ChicagoX

jpohl402 brought up a very good question elsewhere, and I thought the answer deserved its own thread.

There has been much discussion about launch techniques, but no quantification of them.

I've always said that the best way to set up our cars was to go full Comfort mode with the airmatic, then raise the car to its "off-road" height.


As far as drag racing goes, one wants weight transfer to the rear. Increasing the height of the car helps do this.

Here's the math:

Weight transfer = weight x CG height
........................------------------- x g = weight to wheels.
..............................wheelbase

CG height is the Center of Gravity height, g is gravity, weight and wheelbase are themselves.

Now a 1.8 60' gives you about a 1.15 g average (3.73/TimeSquared)

A 1.7 60' gives you a 1.29 g launch.

Lets estimate the CG height at about 21 inches, raised 22.

Wheelbase is 112.4 in.

1.8 60':
((4100lb x 21)/112.4) x 1.15 = ~881 lbs of max potential weight transfer.

With suspension raised, ((4100lb x 22)/112.4) x 1.15 = ~ 923 lbs of max potential weight transfer.

1.7 60' :

((4100 x 21)/112.4) x 1.29 = ~988 lbs
Raised ((4100 x 22)/112.4) x 1.29 = ~1035 lbs.


Hey, 50 pounds is 50 pounds. Sorry for all the math, but it helps.

jtc55

u lost me at "here's the math"

ChicagoX

Feel free to skip to the end. It works.

tthoang1

ughhhh, thanks for the headache!

Jakpro1

I mean if we wanna talk first grade mathematics, perhaps those number can apply, but if we really are talking about weight transfer quantification.....

You have totally missed differentials of the three spatial dimensions. In the geometry of weight transfer relativity, a fourth dimension is added, derived from time, so that the equation for the differential of distance becomes: Then must ask the obvious at specific time of maximum force at launch, are we using Euclidean Metric or the space time Minowski Metric.

Again, not even a mention of tensors in the formula such as the Lorentz Transformation tensor so I typed up a laymans version below.
In conclusion, I hold nothing against one that tries to prove his point through a 3 vector velocity covariant, but one must also lend credence to the four vector summation or one risks sounding completely scalar or being drawn into a paradox.

Jakpro1

Just messin with ya. I just copied a bunch of crap from Wiki about Einsteins theory of relativity.

J 2OOI

good one Jackpro... I laughed out loud at that one

also, nice explanation chicagox

JRAMGV8

lol

DFW01E55

You think we all didn't know that?

boohooramblers

Good to know - thanks for the info!

So, does 'drag force' not factor significantly into short drag races like 1/4 mile? Wouldn't the drag force be lower when the car is lowered?

juicee63

Although the front raises less the energy is still wasted as the front drops back down. A better solution would be to tie down the suspension so the car could not raise up in the front when going WOT off the line.


The raised suspension on my car did not result in better 60 ft times,

ChicagoX

Sure. You can always hit the button after launch, or let the car do it just before the 1/8th mile mark by itself.

Juicee63: how many tries did you give it? Do you think your car has a stiffer suspension mitigating rearward weight transfer? I'm interested in your thoughts on this.

FWIW, the trick setup would be to program the suspension to stiffen the front and soften the rear.

jdeastbay

Has anyone shot down the track in reverse creating a mean front wheel drive monster? Just wondering. The looks alone may be worth the try. I may have to add distronic if this works...

chiromikey

i have no way of knowing this but to me it feels like the suspension gets stiffer when going from "comfort" mode to "off road" mode. this could negate a little bit of weight transfer.

while i do run my car in "comfort" mode for the reason implied above, my reason for raising the car beyond "comfort" mode is based upon tire contact patch. my car is lowered which changes camber. by raising the car beyond comfort mode it reduces the negative camber and allows a better contact patch and improved traction.

juicee63

Maybe because I have the performance suspension?

It actually slowed me by 2/100ths out of the box. We noted that there seemed to be alot of wasted motion in the suspension when the car was raised.. The airmatic has alot of movement so we thought we could tie down the front of the car this would allow the weight to transfer w/o the wasted raise and drop of the front.

running in Comfort on normal ride height has given me my best 60 ft times, and also leaving , rolling into the gas off idle vs. the Power brake. On my next rental I am goingto try the trans brake throttle blast .

chiromikey

you're going to try WHAT!?!?!?

juicee63

set the trans brake slightly rather than stepping on the pedal. rev engine release on third amber...

I have a feeling stepping on the pedal=bad

chiromikey

you crazy nut!

since when does your car have a trans brake?

juicee63

Emergency brake is a cable no?

The pedal electronically sets off "braking" whilethe emergency sets the brake "physically" via a cable? HMMMMMMMM, maybe I should stop talikingto Viper owners. LOL

MRAMG1

Now THATS what I'm Talkin about, GO Einstien

Great Post

See yeah

stevebez

It should give better bite as the car lurches back more, but the transition of the weight will take more time... I guess it comes down to if the additional weight transfer is sufficient to overcome tripping T/C / wheelspin, if not I dont think it will help.

The maths is pretty handy, but does this not tell you what weight transfer you need to achieve those 60' times rather than say what the weight transfer is given the G from the 60'?

I.e. you need GREATER weight transfer to achieve a higher G (lower 60') with a higher CG?

OzE55

Fill the gas tank or add a bag of cement to the trunk would increase the weight over the rear wheels.
The weight over the back wheels is not particularly relevant.
The 'perfect' launch involves applying the maximum turning force to the wheels (per unit time) that just avoids loss of traction through spinning the wheels too much. Some loss of traction may be needed to bring the engine up to maximum 'power' ASAP. Any spin after that is wasted. The real problem is that there are so many variables that affect traction - track, tires, throttle depression rate. All are independent and immeasurable.
A good launch is the drivers best guess at the rate of throttle depression that maximises traction for the conditions. Assuming the same track conditions and tires - 'practice makes perfect'.

rflow306

Actually just the opposite, you want the front shocks to be very loose on the upwards travel and very slow coming down.

The only time you should tie or limit front end travel is when the car shifts way to much weight to the rear tires, ie the car does a complete wheel stand out of the gate or hits the wheelie bars to hard and unloads the rear suspension causing massive wheel spin.

dc63er

isnt this why oldgixxer shallow stages? this all sounds good to me the way he does it and this equation sounds dead on.

oldgixxer

But shallow staging has nothing to do with the launch technique