I have an F103RS that I am borrowing from a fellow racer whilst waiting for my 15th Anniversary kit to arrive...
I run on asphalt with rubber tyres and are currently having an understeer issue unless I slow down too much. The front tyres are TRG hards and the rears are TRG also. It is running pivot ball suspension with 35wt oil in the damper and a red spring.
Any suggestions on how to increase the grip at the front wheels? (without using traction compound)
I noticed a similar condition on carpet with my car. Basically, the wheelbase is pretty long, and the car is light, so it doesn't dump weight on the nose like a touring car. I'm running the lightest front spring, which I think is gold(??). That was helpful to me to get the balance closer. If you can run a stiffer center spring, that also helps.
Another idea that I do like, especially with the softer springs, is to actually preload the front springs slightly. You can do this with a shim, or by using the grub screw in the steering knuckle. A little preload helps to keep the weight over the nose. i noticed at times my car would sort of lift the front end with the soft springs, causing the understeer on power. The CRC 1/12 car uses this as a setup option, via kingpin length. Using the grub screw to control how much kingpin shows at the bottom of the knuckle is a similar idea.
One last thing with the pivot ball suspension is to lift the t bar as i mentioned in the last post. That will remove some rear grip, and help rotation.