minimum jacking is most free setting?

[michael smith]

my kart was setup with max caster, maximum ackerman, and toe out, to promote max jacking.

On the floor, with no driver, if you turned the steering wheel full lock, the inside tire would come up over a half inch

But you couldnt move the kart.

So just for giggles i went the opposite way. Minimum caster, minimum ackerman on steering column and spindles, zero toe.

Why is it that with this setting, turning the wheel full lock does NOT lift the inside wheel, yet the kart will roll with full lock almost as if the front wheels are pointing straight?

[TJ Koyen]

Michael,

A couple things.

First, the reason the kart with no caster felt like it rolled like the wheels were straight is because on-track, that’s what that kart would be doing, going straight. You’re not going to get it to turn with no geometry in the front.

Did you try moving the kart with all the caster while lift up on the inside rear and pushing outward to simulate the centrifugal force you would experience while cornering? I think you would find the kart would rotate pretty easily then.

As a rule, I always try to run as little geometry as possible in the front end because you’re right, it slows the kart down. It generates scrub and all this weight jacking. The issue is, you NEED to run some otherwise your kart will never turn. And I almost always end up running max caster because it suits my driving style/stature. But the less you can run, the less scrub you will have in the front end and the easier the kart will roll off the corner. Taller drivers who can use their body more to induce lift can run less caster and get away with it because they can generate the weight jacking necessary to get the kart to rotate themselves.

Driver/Coach/Wrench : Innovative Performance/Exprit
Owner : Oktane Visual - www.oktanevisual.com
www.facebook.com/oktanevisual
www.instagram.com/oktanevisual

[michael smith]

Ok, thats part of what I’m trying to figure out. The first rule of karting is the inside rear must lift to turn so what i cant figure out why would caster make the kart turn less when the inside wheel is clearly off the ground, and how with the inside wheel still on the ground with less caster, the kart rolls freely.

[Benn Herr]

Watch some of the youtube stuff of guy racing karts on ice – the ultimate low grip surface. They look like they are sitting very upright and leaning out. The fast guys in the rain do it too, it just doesn’t show as much.

[michael smith]

i dont quite understand how that correlates to caster / ackerman setting and how free the kart is.

maybe you can expound?

[michael smith]

Tj, i tried it out this weekend and its the freeest the kart has ever been. I am a very tall guy so maybe thats why i could get away with it but its definitely less bound up around corners

[Steve O’Hara]

Michael,

If you have max ackerman and toe out when the steering is centered and then you turn the steering full lock you’ll basically get the front wheels pointing radically different directions. With a bunch of ackerman the outside wheel will turn in through about 75% of the steering range and then it will reverse direction while the inside wheel will continue to turn sharper in the direction you are turning the steering wheel. The end result will be around 2 to 3 inches of toe out at full lock and no kart will roll free in that condition.

When you made all the adjustments to the front end you nullified a lot of the effect described above so the kart will roll easier. The key thing to keep in mind is that you will never use full lock turning into a corner on the track unless your front tires are bricks and you have a huge understeer condition.

Steve O’Hara

 

[TJ Koyen]

It’s very possible with your height you were way over the necessary jacking to get the kart to turn on your old setting, and taking all that geometry out helped settle the kart down and actually made it usable.

That’s why I always try to shy away from generalizing anything in kart setup because as you’ve just demonstrated, depending on the conditions, you may end up with the opposite results of what is expected.

Karts work within a “box” with regards to setup. There’s a window where the kart reacts predictably to changes, on some chassis this window is bigger. Things like driver size, tires, engine, weight can all alter the size and placement of where this imaginary “tuning window” is. Once you get outside that window, the kart might not react as you would guess because you’ve over-stepped a line somewhere on your setup and the kart is operating outside of it’s comfort zone.

Driver/Coach/Wrench : Innovative Performance/Exprit
Owner : Oktane Visual - www.oktanevisual.com
www.facebook.com/oktanevisual
www.instagram.com/oktanevisual

[Larry Hayashigawa]

@ Michael Smith:

Ok, thats part of what I’m trying to figure out. The first rule of karting is the inside rear must lift to turn so what i cant figure out why would caster make the kart turn less when the inside wheel is clearly off the ground, and how with the inside wheel still on the ground with less caster, the kart rolls freely.

My Take:

At initial turn-in (lots of steering wheel displacement), the front end (caster, track width and tire grip) does most of the work and serves two functions 1) to change direction of the kart and 2) initially hike the IR.  Here you want more front end “geometry”, which is steering wheel angle, caster and track width to a point.

After the initial turn-in (less steering wheel displacement), the lateral acceleration (side g-force) from the cornering acting on the kart & driver creates a force that twists the chassis, which keeps the IR lifted.  In this phase of the turn less front end geometry is needed to keep the IR lifted because the lateral force is should be keeping the IR hiked.  The IR can be hiked a lot or little by adjusting weights, seat position, axle and somewhat the front end. By reducing the front geometry with the right amount of caster & front spacers (usually less) the front end scrub is minimized and the IR is just skimming off the ground, this is condition when the kart is rolling through the turns efficiently.

Sounds simple but feeling it and then setting it up is not so easy to do and there are other ways to make adjustment to IR hike.

 

Larry

[michael smith]

@steve

great point. i did the test because every kart setup document ive ever seen, to illustrate the need to lift the inside rear wheel, asks the reader to turn their wheel full lock and try to steer the kart. it also asks the reader to notice how difficult this is to do BECAUSE BOTH REAR WHEELS ARE ON THE GROUND

now im wondering if the freeness of a kart derives more from the front of the kart than from the rear. i mean- even if both rear wheels are on the ground, they are pointing the same direction. if the front wheels are pointing in two different directions wouldnt this cause a bigger binding effect than the rear wheels?

but i agree with your point. at full lock the wheels are going different ways and it wont move. what i find very interesting is that on the track even though full lock is not in play, it still rolls free-er with less ackerman and caster.

[michael smith]

larry , good point. i guess its a game of testing to find the best setting

[Rob Kozakowski]

Michael – I think one thing you need to consider are the forces in the static vs. the on-track situation.

With the kart sitting still on the ground, no matter how much caster, ackerman, etc. you have, when you turn the wheels, it won’t roll as freely as it will in a straight line.  I think the only point the “books / setup documents” are saying is that a kart naturally wants to drive straight ahead.

Yes, if you take a lot of the geometry out of the front end, it will roll “easier” under no load with the wheels turned than with lots of geometry (apply a simulated load and results may change)… but still not as easily as with the wheels pointed straight ahead… the kart naturally wants to move in a straight line… push it with the wheels turned, and the wheels will straighten themselves out very quickly!

What this little demonstration isn’t doing is telling you about the impact of adjusting caster, ackerman, toe, front track width – those things really come into play when a kart is moving.  That’s where the points that TJ and Larry, etc. are making become relevant.

As to where does the “freeness” of the kart derive from?  I’d say it’s a balance between a LOT of factors… part of it is the front end, part is the rear, part is the overall balance / seat placement, part of it is grip levels – in the track, the tires, the frame, etc.

Yes, you want to lift the inside rear… but (a) there are many ways to do it… and (b) some will make you faster, while some will make you slower.

[michael smith]

let me update this for anyone reading in the future. there is a reason why they say dont change more than one thing at all.

it turns out the “freeness” was all from moving the rod ends to the outer holes on the spindles. i tried different caster/camber settings, and doing the same “crank the steering wheel all the way and push” test. it still rolled relatively free, even with max caster, and STILL with the inside wheel not lifting.

[Author]

Posts