4 Cycle Four Stroke chassis construction

4stroke
briggs206

(Nicholas Bruno) #1

I am entering my third year running an LO206 kart in an area that the class is still growing, so there isn’t so much information on chassis setup for low power karts floating around. Additionally, I’ve begun shopping around for a new chassis and have seen some interesting specs from different kart manufactures 4 cycle specific karts.

I am currently running a 2012 TonyKart EVRR that was a Yamaha kart in a previous life, and has a 50MM axle and 7.1in rear tires. To me, the kart has always felt very fast and neutral - it’s never had any bad handling characteristics that I can feel. the rear end has never felt tight, as the internet says it should, even with the big axle and rear tires.

Looking into new chassis, there doesn’t seem to be any sort of consensus on what the hot setup for a 4 cycle kart is. To name a few, here are how manufactures spec their 4 cycle karts:

Margay 4.15: 32/28 frame, 40mm axle, 2 bearing
BirelART AM-29: 30/28 frame, 40mm axle, 2 bearing
Comet Eagle: 32/30 frame, 1.25in axle, 2 bearing
Coyote: 1.125in (28.5mm) frame, 1.25in axle, 2 bearing
Arrow X3 4s: 32mm frame, 40mm axle, 3 bearing (?)
Intrepid FK4: 30mm frame, 50mm axle, 2 bearing

So clearly there is no consensus that has yet developed regarding chassis construction. What gives? How can so many different manufactures who (supposedly) know what they’re doing come to such varied conclusions?


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(Nik Goodfellow) #2

Because they don’t know what their doing and the Briggs karts are a request from the US market for a specific type of kart (sometimes “designed” by the importer. You’ll notice that TAG karts are all roughly the same design, be it through evolution or just copying the OTK (which had that design first). Very rarely does a kart pop up that is truly revolutionary like;

Maranello RS8
http://www.karting1.co.uk/pics/rs8-front.jpg

Jon Targett kart from Australia


(Davin Roberts Sturdivant) #3

Also, even with different tubing diameters, the rigidity of the frames can differ as well depending on who has built the chassis, so that’s another element to factor in there.


(Nik Goodfellow) #4

Its like opening a can of worms. You have tubing diameter, wall thickness, material, frame shape (bend and tube location), weld quality or type, front end geometry, axle support design, axle size.

Most of the dealers I’ve spoken to have panic designed a (mostly) 28mm frame with a 40mm axle without putting much thought into it.

I suspect a standard CIK kart would work quite because even though it has less power it has quite a lot grip for that power and thats where CIK karts excel (more grip than power). The karts I have driven with LO206 are CIK karts and apart from a little push on fast corners I wouldn’t say there was anything wrong it. Bare in mind I did no tuning and it was straight out of the box.

Best option is discussed in another topic, but generally speaking stay with a decent brand with decent support that’s winning races.


(James McMahon) #5

There’s probably no consensus because it’s more about folks looking for something “special” for 206 when really it’s not as different to other motor packages in the past (as far as tuning/power goes). So chassis makers are accommodating that by providing something different.

The US seems to be the only place that worries about “4 Cycle Chassis”. You can make practically any CIK kart work.

A Yamaha KT100 can doesn’t make much more power than a World Formula, yet many would have you believe that the chassis should be different. 206 is not wildly different from these, all three of these are low powered motors.

Another thing to consider is that tires being used across the nation are all over the place with 206. That’s an even bigger factor, especially when some are running CIK hard and other are running CIK medium (US market considers a CIK Medium a soft tire).


(Andre Molina) #6

Jon Targett is my spirit animal.

Nbruno, where are you located? USA?


(Nicholas Bruno) #7

Yes., the Northeast US.


(Andre Molina) #8

Now especially when talking Lo206 and 4 cycle sprint racing you should also consider the Ionic Edge and Benik Rocket frames.

The Ionic Edge has been pretty successful here in the Midwest. It’s a 4 cycle-specific frame and is really high quality stuff.

http://ionicedgechassis.com/

The Benik Rocket is unique in that it is a 4-cycle frame with a LEFT side motor mount, making sprocket changes and clutch adjustments easier, and balancing the setup by moving the motor inboard. It could be a nice gamble for 2017.

