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Color0's Micro RC Blog -- A technical brain dump from the mind of yours truly...
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Crafting a Race Body for Your Mini-Z

Posted 03-26-2009 at 12:57 AM by color0
Updated 03-08-2011 at 09:36 AM by color0
So you have your race body of choice, either chosen by yourself, with the help of a local racer, or with the help of my blog article last week. Now while you could just glue in the clips, slap it on your car and go racing, there are several things you can do to any body to make it faster, more stable, lighter, stronger, etc., all of which add up to a better racing body.

This week I'm building a new McLaren F1 GTR longtail (the last one got crushed... long story), so I'll cover some of the more popular and effective modifications you can do to make your race bodies faster.

Cutting out non-visible window glass, aka "the sunroof mod":

Most track rules dictate that Mini-Z bodies cannot have any of the visible window glass removed, except in the case of rear suspension clearance. However, you are allowed to remove anything that isn't visible from outside.

Done right, you can cut from 1-3g of weight from your body. The best part is that this weight is lost from the very top of the body, so you get the bonus of lowering your CG as well! I highly recommend doing this to all your racing bodies, so long as you have a dremel/rotary tool and a cutting disk. Warning: Always be very very careful with power tools. I have personally had a cutting disk explode in my face before by not being careful and accidentally angling the disk the wrong way!

The sunroof mod can be taken one step further on the McLaren F1 GTR by cutting out material under the roof scoop. I like keeping the roof scoop on for aesthetic purposes, so I cut an "H" into the roof to make up for the extra weight I attach.

Obviously you shouldn't do this to your body if you don't have an additional piece to cover up such an ugly hole.

Rear bumper: Aerodynamics matter. When your car is at speed, air gets pushed away by the nose of the car, creating a low-pressure region in front that produces a small amount of downforce. But in the rear, you get air bunching up against the inside of the rear bumper, which creates a high-pressure region, which lifts the rear end instead of planting it down! The solution is simple: cutting out bits of the rear bumper will let the air escape, creating a psuedo-diffuser effect: the low pressure region left behind by your chassis will pull the body downwards, resulting in downforce, or at least reduced lift. The plastic removed also makes the rear end lighter, for more responsive and aggressive steering. Go ahead and remove as much as you want:

This particular body is a more extreme case, but on other race bodies (particularly the JGTC/Super GT cars) you can also remove lights, cut out vents, remove diffusers, etc. to reduce weight as well as improve aerodynamics. In any case, cutting holes into the rear bumper makes a huge difference on the track. The aero advantage gives you more stability at speed while the reduced weight gives you more agility infield -- there is no drawback whatsoever.

Headlights: Or more accurately, headlight buckets. My general preference is to keep them -- they keep the cars looking scale, and give your car more front end bite. But if you want to cut the weight you can always omit them, or shave off the non-visible plastic like with the window glass. I just keep mine whole:

Front end reinforcement/repair: I've never actually done this, but on some of the more fragile bodies (especially the Audi A4 DTM) you should consider reinforcing the inside of the front bumper with a sheet of plastic or fiberglass cut to match the inside of the front bumper. This modification has saved tons of A4's, so if you think your race body may be one of the fragile ones (just check how thick the front bumper plastic is... if you can bend it, you're at risk) then you should look into this. In fact, Atomic sells pre-cut SSG carbon fiber reinforcement plates for several bodies.

Spoilers/Wings: As I mentioned early, aerodynamics matter. Most of the good racing bodies coincidentally have decently-sized replica wings that actually provide good downforce at speed, but if yours doesn't (or it's not enough downforce), then it's time to consider fabricating your own spoiler. It doesn't have to be anything really gorgeous; even an expired credit card can be turned into an effective spoiler. You just want your spoiler to be angled up a bit, and just the right size and angle to give you the right "feel" when the car's at speed. Play around with this, and keep in mind that a little change can make a big difference: attaching a small Lexan lip to the rear of your car can make a larger difference at speed than changing your springs or your T-plate from the hardest to the softest ones.

Also remember that if you have the rear bumper of your car partially or fully cut out, you won't need as tall/large of a spoiler to get the same effect, since the body itself acts as a crude diffuser when you cut out the rear end. In fact, the McLaren F1 GTR as I'm running it now doesn't seem to need a rear spoiler at all, due to the relatively long rear overhang and the comprehensive dremel work on the rear bumper (as mentioned earlier).

Some other little tips should go without saying, for example, omitting the side mirrors since they're easily lost anyways. If your tires are rubbing on the body, either sand the body or remount the body a millimeter higher or so. But after all is said and done you should have a nice and lightweight body that will serve you well for many races to come.

Check that out, won't you? The McLaren F1 GTR autoscales weigh 44g, and here we've cut nearly 10g from that number just by cutting out windows, rear bumper, and omitting the spoiler and other unnecessary parts. As soon as I get this body all prettied up, it'll be good to go!
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