Rear Axles and keys
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Rear axles and wedges for Go Karts
Your rear axle is an important part of the go kart chassis and affects the grip and feel will have in your go kart.
If you are to own only one single rear axle we recommend one in hardness Medium which works for most conditions, but the best thing is to have a couple of different hardness’s to test in between.
Read our guide below on what to consider when choosing a rear axle for the kart
The 3 main categories of Go Kart rear axles
The rear axle changes a very large part of how the kart behaves because there is no suspension on the kart. The rear axle regulates power to the go-kart's rear wheel. The axle is what springs the go-kart in the rear part. There are three different axles: Medium (or neutral), Soft and Hard.
Medium (neutral) axles
Most of the time, you drive the middle or neutral axle. It tends to be the best axle overall as it helps the go kart efficiently around the curves. It responds and adapts well to different conditions on the track.
If you're ever having trouble deciding which axle to use and you've tried different types, your best bet is to put the neutral/medium axle back on and start from the beginning.
Soft rear axles:
One step down from the intermediate axle is the soft axle.
The soft axle is giving the kart a different feel. The soft axle allows the go kart to have much more braking stability when entering the corners.
It feels like the chassis sticks to the ground and sort of seats a little extra in the braking zone. This can make you more confident about the brakes and allow you to corner with more confidence.
Coming into the corners, the axle doesn't lift as high as it would with the medium hard axle, but you have a lot more grip in the first section of the corner and can carry more speed into the center/apex.
The problem with the soft axle is when you get to the middle of the corner you don't have that cushioning cornering that you get with the medium axle:
When you come into the middle of the turn, there is a lot of stress on the go-kart. You want the go-kart to spring back and straighten out a bit when the load is released. With the softer axle, it tends to absorb that load well, but it doesn't let go mid-corner. You don't have the same springy corner that you have with the other axle. It can lead to bogging or other similar problems.
A step up from the medium axle is the hard go kart rear axle.
This one behaves a little different as you instead are lose braking stability as you enter the corner. The way I've always imagined it is that the softer the axle, the more the go-kart works. The harder the axle, the more the tires work.
When you go to a hard axle, you lose braking stability at the entrance to the corner because the chassis does not attach much to the ground.
As you drive from the entrance to the middle of the corner, a stiffer axle allows the tires to work and flex more and you get more movement of the inside rear tire. It helps with rotation, and it also helps you get the kart straighter.
This makes the kart freer when you go into the middle of the corner and center yourself - you lose a bit of the stability you had on the softer axles. The advantage of the hard axle is that you still get the suspension that you lost with the softer axles.
Every axle has positives and negatives, which is why many kart racers end up with the neutral medium axle. The best axle is normally the stock axle as it works in 75% of the conditions you race.
It works more efficiently overall, and you still have good rebound from the tires without sacrificing the grip you get when entering the corner.
Axle Length: Short vs. Long
Another aspect of rear axles is a short rear axle versus a long axle.
You may be wondering "What length of axle do I need for my go-kart?"
With a short axle you tend to lose braking stability. When entering the corner on a shorter axle, the kart is more responsive. It feels like when you get into the middle of the curve, the axle will lift off the ground quickly and stay up all the way to the apex.
With the short axle, the kart can sometimes lift too quickly and then throw the rear around. Or it goes up too high, and when the axle wants to sink back down it drops too hard and it throws the rear end around. These axles normally work well around tight tracks where you want a responsive / nimble kart.
When you go to the tracks with longer sweeping corners, you don't want a kart that turns super fast. Maybe you should try a longer axle or your standard axle. The longer axle gives you more braking stability. You get less slip from the tire from entry to the middle of the corner and you get a little less rotation in the go-kart.
If you want a go-kart that is much more agile and can change direction much faster, it may be time to cut the axle. If you want a kart that is a bit more stable and you feel your kart is too responsive right now, maybe go for a longer axle.
Guide to choosing the diameter of your rear axle:
950 kart for children - 30mm axle
DD2 - 40mm shaft
OK/OKJ/Senior/Junior/KZ – 50mm axle