Given the debate about crankarm length…shorter is better 
Let’s say that the crankarm length for this discussion is 172.5mm (hopefully both Slowman and Rappstar can add to this, since I believe this is what they ride)
What advantage or disadvantage is there with switching from a standard 53/39 chainring combination to something like either the 52/36 or 52/38 combinations that SRAM Red provides?
At what point do you really need compact gearing? Is bigger better?
bigger is better if you need it.
if you can do the course and never reach a point where you want to shift to a bigger gear
then you don’t need a bigger front gear.
if you are on a descent and you hit 120 rpm and want to go faster, you could use a bigger gear
pretty simple stuff really!
I swear every time I look at my big-ass 54T “Darth Vader” FSA TT ring, I feel dream-crushingly faster… of course it’s all in my head, but that don’t mean the pump ain’t for real, dammit!
big?
my girlfriend rides a 54x11
ok ok shes on 650cs
Okay, so what if you went with a 52/36 or 52/38 and opted to put on a bigger chainring like a 54? Would the gear ratio’s of 54/36 or 54/38 be too wide to were there is no benefit?
Just did my homework and realized that you can’t swap out the big ring on SRAM’s compact cranks due to the bolt pattern/diameter. So much for that theory.
I’m trying to imagine how I can be more clear.
I mean, assuming you can’t ride the course beforehand, you take a guess. Is there a huge downhill that is straight enough to hammer down? You might want a big gear.
if there are steep uphills you will also want a real little gear available.
if you are really strong on the bike, you might want a bigger gear no matter the course
Okay, so what if you went with a 52/36 or 52/38 and opted to put on a bigger chainring like a 54? Would the gear ratio’s of 54/36 or 54/38 be too wide to were there is no benefit?
Just trying to understand since 53/39 is the standard, is there a better choice or how do you determine your “optimal” gear ratios based upon riding style and course?
I’m not sure that I actually ***needed ***compact gearing. I just got it because for me it cuts down on the number of front derailleur shifts I need to do.
But why worry about chainrings up front? Isn’t it a lot cheaper (and simpler) to just use a different cassette in back?
why don’t you just change your cassette based on the course?
My road bike has 39/54 up front. I love it particularly on flats and downhills. It’s a bit of work on the uphills, though. With that said, I rarely use the 54x11 combination. I’m usually in the middle of the cogs on the back.
My TT bike has 36/52, which I also love, because most of my races are on the hills and I suck at climbing. The 52 is good on the flats, but I still have climbing gears. I recently switched from 34/50, because I was tired of spinning out on the downhills. Still spin out sooner than the road bike, but the easier gearing for climbing is worth the trade off. I’ll pretty much use every gearing combination with this set up.
Good luck!
Okay, so what if you went with a 52/36 or 52/38 and opted to put on a bigger chainring like a 54? Would the gear ratio’s of 54/36 or 54/38 be too wide to were there is no benefit?
Just trying to understand since 53/39 is the standard, is there a better choice or how do you determine your “optimal” gear ratios based upon riding style and course?
The 54 typically gets paired w/ a 42; I think the jump for a 54/36 or 38 gets too big for the FD. For most of the Tri/TT courses I do (flat), the 42 only gets used in warm-up & warm-down, the entire race is big ring. Last hilly Tri I did, I swapped back to a conventional 53/39. Going from an 11x21 to a 12x25 in back made a bigger difference, though, just coasted the downhills on account of the run; if it were just a bike race I’d have kept the 11.
Most triathletes are vastly overgeared given the speed they ride. I ride 50x40 and really like that combo since it creates a very small jump in between rings. I have a 12 on back, but I have my set screws adjusted so it doesn’t even drop that far. I don’t want to be pedalling hard in 50x12 and elimininating the 12 is a good way of reminding me to go into a tight tuck. I could probably do without the 13 as well. I recommend trying out a 50 teeth on the upper end, or even a 48. I’ve raced on a 48x38 combo and never wanted for extra gear on the top end. That combo will work on your 130mm bolt circle cranks.
