Dude, calm down. I am not intending to mess with any of the motion ratios. I am just intending to perform some basic calculations to know my starting point.
I posted my question under the corner carver section because I assumed that would be the place where somebody would know the answer. If that was the wrong choice or a choice that is offending somebody, can a moderator please delete the entire thread…?
It was not a matter of "calming down". I was trying to answer your question appropriately based on relevant information supplied.
I wasn't offended in anyway at all
If we forget about motion ratios and actually refer to "Wheel Rate" [spring stiffness divided by motion ratio squared] it is the answer you are really seeking.
With Road Racing [Circuit Racing] weight transfer is multi-dimensional [forward /aft and left/right] so we play with roll centers vs CGH and Squat / Dive vs CGH.
With drag racing it is one-directional with Squat / Anti-squat vs CGH
The wheelbase and motion ratios are generally fixed so it limits you to ride height[CGH] and spring stiffness.
And shocks / tyres are a big factor to how the car reacts.
With "wheel rate" you need to understand suspension stiffness AND suspension load [this creates a suspension frequency which is relatively slow ]
A good example is a car with a 100 lb/in wheel rate supporting 450 lbs on that corner . The car actually settles 4-1/2" to meet a point of equilibrium [spring load]
So this explains why a lot of softer springs are longer when static AND why spring compressors are needed for installs.
So for drag racing you want soft / tall front springs on the front [these are slow frequency] and 90/10 shocks.
The frequency is slow, needed for a fast lift/extension [slow compared to the rate it absorbs bumps at speed]
On the rear you want the wheel rate relatively stiff ,so "overtuning moment" [weight transfer] is planted into the tyre footprint instead of absorbed in the springs.
It helps if the rear LCA's are set up for Anti-squat [so if the car is lowered, these need to be corrected]
Now here is the "elephant in the room" regarding live axles.
There are 2 motion ratios . one for suspension stiffness and one for roll stiffness.
For straight line suspension stiffness over bumps the motion ratio is 1:1 [a 150 lb/in spring = 150 lb/in wheel rate]
But for roll stiffness the roll center is where the panhard bar intersects the centerline of the car.
And the spring is inboard mounted on the rear axle.
The outer edge of the rear tires are 74" apart [the outer edge is measured for cornering loads] that =
37" from the centerline
The rear springs mounted directly on the axle are 38.6" apart =
19.3" from the centerline
The motion ratio of a standard mustang is 1.91:1 so if you wanted a 150 lb/in wheel rate roll stiffness on the rear it would require a 547 lb/in spring [which is crazy too stiff for suspension stiffness]
So the remedy here is to add a rear anti-roll bar which doesn't affect suspension stiffness.
On my FR500C Ford moved the springs outboard by using coilover shocks .
These are mounted 54.4" apart or
27.2" from the centerline
The motion ratio of a FR500C mustang is 1.36:1 so if you wanted a 150 lb/in wheel rate roll stiffness on the rear it would require a 277 lb/in spring
The FR500C does not have rear anti roll bars
So Ford [Multimatic] played with motion ratios on race cars.
While dancing on the subject of lowering the rear suspension. When you do this the LCA's are lower at the front. This creates "squat" [the forward thrust drives the wheels upwards/ frame downwards]
On a street car or drag car these LCA's need to be horizontal or slightly higher at the front [pointing upwards]
This is one of the main causes of Mustangs attacking crowds on youtube videos.
So correct this with relocation brackets ,so the car "hooks better" [unless you like doing skids ]
My FR500C has the LCA's pointing down for a different reason [my car will "bake" the tires from a standing start]
Having the LCA's pointing down causes the rear axle to arc forward on compression creating "roll-steer"
But this is Rear Roll Understeer, which increases "side bite" mid corner and allows the car to corner exit a lot earlier.
My car "tramlines" really bad on bumpy straights but it is actually quite stable [I can take my hands off the wheel at 170mph while it is dancing all over the bumps]
Rear Roll Understeer is quite stable and self corrects, whereas Rear Roll Oversteer is unstable and require driver input to correct.
When I said "don't f*** with it" it wasn't meant to be an insult but good advice...... meaning
"LESS IS MORE" have a good look at stock eliminators.
These guys can get a 4.6 3v into the 11's with stock heads / intake /TB etc [they play with mechanical leverage off the line. eg: hi-stall converters and low gearing]
Any help wanted just keep posting or pm me
