Chainring questions

Yes I'd be curious as to what your motivations are for switching to a ring that big. What sort of speeds/cadences are you doing now?

55 seems like more of a time-trial type chainring than for a triathlon type setup.

I'm currently training in a hilly terrain and climb using my 36T inner chainring,doing flats with the outer 52T at 40-45km/h.It's just that when descending I feel I can push harder than my 52T chainring permits although I travel at 70km/h-110 RPM.
I see pros using 55T on big descents and thought to give it a go.Problem is I'm not sure about changing to a disc-like chainring which the pros use but I see it's heavier or to a ring-like chainring which is lighter.

Kind of sounds like your minds made up, but here's a quote from Kevin Metcalfe after he set a new record for M50-54 40k TT at 49:29 talking about chainrings:

Kevin: I think that the vast majority of people don’t need a standard crank and especially not a 54 or 55 tooth chain ring. The fact that I was able to average 30 mph and except for about 10 seconds in my 12, never used anything bigger than a 50x13 tells me that you don’t need a huge gear to go fast. There are a lot of variables, but a 50x11 is a bigger gear than Eddy Merckx ever had. Of course, on the other hand if you live in Kansas you probably don’t need a compact either. I just think that a lot of people never learn to pedal properly. I’m not saying that somebody should do a time trial or triathlon a 100+ rpm, but if a rider can’t pedal for relatively short (1 minute or so) durations at 100 or 110, they need to work on their pedaling, not buy a bigger chain ring. BTW, in that vein racing on the track does wonders for your abilities as a cyclist.

Unless you've got some Tony Martin type skills, you could be making a change that's counter-productive. You can find the interview at the link below:

http://www.slowtwitch.com/Interview/Getting_faster_with_age_3693.ht...

As far as style and weight of your chainring, I'd have to say that it makes not appreciable difference.

One of the fundamental approaches to system optimization is to identify the part of the system that makes the largest contribution to the outcome of interest, and try to make improvements there. For example: a 100% improvement in a subsystem that contributes 1% of the total outcome will yield a 1% overall system improvement; however, a 5% improvement to a subsystem used 50% of the time will yield a 2.5% overall system improvement. So, all other things being equal, the small 5% improvement on the 50% subsystem would be optimal.

How does this apply to your question?

You are trying to optimize the transmission for a terrain with hills and flats. You need to know how much time is spent climbing, descending, and cruising, along with the gearing. If the time spent pedaling out on the downhill is less than 1% of the total time of the ride, then a 55 T chain ring will improve descents 3-4% since 55T chainring size increase is 3-4% larger. The overall system improvement expected would be 0.03 to 0.04% - ~2 seconds in a 2 hour ride. THAT'S TRIVIAL!!!

The tradeoff would be a larger inner chainring and a cassette with a greater range. A greater range has larger gear ratio spacing between cogs, which will result in a greater than 1% loss through in all phases of the ride. A 1% system degradation for a 2 hour bike ride is 1 minute. THE LOSS IS SIGNIFICANT!!!

I really like your approach on contribution I I agree that not much will change upgrading to a 55T chainring.My training terrain consists of 40% flats-60% climb-descent and is a circular 4 hour ride (not everyday ofcourse!).During climbs and flats I push as hard as I can and there is no problem.As I wrote before is during some descents that I feel I can push even more but my 52-11 gear combination doesn't allow me to.That's why I thought of a bigger chainring.I'm not sure if a 55T is the best choice (maybe a 53 or 54T would be more appropriate) but in any case I don't know if a disc- or ring-shaped chainring is better for a triathlon configuration.From the answers above it seems it doesn't make a big difference but then again looking at pros bikes they all wear disc-shaped outer chainrings.

That's what I found on STRAVA regarding the big Hawi descent and speed/power http://www.strava.com/segments/hawi-descent-797251
I don't think I have to spin faster than 110 RPM and I don't think it's too safe to spin so fast while speeding on a descent.I would prefer spinning at 90 (or less) RPM on a bigger chainring.