OK, KZ or DD2: The Differences and Which Kart Class to Choose
When people talk about “serious” racing karts, three acronyms always come up: OK, KZ and DD2. They are not just different classes: they are different engines and mechanics, with ways of starting, clutches and transmissions that have nothing in common. Here are the real differences, the ones that really count.
In short OK is direct drive, with no gearbox, and is push-started; KZ has a gearbox and is push-started using the clutch; DD2 has two gears with paddles on the steering wheel, electric starting and a chainless transmission. The choice depends on experience and age.
OK: pure direct drive
OK is the queen of direct drive engines: 125 cc liquid-cooled, no gearbox and no clutch. The engine is connected directly to the wheel: you accelerate and go. It is built on absolute simplicity: no electric starter, no battery, no electrical system and only the rear brake (by regulation it has no front brakes).
It is started by pushing, helped by an automatic decompressor: you open the decompression valve, give the kart a short push and, as the valve is released, the engine comes to life. Fewer components, less weight, the purest driving: here what counts is keeping the revs up mid-corner. The junior version is OK-Junior; OK-N is the “national” variant, more affordable in terms of costs.
KZ: the gearbox, the “F1 of karting”
KZ is the absolute top: 125 cc with a 6-speed sequential gearbox and a manual clutch operated by a lever. Here too starting is by pushing, but you start by releasing the clutch by hand in second gear.
With higher speed and power, the KZ has a full braking system, with front brakes as well. It is the most demanding and complete class: you have to manage gears, clutch and much greater torque and power. KZ2 is the club/national version, the entry step into the world of gearbox karts.
DD2: the two-speed Rotax world
The DD2 is the top Rotax, and it is mechanically different from both OK and KZ: it has a 2-speed gearbox, but the transmission is direct, without a chain, with a centrifugal clutch running in an oil bath and gear changes managed by paddles on the steering wheel.
Unlike OK and KZ, the DD2 is not push-started: it has electric starting with a battery which, as on all Rotax engines, also powers the ignition. It gives sensations close to a real single-seater, with much simpler and less demanding management than the KZ.
The DD2 has 34 hp at 12,000 rpm, and is reserved for the most experienced drivers.
OK, KZ or DD2: the differences in brief
Side by side, here is what really changes between the three:
Gearbox: OK none (direct drive) · KZ 6-speed sequential · DD2 2 gears.
Clutch: OK none · KZ manual lever · DD2 centrifugal in an oil bath.
Starting: OK and KZ by pushing (the OK with an automatic decompressor, the KZ with the clutch in second gear) · DD2 electric, with a battery.
Transmission to the wheel: OK and KZ via chain · DD2 direct, without a chain.
Brakes: the OK has only the rear brake · the KZ and DD2 also have front brakes.
How to choose
Do you want the purity of direct drive and technical, light driving? OK (or OK-N at lower cost).
Do you want the very best, a real gearbox and the class of the top drivers? KZ, but you need skill and physical preparation; you start from KZ2.
Are you in the Rotax world and looking for two gears with electric starting and simpler management? DD2.
Golden rule: the right class is the one suited to your level and age, not the one with the most horsepower or gears. You grow by climbing one step at a time.
Not sure which class is right for you? With our Arrive & Drive you get the kart, the track and the technical support of the TKS RaceLab team, at Lonato, Franciacorta, Cremona and Ala. → Discover Arrive & Drive →
Frequently asked questions
Is it true that OK and KZ are push-started?
Yes: they have no starter motor or battery. The OK is started with the help of an automatic decompressor; the KZ by releasing the hand clutch in second gear. The DD2, on the other hand, has electric starting.
What is the main difference between OK and KZ?
The OK is direct drive, with no gearbox or clutch; the KZ has a 6-speed sequential gearbox and a manual clutch. The OK is the queen of direct drive, the KZ the absolute top of karting.
Is the DD2 a gearbox class like the KZ?
It has two gears, but direct transmission without a chain and a centrifugal clutch, with paddle shifting. It is easier to manage than the KZ, while still giving single-seater sensations.
Does the OK have front brakes?
No: the OK only has a rear brake, a rule of the class and part of its philosophy of simplicity and lightness. The KZ, faster and more powerful, also has front brakes.
Which class should you start in?
As an adult without racing experience, direct drive (OK/OK-N or the Rotax Senior) is the natural reference. KZ and DD2 come later, with experience.
Conclusion
OK, KZ and DD2 are not “better or worse”: they are different philosophies. OK focuses on simplicity and purity, KZ on the gearbox and absolute performance, DD2 on two gears with the convenience of electric starting. Choose according to age, experience and ambition, climb one step at a time, and every class will give you the best.
TKS RaceLab runs the Arrive & Drive Pro service: 2026 karts with Rotax Senior MAX and DD2 engines, Alfano 7 telemetry and trackside technical support at Lonato, Franciacorta, Cremona and Ala.
Data checked against: CIK-FIA / ACI Sport regulations, official Rotax technical sheets (DD2) and the track experience of the TKS RaceLab team.
Questions about this topic?
Message us on WhatsApp: we answer personally, with the experience of people who live at the track. And if you want to drive a real racing kart, with Arrive & Drive you get into one of ours, ready on track. The right spare part? You will find it in the shop.
Arrive & Drive Pro by TKS RaceLab: 2026 karts with Rotax Senior MAX and DD2 engines, Alfano 7 telemetry and trackside technical support at Lonato, Franciacorta, Cremona and Ala. Message us on WhatsApp for information and availability.
TKS RaceLab | Performance Engineering Karting | tksracelab.com
Read also: How to choose the right engine for your go-kart → · How to choose your first gear for driving a racing kart → · How to choose the right kart axle: track, conditions and behaviour → · Karting classes explained: from Mini to KZ → · Rotax Senior vs DD2 → · Chassis and engine: how they work together →
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Author: Sergio, TKS RaceLab | Published: 28 July 2026 | Updated: 4 October 2026
TKS RaceLab is the Italian online store dedicated to karting: spare parts, accessories and everything you need to get on track. With Arrive & Drive you arrive at South Garda Karting (Lonato), Franciacorta, Cremona or Ala and find your kart ready to go. No hassle, just driving.
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