Believe it or not, most important tool for tuning and modifying RC cars, in any RC racer's pit box, probably isn't even sold at your local hobby store. Despite thier absence at hobby stores, you will see them laying on EVERY serious RC pro's pit area.
The tool is, collectively, pencil and paper. One of most enjoyable experiences in RC cars, besides buying a new trick ride, is testing something new, in hope you will discover slight edge, or even a HUGE edge.
Today's RC cars, buggies, and trucks have so many variables that can be tinkered with, even slightest adjustment can have a drastic effect on handling and speed of your ride. Whether you race or just bash, you really should write down current operating state of your RC ride. Variables such as ride hieght, camber, caster, toe-in, fuel mixture you use, charge time of your batteries, needle settings of your nitro, running temp, how many races you get in before you need to rebuild your motor, shock oil you use, and any thing else that you can think of.
As I've shared with subscribers to my RC ezine, you can't improve what you don't measure. If you are serious about racing RC cars, you not only need to master your hand eye coordination, but you should become compatent at adjusting your RC car to conditions you race under. Your RC car performs differently on asphalt at 10 a.m., with a certain compound tire, than it will at 5 p.m., after oil and moisture has heated up from exposure from sun. The traction can vary greatly. And with all excitement and preparation of day's events, writing down these changes can be of great value for when you prepare your chassis or tire choice for following week. If you didn't write them down, you will probably forget them.
And you weekend bashers might be thinking that you aren't serious at RC, so it's not necesary. But let me tell you, if you take time to write down current state of your RC cars and trucks, when you eventually change something, or fate throws a tree in your way and "adjusts" your car setup for you, you will be able to measure your setup and get back to that original state, with no guess work. That means less down time, and more bashing. And if you are still at a loss on how to get back to that original state, you've got it in writing for someone else, like local hobby store guy, to look over.