General Discussion Triathlon Talk » Compact crankset - questions! Rss Feed  
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2014-04-19 5:26 PM


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Subject: Compact crankset - questions!
I purchased my first "real" tri bike (2012 Felt B12) for Christmas. Finally going to take it out on its maiden outdoor voyage tomorrow after a few months on the trainer.

A good friend of mine who is a two-time IM finisher and excellent triathlete told me yesterday I should consider a compact crankset. For me, it sounds like a great move as I am awfully weak up hills (and there are plenty of them where I live). I currently have the Vision TriMax Compact TT MegaExo 52/38T crankset that came with the bike (110 mm BCD).

Questions:
1) Good move? I've read a couple of places that *most* triathletes should get a compact crankset. (so why don't they just make them standard?)

2) Should I just consider buying the Vision 50/34 model since I already have the Vision crankset? Or doesn't it really matter?

3) Is there anything else I need to swap out / swap in if I make this move? (chain, derailleur, etc) - forgive me if this is a stupid question but I honestly don't know!

Anything else I should know / general thoughts / comments?

Thanks in advance BT community!


2014-04-20 11:45 AM
in reply to: 0

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Subject: RE: Compact crankset - questions!

Since you already have a 110mm cranskset, you should be able to just swap the chainrings to 50/34.  You don't need to replace the entire crankset.  

If you had a standard 130mm (53/39) crankset then you would need to replace the whole thing

The front derailleur will need to be slid down a few millimeters and re-adjusted once you swap the chainrings.   



Edited by ultramike 2014-04-20 11:49 AM
2014-04-20 5:25 PM
in reply to: DorkRocketKirk

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Subject: RE: Compact crankset - questions!
More and more, compact cranks are becoming standard. There's still a bit of a predisposition, especially among the hardcore roadie crowd, favoring big standard cranks.

You may want to start with perhaps changing cassettes - it's a bit cheaper; stock on the 2012 B12 was a 11-25, so going to an 11-28 will give you a cheaper option without having to change anything else.

For a hilly area, a compact is a nice options. Swap chainrings and you should be good to go.

Swapping make take some getting used to; my roadie runs a compact and my tri bike has a standard, so going back and forth takes some thinking for shifting. On the compact, unless I'm hitting some pretty significant hills, I'll spend 90% of my time in the big ring. However, if I'm down pretty far in the cassette in the big ring, dropping to the small ring will leave me spinning, so a downshift to the small ring can require a simultaneous upshift on the little ring.

If you decide to change cranksets, instead of just chainrings, I'd recommend an Ultegra 6800; it's nominally an 11 speed, but Shimano's proprietary 4-bolt setup runs any Shimano chainring (standard, compact, or midcompact), and Shimano's hollow, forged chainrings are some of the best (if not the best) available.
2014-04-21 9:04 AM
in reply to: mirthfuldragon


13

Subject: RE: Compact crankset - questions!
Thanks guys - one potentially dumb question, if I just change the cassette on the back, is there anything else I need to do? The same derailleur will work just fine? That might be the better option I'm thinking - I seem to have spent a lot of time in the lower gears on my big (52) ring while riding around yesterday. Keeping the same 52/38 setup but having a couple of easier gears on the back may not be a bad idea.

Is the shifting a little wonky with the wider (11-28) spread though?
2014-04-21 10:34 AM
in reply to: DorkRocketKirk

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Subject: RE: Compact crankset - questions!
An 11-25 and an 11-18 cassette should work interchangeably. The calculated difference in chain length is about half a length, so as a practical matter it doesn't matter. My trainer wheel and tire runs an 11-25 and my road rear wheel setup runs an 11-28, and I swap back and forth during the week without issue. The tooth spacing on both cassettes should be identical, so you probably won't have any shifting problems.

Anything bigger than a 11-28 will probably require a derailleur change, but I would go to a compact first if I needed an 32 tooth cassette.

I would also suggest you may want to examine your cadence. Running low in the cassette (higher numerical tooth count) in the big ring probably means you're mashing pedals at low cadence. Cadence is a personal thing, but consensus is 85+ is good, with the new-fangled crowd (myself included) liking 95+. It brings your cycling cadence closer to your running cadence, and seems easier at a given exertion level. I would especially examine the cadence and gear selection issue if you are running in the big ring and low in the cassette most of the time on relatively flat terrain - if that's the case, try to spend more time in the little ring.

