Wednesday, December 7, 2011


The F103 was a great car when "wide" 200mm cars were the most popular.  At this point, 180mm cars are making a big push, with the publicity of the class at the IIC, the UF1 series, and Tamiya's many F104 based kits.  At the same time, the F103 has some upside that other cars don't.  It is a bit shorter, which is an advantage on the tight indoor carpet tracks raced in the winter.  All the Tamiya front ends interchange, so it's a pretty simple operation to bolt an F104 front end and the proper tires on and get to work.  The two biggest obstacles are the body fitment and battery selection.  The battery turns out to be easy to take care of - a Losi 22 "shorty" pack fits perfectly with an F104 body.  To get the body to fit, a few things must be modified.  First off the rear of the body must be shortened due to the wheelbase of the car.  Secondly, the top deck must be cut down and the holes for the body posts re drilled so that the body will fit over the car without being stretched by the upper deck.
You can see in the picture that the rear of the upper deck is cut down and the posts moved in.  Also note the width of the short pack.

Body fitted, stock holes for posts in body line up perfectly.

This is again an F104 lower arm, with the camber plate directly on top of the arm.  Xpress parts are used to control the caster, and as the upper eyelet on the kingpin.  35mm turnbuckles for all links are a good size if you want to set up a front end like this.  Everything else is from a 104 front end.  Generally, 1* camber or less and 6* caster are a good place to start, with black springs.  Ride height should be at the minimum legal.

Another look at the front end.

I should point out that I like to try to control the roll of the car at the t bar.  Rubber tires are heavy, and i think that they require a bit more roll stiffness. To that end, I have been using the standard t bar, with a .5mm metal shim on the forward screw, and an .060" nylon washer at the rear, with the large outer o ring from an F104 t bar around the washer.  I was trying to limit the movement of the T bar without making it solid or too stiff.  The car's short length makes it prone to traction roll at times, from the small amount of running i have done with it.  Taking a stab at things, I did try both OFNA Diff Lock  and 100,000wt diff oil on the damper plates.  The OFNA lube, which is like glue, made the car do some strange things, like pirouettes...  Anyway, 100,000 wt may have been better, but I cut a tire sidewall and the car was looping out randomly.   I'm not sure how to handle the t bar setup with this car yet.  I may just throw everything out the window and run the car soft with minimal caster.  Caster is a problem if you run too much in a high traction situation, since it cross weights the car and induces even more roll.  So as the car wants to traction roll, you have to take caster out.

The first night i ran the car, it was actually pretty good, and the week I had to think about it may have just resulted in some over thinking.  It probably just needs a solid practice day to get an idea of what it likes and it will be very good.


  1. BTW you can run the whole F104 front end as is, I am just a tinkerer...

  2. Awrsome good info i will be doing this to one of my f103