Front End Set Up - What is Toe?

Toe is a pretty important piece of kart setup, because of the way it affects the contact patch's interaction with the road. Toe is a measure of the amount the tyres are not pointed directly straight ahead when the steering wheel is centred.

Toe in means the kart looks "pigeon toed". Toe out means the kart looks "flat footed". So how does it affect the handling of the kart?
Tyres are, unfortunately, incredibly complicated beasts and I'm not sure that even elite karters have a good understanding of exactly why tyres react to changes the way they do. That said, by testing changes (and recording the results) we can understand how changes affect laptimes, even if we don't fully understand the physics behind it.
Toe is a perfect example - adjusting toe (generally in the range between 0 and 6mm overall toe out) has a subtle but measurable affect on tyre performance. You'll see it in the wear pattern on the tyre, and in your laptimes.
If you reckon the front tyres aren't working hard enough (not warming up, not much grain in the tread) you can increase the toe. Conversely, if you think the front tyres are overworked, reducing toe will often help. I generally add or remove 1mm of toe per side (half the square on a Sniper laser aligner) each time.
Because I know that such minor adjustments make a noticeable difference, I'm a stickler for perfect front-end setup. When I'm at the track I'm always happy to stop and help someone tweak their front end to get it "just right". One of my pet hates though, is tie-rod ends that have a sloppy ball joint, causing the toe setting to fluctuate wildly out on the track. You can't expect a kart to perform consistently when the front end is randomly adjusting itself.
How do we solve that problem? It's pretty easy, actually: replace them!
So, if you want me to do a front end alignment for you next time you see me at the track (which is free, and I'm happy to do it), make sure you have good quality Tie rod ends in your set up first.