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bully wrote:I measured a slighty worn set of original zx fronts an they are just under 80mm,new prob 81mm or maybe 82mm max mate..

Thanks bully, that sounds about right. If 82mm was the stock new tire diameter, then the rollout ratio of both Lazer ZX and ZX-R (stock pinion & spur gears) is almost exactly 1:1 (well within the +/- 10% range anyway). Kyosho knew what they were doing when they selected the spurs & pinions for those cars. Here's a partial screenshot of the spreadsheet I'm working on, which helps to calculate pinion, spur or tire size to achieve a more or less optimal rollout ratio of +/- 10% of 1.00:1. The bottom numbers highlighted in red are the calculated values for rollout.