Originally Posted by
razo125
I don't understand. Given the springs natural frequencies are matched, I thought the rear which is heavier needs more damping vs the front. In doing so, the chassis should settle evenly when hitting bumps or landing off jumps. However, using heavier oil in the front which weighs less doesn't make sense to me? When you do the drop test WITH these oils in your car, does the chassis still bounce evenly? The reason I ask, is because I have tested this extensively years ago and the front end was overdamped.
I had a similar setup when I tested matching f/r spring frequencies. I had to use a heavier oil than I would like to in the front. Otherwise the front end would dump in the middle of the corner. The heavier oil cured that, but I didn't like it because the front end was overdamped and didn't rebound fast enough. BTW no amount of adjusting camber links, tire selection corrected this so I HAD to run heavier oil like you do OR just increase the front spring rate slightly.
I realize I'm contradicting your preference in setup and I'm not saying it's wrong, it just didn't work best for me. As I said in my previous posts, I personally prefer a slightly stiffer front when compared to the back. This allowed me to run a lighter front oil, so when you do the drop test WITH oil the chassis settles evenly. It also allowed me to enter the corners without the front end dumping. Overall I got faster lap times and it was easier to drive at the limit.
You aren't choosing your shocks oils on the bench. You are systematically determining what to use based on how the car drives. For me when I tune 2WD buggies, the fronts always end up with a heavier weight. Why? It's due to the front end rake. The more rake you have, the more oil weight you need. If we had no front end rake we'd probably end up with the same or near the same weight front to rear.
Think of it this way. A shock that is mounted straight up and down and is getting a purely vertical load exerted on it will be utilized 100%. You are fully using the spring rate and dampening rate. Now let's say we lean that shock over 45 degrees yet keep the vertical load. Suddenly the shock is only 50% effective. Our effective spring rate and dampening rate has decreased. How do we get the effective rate back? We stiffen the spring and increase the oil weight. Remember that the front of a 2WD buggy is laid back anywhere from 20 to 30 degrees thereby lessing the effective dampening ability.
We have 2 things to understand and those are the static dampening and the effective dampening. The static dampening/spring rate is what the shock is sitting on a bench. A 4 lb spring is a 4 lb spring. 30W oil is 30W oil. The effective dampening/spring rate is what it ends up being in the real world. Let's say we install that shock directly in the middle of the a-arm. Let's say the a-arm is 2" long. With the shock being at the mid point suddenly our 4 lb spring behaves like a 2 lb spring due to the leverage the arm has on it. Our 30W oil acts like 15W. What if we lean the top of the shock over 45 degrees? Suddenly our effectively 2 lb spring acts like a 1 lb spring and our effectively 15W oil is now 7.5W. See how this works? Again, please no one get too picky about the examples. They are there to get a point across without getting overly complicated. A 2WD has far more rake than a 4WD and will have stiffer oil as a consequence.
When you drop the car on a bench, hopefully it won't bounce at all! It should just absorb the impact.