Originally Posted by
JT101
I would like to understand what is going on here. It's almost like, when the large chainring is used, the tension is greater and the chain sits in the teeth more firmly so it doesn't slip. In the small chainring, the tension is so low that it won't slip, and in the middle chainraing, it's just enough to make it slip. Dunno..
Chainring selection makes very little difference in chain tension. The tension in the lower loop is set by the RD cage, and while there's a small change in tension as the cage angle changes, it's a very small difference. The tension in the upper loop is what drives the bike and is proportional to how hard you push the pedals.
You describe a bike with drive train wear, that slips under load. The slippage seems to be dependent on the chainring used, yet you refuse to consider that the chainrings themselves (middle an maybe small) may be worn also, and be the real cause of the problem.