They don’t have any pictures on Benik’s website (I don’t think the frame is in full production yet) but I know it exists and can be purchased. SSC Karting has them.

http://www.ssckarting.com/Default.asp

So both of those options throw something else in the chassis construction can of worms, the Benik throwing even more of a curveball.

Also, as a heads up, Viking Karting Products is working with HAASE in building new 4 stroke-specific frames. I believe 30/28 with a 50mm 2 bearing axle. Probably to be sold under the Corsa brand. I’ve seen a prototype.


(Andre Molina) #9

From a ballast standpoint chassis construction matters. A 206 weights more then a KT100 can. And a 206 puts down power way differently, there is less available under the curve and you would benefit from a stiffer frame.

But like you alluded to, perhaps nothing that can’t be fixed in any other chassis out there.


(Nik Goodfellow) #10

Have to ask, why do you think that? All the manufacturers are generally going softer.

This has been is use in the UK with a Honda GX160 for as long as I can remember. Not surprising Benik did it as both founders are British.

http://www.kartingmagazine.com/wp-content/uploads/Head-down-Oliver-Bearman-pulls-a-gap-at-the-end-of-the-1st-lap-in-the-Honda-Cadet-0-plate-final.-1024x637.jpg


(Andre Molina) #11

So cool :brap:

I like to generalize that you soften the frame if you have more power, more powerband, and a lot stickier tires available. Lift that wheel up and you’ll need the grip to keep it from becoming too much. A 4 cycle class has less of all of that and especially tires, so it would take a stiffer frame better?

But I am mostly talking out of my ass and in the end giving bad advice, because unless you go through painstaking on-track R&D and methodically fine tune chassis jack and behavior as you go, with the tires you will use, the ballast where it should be, and the driver that drives the thing, none of that really matters.

Ergo the comment that that’s frame behavior that can be fixed in pretty much any chassis out there, if you have the time and the patience to do it.

…And I would still prefer that Benik because an outboard sprocket and clutch are a dream come true in this stupid package.


(Davin Roberts Sturdivant) #12

That’s interesting. I always assumed the opposite, due to the chassis being a spring.

I assumed that a softer frame would be better for lower horsepower applications, so that it was easier to jack the frame, and that a stiffer frame would be needed to manage the added horsepower.


(Andre Molina) #13

It’s a combination of many variables, in the end I shouldn’t generalize like I did (BAD mechanic.)

You want jack. All karts need to set up to jack or they won’t turn. When it comes to how much jack, in my experience with low power and HARD tires I don’t think you want to risk introducing too much of it. Example, our home track has a big sweeper that on MG Blues is really freaking hairy on a soft frame. You’re constantly fighting it, and the key limiting factor is the hard tires.

I’ve seen better luck with hard setups at our particular track. Gold cup frames are very popular. They are very stiff and limit the weight transfer from the seat. Everything kind of gravitates towards keeping the back end in check. Rear end set up as narrow as it can go, front end as narrow as it can go, taking all the square off the geometry… Bleh. Ugly stuff.

That’s for my local track, within our Masters/Senior class. I did also see a sit up sprint 1990’s Birel with a 206 stuffed in it win two heats. The lesson learned was that nothing beats seat time and NOTHING beats set up and R&D time.


(Aaron Hachmeister) #14

I can understand both statements. One one hand, the softer the frame, the more flex you will get. That can be very beneficial in hard compound tires as they’re limited by the grip, so you would think conversely a harder frame for softer tires/more power.

However, I’ve found a soft frame on hard tires can also overload the outside rear causing the kart to hop through the turn. This doesn’t come on softer tires since they can hold more grip in them, benefiting the higher horsepower classes in racing.

The way I see it they both cancel out and can be fixed on the chassis. The American obsession with gold cup chassis likely comes from the time when there was an actual key difference between them. One thing I am aware of in the chassis construction is that the gold cup karts are much narrower. They can get away with a stiffer frame since there is more grip in the kart from the narrow track width. Those karts require very little steering input compared to the European sprint chassis, at least in the one I drove.

@The_Karting_Channel you’re talking about Concept Haulers, right? I’ve run a couple times for practice for a race I never actually ended up going to, but I can agree to the Monza being an… interesting turn to take.


(Nik Goodfellow) #15

I disagree.

For the initial jack you want as stiff a chassis as possible. The initial jack is geometry, not chassis flex. As the inside front wheel is pushed into the ground and the outside front wheel is lifted the kart pivots across the front inside and rear outside lifting the inside rear wheel.

