07-14-2018, 06:31 PM | #1 |
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On a quest!!! Spring rates
BMW in there infanant wisdom will not provide spring rates in its product description. I would like to know if anyone on this forum has the spring rates for the M235i with adaptive suspension f/r, along with the MPerformance (Red Spring) rates?
I'm hoping someone might have a spring dyno and have quantitative information or specifications. Last edited by Shadowfax028; 07-14-2018 at 07:41 PM.. |
01-01-2019, 09:00 AM | #4 |
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I found this a few weeks ago while wondering the same question. I'm not sure if US/UK Spec M235i have the same spring rates but the guys in the UK have done a bit of work to figure this out. Rates for rears are below, as is a link to the discussion on babybmw.net. It seems like the fronts are 120-180 lb/in depending on the model of your car or aftermarket springs you buy. If someone here knows better, please share! OP - Hope this helps!
H&R M135i Rear = 348 lb/inch OEM M135i Rears = 383 lb/inch Eibach Rear = 384 lb/inch 'AC Schnitzer' Rear = 384 lb/inch H&R M235i Rear = 392 lb/inch OEM M235i Rears = 417 lb/inch OEM M140i Rears = 587 lb/inch (~same as OEM M3/M4) https://www.babybmw.net/forum/viewto...44195#p1344195
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01-01-2019, 10:33 AM | #5 | |
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01-02-2019, 08:46 PM | #6 | |
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Reading the below thread you'll find the F80/F82 crowd as well as the engineers at Swift Springs would disagree with you about the handling characteristics of high spring rate variances between front and rear on F-Series bmws. In addition, the AFE Control Coilovers for F30s (couldn't find any reviews on these) have an even higher front rear variance than the Swift Springs! Not trying to argue here, just suggesting the data seems to go against your intuition on this and maybe the front rate estimates on babybmw aren't too far off. https://f80.bimmerpost.com/forums/sh....php?t=1054041 185 lb/in Stock M3/4 Front Springs 575 lb/in Stock M3/4 Rear Springs 268 lb/in M3 Swift Spec-R Front Springs 715 lb/in M3 Swift Spec-R Rear Springs 279 lb/in M4 Swift Spec-R Front Springs 726 lb/in M4 Swift Spec-R Rear Springs https://afepower.com/afe-power-430-5...oilover-system 275 lbs/in Front, 1100 lbs/in rear |
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01-02-2019, 11:40 PM | #7 | |
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The compound spring rate under hard cornering is going to be a lot higher than the quoted rate. The polymer bump stops also have a progressive spring rate that increases with compression, compared with a steel spring being either linear, or progressive when coil-bound with variable pitch coils. The F20 OEM front struts only have about 10mm of compression at normal ride height until the polymer bump-stop adds to the spring rate. Another issue is going to be the effect of the rear anti-roll (sway) bar with stiff rear springs relative to the front, ensuring that it isn’t too stiff to give balanced handling and good traction under acceleration, too stiff and the inside rear wheel will easily lift while the front outside wheel is too heavily loaded. If the front to rear rates are this disparate, then I wouldn’t change the strut / coil-over springs without understanding the total effective rate and adjusting the other components too. |
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01-03-2019, 01:30 PM | #9 |
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From a qualitative evaluation of suspension stiffness, here is some information on perceived suspension stiffness:
