Rear LCA and relocation bracket angles

Discussion in 'Corner Carver Racing Tech Discussion' started by mikek2111987, Aug 29, 2019.

  1. mikek2111987

    mikek2111987 Member

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    With a lowered car with fixed rear lower control arms, adjustable upper, and steeda relocation brackets, you want the lowers to be as level with the ground as possible, correct?
    I would split this question between drag and corner carving if I could. I don't really do either just yet
     
  2. fdjizm

    fdjizm Drag Queen

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    Level is good for all around.
    Higher in the front than the back is good for drag racing (anti-squat)
     
  3. Pentalab

    Pentalab forum member

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    Even corner carvers will drop the LCA's to a lower position..at axle end. With lca's level, I had wheel hop.... but that's on a 2010. The 10-12 cars come with wheel hop... right outa the box.

    I use BMR's lca relocate brackets..which allow for a 2-3-4" drop.... pick one. I'm lowered 1.25" at the rear.... so even when using the top holes (2" drop)... the lca's are still lower at axle end. (2"-1.25" = .75" ) .

    FRPP + whiteline versions are both fixed at a 3" rear drop.... ditto with boss 302 etc.

    The steeda has 3 x holes to pick from....similar to the BMR version.
     
    Last edited: Aug 29, 2019
  4. Norm Peterson

    Norm Peterson corner barstool sitter

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    For corner carvers, that would normally be done only in combination with lowering of the car (think at least an inch, like most lowering springs are set up to give you). With no drop to maybe 1/2" lower than stock, even the highest predrilled holes in relo brackets are probably a bit too low.

    Running the LCAs "uphill" going toward the chassis introduces 'oversteerish' axle roll steer. There is some amount of driver preference involved, but too much tailhappiness in street driving wouldn't be your friend.


    Norm
     
  5. Sky Render

    Sky Render Stig's Retarded Cousin S197 Team Member

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  6. Norm Peterson

    Norm Peterson corner barstool sitter

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    Appreciate the motoiq link, I'll have to read it more thoroughly later.

    But I did catch something that's easily missed - Whiteline's specific contouring of the end faces of the poly - and I'm betting that their face contouring is what's almost entirely responsible for reducing bind.

    FWIW, I've been kicking around the idea of revising the roll steer spreadsheet that plots roll steer as a function of ride height (it's not a constant value) to also include the effects of roll. Side note: the PHB is involved, more precisely its midpoint height.

    In its current form, where roll = zero, the curves typically look something like this ↓↓↓
    Typical S197 Rollsteer & Antisquat Curves.jpg


    Roll oversteer is probably a lot more useful at autocross than at the much higher speeds encountered out on the big tracks. I rather doubt I'd want roll oversteer in a 1.2g corner at 100 mph . . . it's a slightly self-energizing situation that would get worse if I don't win the fight against the urge to lift and let the tail rise up.


    Norm
     
    Last edited: Aug 31, 2019
  7. Sky Render

    Sky Render Stig's Retarded Cousin S197 Team Member

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    I've since switched to the adjustable BMR brackets. I don't have a lot of roll oversteer, but I prefer that to the roll understeer "crab walking" it does when the control arms are parallel or angled up towards the axle.
     
  8. Pentalab

    Pentalab forum member

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    Vince, how much are you lowered at the rear ? Which of the 3 holes on the BMR bracket did you use ?

    I'm lowered 1.25" on the rear.... and used the top holes on the BMR brackets. A yr later, I moved down to the middle holes.
     
  9. Anti

    Anti forum member

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    I was going to search more on this subject, but found this thread basically on the same subject. Are LCA relocation brackets basically a requirement if lowering your car? Also in both situations of adjustable or non-adjustable lca's?
     
  10. Sky Render

    Sky Render Stig's Retarded Cousin S197 Team Member

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    Uh, about an inch and a half, I think. Steeda Ultra Light springs. I'm also using the middle setting.

    Adjustable BMR upper arm is set to the stock '11+ setting with the arm length set to correct pinion angle.
     
