The 1040 axle is pretty much the standard width. I use a 40mm rear axle, 1040 width, 80 mm hubs ( also use 50 mm hubs ) and have no problem going to the 55″ max. We also run 6″ width rear tires BUT we mount them on 210/212 wide rims ( usually used for 7.10 wide tires). This wider rim gives a stiffer sidewall and tends to free up the kart. Very common to use this set-up on 4 cycles, both WF and LO206.
A. Use whatever hubs are needed to get to 55″. In many situations, longer hubs will actually help free up the kart. This goes against some of the traditional thinking.
B. When using a 6″ wide tire, use an 8″ (212mm) wheel to keep the kart free.
As most pointed out indirectly you can’t get the rear to 55″ because you have 180mm wheels for your 6″ tires. 53 1/2 is plenty wide for those wheels or go with the 210 and run 55
Would you suspect any significant performance difference (overall cornering ability) between a 53″ and 55″ track, or is the benefit being changing the balance of the car?