Rotella T6 -> 5w40 vs 15w40?

[redbirds_imp]

I used Rotella T6 5W40 with no known side-effects or extra noise - in fact, the lump was quieter and gear shifting remarkably smoother compared to GN-4. Sub-zero winter riding also benefited being 5W and synthetic.

I would have never considered 15W40 for the CB1100, especially for cooler riding weather.

I've used Rotella T6 synthetic for years in all my bikes with good result. When I got my 2013 CB1100 the transmission was a bit noisy and the shift from second to third balky at times. This continued with the 2nd an 3rd oil changes while I was using the Honda brand synthetic 10W-30. I got a factory service manual which said that 10W-40 oils were an acceptable alternative so next change I went back to my old favorite Rotella 5W-40. That was the end of the balky shift and a slight reduction in noise. Whether the Rotella oil was the solution or the transmission finally broke in I don't know. All modern oils are good but the Rotella can be found for so much less than branded motorcycle oils.