Inside tire unloading

I am aware that steering geometry or kart flex allows the inside rear tire to unload while turning. Since the rear axles have no differentials, I am curious does this “designed in lifting” eliminate squirrelliness during turning whether high or low speed? Obviously the inside and outside tires are turning on different radiuses. Since tires under race conditions have a certain amount of slip does the slip itself resolve the radius problem. If the chassis is not set up to lift the inside rear does it get squirrelly then?

I can not remember ever seeing this used on a race car. How do superkarts handle this if they have downforce that might inhibit lifting the inside?

Ain’t I full of questions.

Supers unload the inside, we just don’t see the extreme lift compared to a sprint kart. Also the turns on road courses are a larger radius so that helps with the scrub.

On twitchyness, in what kinds of turns is this happening and at what part of the turns…

I’m not really following the question. You’re asking if the kart is loose when the inside rear is not lifted?

No, it’s the opposite. The kart is stable and “tight” when the inside rear doesn’t lift properly. That’s why you often hear from newer drivers that the kart “feels good” when it’s slow. Because the kart is stable and locked down to the track from having both rear tires on the track.

A kart that lifts properly will definitely have a slightly floaty feeling in the rear end when that lift is happening. That’s the purpose of the lift, to get the rear end free and rotating without scrub. Some drivers can’t feel that lift happening, and some intuitively try to countersteer when they feel that slight instability.

Race cars have a differential, so they don’t need to lift the inside rear.
Superkarts are moving at a much faster rate, with more power, and wider turns so the scrub isn’t as detrimental, as James said.

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I am trying to understand how turning works without a differential. Your replies are helping. :grinning:

I have felt that floaty feel. I had a front drive autocross car that would pick up its rear inside. The rear felt loose but it didn’t induce oversteer.

Basically, when you turn in, the inside rear lifts. Accelerate and it comes back down. It’s done without noticing it, but that’s it in a nutshell. Managing this becomes intuitive.

Well in that case, good!

Similar feeling I would imagine. I haven’t driven an FWD in competition but they do lift the inside rear sometimes too.

The main difference obviously is a kart is RWD and also needs to lift the rear, so that’s what makes the kart unique.

Just being nitpicky, but not necessarily. The acceleration is providing more force through the kart and building up lateral load. So the inside rear comes down when you unwind steering or reduce force through the kart typically. It just so happens you’re usually accelerating when the steering starts to unwind.

I’m sure I’m just arguing semantics, but just wanted to point that out.

True true… you can indeed accelerate and keep wheel up, in a turn, it’s a balancing act. Maybe another way of thinking about is that unwinding the turn and transitioning out is what drops the wheel. Well, I tried. It is subtle.

When I mentioned squirreliness I was imagining the inside rear tire could cause the kart to turn less/more during transition or bumps as it loaded/unloaded.

Guys, thank you very much for the discussion. I appreciate an intelligent discussion with me even though I am not currently racing karts. I’ve raced and still race other stuff.

This discussion has made me read about tire slip angle and slip ratio. Interesting stuff.


Karting and slip angle = much fun. Once you start getting the hang of this, and you start being able to ride consistently in the rubber, you’ll be rotating the kart at your pleasure.

With the inside rear tire not unloading, the kart will not turn in, at least not at well. Sometimes if a driver has snap oversteer in a corner, the kart is not rotating on turn in, and then suddenly the tire will unload/rotate and slide because of how much steering input the kart has in it.

This can lead to a kart feeling “squirrely” when the kart is not unloading the inside tire, but not unloading the tire is not directly making the kart squirrely.

Actually the wheel lift turns the kart into the opposite of squirrely. When you are on three wheels, the kart turns freely. It’s to the point that in some tighter turns, it feels like you reached out and grabbed a pole at the apex and the kart literally pivots around that. Not squirrelly. However, with wheel down, the kart is all bound up and probably hopping.

I understand the kart would not be squirrely when cornering correctly with the inside rear up. I was wondering about transitions or bumps loading/unloading the tire when it should be unloaded.

Yes and no. In a normal turn your inside will be light. Let’s say you take some kerb with the inside of the kart. You will feel it, but since the weight is mostly over the outside wheels, it won’t feel as impactful. Yes bumps can and will upset the kart mid turn. Most turns aren’t going to be bumpy on the racing line though.

Does that help or am I not quite understanding?

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Track surface imperfections can definitely upset the kart. Sometimes an inside curb, if hit with the inside rear wheel unloaded, will feel like nothing. But bumps on the racing line or rough tracks will have a pretty big impact on the kart. Before it was repaved, the kart track at Road America was so rough we would purposely soften the frame to absorb some of the bumps and keep the tires on the ground, rather than skipping over the bumps.

Think of it like this: the kart frame is a spring. When you stretch a spring, or load up a kart frame with torsional force, it will react substantially to outside forces. If you have the kart loaded up in a corner and hit a large bump or curb at the wrong angle, or try to carry too much speed through a particularly grippy corner, the kart can become unsettled pretty easily, and sometimes pretty violently. If the track is super gripped up, it’s completely common to charge a corner too hard, give the kart more load than it can take, and have it start bucking like a bull mid-corner. Sometimes enough to hurt your ribs or throw a chain even.

Thank you both. That helps.

I think if you’re not super used to kart, it might feel a bit twitchy due the frame and tire sidewalls flexing, but the kart itself is pretty stable, if that makes any sense.

@tjkoyen you hit it hard when you said this about new kart drivers. I am still struggling to find that feel. I have raced high horsepower fwd cars for years. And when you feel something start to rotate you fix it immediately or you’re in for a bad day.

My last race when I finally was mixing it up for a podium in the dry. I started to notice the feel of it “stepping out” and just kinda went along for the ride around the turn. Found speed in that instead of constant counter steer. I really need to run a rear facing camera or a 360 cam so I can watch when it’s lifting to see if that’s what I’m feeling. Or if it’s actual oversteer that I’m trying to correct.

I did a thread recently when I came back from OKC. I had done a couple test days and messed up my rib again. In that thread, I was questioning why I got so much “hopping” in the first turn. Past a certain speed, even though I was within the grip of the tire, the chassis could not handle the lateral load. I was pushing the kart too much at apex, asking too much of it. The result was TJ’s bucking bronco of a kart.
Making the turn a bit rounder at apex stopped the hop.

The rear camera is a good idea. I tried to get someone to follow me with a camera but that practice ended up being cancelled. I also am not sure what unloading is supposed to feel like or if I’m unloading.