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Three link question, angled lower arms?
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Author:  RichardSIA [ March 21, 2018, 3:45 am ]
Post subject:  Three link question, angled lower arms?
Been working on getting the engine mounted in the Dio-Alfa but until the dry-sump system arrives I would like to get back on the rear suspension.

My plan has been to mostly recreate the original Alfa Three-Link, which I guess is not a true Three-Link as it uses a triangulated upper link instead of a Panhard rod.

For convenience and minor weight savings I'm wondering if there is any real penalty to having the lower trailing arms at a shallow angle rather than strait to the rear as seems to be standard?
Seems it might marginally help with limiting sideways movement, which is really the upper links job, but would it also cause any sort of binding or other issues?

I have to admit that suspension development is my personal weak link. :oops:
Author:  davew [ March 21, 2018, 8:24 am ]
Post subject:  Re: Three link question, angled lower arms?
Should not be an issue, as long as one or both ends of your control arms have rubber bushings. Several leaf spring suspension systems are designed with slight angles.
DaveW
Author:  ngpmike [ March 21, 2018, 8:38 am ]
Post subject:  Re: Three link question, angled lower arms?
If you're concerned, you can always mock it up in miniature. Get some turnbuckles, or something similar for your links.
Author:  RichardSIA [ March 22, 2018, 2:45 am ]
Post subject:  Re: Three link question, angled lower arms?
It "Seems" that 4" of vertical movement on an 18" arm should not be a real issue.
I think I can mock it up in CAD and see how much the arc wants to pull it inward.
Looks like about 20º angle, a little more than I had thought it would be.
Plan has been rod ends at the axle end and bushings at the frame end.
Author:  horizenjob [ March 22, 2018, 3:16 am ]
Post subject:  Re: Three link question, angled lower arms?
The pivot could be aligned to be perpendicular with the chassis centerline? Then it would still be more of a trailing arm.
Author:  RichardSIA [ March 22, 2018, 3:20 am ]
Post subject:  Re: Three link question, angled lower arms?
20º as viewed from the top.
Level or close to it from the side.
Author:  horizenjob [ March 22, 2018, 11:35 am ]
Post subject:  Re: Three link question, angled lower arms?
Quote:
For convenience and minor weight savings I'm wondering if there is any real penalty to having the lower trailing arms at a shallow angle rather than strait to the rear as seems to be standard?
Seems it might marginally help with limiting sideways movement, which is really the upper links job, but would it also cause any sort of binding or other issues?


Quote:
I think I can mock it up in CAD and see how much the arc wants to pull it inward.


If the arm tries to pull it inward, it won't work at all because the axle can't move up for bumps, both sides would try to pull it inward. So it is fine to have the lower arms at an angle in top view, but the pivots at the front of the arm need to be mounted at an angle on the arm so the pivots are perpendicular to the car centerline. If you grabbed the trailing arm and rotated it in a full circle, that circle must line up with the car centerline.

So if you were using a bushing, you need to weld the trailing arm on to the bushing at an angle and the bolt of the bushing needs to be perpendicular to the car centerline.

Are you going to use a Panhard rod or use the upper link to keep the axle centered? You want the pivot of the centering link as low as possible. You can make one of the lower trailing arms into a wishbone so it does the centering. That was done on some of the Super 7s.
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