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.