Looking for 4 stroke advice

Dipping my toes in the 4-stroke pond and have made some observations that hopefully some can clarify for me…

Why are lower HP chassis typically on smaller diameter tubing. I can understand higher HP classes which typically run softer tires since they generate more grip would need a chassis that resists flex. Where I am confused is in a situation where 206 and KA run the same (harder) tire what benefit does the 206 have with say a 28mm chassis vs a 30mm chassis?

I have noticed sprocket guards are often used in 206 but seldom used in 4 stroke, is there a reason for this?

Thanks for your input

I’ve always assumed the lower power calls for a flexier chassis. It might be an intersting experiment to try an lo on a 32mm chassis, followed by trying a 28mm.

They aren’t. The majority of 206 chassis are 30mm+

MGM 1.25"
Comet Eagle 32mm front hoop, 30mm elsewhere
OTK 30mm

206s like to throw chains without a guard, I don’t know why, but they do.

Small tubes are the minority.

206s throw chains without a guard because the flimsy multi-piece mounts, tiny frame clamps, and flexible rear frames everyone uses allow the entire engine to rotate around its vertical axis when you go from acceleration to braking. I have driven karts where a single lockup for a pass was enough to cause derailment.

If you want to not throw your 206 chain, move your engine pusher to the top of your left bearing mount, have it push the engine rather than the mount, clamp the mount to the chassis with M10 or 3/8" bolts, and consider a chassis that can fit a 206 with a crossmember behind the seat that goes somewhere other than behind the bearing to laterally reinforce the frame.

OTKs, Birels, Comets, and Margays are all pretty good, but if you really want the hot ticket get a Factory…

I hope you don’t consider Odenthals a flimsy mount with tiny clamps.

No, the Odenthal is a very strong mount, but they’re clearly designed to have the engine pusher against the top part of the mount or the engine. Sketch a quick diagram of the slider assembly as it takes a torque around the vertical axis; you’ll find there’s not much material resisting that moment!


Your points make sense, but I am still confused how a 9hp brings can generate enough flex to cause this issue while a KA with over double the HP or even a 125 with triple the HP doesn’t have this issue. The Odenthal design is basically the same for each motor too. Does the inboard drive have something to do with it?

He’s repping Factory Karts. Cant blame him for the plug.

I think the gear guards is more of a product of gear location and track conditions than it is motor choice. In an outboard drive class, with the gear closer to the safety of the RR tire, you dont have as much “contact” with curbs, off track excursions, and bumps. Axle flex could also be attributed, but I don’t have enough data to say that is a cause.

HP doesn’t produce flex, corner speed/loading does. In our area the highest corner speed comes in the lower HP classes where the good drivers know they need to keep momentum up.

(Disclaimer before I start a fight: obviously good high HP drivers know how to keep momentum up too. Just proving a point here.)

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I’d argue the numbers are somewhat area/dealer dependent. The Birels, Crocs, original RFs, VLRs and Comp all have 28mm tubes as dominant with some 30mm mixed in. As far as chain guards I personally never run them on the rare occasion I run 206. I also always align the bottom side of the sprocket to the bottom side of the clutch with a straight edge.

Understood on the HP not producing flex, but softer tires in the higher HP classes should, no?

Does type of chain factor in at all? 219 vs 35? The 35 pitch seems to have deeper slots for the chain.

In my opinion, you should look at it from the opposite angle. It’s not the engine producing flex, but the flex impacting the engine. What I mean by that is excessive grip on a low hp engine will bog the engine down and leave you planted, stationary like a flower pot in the middle of a corner. High flex chassis and medium/hard compound tires helps the kart turn free with less impact on engine revs, keeping momentum going



The KA and X30 use a one-piece mount with a much smaller overhang from the sprocket to the centerline of the tubes, so it is effectively much stiffer.

Andy’s explanation is correct and otherwise complete.

I didn’t invest in chain guards early on, but then I threw a few chains and it seemed like cheap insurance, and I haven’t had that issue since. Not sure if its the guard doing its job, or me just paying more attention to chain tightness. Maybe a little of both.

Areas are definitely dealer driven, but if you go look at the overall 206 market, the majority of chassis are 30+. I was talking pure numbers and percentage of chassis being used, not that one is better than the other.

No I get that, but I think west coast is definitely more predominant in the 28mm stuff besides OTK anyhow. We don’t get much for MGM, Comet, or really American made karts much at all. I suppose with Factory there’s more American made stuff, we don’t see those up in the PNW however. Invader is west coast too, but not sure exactly what their frame sizing consists of.

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Totally, MGM and Eagle is definitely mostly Eastern 1/3 of the country. Heck, a lot of people I’ve talked to out west don’t even know what they are!

I think I’ve seen one MGM in person before, never seen an Eagle. :joy:

In the Midwest at least it seems like a pretty good mix. But in general the lighter the class the smaller tubing everyone runs. For junior, light and even medium 28 or 30 mm otk/birel/merlin etc is pretty popular but at least for ckna eagle is the most popular heavy kart with the 32 mm.

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On those chain guards, there seems to be a wide variety of prices and types. Plastic, aluminum, carbon fiber, 1 piece, 2 piece, plus some that have other “features”, so which one should I get? Is there a reason to not get the least expensive?