The natural frequency of road car suspension is usually between 1 Hz and 2.5 Hz, with the following ride qualities: "Pillow soft" - 1.0Hz is a soft traditional Cadillac ride "Normal but a bit stodgy" - 1.5Hz is typical of a modern SUV or family sedan "Quite hard and sometimes uncomfortable" - 2.0Hz is typical of many sports cars "Teeth rattling harsh" - 2.5Hz is stiff and somewhat harsh, typical of the stiffest OEM suspensions. With a sprung corner mass of 350kg (close to that of an M240i with driver and tank of fuel, minus unsprung mass), the effective spring rate when hitting a speed bump squarely and not invoking the anti-roll (sway) bar for each of these frequencies will be expressed as f = √(k / m) ÷ 2π, or k = (2πf ^ 2)m. k = spring rate in N/m (1 N/m = 0.00571 lb/in) m = sprung mass in kg f = natural frequency in Hz For 1.0Hz - 13,821N/m (79 lb/in) 1.5Hz - 31,089N/m (178 lb/in) 2.0Hz - 55,270N/m (316 lb/in) 2.5Hz - 86,359N/m (493 lb/in) Track cars can go as high as 5.0Hz if bump absorption is not a significant consideration, leading to spring rates as high as 345,000 N/m or 1,970 lb/in. From the perspective of tyre impact absorption, a typical tyre at 2 bar / 30psi pressure will deflect about 10mm under a total mass of 400kg (sprung + unsprung), leading to a spring rate of about 400,000N/m (2,284 lb/in), so will not affect the perceived ride quality when hitting large bumps to any significant degree, instead being responsible for high frequency / small deflection bump absorption. |
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01-03-2019, 04:04 PM | #10 | |
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RF – 886# / 403kg RR – 790# / 359kg LR – 820# / 373kg LF – 926# / 421kg. FWIW, the coilover spring rates are: Front – 350# / 61296N/m Rear – 600# / 105079N/m. With OEM anti-roll bars, I would say that qualitatively the car feels stiff, but not uncomfortably so. I find it to be both usefully trackable and very responsive away from the track.
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01-03-2019, 04:26 PM | #11 | |
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a +/-7% variance in the spring rate at resonance i.e. 51,322N/m to 59,218N/m or 293 lb/in to 338 lb/in. |
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01-03-2019, 05:08 PM | #12 | |
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2017 M240i: 25.9K, 28.9 mpg, MT, Sunroof Delete, 3,432#, EB, Leather, Driving Assistance Package, Heated Front Seats | Sold: E12 530i, E24 M635CSi, E39 520i, E30 325is, E36 M3 (2)
TC Kline Coilovers; H&R Front Bar; Wavetrac; Al Subframe Bushings; 18X9/9½ ARC-8s; 255/35-18 PS4S (4); Dinan Elite V2 & CAI; MPerf Orange BBK; Schroth Quick Fit Pro; Full PPF |
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01-03-2019, 06:26 PM | #13 |
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50% is a good approximation overall, especially for items such as driveshafts, springs and suspension arms that have even weight distribution along their length, less so for other semi-sprung components such as the struts.
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01-04-2019, 12:22 AM | #14 |
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Rear spring rates are also typically higher (higher frequency) to produce a "flat ride" effect.
Here's a video explaining it. |
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01-04-2019, 01:27 AM | #15 | |
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01-05-2019, 02:23 PM | #16 | |
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My dalema is finding a aftermarket manufacturer that produces OEM style springs to work with factory dampers, and larger then OEM sway bars. All I have been able to find are (Beauty Springs) that just lower the car!!!! I need something suitable for Autocross..... Does as anyone know the spring rates for the BMW Mperformance (Red) springs BMW doesn't trust its consumers with that kinda information |
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01-05-2019, 03:44 PM | #17 | |
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F – 1,599# R – 343#. The front anti-roll bar was hollow and 1½" in diameter w/6 holes of adjustment, while the rear bar was 1" in diameter w/no adjustment. Each one-hole adjustment of the front bar made a significant difference. I didn't watch the video, but I think that E36 had a very "flat ride".
