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tamar
Posts: 804
Registered: 5-1-1989
Location: Gouda
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Mood: A new beginning 
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posted on 4-12-2007 at 15:54
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FIA GT Models and Rules: what is a true 1/24 model?
Got this interesting mail from Kai today, thought that posting it here might be a good topic as it adresses 2 main topics in Modelcar racing and the
FIA GT rules.
Op 4-dec-2007, om 9:53 heeft xkaide@kolumbus.fi het volgende geschreven:
Hello Tamar,
I know you're busy but these FIA GT rules are new for me.
Rules says: "Dimensions of the RtR car must be 1/24 of the 1/1 car (with a tolerance of 4%) as noted in the Cars & Models pages".
If I check the Cars & Models pages I found the height of Ferrari F430 GT2 is 1183,7 mm. This means 49,3 mm in 1/24 scale. If I use -4% tolerance I
will get 47,3 mm.
The height of my Fujimi Ferrari body is about 45 mm. With 1 mm ground clearance the height of car is about 46 mm.
If I understand the rules correct way the minimum height of my Ferrari is 47,3 mm? Do they check in techcontrol that all cars are in minimum height?
Or do they check the heights for weight calculation only?
Best Regards
Kai
The reason for 4% tolerance
To create our beloved 1/24 slotcars most slotracers use a modelkit (plastic metal or resin) for the body. And although it usualy says on the box that
the scale of the kit is 1/24 in reality this is rarely true!
Some are closer to 1/23 and some are actually 1/25. But all are within a 4% of the 1/24 dimensions.
So the reason for the 4% tolerance in the rules is to have as many modelkits as possible to choose from.
It is not intended to be used as a reference to see how low you can mount your body.
True scale dimensions: Not as low as you may think
If you scale down a F430 to 1/24 you get a height of 49,3 mm. Kai mentions that his Fujimi kit body is 45mm high and will reach "only" 46mm if run @
the min ground clearance of 1mm.
Yes Kai this is all correct, if you were to take the stock body and would mount it as low as possible within the slotcar rules. But you're not
supposed to mount the stock body, you're supposed to turn the street body in to a 1/24 scale copy of the GT2 racer by adding the sideskirts as shown
in the image below
These extend downwards from the stock kit body by some 2 mm.
Why does the F430 GT2 have these skirts, simple to keep the air from flowing from the sides of the body underneath the car, spoiling the underbody
aerodynamics.
Why don't they just lower the car, because the wheel sizes are fixed as are the dimensions of the wheel arches!
So what is the actual groundclearance of a FIA GT2 car?
Well ...in the Official FIA rules for GT2 article 10 Suspension
/10.1.1 Ground clearance states b/ At any time, it must be possible to slide under the car a block measuring 50 cm (width) x 10 cm (length) x 5
cm (height);
Which means that on a true scale a 1/24 GT2 slotcar the body should be at least 2mm above the track. 
So add 2mm ground clearance and 2mm skirts to your Fujimi kit and you are at a true to scale 49mm.
1/24 modelcar pages
The purpose of the modelcar pages is to create a reference of what the true scale dimensions of a sportscar are.
But we're using this reference only to keep slot bodies "evolving" from proper models into fast and low "thingies"
Already there are some "manufacturers" that offer "improved" bodies that are "more" competitive.
This is what we use it for...to make sure that the slotcars remain model racecars.....not to check if the roof of your body is at a true scale
49,3mm.
1/24 Weight calculation
As mentioned before the Weightcalculation is a tool to minimise the differences between the 1/1 cars and the modelcars made from them. And that these
differences exist should by now be obvious to all.
It ads or removes weight by checking the actual dimension of the slotcar compared to a reference average value.
Basically the lower,wider, longer your car is the heavier it will be.
It is a crude tool (you can only add or reduce a limited amount of weight before the car becomes uncontrollable) and no amount of weight will balance
the difference between a MC12 to a Porsche 997.
Which I told Jean Pierre and this is why there will be 2 classes GT1 and GT2.
Even at 49mm your F430 will be a lot lower than the Porsche 997 it competes against, so undoubtably it will be have to be heavier as well.
It may not be perfect but I still believe it is the best option to ensure that the diffrences remain minimal between each car within its class.
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beaufort12
Posts: 14
Registered: 6-3-2007
Location: Germany
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Mood: No Mood
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posted on 4-12-2007 at 21:51
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Hi Tamar,
i also think in such a way, therefore we will try to start a GT Series
in Kamp-Lintfort in 2008, which based on the calculator.  We added some
cars, which are not really GT´s(remember, we are in KL ), but they are all
competive to each other. Our references will be a cut through of all cars in the entry list. We´ll see if it works
Kind regards
Udo
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Big Al
Posts: 221
Registered: 4-6-2004
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posted on 5-12-2007 at 06:22
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Mr T, that is one of your best pieces of work dude...
A very well written article, and should actually be placed on the RFH Website as a technical definition for our hobby..
cheers
regards
BA
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