[RLG34750]

the most important thing when launching you car is weight tranfer to the rear tires ....

Hope this clear that up......

Weight Distribution

Weight distribution plays a roll on how the Percentage of Rise (PR) is determined and how the front end is set up. If you are setting up a vehicle that is nose heavy, here are some things to try. For ladder bar equipped cars you can raise the IC so that it Shocks the tires harder. Remember that the tires already have 100% traction while sitting still. Shocking or Hitting the tires harder will maintain that traction and help get the front end to start lifting. For 4-link equipped cars you can lengthen the IC while still maintaining around 100% AS. Fine tuning the front shocks, either stiffer of softer, can get the best launch. Raising the PR can also slow down the 60' if it needs to be raised too far to get traction. When the PR is raised, the energy is directed towards pushing the front end up instead of forward.
If the above doesn't work then increasing the front end travel can have huge benifits.
This can allow the PR and AS to remain lower, thus pushing the car forward instead of up and the increased travel will also allow More weight to be transfered to the rear tires.
Remember the example of lifting the board noted above? Let's apply that theory to this scenario. With a stiffer (70/30) front shock we are going to have more force applied to the rear tires during the initial launch. But because the nose is so heavy it doesn't want to lift and the rear tires spin too much. Now we use a softer front shock (90/10). This doesn't apply as much force to the rear tires and causes the tires to hook initially but then spin but does allow the front end to rise.

The Further the front end rises, the more force is applied to the rear tires and helps those vehicles with poor weight distribution. So the next step is to try a shock valving of 80/20. Lets' say that this works as expected and nets us 100% traction with just the right amount of front end rise but now we have some more tuning to do. If the 80/20 shock works then there may be Un-necessary front end travel. Remember, we don't want front end travel if we don't need it. So now is the time to start limiting the front end travel until only the minimal amount of front end rise is needed. If this achieved with the proper PR then you can be certain that every bit of energy is being used to propel the car Forward which is what we want.

*The shock valving used in the above examples were used for simplicity only. In actuality Fully Adjustable shocks would be much better so one can adjust the shocks compression and rebounding characteristics.

"Weight Transfer" is a term that is used to mean "shifting" weight to get traction.

Question: If your car Can Not spin the tires on launch, do you need to Transfer the weight?

Answer: No
The reason at this point for transferring weight is NOT to get traction but to allow the front end to rise so the engine can rev quicker and get into its power band. If the car is already in its power band then try limiting the front end travel. There is no need to have any more travel if you already have traction and the car is in the power band during launch.

Information source
http://www.baselinesuspensions.com/

[302Feen]

Good to know, but what is "IC" and "AS"?

[RLG34750]

Originally Posted by 302Feen

Good to know, but what is "IC" and "AS"?

Instant Center (IC):
Ladder Bar- The IC is the front ladder bar mounting hole.


Anti Squat (AS):
This is a term used to describe how much the rear of the car will Rise or Squat during launch. If a chassis has 160% of AS then the rear will rise drastically, planting the tires violently. By comparison if a chassis has 100% AS then the rear of the car will not rise or squat and if a chassis has less than 100% the rear of the car will squat.
~A common problem with high horsepower cars running Too Much AS is that the tires will plant the tires very hard for the first several feet but then start to unload the tires and spin when the chassis starts to settle. If your car does this, then look into the value of the AS. Much too often racers will detune the engine to "calm down" the launch instead of look into the suspension geometry.
~A common problem with high horsepower cars running Too Little AS is that the suspension will cause the rear of the car to squat which tries to unload the tires. Again racers detune the engine to maintain traction instead of looking into the suspension geometry.

[UBie]

Excellent thread Reggie. Even I learned a a few things from your post. The only thing that I would like to add deals with shock valuing ratios and its pros and cons. However, there is another variable that needs to be put in the equation, which is sprung body weight and unsprung weight. Both of these parameters are associated with the spring travel, known as jounce travel and rebound travel. This two factors are the reason shocks are needed as part of the suspension. To keep this subject a little simpler, let's look at a car with bad shocks, which I'm sure we all have seen are car that bounces up and down as the spring loads and unloads, and continues to do so over several cycles. This means that the jounce and rebound travel isn't being controlled by the shocks. So, let's revisit the 90/10 shock ratio, which means that 90% of the shock rate is used to keep the nose of the car upward, and only 10% of the rate is allowing the nose of the car to come down. This type of shock should never be used in a street driven vehicle, because you have very little weight on the front tires for cornering.

Now let's look at the 80/20 ratio. The same dynamics are occurring during spring travel, but in this case enough what is on the front wheels to help cornering; however, is the minimum rebound rate that I believe can safely be used on the street. This shock should only be used as a stripe/street machine, and is the shock that I used with the front sway bar removed, but is an unsafe rate for road racing or severe cornering. The information of given is still quite simplistic, because it doesn't take into account the various spring ratios that are available. This is why I would leave the suspension systems to the experts; meaning, that you buy a complete suspension system from the same manufacturer, like Eibach, Lakewood, or other specialty suspension companies.

On another note, problems with unloading, because of too little or too much AS isn't a problem that I know of unless the car has wheelie bars. What I typically see is high horsepower cars doing outrageous wheel stands, which looks good but as Reggie states isn't ideal for maximum forward momentum. My stang carries the front wheels about a foot off the ground in 1st and 2nd gear, so there is no need the nitrous system to kick-in before 3rd. By the way, I've just about completed upgrading the nitrous to a 600 shot system, so I may have to make some suspension issues once I've completed everything, which would include a complete roll cage and possibly a parachute before I'm allowed to run it on the track.

[RLG34750]

thanks UBie for embellishing the post....

[stang93mustang]

Thanks for the 101 guys. I just learned something too!