/in. Sway bars add another 100-300lb/in depending on the part number/package. Even the sway bar bushings themselves contribute to effective wheels rate and performance package cars do differ from base model cars in this regard. Reality is that most cars on the road have effective roll rates of over 1500lb/in+ regardless of the 100lb/in spring rate you are finding up front.

Lowering a car should generally be accompanied by cutting or replacing the bump stops. This is something Dinan is a good example to follow as they usually always do this with their lowering springs. Since stock suspension already has very little bump travel before touching the bump stop you can create a very jarring ride by reducing bump travel by an inch without cutting the bump stops back a bit to regain some of the lost bump travel.

hopefully this information helps basic understanding of why the stock rates are what they are and some of the other considerations to be made when messing suspension.

Last edited by bbnks2; 11-22-2019 at 08:03 AM..
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      11-21-2019, 11:39 AM   #28
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Quote:
Originally Posted by PeanuKeeyes View Post
Ok, good to know! Not too worried about the stiffness, (unless there are consequences to the shocks that I’m missing?) — mostly wondering if the front end will sit noticeably taller as a result.
The stiffer springs will make your car underdamped since the dampers are tuned for the OE springs. You'll have a stiffer ride, but it'll also be more "floaty" or unsettled.

I have the ability and info to do ride height comparison calcs for your OE and the m240i springs, but I charge a small fee for it.
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      11-21-2019, 02:52 PM   #29
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Quote:
Originally Posted by FaRKle! View Post
The stiffer springs will make your car underdamped since the dampers are tuned for the OE springs. You'll have a stiffer ride, but it'll also be more "floaty" or unsettled.

I have the ability and info to do ride height comparison calcs for your OE and the m240i springs, but I charge a small fee for it.
I have the M adaptive suspension which is what the M235i/240i comes with. Are you sure the springs are 50% and 30% stiffer or is that a comparison of the base model 228i suspension vs m240? — There’s about a 200 lb difference up front between cars but same adaptive sport suspension.. shouldn’t that close the gap a bit or do you still think the difference is that significant?
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      11-21-2019, 04:06 PM   #30
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Quote:
Originally Posted by PeanuKeeyes View Post
I have the M adaptive suspension which is what the M235i/240i comes with. Are you sure the springs are 50% and 30% stiffer or is that a comparison of the base model 228i suspension vs m240? — There’s about a 200 lb difference up front between cars but same adaptive sport suspension.. shouldn’t that close the gap a bit or do you still think the difference is that significant?
Yes, I'm pretty sure. You can use my below video to configure the vehicles in the ETK System and look up the spring PNs. Additionally if you look up your EDC damper PNs you'll see they're different from the m240i.

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      11-21-2019, 06:24 PM   #31
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The exposition offered to us by bbnks2 is why I turn this over to professionals.

I've owned cars built by shops that build championship-level road-racing and autocross cars, and I've had those cars maintained by shops that operate at the same level. I've also had street cars built-up for track duty on road courses by shops with a record of producing winning race cars.

My thinking on this is that unless you really want to get into the physics of automobile suspensions (and there are important books on the subject out there to help a novice get started), it's way easier (and, I believe, cheaper) to hire a professional to do the task for you. In my experience, one upside to using those professionals is that they're quite willing to share their expertise with their customers.
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      11-28-2019, 01:14 AM   #32
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Just to add to the list of known spring rates

Swift Spec-R F30 335i (fits F22 w/THP): 251#F / 603#R

Installed with BMW m-Performance Auxillary Dampers (bumpstops) PN 33-50-2-411-196
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      11-02-2022, 01:00 PM   #33
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Does anyone know what the spring rates are for F22 M240i rear wheel? Can't seem to find a firm answer.
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      11-02-2022, 08:06 PM   #34
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anyone?
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      03-24-2024, 11:03 PM   #35
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Originally Posted by brakthru View Post
anyone?
Per Dinan, the F22 M240i front spring is 217 lb/in and the rear is 526 lb/in.
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      04-18-2024, 04:49 PM   #36
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I dont know spring rates but Ive tried multiple springs for the F22 and imo the dinan are the stiffest you can physically see this be measuring the coil diameter and weighing the springs

HR came in second the eibach and vogtland are last

Dinans front measurred 13.6mm for the front for both RWD and AWD with the AWD being slight shorter the the RWD the 4cyl are 12.8mm

Dinans rear are also the tightest wound they measure 14.4mm the 4cyl are the same mm but a tad taller good for those that dont want the rear rake

the H&Rs have two versions AWD and RWD the RWD are the same for both 6 and 4 cyls and are red in color the AWD are blue

the AWD are 13.2mm the RWD are the same but are wound wider than the awd front
H&R rears measure 13.3mm and i couldnt tell the difference between awd or rwd the coils are more spaced out than dinans and are softer

I would advise in using dinans rear that are part number 0795 and there RWD fronts that are 0790
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      04-18-2024, 07:34 PM   #37
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Generally, if the manufacturer or retailer hasn't provided reliable information, measuring the spring rates on a spring rate tester is the way to find out what they are.
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      04-18-2024, 09:33 PM   #38
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Dinan said the F22 M240i front spring is 217 lb/in and the rear is 526 lb/in are the stock rates. They said the Dinan fronts are 238 lb/in and rears are 668 lb/in which is exactly 10% increase front and 27% rears as they advertise. This explains the additional stiffness felt.
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      04-18-2024, 10:04 PM   #39
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Quote:
Originally Posted by BHR388 View Post
I dont know spring rates but Ive tried multiple springs for the F22 and imo the dinan are the stiffest you can physically see this be measuring the coil diameter and weighing the springs

HR came in second the eibach and vogtland are last

Dinans front measurred 13.6mm for the front for both RWD and AWD with the AWD being slight shorter the the RWD the 4cyl are 12.8mm

Dinans rear are also the tightest wound they measure 14.4mm the 4cyl are the same mm but a tad taller good for those that dont want the rear rake

the H&Rs have two versions AWD and RWD the RWD are the same for both 6 and 4 cyls and are red in color the AWD are blue

the AWD are 13.2mm the RWD are the same but are wound wider than the awd front
H&R rears measure 13.3mm and i couldnt tell the difference between awd or rwd the coils are more spaced out than dinans and are softer

I would advise in using dinans rear that are part number 0795 and there RWD fronts that are 0790
This is good information. How did the dinans improve your ride? I was thinking about trying stiffer rear stock springs from a M140i or a Xdrive M240i. I wonder if one will lower or raise the car though. I'm fine with the stock height. I'm still on stock dampers and recently coded VDC and some other modules to M2 cs settings. Dampers are are stiffer and car drives more sporty and balanced. Cornering improved too and this is with 70k miles on original dampers. I'm squeezing all the performance I can get out of these before paying for new ones. Damptronics are way too expensive.
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