Also, running in the big ring and low in the cassette means you may be cross-chaining, which can cause premature chainwear. Not a huge issue, but it might drop your chain life by 500 miles, and chains are cheap enough anyway. Try to avoid running in the big ring with the bottom two gears of the cassette.
2014-04-21 7:57 PM
in reply to: mirthfuldragon

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Subject: RE: Compact crankset - questions!
I swapped to a 12-27 cassette on my tri rig. Hilly race course around here make me do it. Nice to have a bail-out gear to get you though.


2014-04-22 6:19 AM
in reply to: DorkRocketKirk

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Subject: RE: Compact crankset - questions!
Wider spaced cassette doesn't affect shifting per se. But you will have more of a gap between gears, so you'll either be over geared or under geared, i.e. it's harder to find the right gear at any given point. I prefer a 12-25 (10 speed) with a compact. It'll give you more than enough top end and with a 50/34 or 50/36, you can climb almost anything but the absolutely longest and steepest climbs. Another option would be to get a 36 inner to use with your 52 outer. Works fine.
2014-04-22 6:55 AM
in reply to: DorkRocketKirk

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Subject: RE: Compact crankset - questions!
Are you in the Twin Cities? I honestly think you'd be okay without one...even in and out of afton, I've not felt I was short gears. But if you're not from the TC (I was guessing based on your name), never mind! :p
2014-04-22 7:14 AM
in reply to: #4983965

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Subject: RE: Compact crankset - questions!
I love my 11-28. We have a lot if hills around here with grades between 10-15%. At 190lbs, I couldn't climb most of them without my 39/28 gear. Shimano also has a Tiagra 12-30 cassette if you are looking for an even smaller gear. My winter bike came stock with a 12-30 and a short cage derailleur. But I really do miss the 11 speed gear when I'm riding down hills on that bike. I usually end up coasting because my legs are useless above 130rpm.

The only time I've ever wished for gears closer together is when I'm on the trainer, and I'm using TrainerRoad with a Sufferfest video. TrainerRoad will give you a wattage target and the video will give you a cadence target. If you have big gaps in your cassette then it is sometimes mathematically impossible to hit both targets simultaneously.
2014-04-22 11:48 AM
in reply to: mmrocker13


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Subject: RE: Compact crankset - questions!
Originally posted by mmrocker13

Are you in the Twin Cities? I honestly think you'd be okay without one...even in and out of afton, I've not felt I was short gears. But if you're not from the TC (I was guessing based on your name), never mind! :p


Yep! I live out in Chanhassen / Chaska specifically - and it can be pretty hilly out here (long, gradual hills).

This is all great advice! I'll look into both cassette and chainring options. It looks like I can purchase a Vision 50t ring, but I haven't been able to find a 34t ring just yet (and that one is the more important one of course). There's some pretty good deals out on eBay for a full 50/34 crankset, so that's an option too!
2014-04-22 1:37 PM
in reply to: DorkRocketKirk


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Subject: RE: Compact crankset - questions!
So, doing even a little bit of research, it looks like I can get the 50/34t equivalent of the crankset I have now for about $90 or so. I can get a Shimano Ultegra 11-28 cassette for about $70.

I guess I don't totally know enough here to say "that's definitely the better option." And, just how much additional tinkering would be necessary to make either option work. Again, any advice would be really appreciated!


2014-11-16 1:58 PM
in reply to: ultramike

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Subject: RE: Compact crankset - questions!
Hey all,

I found this some time ago when I started experimenting with different gear set-ups.

http://gear-calculator.com/#

It computes several different variables (crank rings, cassette, wheel size, cadence), and you can compare different set-ups. You can really "geek-out" with it, and it's FREE.

Don't forget about race distance, and the run off the bike. Maybe you can push larger rings in a sprint or an oly and be okay. I did IM Louisville in 2010 with a 53/39, and 2012 with a 50/34. The run felt WAY better and was 54 minutes faster in 2012. The compact cranks weren't the only reason for the improvement, but I'm positive it played a large role.

Good luck!
Brad
Indianapolis
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