Ground Clearances

[gordon]

Hi Guys,

For quite some time now I've been thinking about a way to manage the magnet and bottoming-out situation for cars at FRC. We've tried the magnet marshal but there's too much variation in the readings, even for the same car. I even thought about one or more non-magnet classes and investigated this again today, but will defer that to the future.

Back when I started racing cars in the early '70s and drove in stock classes, one of the problems was that guys were lowering their cars an inch or two to improve handling. To stem this, the organisers came up with a minimum ground clearance rule and, to implement it, all cars had to be able to drive over a block without coming into contact with it. This idea of a minimum ground clearance has been on mind for a while now and so I decided to do some research online, followed by some tests here with my cars. My research found that many slot car clubs do in fact have minimum ground clearance rules, with the minimum ranging from .5mm to 3mm. With this in mind, I cut a strip of plastic from a 1mm sheet I have to a size of about 7" x .5" and proceeded to test all my active slot cars, first on a piece of track (so that the magnet effect is included), then on my non-magnetic tech block. Here are the interesting results:



Whilst many of our classes allow for substitution tyres - an easy way to adjust ground clearance - some stock classes require that the original tyres be used (although they may be trued). Most of us have stretched that rule and actually ground down the stock tyres to reduce ground clearance and this has led to ever faster lap times which, to some extent, defeats the purpose of having "stock" classes. This can be clearly seen in the chart above for my HS cars as well as some of my VS cars. Assuming that returning to the original-diameter tyres will solve this problem for those, the one which bothers me is my completely stock VS Ferrari 275P which doesn't even have ground tyres. There is one place on the chassis which cannot clear the 1mm plastic strip (no wonder why it handles as well as it does!). I would like to experiment with a .75mm strip and see if the car passes this very low minimum, however I'd like to see how other FRC cars besides mine test with the 1mm strip. Next event we can check the cars you bring and record the results.

I am proposing that we try whatever minimum is decided upon with a single class initially as an experiment. Perhaps Slot.It Challenge or Restricted GT since its easy to adjust ride height with a simple tyre change, which is allowed in these classes. I feel that by having a sensible minimum ground clearance we will bring the performance of cars closer together and at the same time stop having cars touch the track rails and causing potential problems both for the car in question as well as the track (overloads). The obvious way to do it would be to measure it on-track with full magnet effect since this is the actual running ground clearance.

Let me know your thoughts.

Gordon

[steveaca]

It certainly would be interesting to compare the ground clearance of all the actively competing cars.

[Luke]

Gordon ~ Your slot car test (research) list looks like a check list for a flight simulator...

All in all this isn't a bad - Ground Clearance on your FRC track.

I have 3

1. Is your non-magnetic tech block the 1mm plastic 7"x5" strip?
2. Is "bottoming-out" a next term for under-steer?
3. Hope this GC don't deter other FRC racers?

Luke

[gordon]

I have 3

1. Is your non-magnetic tech block the 1mm plastic 7"x5" strip?

No, I have a tech block. The car is placed on the tech block (or track) and the 7" x 0.5" (not 5") strip is slid under the car from the rear till it either touches the guide flag (pass) or is stopped by the chassis (fail).

2. Is "bottoming-out" a next term for under-steer?

Its a next term for making contact with the track, something most of the cars in their present trim tend to do at some point in the lap.

3. Hope this GC don't deter other FRC racers?

Its not a rule as yet, just a suggestion. Most of us talk about how much we enjoy the Porsche Cup races because of how close and challenging they are. If we can get all (or at least more) of the classes to be as close and challenging- even at higher speeds - we'll have even more fun at FRC.

Let's take your Historic Saloon BMW Mini for example. Right now it has the straight line speed but cannot corner with the lowered Escorts. Theoretically, you can lower your Mini and improve its cornering (but only with rubber tyres, not the silicones allowed for that type of car). This is supposed to be a stock class but cars are being lowered (by grinding away the tyres) to improve performance. Vintage Sports is the same. I've thought and thought about this and feel that the minimum ground clearance is worth trying. It may be the best way to even-out the cars as they were intended to run when the classes were created. Alternatively, we can do as some clubs do and have minimum wheel/tyre diameters, its just that I feel its easier to slip a strip of plastic under the car and set the ground clearance to an agreed value than be measuring wheels. BTW, new original tyres can be purchased - I have new ones for my Ford GT40, Escort and Cortina waiting for when they're needed.

I want to gather the stats from everyone's cars first. Then maybe we can try it in a class like Slot-It Challenge (just a tyre change). After that we can decide which way to go.

Gordon