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Thread: Evo double down
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post #42 of Old 05-10-2019, 07:53 AM
christensent
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Join Date: May 2016
Location: Woodinville, WA
Posts: 893

Quote:
Originally Posted by ALASHA View Post
Ok so its an issue with their link geometry and not the actual DTD cantilever set up. I was always under the impression that because of packaging with the cantilever, their track bar was too short (and not flat enough at ride height) for the amount of travel that suspension produces and caused a lot of left to right motion.


As for the rear lower control arm, whats the benefit of inboarding it? Cant you produce the same result by mounting the frame side flush with the frame and moving the axle side up to just below the tube? You would have to solve some clearance issues with the body mount.
I'm not sure about track bar length, but otherwise there's no problem with the cantilever setup on axle steer. The big down fall of the cantilever is that the mounts are really close together so there's a lot less roll stability (more sway-bar need than if they were far apart). Essentially it's the equivalent of an inboard coilover mount, which is far inferior to outboard coilovers.


As for lower control arms, you indeed want them flatter so raising both axle and frame together rather than just frame is a big step in the right direction. It's not the entire solution though. You really want the axle mounts to be much further apart than the frame mounts, which necessitates having the frame side inboard. You can envision how this helps prevent rear steer. If the frame sides are closer together than the axle sides, then during articulation the side that is extending has its axle side control arm bracket traveling inward closer to the plane in the front-to-back axis passing through the frame bracket. This motion counters the axle steer induced by having the control arm traveling down. On the other hand if the frame sides are further out than the axle, then during articulation the side that is extending has its axle side control arm bracket traveling even further away from the frame bracket which makes rear steer even worse.

Essentially, having the frame mounts closer together than the axle directly counters the imperfection of having control arms that aren't infinitely long, with regard to rear steer at least. This is the basis for a double triangulated suspension. Triangulated uppers prevent the side-to-side travel you get from a track bar, and triangulated lowers prevent rear steer (hence a single-triangulated suspension still has rear steer).
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