GT350/R and GT500 knuckle comparison.

Discussion in 'Shelby GT350 Mustang' started by Epiphany, May 4, 2020.

  1. Epiphany

    Epiphany Well-Known Member

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    The media mentioned caster trail improvement as being built in to the 2020 GT350R and also implied that the car was using the GT500 knuckle. Since I happened to have both an older GT350 knuckle (that I picked up in 2016) as well as 2020 GT500 knuckles, I knew that the two cars could not share the same knuckle. Quite simply, the larger rotor and caliper used on the GT500 meant you couldn't use the knuckle from it along with a GT350 rotor and caliper. You can physically interchange the parts though even though they wouldn't work right. So I ordered a 2020 GT350R knuckle and when it came in I laid all of them next to each other in search of the truth.

    20200504_172122-2%20KNUCKLE%20COMPARISON-XL.jpg

    I have yet to verify geometrical changes made but I'm quite certain that caster trail was improved for 2020 in the R. Why it wasn't done for the non-R GT350.....tire differences made it unnecessary?...something else? Anyway, here's a quick video I did this afternoon to try to clarify what Ford did.





    You can study the '20 GT350R knuckle (on left) versus the '20 GT500 knuckle and see what I've been saying.

    20200504_174005-2-X3.jpg
     
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  2. Inthehighdesert

    Inthehighdesert Well-Known Member

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    What do the knuckles price out at? Curious.
     
  3. OP
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    Epiphany

    Epiphany Well-Known Member

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    I believe the R knuckle has a dealer list price of $289 but got it for right around $200.
     
  4. Inthehighdesert

    Inthehighdesert Well-Known Member

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    That’s really reasonable if one wanted to do that change.

     
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  5. Montoya

    Montoya Well-Known Member

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    I'm so glad I paid thousands more for a 2020 GT350R to have this unique part... LOL! But thanks for the parts comparison, it's very interesting.
     
  6. Caballus

    Caballus Well-Known Member

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    @Epiphany I would imagine that "upgrading" a non-R would also require suspension tuning to go along with the knuckle, no? Other changes required as well; i.e., springs, wheels? No desire to do so; just curious.
     
  7. BoomBoy

    BoomBoy Racer

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    But why changes to only 2020 R just for one year? It doesn’t make sense.
     
  8. shogun32

    shogun32 Well-Known Member

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    #8 shogun32, May 5, 2020
    Last edited: May 5, 2020
    when the part was designed lifetime of 350 was likely not set and marketing no doubt stuck their nose in and said "we need to make the 'R' special again in some manner".

    The original part looks like someone maximized the 'cuteness' of the casting (gratuitous material savings and lightening) - kept removing material if the FEA didn't bitch too much. My guess done by a junior engineer with way too much time on his hands.

    While the 2020 a more senior engineer with actual real-world experience had their hand in it - or it was outsourced to an engineering firm that knows better. They used straight lines for ease of machining and beefed up parts for max strength and shot the guy who kept insisting on minimum weight regardless of increased stress risers.

    The 2020R vs 500 the one half of the mold looks to be common and it's the other half that is slightly offset. (edit) On second look the castings are likely identical. Notice how they machine off the 'wrong' part number.
     
  9. svassh

    svassh Well-Known Member

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    #9 svassh, May 5, 2020
    Last edited: May 5, 2020
    It looks like a very minor change but from my experience minor changes have impact on the tramlining. For example:

    My 2018 GT350 on PS4 tires, no tramlining at all till after my 2nd track day on an alignment between street and track. So the tire wear and alignment played a role.

    My 2019 GT350R on Cup 2 tires quite a bit of tramlining brand new. Had the adjustable camber plates installed and street alignment done, tramlining significantly reduced even on Cup 2 tires. Same alignment installed Signature Wheels and PS4 tires this weekend tramlining completely gone again.
     
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  10. JAJ

    JAJ Well-Known Member

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    #10 JAJ, May 5, 2020
    Last edited: May 5, 2020
    Thanks to @Epiphany for this tutorial on the knuckles - it's definitely a bare knuckles contest.

