Chainring 55/42

What size are the wheels - 650c or 700c?

Shane

700

What would be the advantage to the big rings for you? 

If you have to go to a 12-27 in back to make it work, then you've defeated the purpose of supersizing the chain rings since you've reduced the size of your biggest gear anyway (a 53x11 is actually quite a bit bigger than a 55x12)

I used to run a 54/42 set-up with a 12-23 or 12-25 8-speed when I was road racing... Of course it's a whole different animal cranking along in a peleton at 28-plus than trying to gut out a solo effort.

Good luck with that.

I would say it depends much more on your preferred cadence than how strong of a rider you are. I am not that fast, yet on a windy day, I will be in the 53-11/12 the whole time with the wind at my back (so I might be considering a 55/42 for my next bike, as I will be getting faster...). Do the calculations and compare your preferred cadence with that of the typical course conditions you will most likely be riding and you should be able to figure out which crankset will work best.

Thanks guys. The 55/42 came in a package that I got a good deal at, thats it.  No experience so trying to educate myself but understand that I need to get mileage to really know.  From reading on the internet I get some mixed signals, overall I believe I would be better of with a 53/39.  It is a sweet FSA BB30 K Force light crank so if I am able to keep that and only change the rings that would be great.

I am getting a bike fit at LBS, hope we can work it out then.

Again, thanks

Pie

There is a rough guideline that a 53/39 makes sense for a rider that is around 4W/kg.

If you are under that, then I would go compact; if you find that a 50/36 paired with an 11-21 doesn't give you enough gear, then you could swap out the 50 for a 52.

For reference, here are the speeds (in km/h) you get from the 50/36 with 11-21 at 90rpm:

	50	38.9 %	36
11	52.9		38.1
9.1 %
12	48.5		34.9
8.3 %
13	44.7		32.2
7.7 %
14	41.6		29.9
7.1 %
15	38.8		27.9
6.7 %
16	36.4		26.2
6.3 %
17	34.2		24.6
5.9 %
18	32.3		23.3
5.6 %
19	30.6		22.0
10.5 %
21	27.7		19.9

What is your typical cadence?

ETA - I would suggest that gearing for triathletes should not be determined by the biggest gear you ever push during a ride but rather the smallest gear you need.  A 50 with an 11 tooth cog gives 53km/h at 90rpm and 70km/h at 120rpm.  I don't often ride faster than 50km/h and can count on one hand the number of times that I've hit >70km/h this season and in every case, I was tucked and coasting until it was worth my while to pedal again.  OTOH, at 90rpm the difference between a 42, 39 and 36 paired with a 25 tooth cog is the difference between climbing at 20km/h, 18km/h and 17km/h.

Shane

Edited by gsmacleod 2010-11-29 7:22 AM

Here's my take, from a guy who used to be a "bigger is better" chainring guy, who used to think compact cranks were for "old guys" - then the engineer geek in me took over. I had a 55T big ring on my 650c bike, and currently have a 53/39 on my 700c bike with a 12-25T cassette. I put the 53/39 on my current bike when I built it up because that's pretty much what all the tri bikes that I looked at came with.

Now the gieek part. I typically ride about 90 rpm and about 21-22 mph on the flats, which puts me in a 53x17 gear most of the time when I'm not climbing. If I have a good tailwind, maybe I can push down to the 15T cog - so the 14, 13 and 12T cogs are pretty much shiny new. At 43 years old, I'll never be heading to Europe to ride with the pros, but in my last HIM I averaged over 21 mph on the bike...

What got me started looking at compact cranks was that most 12-25 cassettes don't have an 18-tooth cog, which would be really useful, since a 53x19 cog (my next available gear) puts me at 19.6 mph @90 rpm. It's a more than 2 mph drop. I am now changing over to a 50-34 compact with a 12-23 10 speed cassette. Using the gear calculator above, that gives me a lower bottom gear than I had before for climbing and a more balanced mid range for where I ride the most. The theoretical top speed is less (29.3 mph @90 rpm for the 50x12 vs. 31 mph for the 53x12), but most of us mortals are going downhill when we're going that fast, so does it really matter?

I would seriously reconsider buying the 55/42, and - more importantly - even going with 53/39 - until you do the math. There are plenty of good deals to be had on e-bay or elsewhere if you bide your time.





Edited by 40isnotold 2010-11-29 7:56 AM

Thanks guys, this has been extremely helpfull.  Stil inclined to go for the 53/39 (guess I am not yet ready to go for the 50...;-).  I have a 53 on my road bike (which I also used for last years tris), on race day I stay in the 53 (on a flat course) pretty much all the time.

What cassette are you running with the 53?  Unless you are running an 11, then a 50-11 would actually be a bigger top gear than a 53-12.  Beyond that, the true beauty of a 50-36 for an athlete who rides just over 60' for 40km is that with an 11-21 you are able to find the gear that feels right in every situation because there is only one two-tooth jump.

Shane

Why do you think you would need a 55/42? Most of the pro triathletes are using a standard 53/39 and if you look at the pro cyclists, they are also using standard 53/39 for most TT's...

... and if you add a 12/27 cassette to a 55/42, you really have a strange set up... You should try to get a cassette that is as tight as possible, a 11-21 or 12-23 would be the best (minimal jump between each cog). I would guess that most would be much better off with a 50 rather than a 53... and very, very few can ride a 55 while maintaining good efficiency... cranking it over is one thing, riding it efficient is something very, very different...