Can anyone advise on best 56 tooth chainring for a Di2 set up tri bike?
Thanks in advance
How often do you need to go faster than 45mph?
not very, but with a severe back injury and only the ability to pedal at a max of about 70 rps, a 56 will allow me to get some more pace, if you must know!
I did find myself out of gear a few days back with a tail wind and was only doing 52KPH.
If you cant assist with the post dont be trying to take the piss out of me, just keep reading until you find someone you can help.
Shimano makes a 56-44 for Dura Ace 7900. Seems like it would be a good choice.
wow, relax, I do relise there are legitimate reasons as to why someone would want a 56 tooth chainring, your’s being one of them, 650 wheels being another and I’m sure some people just like pedalling slow. But this is slowtwitch and the general consensus around here it that bigger is better (If I can ride 75km/h with a 55, I can ride 76.5 with a 56), not trying to take the piss out of you, maybe trying to be a little bit of a smartass so I’m sorry if I offended you.
FWIW, here is a 57 tooth chainring though I have no idea if it’s compatible with di2 so I’m sorry if I’ve wasted your time by making you read this last sentence.
Why stop at 56T? With a 700x23 wheel that’s only 10.684 meter’s per revolution of the pedals 
A 60T would get you 11.447m. This becomes an intrinsic question of force your willing to apply, and acceleration. Shifting from 52T/12T to 52/11 is a difference of 0.827m verses 56/12 to 56/11 is 0.890m (.07% difference) and that’s just in a single tooth difference. Imagine (or calculate) if your ratio has to go from 13T to 11T. While your at it make sure you have 175mm or longer crank arms so that you can apply more force to each revolution.
All that being said, I’d do the 56T and perhaps the 60T if I still felt unchallenged with the 56. So pick your own battles and have fun. I’d say only you can pick what is best for your training but I’m sure someone out there has all the equipment needed to assess your power/aerobic/endurance levels and they would be able to answer this better than me.
Mike L.