Ackermann is Massively Misunderstood

As the title says, I get the feeling that Ackermann is massively misunderstood in how it applies to karting. It isn’t helped by chassis manufacturers suggesting that you can change Ackermann to get a different steering feel. I’m hoping to bring some clarity to this topic.

I’ll start by saying that Ackermann is a needed function to reduce front tire scrub, and that’s really its only function. It’s my personal opinion, but karts really shouldn’t have Ackermann adjustment in my opinion, and the rest of this post is how I come to that conclusion.

So, let’s start with the basics! Here’s a nice picture of what Ackermann is. Notice that the left tire is turned more than the right, for the vehicle to make a left turn. With your kart on the stand, you can visually see this as you turn your steering wheel that the inside front tire will turn more than the outside.
ackermann principle.PNG

This is because the inside front tire will be on a tighter turning radius than the outside front tire. This effect is more pronounced for tighter turns.

With that in mind, there are three factors that contribute to the required Ackermann setup - front width, wheelbase, and toe. That’s it! The rest is designing a setup that always provides the correct amount of Ackermann regardless of how tight the corner is.

So, how does a kart provide Ackermann? Through the steering column and the spindles. In the below picture (taken from TKART, and edited) I draw some circles to help you visualize what’s happening.
annotated column.PNG
On the graphic of the steering column, I’ve drawn two circles, a red and a yellow one. Before we get to the difference between them, notice the green arrows too. Notice how different the X-axis distances are for when the steering column rotates left versus right. Effectively this is how the kart achieves Ackermann, and the spindles play a part too (you can see the differences in those circles if you like). OTK was smart enough to only provide you the ability to make changes on the steering column, because I GUARANTEE they have thought this through given their stack of world championships :slight_smile: Even then, they’re providing too much flexibility but we’ll get there.

With some math, you can figure out what angle each wheel needs to be turned at for any given corner radius, front track width, and wheelbase. I’ve done that using some standard numbers for wheelbase and front track width and plotted it vs. corner radius.


As expected, you can see that for tighter corner radii you need a bigger difference in angle of the inner wheel vs outer wheel as I described earlier. It seems to me that most kart track corner radii are between 14 meters and 28 meters, but I put data into the chart for more anyway.

The next step is plot the ratio between these two based on corner radii, which has a similar shape.


The green line is the correct ratio to have no scrub regardless of corner radius, the red line shows too much Ackermann (meaning the inside wheel will be turned too much), and the blue line shows too little Ackermann (meaning the inside wheel won’t be turned enough). This ratio is effectively how big the green arrows in the second graphic are compared to each other.

If you take a drastic example and say that the front track width is 0, your Ackermann ratio should be 1 regardless of corner radius since it’s effectively one wheel. If you take the opposite example and say your front track width is 20 feet, you have to have a massive amount of Ackermann because the inside wheel will be turning much sharper compared to the outside.

So, here’s why I say Ackermann shouldn’t be adjustable on karts. If we get back to a real example, let’s say you pull in your track width by 10mm on each side, which is a decent change. If you calculate how that Ackermann graph changes, it’s about a tenth of a percent difference for most corners. That’s really not even worth mentioning! The changes you can make on your kart’s steering column or spindles changes the Ackermann by much, much more. If you don’t believe me, change the setting on the steering column and see how much different the wheels turn when you turn the steering wheel! Toe alignment would require more of a change since with more toe-out you would technically want to take a little bit of Ackermann out in order to keep the ratio close to optimal, but again, we don’t have an adjustment small enough to do that on our karts.

There are definitely ways we could have finer Ackermann adjustment on karts, but in short, if the manufacturer does their math you should never need to adjust Ackermann. Those finer adjustments would be expensive anyhow :slight_smile:

I hope this helped a bit.

You are limited by your two dimensional thinking. Consider caster angle while steering and get back to us

Ackerman can be used on karts to change rate of lift for the rear. It may not be optimal, but it’s often used in that manner.

