Originally Posted by
guadzilla
So I am a ~40kph/hr TT guy - respectable, but nothing special. I run a 53/39 on my TT bike. I've had a couple of friends who are strongly suggesting that I consider putting a bigger chainring up front. I have never really paid this much attention but these guys have improved their speeds significantly (by around 1kph) and claim that the bigger chainring helps.
Other than the fact that this will let me use a bigger cog and so perhaps gain a watt or so in drivetrain efficiency, I am not really sure how this would make a difference (I have never spun out my 53t yet either). Watts are watts, and as long as I can get my desired wattage at a comfortable cadence (80-85c for TTs, for me), it shouldnt matter, right? Or am I missing something?
TIA.
It is a thing. The juniors do it a lot. If the course is flat they will put spacers where cogs were and run 1-3 cogs on back.
It is one of those small things, but if you TT a lot there will be some race where <1sec determines a place.
It is marginal gain area alone, but psycologically it might be 5-10 sec - esp for a kid. Grown ups know too much and loose that advantage.
Why...
Chain angle - run big to middle - 15T-17T. The side plates of the chain rub less under tension because of the straight pull. This may be the biggest thing. I don't know the watts here, but it is something. Of course the chain matters too.
Chain tension is less, so there is less chain stay flex. This was a bigger deal in the old days, but frames are pretty stiff now.
Get rid of extra cogs as mentioned above.
Something to talk about.