11-17-2021, 04:35 PM | #1 |
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Anyone convert 3-bolt strut towers to 5-bolt configuration?
I'm planning out my suspension for next season, and part of the kit I've ordered is a set of Millway street camber plates.
While Millway says these can be used for both 5 and 3 bolt applications, I have some concern from a motorsport standpoint, since the included fasteners are a smaller diameter than the stock 3-bolt, and also rated lower (or I've read the old bolts were rated lower, not sure about the new studs). I don't believe there should be any structural difference in the strut tower itself, and it would be fairly easy to create a template and drill 2 additional mounting holes. Has anyone done this before? The only consideration I can see is compromising the oem corrosion protection - and needing to be sure to coat and re-seal the exposed sheet metal - and cure it appropriately. Or alternatively, is there significant experience running these plates in 3-bolt configuration on the track, with no issues? Part of my concern is I've already seen impact from running a new Weichers strut brace designed for 5 bolt, and the mounting plates have deformed. |
11-18-2021, 07:22 AM | #2 |
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The plates will be fine. 3 bolts are more than enough. Plenty of 3bolt cars on track with stiffer suspension and no damage from the use case. Don't drill your shock towers.
Why would you run a 5 bolt strut bar on your 3bolt car?
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11-18-2021, 08:58 AM | #3 |
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Generally speaking strut braces aren’t marketed as being 3 bolt or 5 bolt specific. Weicher’s indicates 2012-2019 for their braces.
Stiffer suspension isn’t the problem, or concern. It’s the smaller, weaker hardware from the Millway camber plates compared to OEM. |
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11-18-2021, 10:24 AM | #4 | |
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11-19-2021, 10:34 PM | #5 |
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The 3 bolts match 3 of 5 positions on the 5 bolts. I’m actually running 5 bolt tops in my 3 bolt car on my KWs. Left the 3 bolts on the stock suspension set up.
And no issues. I see no reason to drill two more.
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11-20-2021, 07:23 AM | #6 |
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11-20-2021, 02:10 PM | #7 |
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I hit potholes. That’s worse than anything you can do autocrossing.
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11-21-2021, 09:55 AM | #8 |
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11-21-2021, 10:29 AM | #9 |
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What is your thinking process that has you so stressed?
3bolt vs 5 bolt it’s the exact same total area and mechanical interface. There really is no difference between using a 3 or a 5 on a 3 bolt car (Other than needing matching bolts). So why are you particularly worried about it?
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11-21-2021, 07:04 PM | #10 |
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Well, as an automotive engineer and a mechanical engineer I know three things: 1) automotive design try’s to hit a safety factor target. If they could use three 8mm bolt instead of 10mm they would and they’d save the money. 2) In broad terms stress is dependent on cross sectional area. For three 10mm bolt vs three 8mm bolt you’re looking at a 36% reduction in area - which will roughly correspond to a similar increase in stress in the fastener for the same loading. (Five 8mm bolts is a 6% increase in area, for reference) 3) I don’t know the current fastener grade for the new studs on the Millway plates, but I believe the old design came with metric grade 8.8 fasteners, vs metric grade 10.9 OEM.
So there’s increased stress in the fastener for the same loading, and less available strength. Which makes me concerned for sustained high stress applications like in motorsport. Especially because fatigue failure is a thing, it’s possible the cycle life is significantly reduced. |
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11-21-2021, 09:29 PM | #11 |
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Three or 5 bolts doesn't matter. They are there just to fasten the top hat to the chassis. All suspension stress is transferred through the top hat to the chassis. Not the bolts. Nothing at the track or any driving scenario PULLS the suspension down other than gravity. Even so all that force only at the center bolt in the strut tower. That section of the top hat would sheer before those 3/5 bolts. Any perpendicular forces to the bolt are handled by the control arms far before the strut bolts come into the picture.
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11-21-2021, 11:39 PM | #12 |
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Exactly. Glad someone gets it.
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11-22-2021, 06:12 AM | #13 | |
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I’m not saying your wrong - I’m not a suspension engineer/expert, which is why I asked the questions to begin with. But I’m also not in the habit of just trusting “random internet guy”. Neither of you have expressed any actual experience racing with this type of setup, either. Last edited by SuperLomi; 11-22-2021 at 06:53 AM.. |
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11-22-2021, 07:28 AM | #14 |
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Engineer who loved his physics classes, and has installed suspension quite a few times.
Since you are an "automotive engineer" you should have taken one look at the McPherson strut setup on your car and be able to tell right away those bolts have nothing to do with the suspension stress. All cars with McPherson struts have the same engineering behind them. They may place the control arms in different places but they are there to deal with the same directional forces and there is always a top hat.
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11-22-2021, 08:10 AM | #15 | |
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Real world loading is a lot more complex than your simplified suspension force loading diagram. The bolts are certainly under loading. They resist the car body separating from the suspension during bumps and cornering.. They resist sheer and moment loads at the top mount. 100% of side loading does not transfer through the lower arms. They resist the loads the strut tower brace transfer between them (the load that bent the mounting plates...). The only force that transfers directly to the tower would be direct suspension compression loads. It's asinine to say they resist zero loading. Anyway, this conversation is going nowhere. |
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11-22-2021, 09:19 AM | #16 | ||
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Since you are an elite automotive engineer and know more than BMW engineers and everyone here please write them a fuming email to show how incompetent we all are. Drill more holes on your chassis and let us know how it goes oh chosen one. Save us all from our own demise Bimmerpost Messiah.
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11-22-2021, 09:32 AM | #17 | ||
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I'm an engineer. I work in the automotive industry, for a major manufacturer. I have experience with the design process, and the cost analysis that goes with it. What would you call yourself? I feel like you're reading a lot more into what I'm saying than I'm actually saying. "elite" What?!? Claiming to know more than BMW engineers? What?!? I really don't know where you get that. Also, Quote:
Last edited by SuperLomi; 11-22-2021 at 10:01 AM.. |
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11-22-2021, 10:27 AM | #18 |
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So then don’t change.
Since you have such aversion to decreasing the number of bolts from 5 to 3, amd running OEM or better then don’t. Fuck a camber plate and it’s 0.5 degrees of extra camber. I wouldn’t run one of the sonsavitches on a street car because they are nasty, noisy, and, jsut like Teflon brake lines, it can lead to very dramatic failures unless you tear down and inspect and proactively replace routinely. Tune the tire pressure instead to get better rotation. Especially for autocross. Edit. To be constructive perhaps Drill amd tap for the larger bolt size? It’s onLy about 1mm bigger shaft size. As an “automotive engineer” you know full well that amount of beans required to assemble is the only reason parts change once the line is set up. Ergo 5 bolts must be easier and faster to align and install than 3 bolts while offering equal performance.
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‘06 e91 manual 325ix BarriqueRot
over Terra (one of 1), Nav, Sport, L7 A few OEM+ mods: MTech front bumper, MSport wheel & handbrake, 4AD trim, full rear shades, more to come… Last edited by Onizukachan; 11-22-2021 at 02:59 PM.. |
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12-09-2021, 02:10 PM | #19 |
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Uh-oh...
I think my s*#t may fly apart soon... Only 3 bolts... (Studs and Nuts I should say) JK - One of the many reasons I chose Vorshlag Camber Plates
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