I am running the LO206 senior class in the Florida Pro Kart Series on a 32mm FA Kart (I know its way too much chassis for the engine). I am having some trouble freeing up the back end and I think I’ve done everything I can do except narrow the rear track width and change the axle and that’s my question. Which axle do I go to, softer or harder? I currently have the medium “N” axle and have been informed of both options, but haven’t gotten a definite answer to which will actually free up the chassis?…I personally think a softer axle but my good friend that runs tag said to go harder to free up the chassis. Please help me out with some insight…
It depends on what you’re specifically trying to do.
With the OTK chassis, you typically go to a harder axle once the track tightens up to free the kart up. But a lot of factors come into play.
Is the kart the lifting the inside rear on turn-in?
My suggestion would be to narrow the rear track up a bit and see if that helps. If so, you need quicker lifter action. Also try tightening the 3rd axle bearing. If that helps you then know you need to go stiffer.
My gut thought is on a 32mm chassis in LO206, you’re not going to want the kart super stiff because you simply don’t have any power to flex the kart, but who knows.
Driver/Coach/Wrench : Innovative Performance/Exprit
Owner : Oktane Visual - www.oktanevisual.com
Thanks for the response TJ. The kart is developing a hop on the outside tire mid-corner. I removed all the extra seat struts, lowered the rear ride height and took out the caster and that all worked but still have this small hop..Everyone else is running no 3rd bearing and smaller diameter axles, like 40mm on arrows and 30mm on coyotes. That’s why I’m having trouble understanding how a stiffer axle would help with such a low hp motor…ill try the tightening of the 3rd bearing to see what it does..thanks again!
I would say don’t try to compare your OTK tuning to what the 4-stroke chassis guys are doing. The same tuning formulas don’t always apply between different chassis, especially those 4-stroke chassis. Typically a softer on axle in an Arrow 4S will free the kart up, the opposite is true in my EVRR. The harder axle frees the rear.
If you don’t already have it, download the and print out the 2011 J3 Competition Knowledge Packet. It’s a great tuning guide for the OTK cassis.
From the J3 Packet:
9. Axle Chart and the effectiveness
Axles are very much talked about regarding tuning a Kart and rightfully so. OTK produces six (6) axles for the 100cc category and five (5) for the 125cc gearbox category. OTK Type ‘N’ is the standard axle and medium stiffness for the entire range. This axle is also what each chassis comes standard with from the factory.
Which is the best axle to use when? Generally the consensus is that a softer axle (Type U) will free the chassis letting it operate more freely around the track. This may be true in some instances but typically not with the OTK material. Typically it is recommended to use a harder axle (Type H or HH) when the grip levels increase. Softer axles are recommended more for use when the grip levels are low. Why is this true? This holds true mainly due to the fact the chassis are made of soft 30mm tubular steel. With a soft chassis and a softer axle you will essential create the tire to create “Side Bite” or the sidewall of the tire to rollover. This will cause the chassis to ‘Hop’ and therefore lose its effectiveness throughout the race. Keep with the ‘N’ axle; we use this axle 80% of the time and as the grip level increase the ‘H’ will work for your needs. Remember that the axle doesn’t simply work outside the chassis, it also creates balance between the frame rails, and therefore, increased stiffness on your axle selection will give the chassis more balance as well.