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02-02-2014, 08:06 AM | #45 |
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It's probably a topping out spring or whatever the technical term is, and prevents the strut from crashing on full extension much like the bump stop does for compression.
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02-02-2014, 09:31 AM | #46 | |
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Another interesting factoid that surprised me - on the OE suspension the 135i runs on the rear runs on its bump rubbers even at static ride height. With the dust cover on you can't see this. Obviously the effective spring rate is very progressive, despite the fact that the spring is linear. |
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02-02-2014, 01:36 PM | #47 |
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I'm curious how much of an effect the bump rubbers have on dampening control. I noted the the front ones are actually pretty stiff. On my Mazda for example, the front and rears were very soft.
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02-02-2014, 09:27 PM | #48 |
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For what it is worth, the initial stiffness of the bump rubber is very soft, so one could argue its contact is incidental.
Milliken and Milliken say this (in "Race Car Vehicle Dynamics") about bump rubbers: "While these have nothing to do with the damping performance as such, ... The 'rising rate' (nonlinear spring) provided by the bump stop is often critical to overall race car performance, especially on rough surfaces." Of course the 135i is not a race car, but conventional wisdom seems to be that the car rides on its springs on normal surfaces and only engages its bump rubbers on rough ones. It would be interesting to know if the M cars also ride on their bump rubbers. |
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02-03-2014, 03:03 PM | #49 | |
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Here is what I have found as an explanation of internal rebound springs. This from SAE: "These shock absorbers with anti-roll springs are used normally in front suspension (McPherson Struts) as an auxiliary to reduce vehicle roll and, in some cases, it may replace the stabilizer bar. Vehicles with low center of gravity and low weight may allow the elimination of the stabilizer bar and the anti-roll function will be replaced by an internal rebound spring in the shock absorber. This alternative brings to the client significant cost savings and mass reduction." |
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02-03-2014, 03:29 PM | #50 | |
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I still don't understand how an automotive shock "can't crash on full extension because it is hydraulically damped". Is there some mechanism that closes off the hydraulic fluid orifice just before it reaches maximum stroke? Going to see if I can find some diagrams. |
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02-03-2014, 03:46 PM | #51 | |
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This is all part of the witchcraft and wizardry that is shock design. I'm curious Felix, when you had the damper apart, could you spot any shims or other internal damper design cues? As I understand it, it's all a matter of fluid control inside of the damper. This thread is proving to be an excellent learning tool!
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02-03-2014, 06:16 PM | #52 | |
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02-03-2014, 07:54 PM | #53 | |
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Under compression the fluid flows past a single shim through the outer slots in the piston and also out past a shim (up in next photo) through the foot valve (to compensate for the volume lost to the piston rod). Under rebound, the fluid flows through the inner holes in the piston and fairly freely in through the lightly sprung foot valve (up in next photo). Rebound flow through the main piston is controlled by a small spring-loaded piston under set-on-assembly spring pressure. |
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02-10-2014, 02:16 AM | #54 | |
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I am also on non-adjustable damper (Bilstein, custom valved), I wish to have more camber but I am not sure whether the stack height increase will throw the balance off, I have no other means of adjusting the ride height. |
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02-10-2014, 01:40 PM | #55 |
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fe1rx, just wanted to say thanks for sharing and documenting all the details so far! It's information like this that helps others in the community learn from others' "doing".
Although I personally would not be running the stock dampers with ANY kind of aftermarket spring (I dislike them with even the stock springs, ha ha), it's interesting nevertheless to see how the OEM strut was designed. |
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02-10-2014, 09:29 PM | #56 | |
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Streets of Willow: 1:27.7 CW 11/15/15; 1:29.5 CCW 8/15/15 |||| Autoclub Speedway ROVAL (CCW): 1.52.6 - 12/2/17
Willow Springs - Big Willow (CW): 1:35.8 - 3/31/18 |||| Buttonwillow #13 (CW): 1:59.3 1/27/18 https://www.facebook.com/JakeStumphRacing |||| http://www.youtube.com/user/RaceMeMZ3 |
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02-10-2014, 11:35 PM | #57 |
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after installing vorshlag plates on a OEM suspension, my before alignment results were very close to OEM specs on the fronts.
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02-11-2014, 10:30 AM | #58 |
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