    If you do the swap, the thing that changes is the displacement of the steering tie-rod from the axis of the knuckle:

    upload_2020-5-5_8-10-37.png

    The red arrow indicates the tie rod location, the blue line is the axis of the strut and the green line is the lever length that the steering tie rod uses to pull or push the knuckle to make your car turn. The 2020 knuckle has a longer lever. Other than that, they look very similar.

    What this means to vehicle systems is that the suspension won't notice the change, but the power steering controller and possibly stability control (AdvanceTrak) will notice. The computers in these parts are programmed for a certain rate of turn at a specific position of the steering wheel. By making the lever longer, for any given steering input you'll get less turning effect. That's why it reduces tramlining and kick-back in the steering - literally there's "more leverage". In terms of raw handling performance, I wouldn't expect much difference, if any.

    There are a couple of risks worth considering. First, the surprisingly complex programming in the PSCM - Power Steering Control Module - might not be suited to the higher lever ratio. It adjusts power steering boost to correct for all kinds of things, like cross-winds and other disturbances. There's no way to know until someone tries, but there's a risk that the PSCM might cause unexpected outputs when the lever length is wrong. I'm sensitive to this because my first Mustang, a 2011 GT, had early PSCM programming and it would occasionally shake the steering wheel on corner entry at the track. Apparently it was a known problem with the early cars and wasn't fixable without replacing the power steering rack.

    So that's the PSCM risk. ABS (AdvanceTrak) risk is similar but different. It knows how far the steering wheel is turned and it has sensors to tell it how fast the vehicle is turning. It expects a certain rotation of the car, and if it's getting less rotation than expected, it might just decide your tires have lost their grip on some slippery pavement and start working the brakes to get the "clearly out of control" chassis back under control.

    So, do the benefits outweigh the risks? Probably not. Somebody should try it, but I'm not anxious to go first. If you're tracking the car, tramlining doesn't matter, and if you're dailying the car, you can fix the tramlining by changing tires.

    EDIT: I took a closer look at the geometry of the piece - the other change is that the steering tie rod pickup point is also positioned lower as well as further away relative to the wheel hub. This will affect bump steer, although without the rest of the geometry, it's hard to know how the difference will play out.
     
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  11. OP
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    Epiphany

    Epiphany Well-Known Member

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    When I can I'll delve deeper into the geometry changes.

    And if it matters, Terrance added the GT500 knuckles/brakes to his GT350R (pre-2020) and I haven't heard him complain of any handling or steering quirks.
     
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  12. nastang87xx

    nastang87xx Well-Known Member

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    lol you got more than just the knuckles. The block and heads alone are worth it. In my opinion anyway.
     
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  13. mustangguy88

    mustangguy88 Well-Known Member

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    Other than maybe changing to shocks and strut of your choosing. The main step to remember in this part swap is to preload the knuckle before torqueing the bolts to spec, otherwise you end up with a horrible vibration in the suspension.

    Did this conversion to my 15 GT to GT350R components with a shock and lowering spring upgrade.
     
  14. XCRN

    XCRN Well-Known Member

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    I think it is the exact same casting between the 2. It looks like the only difference is where the caliper mounts are machined at different offsets. I my guess is if you had a 20 R you could put some spacers between the knuckle and the caliper and run the 500 rotor. I don't know if it was covered at all but I would think the caliper is the same part between the 2 as well. But good catch on the machined part number I had to go back and look after you mentioned that.
     
  15. JAJ

    JAJ Well-Known Member

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    Mixing and matching GT500 parts with GT350R parts was covered on a thread where @50 Deep put the GT500 knuckles, calipers and rotors onto his GT350R. The GT500 calipers are much bigger and heavier than the GT350 calipers.

    https://www.mustang6g.com/forums/threads/gt500-brake-swapping-the-r.133213/

    All that said, if you have any GT350, not just a 2020 R, you could probably put some spacers in and run the GT350 calipers with the bigger GT500 rotors and get away with it, although finding a pad of the right dimensions might be a challenge.
     
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