L motors already out and are great, however I have no issues running a 5.5R in my X5 (belt driven) and have run it all year (except when I tried a 4.5
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Don't think the Mamba will fit in Swiftkids X5 to be honest, I would like to try one sometime to see what they feel like, same as Tekin. In my mind I can't see how they could be any better than a sensored system and you do read of people having issues (more issues) with cogging.