30mm or 32mm for X30 Heavy?

I am looking at getting back into karting after a LONG time off. I anticipate running X30 Masters (390# on MG Reds), and X30 Senior (365# on MG Yellows) - if I want to try hanging with the fast young kids! I have pretty much settled on an OTK, mainly because of good support, and well regarded tuneability.

I am looking at a mix of racing on grippy tires (MG Yellow) and harder tires (MG Red). From what I can see, the 32mm is definitely the ticket for MG Yellow, whereas the 30mm would be better for masters racing, club racing etc (MG Reds). But since when I race reds, it will likely be in Masters, at a higher weight…I am leaning towards 32mm.


I think 32mm is the way to go for Masters. The 30 can work, but I think the 32 is more suited.

We had one driver on the 30 for Masters this season at USPKS and he was in podium contention every event, but I think even he felt like the 32 might’ve been slightly easier to keep within the tuning window.

From other Masters drivers, I have heard they prefer the 32 over the 30. One stated, “I tested the 30 and it felt like the inside rear wheel was going to hit me in the head every time I turned the wheel”.

That being said, I think the 30 is going to be much easier to work with at 365. If you plan on doing both, the 30 might be the way to go, and your setup might end up being a little out-there for Masters to keep it working.

Do you think I’d be better off in a 32mm frame? I’m about 173lbs these days, racing at 390. The compkart covert 2018 I have is 30mm I believe.

Edit: basically, what’s the difference? I don’t understand what thicker gauge tubing does.

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TJ, even with X30 Senior being on MG Yellows? That was the thing that got me thinking about the 32mm chassis. If you look at the Tony Kart Aus website, for MG yellows, they show a set up for 32mm. For the 30mm chassis, they do not even show a set up for softer tires. My understanding is that the yellows are a LOT softer and more grippy than reds (from the CIK docs…hardness = 50 for reds…and 37 for yellows. For Ref…VEGA Whites are 45!)

Here are the set up references…



Why do they show a set up for yellows for the 32mm, and only show harder tire set ups for the 30mm?

Thanks for your reply…


It is not necessarily thicker. It is larger in diameter. For reference, if you have 32mm tubing, and 30 mm tubing of the same thickness and material, the 32mm will be 21% stiffer. So, it will deflect less under the same loads. This could conceivably mean the 32mm chassis will deflect similarly to a 30mm chassis if you have 20% more grip in the corners, etc.

Tony Karts as they evolved after about 1999 became stiff in the front, and very twisty in the back. I have long thought that Tony Kart was was using butted/etched tubing in their karts to manage flex. In other words, the wall thickness is not the same everywhere. To do this, you acid etch the tubing ID, the same way bicycle mfgs use butted tubing for frames. This give you thick walls right where you are welding, but thinner where needed for flex.

So a 32mm chassis is going to need more load to twist and unload the read inside tire. Under a lot of load (more weight or more grip) a 30 mm chassis might twist more than intended.

With a 30mm chassis with more weight/grip that is twisting too much, you might lower the seat as much as possible, and add in the rear bar. With a 32mm chassis that is not twisting enough, you might raise the seat, loosen 3rd bearing or change seat flex and how it is mounted to allow it to twist more.

Ok so basically it is stiffer and for heavier drivers that is better on 125cc TAG on softer tires because what exactly? There’s not as much wheel lift?

It is more complex than just saying “too much wheel lift”…but you are on the right track. When a chassis flexes a lot, your contact patch geometry is changing, which means your handling feel is changing. Once the wheel lifts, any more lift beyond that is just weirding things up, in my distant experience.

Hmm. Ok thank you. :zap::zap::zap::zap:

The 30 is the standard chassis for almost all applications. That’s what every driver is running on MG Yellows here in the senior classes, and even the on Reds. I’ve run it in everything from Senior Yamaha on Yellows, to X30 on Yellows (and Bridgestone YLBs, Maxxis Greens, and LeCont) and KA100 on Reds. It works across 90% of the applications. And I run nearly baseline setup on all those combinations of chassis/engine/tires.

The 32 is really built more for shifter categories or heavier single-gear categories.

My guess is they are mostly referencing Rotax setups with the Mojo tires in their setup sheets. Not sure why they don’t have a Yellow setup in there.

I would say 90% of drivers in senior categories here are on the 30, regardless of Red or Yellow tires.


The 32 is going to be stiffer so it’ll be more resistant to lift. At higher weights, grippier tires, and more power, the kart is going to twist much more, so the stiffer chassis keeps it from over-flexing.

I’m not sure of the exact build of the CompKart, though I’ve heard it handles similarly to an OTK kart. You would have to ask CompKart what they recommend for your size. I would imagine your 30 is probably the right kart for you since you aren’t racing in particularly high-grip situations.

Thanks for the detailed response TJ. So 30mm it is…

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I think that’s a good choice. Always easier to stiffen up a soft kart rather than softening up a stiff kart. Unless you enjoy taking a Sawzall to your frame!

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Thanks. I think I understand. If it’s too stiff, I would have trouble rotating the kart. Thanks!

30mm Compkarts do well in X30 Masters (heavy). 2018 SKUSA masters championship, 2017 Supernats championship, etc… The drivers that race them can peddle so I am sure they would be good on any chassis but they did choose the Compkart. SKUSA New Castle X30 Masters results had 30mm Compkarts all over the top 10.

I had a 32mm chassis when I raced ICA in 2000-2002. I did not like it. Ever since I have been on 30mm chassis from Firstkart to Compkart. Won FWT on a 30mm Firstkart – Rotax Masters 405lbs.

So I guess 30mm works for TAG heavy; don’t chase a number but go with what people are being successful with in a class. If it is working for others, there is 1 less variable you need to worry about.

Isn’t the Compkart just a nameplated Birel with Compkart’s own proprietary (and quite nice) parts on it? The chassis Homologation looks identical for Compkart Covert, Birel RY30 and Ricciardo DR01. The only difference I can see is the bend of the inner right rail before it runs into the cross member. The reason I ask is that the only kart shop in my area is a Ricciardo dealer, so I am thinking about going that route… The only thing is they actually cost $400 more than an OTK!..and parts are more too… But I would rather not deal with the politics of not running with the local shop.

I don’t know the exact details but I spoke with John at J3 before buying and as I recollect and he said the tube material is their own, the axles except possibly 1 are their own and, as you mention, components can be different. Brakes are Freeline as an example.

Chassis design - I believe you are right. I know the steering shaft upright tubes are different. And of course the flou color is unique.

I think you should be fine with a Ricciardo.