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Where do you guys like to run ballast. High or low, left or right. Talk to an engineer who thinks always lower inc car so center of gravity is lower and will effect weight transfer less keeping tires more balanced. But also talked to someone who like weight higher in car so it's load tires in a more vertical direction. Thoughts?
I put it where it needs to go. Higher limits the ultimate cornering ability, but it may get your chassis back into a range of roll where it works better at the speeds you are operating in.Quote:
Originally Posted by racefastnow
What works in high grip scenarios (pavement) may not translate into dirt racing.
Dirt is a place where you can use unbalanced tire loadings to your advantage.
It's all about weight transfer. High weight transfers quicker and more efficient than low weight. So much so, that you could get bicycling or wheel stands, given enough traction and power. If you don't believe it, I have a Barstool racer, you should drive. Low weight could not load a tire enough and make it slide. It comes down to balance. Balance of traction / power and / or g force and center of gravity. The trick is getting what weight, you want where.
http://www.circletrack.com/techartic...lacement_tech/
Old article but the information is probably more relevant than ever. This was written by some guy named Bloomquist...maybe you've heard of him :-)
Can you folks explain height of ballast, angle of J bar and their relationships to roll and loading? I think that relates to this thread, if not I will delete.
It certainly relates to this thread as there is no single correct answer to "where should I place ballast" without having an understanding of how these other factors play in. Knowing your center of gravity height doesn't provide you with much information unless you know your roll axis.
Angle of j-bar is doing some other funny things though because it also changes the rate of lateral movement of the rear end for a given amount left side chassis lift. This lateral movement changes dynamic tire loading.
I'll keep it brief for now...not because I want to be secretive but because I don't have much time to type right now :-)
Well can you help?... I'm listening and would like to know more.Quote:
Originally Posted by hpmaster
The J-bar establishes the rear roll center for your car. If you're running a conventional J-bar that is mounted to the chassis on the left side and the rear end just right of the pinion, Lowering the J-bar at the pinion will lower the roll center. Raising the J-bar on the chassis will also lower the roll center, but to a lesser degree.Quote:
Originally Posted by hpmaster
Where you mount your weight vertically impacts the cars CG (center of gravity). The further away from the roll center the CG is, the more leverage is has to transfer weight from left to right. The closer the CG is to the roll center, the less leverage is has to transfer weight.
If you Increase the distance between the two by raising the CG or lowering the roll center you will get more weight transfer! I hope that helps...
I understand all that if we prying up a concrete slab you got it , in real life it is an over simplified explanation to all that is going on. I have experimented with higher CG a lot and you hit a point of diminishing returns of sorts and then start magnifying other negative effects. Simply put if all we were dealing with is leverage and weight all you would have to do is mount every thing as high as possible in a chassis then you could do away with weight as we increase the height and relied on leverage for side bite in planting the right side tires, this is not the case. This brings the effects of the simple J bar as a much more complex element because of the side to side control the J bar or pan hard bar as to rear end location, the effects on spring loading on the right side, the unloading the left side as the weight seems to travel around the car in a clockwise direction as the car travels in a counter clockwise direction then straightening out and then repeating the entire sequence again and the f-ing over rated and less than convincing "roll center" movement on the rear of a race car. jmho.Quote:
Originally Posted by Garrettshurling
No one so far, has explained how the center of gravity effects the forward bite. This enters into how high also.
HPmaster brought up a good point of weight transfer rotation. The smooth transition may be the second most important part lead only by what weight goes where. You have the front and rear roll centers relationship with the center of gravity that control lateral transfer, but you have the rear bar locations that control the linear transfer also. Technically they are called anti squat values. They need to work together. Just as roll centers work independently you're 4 bars do also, steering weight to load tires. How far or close your tires are from the center of gravity has effect on loadings. Think of it as tires getting loaded with a short or long lever.
Higher CG helps with forward bite off the corner because it allows weight to transfer from front to back under acceleration.
Getting the LR hiked up probably helps more because of the raised CG than because of increased thrust angle.
Lets not forget about the height of the CG in relation to what compound you are running. As a general rule, lower CG/softer tires, higher CG/harder tires. Of course there are a few exceptions to this. I learned a valuable lesson,about 15 yrs ago, how they are related. WE raced at a hard, oil based racetrack and the driver always complained about the car being too loose. I tried everything to get it tight enough for him.
Finally, I put a 25lb piece of lead over the RR, thinking this was a big change, but driver again complained of being loose.The light bulb came on so I knew then we had too much weight transfer as we were already on a hard tire.So I moved the lead back down, low and left, and the car got tighter.I also started jacking more bite in it at all 4 corners.When all was said and done. we had increased bite over 100lbs and we weren't blistering the RR anymore. We went on to set a track record the next week.
I said all that to say this: Tire compound and track conditions will always dictate the CG height.
Good post, but I have a honest question. When you say, moved to low left, would that be more forward also or to the rear? What I'm getting at was the scrubbed tire a side bite balance thing or a forward bite thing or a combination?Quote:
Originally Posted by drtrkr244
No, it was strictly a side bite issue. I moved the lead to right behind the driver as low as possible, slightly forward of where it was on RR framerail.
There are 2 issues I look at when a car isn't handling. Which tire/tires aren't working and why not? There is really only 2 answers. Is it sliding from being underloaded or overloaded? Obviously, it isn't always easy to figure out, or we would be as good as Bloomquist. lol