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2017 M240i: 25.9K, 28.9 mpg, MT, Sunroof Delete, 3,432#, EB, Leather, Driving Assistance Package, Heated Front Seats | Sold: E12 530i, E24 M635CSi, E39 520i, E30 325is, E36 M3 (2)
TC Kline Coilovers; H&R Front Bar; Wavetrac; Al Subframe Bushings; 18X9/9½ ARC-8s; 255/35-18 PS4S (4); Dinan Elite V2 & CAI; MPerf Orange BBK; Schroth Quick Fit Pro; Full PPF |
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01-06-2019, 12:53 AM | #18 | |
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The key suspension settings that make it rapid in auto-X are: - Relatively stiff front sway bar for camber control during maximum lateral g - Minimal rear sway bar (sometimes run disconnected, especially in the wet) to give good traction out of corners and control excessive oversteer - 2.7 deg front camber - 1.5 deg rear camber (minimal dynamic change due to deDion rear suspension) - accurately corner weighted (within 1kg cross weight when necessary ballast to meet minimum class weight is added) - flat ride at medium to high suspension compression (more about this further on) Bearing in mind the car is light (650kg / 1433lb with driver, fuel and ballast), the front springs are 170#, but have an effective rate of 120# due to inclination. The rear springs are progressive, 130# at normal ride height, 110# in droop and 200# in medium to high compression. Adjustable coil overs are used without any bump stops. This means flat ride is achieved under rear suspension compression, but is soft enough when extended that the inside wheel doesn’t lift (due to the low droop spring rate and minimal sway bar), as a RWD car with a fairly aggressive carbon plate LSD, it has great traction exiting corners. The unsprung front corner weights are about 25kg each, rear about 30kg each. The total corner weights are LF=154kg, RF=144kg, LR=181kg, RR=171kg, so the natural frequencies at normal ride height are LF=2.12Hz, RF=2.03Hz, LR=1.95Hz, RR=2.02Hz. When under medium compression the rear frequencies increase to LR=2.42Hz and RR=2.51Hz to give flat ride, this is achieved using the progressive springs on the adjustable coil overs, but engineered bump stops could also be used. I would say the key things to make an F22 competitive in auto-X (depending on class and restrictions), but let’s say just maximize it for raw time without any structural or bodywork changes and otherwise keep it as a competent road car. I would try to increase front camber, bring the front spring rate up, but still achieve flat ride, ensure front sway bar rates are high compared with the rear and use an LSD if possible. All of these changes are going to be dependent on the class you want to run in, of course. I don’t know if anyone manufactures optimized front bump stops, but I think they have to be changed with the springs to reduce the braking dive, especially if adding camber for front end cornering grip. Last edited by aerobod; 01-06-2019 at 01:07 AM.. |
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01-07-2019, 07:16 PM | #19 |
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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. |
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01-07-2019, 11:49 PM | #20 | |
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If I had a spring with an unknown rate and needed that information, I'd have it put on a spring tester.
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2017 M240i: 25.9K, 28.9 mpg, MT, Sunroof Delete, 3,432#, EB, Leather, Driving Assistance Package, Heated Front Seats | Sold: E12 530i, E24 M635CSi, E39 520i, E30 325is, E36 M3 (2)
TC Kline Coilovers; H&R Front Bar; Wavetrac; Al Subframe Bushings; 18X9/9½ ARC-8s; 255/35-18 PS4S (4); Dinan Elite V2 & CAI; MPerf Orange BBK; Schroth Quick Fit Pro; Full PPF Last edited by dradernh; 01-08-2019 at 12:41 AM.. |
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01-08-2019, 11:01 AM | #21 | |
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01-08-2019, 11:50 AM | #22 | |
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2017 M240i: 25.9K, 28.9 mpg, MT, Sunroof Delete, 3,432#, EB, Leather, Driving Assistance Package, Heated Front Seats | Sold: E12 530i, E24 M635CSi, E39 520i, E30 325is, E36 M3 (2)
TC Kline Coilovers; H&R Front Bar; Wavetrac; Al Subframe Bushings; 18X9/9½ ARC-8s; 255/35-18 PS4S (4); Dinan Elite V2 & CAI; MPerf Orange BBK; Schroth Quick Fit Pro; Full PPF |
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