G'day David,
The easiest way to work out the difference between your 55 and 56 grouser tracks is to compare the track lengths. Imagine cutting your track in half and laying it out on the ground as you have done with your T16.
56 (Grousers) x 114.3 (pitch) = 6400.8mm (or 252inches in the old measurement) and 55 (G) x 117.1(P) = 6440.5 (or 253 and 5/8ths inches again in the old measurement) so you are only looking at an overall difference in lengths of 39.7mm or 1inch and 5/8ths. I am not sure where the 4 inches came from. Other than that the only difference I can make out between the 55 and 56 Grouser track is the outside diameter of the drive wheel. As you are most probably aware there are many discussion topics relating to this on the weasel forum. I will see if I can find more information on the track differences and get back to you. I too learn something new everyday and I can admit that I am wrong
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I do think that the T16 track has a lot of similarities to the weasel track when comparing problems.
Cheers
John Wilson