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Discussion in 'Suspension and Chassis' started by Mad Hatter, Feb 8, 2018.
Was wondering if anyone had the angles for the UCA and LCA on a stock Boss 302....
My LCA measures at about 23/32" lower in the front. For the 18.5" arm, that's 2.226º pointing down. *gasp*
I can only eyeball the UCA...my guesstimate is ~12º
Asked and answered!!
@Grant 302, 23/32" lower in the FRONT (chassis side)?
Yup. Lower in the front. Empty car with just over 1/2 tank of gas.
Stock Boss Geometry:
This is interesting. Doing some research and found that the GT500 LCA angle is also more towards squat then you would ever expected.... The 2013 GT500 with stock skinny tires got a time of 1:38.7 at Laguna Seca (with Randy Pobst driving).... The same car/driver with decent pads and tires would obviously go much faster. But still thats faster then many fully track prepped mustangs out there!
Ok, after a quick check with google..... in 2016 @ajaquilante got a lap time of 1:30.7 in a PWC Boss 302..... Thats with 305's and having the same or less power then many of us have already..... Using the stock lca install points.... Some thing Ford is trying to tell us??
I might be exhibiting a little OCD here, but listen to Randy at 11:37......
What was the GT500 UCA angle?
Order of magnitude, the antisquat % probably isn't too far from 30%.
I got a quick measure of minus 2 degrees with my cel.. but the stock lca is hard to measure. I asked a friend with access to a GT500 to measure the heights of the LCA bolts and waiting for the data. But you are right it must be about the same squat as the stock boss.
My guess is that Ford inclined the LCAs the way they did for axle roll-steer reasons. When the LCAs incline uphill (going from the axle to the chassis) the axle starts steering the rear of the car wide in a corner as the car approaches a set. IOW, not right away at the beginning of your steering input when there isn't any roll but a fraction of a second later when there is. A suddenly "loose-feeling tail" makes most drivers nervous, especially given that most drivers wouldn't have a clue as to why it felt that way or trust it to not keep progressing all the way into a full-blown spin. Lifting off the throttle - most drivers' reaction - tends to drive the axle steer even further into vehicle oversteer, and this is a separate effect from forward load transfer "unweighting" the rear tires (costing lateral grip).
Sorry am little confused, you mean as Roll over steer with the antisquat vs the squat that Ford puts in (angle downhill from the axle)? I have been running with my LCA anywhere from 3.5 to 6 degrees uphill from the axle for quite a while now. I liked the setup and I managed to do well against the competition. But I passed my car to my instructor recently and we almost spun out in the first lap (Chevy guy), started me thinking that maybe I have to much roll over steer. So I went form nearly 6 to 3.5 degrees.
Then again, I recently crunched the car into the tire wall for pretty much for the reasons you described above (and worn rubber bushings all over the rear end).
Now looking to try the "Ford" approach with my lca pretty flat and am already thinking of going to 40% antisquat
Sort of. When you go after big antisquat numbers by inclining the LCAs uphill from the axle, the axle steer goes from mildly understeerish to some amount of oversteerish. The steeper you make the uphill LCA angles, the more oversteerish the axle roll steer effect gets.
In the generalized picture below (from RCVD), the "Roll axis" is the axle's own roll axis, which is not to be confused with any notion of a vehicle roll axis (construction line through its suspensions' geometric roll centers). As long as this axis slopes down toward the front as shown, axle steer will be understeerish in the vehicle sense (more on this some other time). Conversely, an upward slope toward the front will be oversteerish. The amount of roll steer can be quantified as the tangent of the slope of the axle's own roll axis.
Note that the geometric roll center isn't precisely on the PHB; it's actually where the axle's own roll axis passes through the vertical plane containing the axle.
In the S197's actual case, the LCAs converge slightly inward going toward the axle end, putting point B out behind the car. But they don't converge fast enough to put point B below point A. Hence the OE roll steer is slightly understeerish.
You mentioned 'bad bushings'. That falls under "compliance steer", which is an entirely separate effect. Compliance steer + axle roll steer + several other effects added together - done separately for both axles and then compared - is your understeer budget (overall car behavior).
Head exploding! On my car I have the lower control mounted in the middle hole of the adjustable mount. This creates a slight down hill angle from the axle to the front. Is more of an upward angle going to the front better, should I go to the bottom hole?
↑↑↑ reads a lot differently from the emailed notice of reply to topic. What are you trying to fix? Measurements to the LCA attachment bolt centerlines would clear up the matter of inclination, and from there a better estimate of axle roll steer as a number could be made.
Are your LCAs OE? If not, do you know if they still converge slightly with the axle ends closer together than the chassis ends?
Sorry for the vague question. My 12' GT is lowered with k. springs and supporting hardware. I binned the factory lca mount for the white line adjustable mount with 3 set of holes in which to mount the lca. The lca is a boxed non adjustable bmr unit. Currently I have the lca mounted in the middle hole of the lca mount. This creates a slight downward angle pointing to the front of the car. The lca are the same length as the oem ones. I'm trying to maximize traction and handling predictability. I desire to use my shocks and adjustable sway bars to fine tune the balance of the car.
Not quite sure that makes sense. If you lowered the car~ 1.5" in the back, and are using ~3" lower rear lca connection, I would guesstimate that you have an upward angle of over ~2° to the front.
I know, thats why im confused. Ill post pictures latter.