40mm or 50mm axle ?

[Tom Dennin]

I am buying a new chassis in the next couple of days and am wondering which axle size to go with. I currently have two karts with 40mm axles and about 10 different 40mm axles. I would like to know the advantages and disadvantages. Also, does the overall weight of kart and driver have an impact on axle diameter considerations? Should the type of tires being ran be considered? etc…..

Thanks in advance for any and all suggestions,

Tom

[Anonymous]

Tom

I would give Doug Welch a call and discuss the axle difference with him. That way you get a perspective on Rotax/Tag. The only comment I could make is that we are using softer axles in 40mm with our arrows and I would think that a 50mm would be harder in general.

Duff

[Anonymous]

Okay Doug.

I am interested also 40 or 50 mm.

Short answer which is better for Rotax/Tag?

Hi duff

[Doug Welch]

I’m on the laptop at home and i hate hte key board. Will give a better response once I get back to work tomorrow.

[Anonymous]

I always thought you were shaky! 😆

Hope things are going well for you.

thanks

[Doug Welch]

40 or 50, its always about size isn’t it?

Lets start just with ths axle. On size alone, the 50mm axle is stiffer in cross section and logitudanly(sp) That is why we have to go with a much thinner wall thickness to make them flexable. This limits the numbers of axles we can offer. Phyically anything thicker than 2.2 is just too stiff in a 50mm and thinner than 1.7 is too thin to produce. While some manufacturers will claim that they offer more grades, for all practicle purposes, there are really only three options in 50 mm axles.

In a 40mm axle, we can offer from about 3.3 to 2.3 and you can have about 6 different choices in that range, so as a tuner, you have more axle choices with a 40 than you do with a 50.

The real question is, do you need those choices. The answer depends on your chassis. The real question should be, was your chassis optimized for a 50mm axle. The 50mm axle gives tremendous forward grip. So much so that it can over power the front leading to an exit push. Dialing in more front grip leads to chassis bind. Not a good thing in TaG. At KGB, we found that when we went to the 50, we had to make several changes to the chassis to balance the kart. They moved the rear cross bar forward, moved the seat location, revised the bearing hangers and changed the kingpin inclination angle.

As you guys know, we are running 50mm axles in our karts and we have had good luck with them locally. But our chassis have been optimized for 50mm axles. We are thinking about changing to a newer chassis that has had further testing done to improve its handling and flexability. It is a combination of 30 and 32mm tubing(we are using a 32mm chassis now) to further reduce bind.

When looking at a new chassis, you need to look for certain things that will tell you if your new kart is a real 50mm kart or just a 40mm kart with a 50mm axle stuffed in it. The best way is to look at the bearings. If they are the small outside diameter bearings(same size as the 40), it is deffinetly a 40mm kart and I would stay away from it. Most likely it will be way too stiff in the rear and you will have to do all kinds of goofy things to make it work and it will never work as good as a kart made for a 50mm axle.

Bottom line, either one will do the job and will win in Tag if set up well and driven well. The only potential problem I see is that there are 40mm chassis out there with 50mm axles in them and they will not work as well as they would if a 40mm was in them.

[Anonymous]

Bottom line, either one will do the job and will win in Tag if set up well and driven well. The only potential problem I see is that there are 40mm chassis out there with 50mm axles in them and they will not work

Doug, I would have to disagree with your statment. Our RBI chassis were built for a 50mm axle, and we use the 80mm (or small) bearings. We do this so we can change to a 40mm if we have to. (some tracks just don’t like 50mm) And we have had no problem getting the 40mm up to speed.

In my opinion the 50mm is for the experanced karter. You only get 1 chance to set the kart in the corner, but it lets you get back on the gas quicker. It is when the driver turns in to early(having to set and unset the chassis), or gets back on the gas to late, when an exit push exists. (or the seat is to far back)

A 40mm is a little more forgiving than a 50mm. If you turn in to early, you can set and unset the chassis very easily. We also have found that a 40mm binds up the chassis more than a 50mm, and the rebound is slower causing loss in exit speed. But when it comes to street or rain races, the 40mm is what I choose to run.

I have used 50mm in a 40mm kart for many years now. So you guys with a 40mm kart, don’t be afraid to try the 50mm. It might be what your driving style needs.

[Marc Elliott]

Our first chassis had a 40mm, and it was much more forgiving on entry of the corner, but oftenly it would push coming out of the corner, where as the 3 chassis I have had since then with 50mm’s have all come out of the corner much better, but push easier going into the corner. We always have run really wide front tracks on 50mm karts, and really narrow front track widths on our old 40mm. Hope that helps. FYI I had a 50mm on my tag kart, and we were pretty successful with that chassis, so I wouldnt see any problem running a 50 on a tag.

[Rodney Ebersole]

Would any of you want to try a 5″ axle? Why don’t we just go to the extreme? I can see us mounting tires directly on our 5″ aluminum axle. The axle might cost a few bucks but you wouldn’t need any wheels or hubs.

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