I have a question for the racers in here. Technically, this could be asked of any brand car... but I figured there would be a greater majority of posters in this thread who had seen the RedRC "Pro Tips" series w/ Michael Salven. I don't race gas on-road anymore, only electric... and predominantly pan-cars(12th, WGT etc). So, you will have to bear with me here. I was watching the first Salven video:
http://www.youtube.com/watch?v=pjecRkYoT6M
At about the 5 min mark or so, after he lubes the front driveshafts and re-installs them, he goes about re-attaching the upper arm mounts to the front bulkheads. Salven places a 2mm shim under the
front of the upper arm mount. This effectively tilts the upper arm hinge-pin/axis of rotation backwards. Being a pan car racer, I am very familiar with reactive caster... it is a very useful tuning aid and can be the difference between a great car and one that is hardly drivable. However, the typical dynamic caster that is used on pan-cars sets the upper arm rotational axis at an angle forward... not back. So what Salven is doing is effectively using "reverse" reactive caster from what is typically used on pan-cars, etc.
Now, what confused me was Salven's subsequent explanation for this modification. He mentions that the "reverse" dynamic caster gives "better turn-in" and responsiveness @ corner entry, without sacrificing steering later in the corner.
This is basically, verbatim, what "normal" reactive caster does. When the upper arm axis of rotation is angled forward, the caster angle
decreases as the front suspension compresses. Thus, at corner entry when you lift off the throttle or tap the brakes, the load is transferred to the front suspension... compressing it and reducing the caster angle(standing the steering hub up in a more vertical configuration) and giving more steering at turn-in. At corner exit, however, as the suspension begins to extend, the caster angle progressively increases... thus aiding in corner-exit steering.
By using the "reverse" reactive caster, Salven is setting the car up so that it
gains caster as the suspension compresses. This makes sense, as a few seconds later he mentions that this allows him to run a smaller static caster angle, as he hates the way the car feels with lots of caster. But... if the front suspension caster angle
increases as the suspension compresses, you will end up with lots of caster @ turn-in, making the car sort of numb and un-responsive... and much less caster @ corner exit, taking away some of the steering there as well.
With the electric pan cars, we have only ever used the "normal" reactive caster. Can someone explain the reasons for using the "reverse" reactive caster on any car? All I can come up with is that it would make a twitchy over-steering car easier to drive... But that is basically the opposite of what Salven is saying. So... is Salven's explanation incorrect? Or is there something I am missing here?