Now after that becomes an exercise in chassis flex, because my opinion is that at this point you want to take lock off the steering wheel but to keep the rear wheel up the chassis has to flex, so it is a combination of the small amount of lock you have on (geometry) and the flex in the chassis and side loads keeping that inside rear wheel off the ground and controlling at what rate it comes back into contact with the ground. In my opinion “release” is about the rate and timing of the rear inside wheel coming back into contact.

I’m writing an article about this very thing that I’m planning on giving kartpulse the exclusive for.

And totally open to discussion on this, i’m not a believe that I’m always right sort of guy.


(TJ Koyen) #16

I’ve attempted a couple times to run sportsman tubed chassis (full-size wheelbase) in senior classes before just to experiment. We had a 28mm Merlin junior chassis with a 1040mm wheelbase we had done to see if it would work in Senior Yamaha. Found the 30mm kart to work better at that weight. I also tested a 28/30 with a Leopard on it once and ran it in TaG and didn’t like it.

I also ran a Tony Kart Rookie chassis in Yamaha Senior in 2015 for one practice session. Besides being impossible to fully weight up, as the chassis was really light, it was really difficult to control. It felt like the inside rear wheel was trying to come up and hit me in the head every corner with minimal steering input.

There’s a reason cadet karts are generally 28mm, junior/senior karts are generally 30mm, and masters karts are generally 32mm. The weight is the biggest factor I think. And the tires. Keeping in mind the actual forces going through the frame, it would make sense that you would need a stiffer frame for higher weight and stickier tires, because it’s going to have a lot more force going through the tubes. A chassis that is too soft will overflex and be a handful. Conversely, running a stiff chassis in a low weight/low grip class won’t flex enough, because hard tires and low weight don’t generate the same torsional force through the frame, so the kart will never lift.

I know a few Masters drivers who usually run 32mm OTK stuff and upon switching to the 30mm for one event, shared the same “wheel is hitting me in the head” sentiment that I felt in my rookie kart.

Also, I tend to think on actually hard club tires, there are a few ways to get a kart to work. When we ran YDS at the club, we were always trying to induce a little slide because the tires never had enough grip to actually make the frame flex like it was supposed to. The tire broke traction before the frame could “load up”. Maybe if we had 25mm frame we could get it to flex properly… But a stiffer frame might work better on that application if you’re going for the 4-wheel drift method.

Another little anecdote… That year Orcic kicked everyone’s butt in TaG at SuperNats, word on the street was he was running an all 28mm chassis (Zanardi) to work better on the low-grip parking lot surface.

Of course that chassis had to be thrown in the trash when the weekend was over because it was made of butter and chewing gum.


(Nik Goodfellow) #17

I do think there comes a point with tire grip, that it becomes better to use the geometry to get you turned in then drop that wheel like its hot and drift through the corner. Certainly in the UK KT100’s where run with YDS and that was the best way to run.

Briggs use comparatively soft tires and I think of it as a grip to power ratio thing. So it comes down to do you have a enough power to over come the grip, if you do then you can drift style but after that it becomes a factor of at what point in a corner can you get away with it. For the me the Briggs requires a high grip driving style, you go in harder, carry more speed and put the power on later (way into the exit of the corner).

Someone should try and super stiff kart, just for funsies. I suspect it would work well.

Maybe Arrow know what their doing :wink:


(Nik Goodfellow) #18

"Buy the chassis that won lasts years SuperNats in TaG Sr.

2012 Zanardi KZ3 ONLY SUPERNATS on chassis. Bottom of the chassis looks brand new. Charged to a convincing victory in the ultra competitive class.

Info on Zanardi KZ3 chassis

28mm Tube
Magnesium Wheels, Hubs, Bearing Cartridges, Sprocket Carrier
Extra large diameter wheel
Custom SuperNats floor pan decal
Sniper front end

SET UP AS IT LEFT THE TRACK ON CHASSIS (including seat position) "


(Davin Roberts Sturdivant) #19

Hey Nik,
Let’s leave the classified comments out of the thread, just so that we can make sure to stay on topic. This is a knowledge topic, not a sales topic :slight_smile: Thanks.

admin hat off


(Nik Goodfellow) #20

Apologies, I was trying to just put the link but all it would do is put the photo, the link says its a 28mm chassis. Which was really all I was trying to get at.