Also given the non linear nature of how it’s implemented on a kart, the amount of Ackerman needed may change from track to track. Extreme example being that road racing generally requires less Ackerman due to the turns being wider.

Care to elaborate? Keep in mind that the steering shaft is also angled.

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See this is where I disagree. I think changing Ackermann makes the rate of lift more/less uneven. If your Ackermann is way off and suddenly you’re turning the inside wheel a ton and the outside wheel hardly at all, you’re just trying to flex the front of the frame instead of create lift by pushing one down and pulling one up.

Ackermann isn’t linear by nature either, I don’t think it should matter for road racing or not unless it’s not correct.

Prove me wrong! :slight_smile:

It’s fine to disagree, theory is fine.

I’m just relaying that regardless of theory, in practice this is what some people use Ackerman to adjust.

It may be suboptimal… but then again so is tuning a four wheeled vehicle to be a tricycle :joy:

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The numerical proof would be on a 4 scale rig. Sit in the kart and watch the weight come off the inside rear as the wheel is turned. This effect increases if the kart is under deceleration as it normally would be as youre trying to get it to rotate approaching the apex. More caster or more ackerman increase this effect.

Its common knowledge and highly repeatable that more ackerman and more caster helps the kart rotate by taking load off of the inside rear tire.

The onus of proving wrong would be on the person making the claim to the contrary of common knowledge that anyone with experience can attest to.

Haha I agree!

@Paolo_Nunzio_Licary I understand that, and I agree! I’m not looking to argue, but more so asking where you’re coming from. I also just like a good debate. My thought there is that it’s like @KartingIsLife is saying that you’re increasing Ackermann in effect to increase that rate of lift, but my counterpoint there is you’re just doing a suboptimal caster change that really shouldn’t come from Ackermann since now you’re likely introducing more front scrub to get the rear to do something.

It’s kind of like increasing toe out to get a better turn-in - it works, but you’re also creating drag everywhere else to do so. My argument is more theoretical that Ackermann should never need to be adjusted for it’s intended purpose of eliminating front scrub since it should be geometrically built in.

David, I can see that you spent some time on this. So I’ll throw some comments into the pile. Some of this is for the benefit of other readers and is my myopic view of karting.

THEORECTICAL STUFF
The other factor is tire slip angle (the angle between the tire direction and the wheel direction). Tire slip angle is non-linear and changes with load, contact patch, tire pressure, track grip and ?? As such, the tire vector direction is not the same as the wheel vector direction to add to the complication, the slip angle of the inside will be different than the outside tire.

TRACK OBSERVATION
At the track, it seems that changing ackerman just changes the ratio between the steering wheel and the front wheels. When the track gets super grippy I change the steering ratio to make the kart easier to steer. Maybe the easier steering is just an artifact.

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I too like debate, if you couldnt tell, its good fun.

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I assume you mean misunderstood?

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hahaha ouch! Corrected - thank you :slight_smile:

Energy Kart has long used these ridiculous spindles:

Also, I’ve seen more teams experimenting with differently spaced steering columns, e.g. 25mm wide, 35mm, etc.

Would be curious to hear your thoughts behind the theory for differently spaced steering colimns, as I can’t say I have a great understanding currently.

Reminds me of the Ionic Edge spindles. Kinda ridiculous looking.

:exploding_head::exploding_head::exploding_head:

Energy also used those spindles in conjunction with a 5-position steering column…

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At some point you just gotta drive the damn kart.

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What’s crazy is that factory doesn’t really elaborate on what all these adjustments do and where to set them. If the factory does elaborate, the message certainly doesn’t get down to the karter.

More than likely if the factory did provide information, it would likely be in the same speak as T-Kart articles, nonsense BS.

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Always made me think the kart must not have a wide “window”.

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I had an ionic edge for about two weeks and immediately sold it. Worst kart I’ve ever had once it was all put together (which took forever since it was riddled with problems).

It was very very apparent that there was no engineering in that kart at all. That spindle is living proof lol

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Pew-pew!!! Laser gun fight in the pits!