Chad
Okay, so what if you went with a 52/36 or 52/38 and opted to put on a bigger chainring like a 54? Would the gear ratio’s of 54/36 or 54/38 be too wide to were there is no benefit?
I have been wondering the same thing. Why not have 53/38 or 53/36 to give more range. The tradeoff would be less overlap between the two chainrings. I think I would rather have a wider range at the expense of overlap.
For example I laid out my current 53/39 11-28 setup in excel and compared it to hypothetical 53/32 11-23. The highest and lowest gear are about the same and this appears to remove some of the holes that a 11-28 creates going from cog to cog at the big end of the cassette. I think the downside is if you were at the top of the 32 and didn’t want to cross chain you may end up in a situation where you are shifting back and forth between chainrings with varying road and wind conditions. With a 53/39 and the increased overlap this is not as necessary. I wonder if electronic shifting would reduce the downside of the chainring shifting?
Recent Tour of Gila TT - Leipheimer sets course record with a 55T. Many other racers on 56, some on 58.
Asked about his “small” chainring, Levi shrugged it off & said something like “you don’t win the races there anyways”.
Oh yeah, Levi was hitting 60 MPH on descents.
Just food for thought…
The risk you run with a wide range between chainrings is that there are limitations on the rear derailleur for how much chain variance can be handled. I think it is typically a 29 tooth limit (combination of the range for front and rear.) A 54-36 front is 18 teeth. A 12-25 rear is 13 teeth. Total count - 31 teeth. It is not a big deal if you don’t cross gear much (i.e. big/big or small/small) but it removes the ability to do so because you will either break your derailleur (attempting the big/big) or risk chain suck or slippage due to slack in the chain (attempting small/small).
The bigger the gap on the front, the higher the likelihood for dropping the chain as well, or getting weird chain rub on the derailleur because the height variance is hard to manage.
You will note, I prefaced my comments with “most triathletes”. What professional road racers do is not always applicable to age group triathletes.
“you don’t win races there anyway”
That’s just asinine. Of course you do. In a triathlon with any kind of hills you probably win the race in the small chainring. The guy who loses it probably hammered down the backside at 400 watts and gain two seconds while the guy who road 400 watts up the hill spinning 100 rpm gains 20.
And 60 mph. I love it when people thrown out that figure. It takes a ridiculously steep road to acheive 60 mph. A mountain next to my house had a very long stretch of 8 percent grade without a turn and I couldn’t get to 60 on that one. I used to have this 12 or 13 percent grade in my neighborhood that sometimes got me to 45 so to get to 60 you need that plus a howling tailwind.
Chad
if you have an 11 out back
and are in need of more gear
you need a bigger gear up front =)
I’m not sure that I actually ***needed ***compact gearing. I just got it because for me it cuts down on the number of front derailleur shifts I need to do.
But why worry about chainrings up front? Isn’t it a lot cheaper (and simpler) to just use a different cassette in back?
I think we can see from the tour d’Italia that Levi doesn’t like to descend
.
he may like it fine but at 25lbs of bodyweight it will be harder for him to do it very fast =)
I think we can see from the tour d’Italia that Levi doesn’t like to descend
.
if you’re only using your 14, why are you using such a big chainring? Honestly, I think even a 50 is overkill for a triathlete. I’m using a 50 for road racing, as in ‘being sucked along in a big pack in downhill tailwinds’, and I can only think of 2 races where I was wishing I had more gear–and even then, is was just ‘uncomfortable’ for a bit, not a huge deal.
If you’re using a 50/40, a 42 or 44 with an 11-26 or 11-28 seems like a lot better option. No shifting the front, no derailleur cables or shifter (you can still use a front derailleur), and you can use a track crank.
if you have an 11 out back
and are in need of more gear
you need a bigger gear up front =)
Whoops, misread that.
Actually I have a 12 out back and don’t need another gear. So an 11 would be overkill. Are you saying you have an 11 and need more?