This is one time where Canada’s karting scene has had an influence on the US market.
The Eastern Canadian 4-cycle scene has been very competitive for a long time. The big Canadian Birel, CRG and Tony (and some other) dealers recognized the ability to sell more karts by offering a “made for 4-cycle” product years ago, and worked with the factories to provide a product that worked well with a 4-cycle engine (first Honda, then Briggs).
This isn’t as much a case of Birel, CRG and Tony putting their “factory” efforts into the products as it the dealers putting in the effort to get the factories to build a kart for their markets, and making refinements when necessary.
For example, the CRG “Tork” or RS-4 and RS-5, was also called the PSL RS-4 or RS-5 because CRG built those karts for PSL when PSL was a huge CRG dealer. When these karts first arrived in Western Canada in the hands of some drivers who brought them from the East, the biggest Western Canadian CRG dealer didn’t even know what they were because the Western Canadian market was focused on 2-cycle at the time.
These chassis have been refined over the years, and other brands have made chassis to suit the market as well (most notably of late, K&K, which is 100% focused on 4-cycle chassis).
These chassis are specifically designed to work with the ASN Canada 4-cycle rules, which mandate a 50″ max width and 180mm rear wheel.
When the rules are opened up to 55″ width and 210mm rear wheels and wider tires, it seems that either a 4-cycle specific chassis or a 2-cycle (TAG) chassis are pretty much on par with each other… the 4-cycle chassis are built for 4-cycle power, while the 2-cycle chassis are designed to be run at the wider track widths.
If you are buying a brand new kart for LO206, I would go with a 4-cycle chassis because of the lower cost. The big differences are they generally use lower-spec brakes, less “beefy” 17mm (instead of 25mm) front spindles, 8mm (instead of 10mm kingpins), only have 2 (instead of 3) rear axle bearings, use 40mm (instead of 50mm) axles, and generally use more aluminum than magnesium components, cheaper steering wheels (i.e. is a $275 steering wheel – about 10% of the cost of some complete 4-cycle karts – really necessary?), etc. to keep the cost down. Some chassis go down to 28mm tubing (or some combo of 28/30), but others are all 30mm.