I choose to remain anonymous for now. I can assure you that all of my answers are based upon years of experience as well as a detailed level of knowledge, based in TRUE vehicular dynamics. If you do not want to trust my answers because you do not know who I am that is fine.
But, I assure you that just because somebody has a name in this industry; it doesn't mean that he knows what he is talking about. There are plenty of fast racers that claim boat loads of knowledge, yet 70 percent of what they explain is completely unfounded in any true understanding of vehicle dynamics. I do not argue that there are individuals that might help you out, giving out there opinions based upon their practical experience.
There is nothing wrong with that, pragmatic advice is as powerful as any advice. I wish to offer advice and help based more on applied theory. Specific practical advice may only work in one circumstance, only a true understanding of theoretical applied vehicle dynamics can extend to all cases at all times.
last weekend we ran a snowbirds size track same carpet flat oval..
most of our cars came back on the scales with maybe 1 or even -1 ounces of wedge on the left rear..a few select cars that were realy fast came back on the scales and had -5 ounces of left rear weight..or 5 ounces of what i would call reverse tweak..
the theory i have always had blasted into my skull year after year was..the left rear tire is what drives the car up off the corner? scales dont lie? so what is the dealio with the current wedge theory in oval?
btw good avice is good advice..theories look awesome on paper and work great on the cad programs..they do not always transfer over to out little cars equaly as well as there full size counterparts.. but you are a expert so you know all this anyways,lol.
FL Flash, I'm not disagreeing with you, practical advice is very valuable. To say I would take it anytime over theory is a little far fetched. Just remember, I am not downing practical advice, there is plenty of it anywhere you go. I am just trying to offer up something that more or less doesn't already exist.
Larry B, you pointed out one of the ever lasting mysteries, side shock springing. The answer is not a cut and dry one. One thing we do know is that R/C car tires do behave similar to conventional tires; Meaning that the property of load sensitivity does exist. How do we know that our tires behave as conventional tires? Without going into pure tire theory, I will say as practical example, if you put more wedge in our cars (more LR/RF weight), it will tighten a car up.
Load sensitivity in simple terms is that as a tire is more heavily loaded its traction coefficient drops. This is to say, as a generic example, if a given tire with 16 oz. of load makes 16 oz. of lateral grip (=16oz lat/16oz vert=coeff=1). Now if that same tire is loaded with 32 oz., it will now only make 30 oz. of grip. (=30oz lat/32oz vert=coeff=.937). This property is what allows us to tune our cars by changing the dynamic weight transfer.
So, by that simplified theory, more roll resistance across the rear would lead to a higher percentage of the roll stiffness distribution to be carried on the rear. With more roll stiffness distribution carried in the rear a higher percentage of the lateral load transfer, would be carried about the rear tires, the rear tires would be come more unevenly load resulting in the car being looser????? Right? Well not really.
As we already know, this does not work like this in reality. The question is why? Here is an example where a simplified theory yields the wrong answer.
The reason why softening the side springs actually works to free a car up is mostly a transient handling property. As the car initiates turn in, lateral forces are developed before a car takes it's full roll angle set. Therefore, the properties of the roll balance (front/rear) of the car(tight or loose), don't take there effect until car establishes its full roll set, which often never occurs on a short flat track.
Under initial lateral force build up (the front tires forming slip angle as they are steered) the car begins to rotate or yaw, the amount based upon three major variables, front tire grip, CG location and aerodynamic side and downforce centers of pressure.
With softer side springs, these effects are more pronounced for reason that the car takes a longer time to get into it's steady state roll angle and therefore steady state balance set (which is a function of a number more variables but also including those listed before).
Our RC oval cars are heavily rear biased in weight (55-65% rear) so there natural transient handling tendency is to oversteer. The longer the delay for the car to achieve a "tighter" steady state set, the more the car will continue to rotate into a corner a quite possibly continue to rotate past center.
This is a common situation seen in modern Winston Cup racing situations. However the situation is found in reverse form. With Winston Cup cars, the majority of the roll stiffness distribution is handled by a large front anti-roll bar. As the front anti-roll bar stiffness is increased, often one will find that the car actually turns (rotates) better. This is based on the same transient handling concept, but on a different end of the car.