  11. Pentalab

    Pentalab forum member

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    Yup, lower the back end, and LCA re-locate brackets are required, (regardless of whether adjustable lca's used or not). If you don't, the lca's will be higher at axle end..... = zero traction /spinfest / 100% guaranteed wheel hop/ total disaster...useless on a street car. It all gets worse when a PD blower is added to the mix.

    Steeda makes good stuff, but their lca relocate brackets are not one of them. The steeda brackets are only bolted in one place... and are then welded. They have to be precisely aligned... before welding.

    The BMR version is bolted in THREE places, and no welding required. BMR version consist of 1/4" + 3/16" steel plates laminated / welded together = 7/16" total thickness.... bomb proof. If the car is lowered 1" to 1.5".... use the middle holes in the relocate brackets. Toss the oem lca's.

    https://www.bmrsuspension.com/?page=products&productid=170&superpro=0
     
    Last edited: Aug 31, 2019
    Anti likes this.
  12. burnboy

    burnboy Junior Member

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    I just bought the t springs and bmr lca and relocation brackets and upper adjustable. Can anyone verify what pinion angle should be or should I just measure it before I install and set it at the same.?
     
  13. Sky Render

    Sky Render Stig's Retarded Cousin S197 Team Member

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    There are a ton of threads about pinion angle. Just use the search bar.
     
  14. tabstang

    tabstang Junior Member

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    I don't think pinion angle has anything to do with it - this drawing I found explains it pretty well IMO, see link. https://www.thirdgen.org/forums/suspension-chassis/245078-lca-angle-relocation-brackets.html [​IMG]

    The purpose is to keep the suspension geometry as intended, essentially proportionally lengthening the LCAs to prevent understeer. I just added UMI brackets to my lowered car (ground control adjustable springs, about 2" drop) and I can feel the difference - the car feels much more planted, making me more confident. I ran autocross after installing them and the car did MUCH better, especially in the long sweeping turns. (Caveat though, I also recently added adjustable Tokico dampers and I ran it way softer than the Steeda Sport dampers I had. IMO those are far harder than they should be, and lead to LESS rather than more traction. A little body roll is not a bad thing. Plus it no longer feels like a turnip truck on bumps.)

    p.s. please don't dis me about the link coming from a Camaro site, it's what Google [​IMG] found quickly and it explains the concept regardless of the car involved.
     
  15. Norm Peterson

    Norm Peterson corner barstool sitter

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    Pinion angle would be involved only if the relo bracket holes were not drilled along an arc corresponding to the LCA length pivoting around the chassis-side pivot. In that situation, the bottom of the diff could move either forward or rearward which would then cause the pinion angle to shift.

    I agree with you on the matter of a little roll not being a bad thing. But you do have to be a bit careful about roll oversteer once speeds increase. Keep in mind that when there is any roll, the antisquat is no longer the same (right side vs left), so the instantaneous amount of available traction will not be balanced. You can get away with running more roll oversteer at autocross where speeds are limited and risks minimized by proper course layout. Not so much on the big tracks where if you put four off you're in for a much longer ride and potentially a much more sudden stop.


    Don't worry about offending me by borrowing information from thirdgen . . . my membership over there dates back to 2001.


    Norm
     
  16. kerrynzl

    kerrynzl forum member

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    Do you know of any LCA relocation brackets available that are drilled on an Arc [for stock length LCA's] ??
    or any LCA relocation brackets available as blanks that I can drill myself??
     
    Last edited: Feb 1, 2020
  17. Pentalab

    Pentalab forum member

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    This is the gold standard for LCA relocation brackets. https://www.bmrsuspension.com/?page=products&productid=170&superpro=0 Each bracket is bolted in THREE places. NO welding required. Brackets mount at an angle, so the 3 x available positions are in an arc. The 3 x positions
    allow for a 2"-3"-4" drop. I started on the top holes (2" drop).... then a year later, swapped to middle holes (3" drop). I'm lowered 1.25" at the rear.

