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Do Bump Rubbers Work The Same In '69 As Other Mods?


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#46 John Woods

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Posted May 22 2016 - 10:10 AM

Truly this thread has to be among the best ever.

One of my most favorite anyway. Mostly because I appreciate it very much when Lee explains things and he dumped a boatload on us here.

Thanks once again Lee for everything.
And Saiph for starting the thread.

Not that I really know enough to offer an expert opinion...but anyway...it took me many years to appreciate at least some little bit the interactions of various components relative to a car's motion.

It is still all questions and guesses.

Shocks are not the same as springs. They do not support a car's weight, (except for load leveler air shocks and height adjustable coil overs which we don't care about here).

Shocks dampen springs and all car suspension motion, so it all moves faster or slower depending on the shock setting. Shock settings determine the speed at which the springs are allowed to travel.

If springs are set at 100lbs, at 1inch of deflection the spring's resistant force will be 100lbs. This does not change due to shock settings, which controls how fast or slow it will take the spring to get there and back. Stiff shocks move faster.

The easiest way for me to think about it is from the POV of the car's center of gravity during a turn, (CG or CoG). First, the CG moves away from its static position, creating a dynamic center, then it moves back. There are subsidiary centers of gravity for the front and rear. So, three CGs to think about.

Ideally, the centers should only move out once, to the exact required position demanded by the car's position in the turn and the forces acting on it, then move back to the exact position of static center.

That's two moves only and this only happens when shocks are in tune with the rest of the car. If shocks are too soft, (allowing too much time), and unable to fully dampen the suspension, the car will bounce back and forth a few times before settling on static center.

The most important component to tune shocks to is the diff because it also controls the speed at which the car's rear moves to and back from a dynamic center. Shocks that are out of tune will fight the diff rather than complement it and allow it to do its job, which is to move the rear away from and back to static center by application of throttle.

This is how the car is steered with throttle...by controlling the diff.

If you let off, the car turns in. If you apply throttle, the car turns out because the diff causes understeer during acceleration. So, sometime during entry, using coast point the car to the inside of the apex then apply throttle which will hold the rear in place by increasing grip and move the front out by causing push.

The fastest diff setting in Grand Prix Legends, using Lee's Setup Manager, is 15/85. (Thanks Pete, for pointing this out awhile back). In other words, when using this setting, the diff is most capable of quickly moving the car's rear from static center to its dynamic center position and back. (If set at 15/15, it will quickly move out and slowly move back in).

The fastest shock setting is 5. No idea why, but I have found cars do not like a setting of 5 in bump...seems always slower with that, so now use 4/5 in front and 3/4 on the rear because RL racers suggest the rear shocks should be slower than the front. Maybe they are slowing the diff's influence on the car so it is easier to control the rear with throttle?

Whatever, (this isn't RL its Grand Prix Legends), and just my preference, when going into coast to set the car on line to accelerate past the apex, I want to be in coast the least amount of time, so I want the fastest diff I can handle and the quickest shocks.

When lifting throttle, the diff goes into coast and the rear moves out, turning the car as if using the steering wheel, (but not), which points the front toward the inside of a corner without using the steering wheel except to hold the car on the resulting line by applying a slight bit of countersteer and pushing the front into the track camber thru the turn. This is noted by tire sounds caused by slip.

More slip angle equals more tire sound. But too much slip will slow the car, so the ideal is some slip but not too much. In other words, if there is too much tire sound, there is too much slip and the car is scrubbing off speed it shouldn't be losing.

You might try this test: set the diff at 15/85 and try the shock settings 4/5F and 3/4R, then try 3/4F and 2/3R. Think you will note a distinct difference in how the car reacts thru a turn...it will move to and from dynamic center at a slower rate.

Then try 30/60, 45/45, 60/30 etc and you will sense the difference you are making in how the car sets itself thru a turn and what happens when you vary throttle. Any or either way, you want the fastest diff you can handle.

Somewhere in the middle of all that you will find a combination of shock and diff settings that is just right for you.

Then tune brake bias so you do not interrupt the diff's intention of taking the rear out to where it needs to be. It will go there by default and the springs will stop it if you let it all happen before freaking out and using the brakes.
:D

Hope this helps, didn't edit it much...sure others will have a different opinion and will maybe/probably correct me on some of it.

Edited by John Woods, May 22 2016 - 10:24 AM.





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