This is not the easiest thing to explain on paper, but one can see especially on a flat track, a car that is softly side sprung, seems to cut more aggressively into the corner and through the center, and if enough yaw momentum is built, the car will actually carry that yaw momentum all the way through the corner.
The best known example of this is a Rally car or dirt track car, the initial steering input creates enough of a yaw moment that the car builds yaw velocity quickly on entry and the rest of the corner is used trying to reduce the yaw velocity to get the car back strait.
Hence the reason why guys such as Ryan Newman and Tony Stewart (guys that are used to transient loose on entry set-ups) have been so successful as of recent in Cup. Getting a car rotated on entry allows one to run a tighter steady-state set-up, which assists in laying down power earlier and more efficiently off the corner.
A lot of these set-up factors are heavily influenced by driver preference. Drivers who prefer a tighter entry set-up give up a lot of speed middle and off of the corner and often complain that they are too loose in, too tight in the center and too loose off.
I can elaborate more on a lot of this stuff but I ought to stop and make sure the explanation up to this point makes any sense to you guys. To summarize in practical form: As a rule of thumb, the less traction that exist in the track the softer you want a car sprung in order to slow down the transients of the car (or to make the car more forgiving to drive). As bite comes up, one wants to stiffen a car as to avoid excessive roll angles and a sloppy handling car.
1-why are we having to run such softer side shock springs now with the new BSR cap tires?
2-leading the caster with the RF does what?
3-IYO,moving the left rear in WITHOUT moving the RR out does what?
The consantacy that the numbers repeat on the scales before and after the race is a factor of tire wear. If the car comes back with less wedge than the car has worn more reverse stagger across the front than across the rear. This can be an indication, but not always, that the car is too tight.
I know that when one runs low wear rubber (pinks or purples) on the left front with standard wear RFs (black) that the RF will wear more, even if the car is neutral.
To further answer your question I would have to know what compounds everybody was running.
If everybody was running the same compounds, the better cars are wearing there tires more equally, one factor that could indicate a better handling car.
One other possibility, is that the better cars have less kinetic friction in their suspension, which allows the car to more easily maintain its wedge value on the scales.
Lastly you are correct, the LR on are cars have the closest distance to the cars center of gravity, thus the least amount of lateral moment about the car's CG. Thus, you are correct the LR tires primary roll(percentagewise) is produce longitudinal or foward traction.
davepull, I need more info, what does the car do on entry, most problem center off are aggravated by a corner entry condition, and are often caused by over driving a car on entry (not allowing it to rotate getting to center).
I am also asuming that your problem is occurring on power. On power pushes can be fixed with a variety of changes. But lets get the root cause of the problem figured out first and then we can formulate a better answer.
DK47, Without any experience with the new BSR caps, I can only venture a educated guess. My guess would be that the new BSR cap tires construction is different, which makes the traction build up (lat force/slip angle=cornering stiffness) of the tire slower. The slower build up in lateral forces make the tire behave more as if an old bias ply tire acted.
With the slower build up in lateral force it gives the feel as if the tire has less grip (or what we refer to as grip, which is called the cornering stiffness of the tire by SAE definition ('Milikan and Milikan, Cha. 2')). This increased time it takes for the tire to build grip makes one have to slow down the transients of the car to make the car feel as if it is more "into the track" and less as if it were driving on ice.
If I could get more information as to what the compound or construction changes were with the new caps I could probably give a more refined answer.
toytowne, The biggest effect of the the gear size has very little to do with the inertias of the gear and or reduced friction of meshing larger gears. I agree with Cliff Lett's fundemental philoshpy that a gear ratio is a gear ratio.
It is my opinion, but not easily provable, that the largest effect, is the position of the motor in the car. A larger gear would push the motor foward in the pod and foward in the car which in a general sense is a positve effect in two ways.
First it reduces the car's polar moment of inertia by placing the motor closer the the CG. Secondly, it decreases the pods inertia which allows the rear unspung inertial weight to better soak up the bumps in the race track.
As always, there is always a place and time and a specific example where you would want more rearward weight distribution with a higher polar moment of inertia and/or a more inertialy heavy rear pod.
There are no absolutes in racing, so there are never absolute answers. This might be left in the same realm as what pinion angle does in a stock car or a dragster. No real solid theoretical answer as to whay it gives more foward bite, but it always seems to give more foward bite???
I would be curious as to what others thoughts and experiences are with different gear sets.