    The BMR lca relocation brackets consist of 1/4" + 3/16" thick steel plates, welded together, so the finished assy is 7/16" thick. My oem ford lca's were bent + twisted. The GT-500 lca's are identical, except slightly stiffer durometer..and both are junk. So in went the BMR boxed type LCA's (poly at both ends). Zero issues for my street car.
    https://www.bmrsuspension.com/?page=products&productid=156&superpro=0 1.25" wide x 2" tall, rectangular steel tubing, tig welded.
     
  18. kerrynzl

    kerrynzl forum member

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    I am not worried about the install procedure. What I am wanting is the lower 3 holes to be drilled on an arc [radius from the front LCA pivot]
    This is so I can alter the LCA's at the track without resetting the pinion angle.

    Do you know if BMR would sell these with the lower holes undrilled [or can you confirm whether these are already on an arc]
    I am using FR500C LCA's.

    My car has a Shit-load of rear roll understeer [because the original regulations prevented moving suspension pivot points] Having a lower CGH was considered better, so they lived with the rear roll understeer. The front LCA pivot is 3" lower than the rear

    But the car really sticks on corners which is great for short track racing [the more you lean on it, the tighter it becomes]

    BUT on straights at 150mph+ the car is really twitchy over bumpy surfaces. But I can still take my hands off the steering wheel on these bumpy surfaces and the car will "self-align" itself. [if it had rear roll oversteer, I would be constantly trying to correct it]
     
    Last edited: Feb 1, 2020
  19. Pentalab

    Pentalab forum member

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    The lca relocate brackets, after mounting, slopes at a slight angle, (bottom of bracket is closer to the front of car)... so even though the 3 x sets of holes are inline, when changing holes, the lca pivots in an arc..and lines up with the holes...... without affecting pinion angle. Check out some of the 31 pix on Am's website. https://www.americanmuscle.com/bmr-lca-relocationbracket-0512.html#customer_pics-0

    Since your front LCA pivot is 3" lower than the rear, you will need to use the middle holes (3" drop)... just to get your lca's parallel to the ground. I prefer the lca's to be lower at the axle end for street use. With my car lowered 1.25", the front lca pivot was 1.25" lower than the axle end, which was a disaster in the wet..and dry. No traction..and loads of wheel hop...too dangerous in the wet imo...car would pull to the left, with foot into the gas. So in went the relocate brackets.

    When swapping from top to middle holes, my pinion angle did not change. (I have a BMR adjustable UCA+ mating BMR UCA mount, but it didn't require tweaking). Rubber mallet used to shift the lca down one hole. Note the BMR boxed lca's were a very tight fit. The oem lca's (+ GT-500 lca's) slid very easily between holes.

    Dunno if BMR will supply relocate brackets..sans holes. AFAIK, you would most likely be using the middle + bottom holes. Dunno how quick you could swap holes..at the track....perhaps 15-30 mins.
     
  20. kerrynzl

    kerrynzl forum member

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    I've highlighted what I originally wrote (quote) "The front LCA pivot is 3" lower than the rear " so the LCA goes up at the rear. I need the 3 holes to arc further rearward when the LCA is horizontal.[not closer to the front of the car at the bottom]

    My car is quite low from the factory [see photo]. I prefer the LCA's to be slightly in roll understeer position, Unless I am doing "slalom racing" [autocross] where you set the car to be slightly pointy [nose-in oversteer [​IMG]]

    People tend to overthink "anti-squat" [we're not trying to "hit" the tyres on a drag racing launch] As the anti squat is lowered, so is the CGH. The difference in these heights creates weight transfer onto the rear [overturning moment /or squat]

    The anti-squat instant centre [for and aft] is controlled in a similar matter as the roll centre [laterally] by suspension stiffness
    So too much squat is remedied with stiffer rear suspension, then either removal of/ or softer rear anti roll bar.[to maintain correct roll couple]
    My car doesn't have a rear anti roll bar [RARB] from the factory.

    I am just trying to remove the twitchy feeling on a front straight at one particular track which is bumpy [and fast at 150mph], The back straight is even faster [but smooth]

    1 In the Pits.JPG
     
    frank s likes this.