# 55/39 - Does it work?



## T-20 (Aug 7, 2014)

Shimano says that the 55 chain ring is designed for use with the 42 chain rings.

That said - has anyone tried the 55/39 combination? (11spd)

55x11 would be fun to get up even more speed on the downhills


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## JCavilia (Sep 12, 2005)

T-20 said:


> Shimano says that the 55 chain ring is designed for use with the 42 chain rings.
> 
> That said - has anyone tried the 55/39 combination? (11spd)
> 
> 55x11 would be fun to get up even more speed on the downhills


Really? You think it would matter? In your 53x11, at 100 rpm you're going 38 mph. With the 55 it's 39.4 mph. Can you actually pedal effectively at that speed? Either way, you'd go faster if you just stopped pedaling and got in an aero tuck.

But it would probably shift adequately, if not smoothly.


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## SystemShock (Jun 14, 2008)

T-20 said:


> 55x11 would be fun to get up even more speed on the downhills


What Cavilla said... on even a moderately steep downhill, not pedaling + deep aero tuck beats any pedaling. If you can handle it.


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## T-20 (Aug 7, 2014)

SystemShock said:


> What Cavilla said... on even a moderately steep downhill, not pedaling + deep aero tuck beats any pedaling. If you can handle it.


From an aerodynamics standpoint there must be a point where it's better to aero tuck - maybe from 60 km/h upwards?

Don't you need 90% more energy going from 50km/h to 60km/h ?


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## MMsRepBike (Apr 1, 2014)

you're doing it wrong.


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## Jay Strongbow (May 8, 2010)

OP, Despite there maybe not being any 'need' for it bombing down hill there's really no negative either in that scenario. I wouldn't mind a 55 on certain steep straight decents and I get what you're thinking but you'd kind of be throwing out the baby with the bathwater so to speak. For the typical amature who spends most of his time cruising at, say, at 19-23 mph, you'd be doing a sht load of cross chaining because one ring is to big and the other too small. Cross chaining ain't the end of the world but you should set up your gearing so you spend the most time in the middle of the cassette. I get that some places are constant up/down with no exception but just about every does plenty of rides where there's significant amounts of cruising along around 20.


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## SystemShock (Jun 14, 2008)

T-20 said:


> From an aerodynamics standpoint there must be a point where it's better to aero tuck - maybe from 60 km/h upwards?
> 
> Don't you need 90% more energy going from 50km/h to 60km/h ?


IIRC Kerry Irons used to say 35mph was the transition point beyond which you're better off deep aero-tucking, but I don't know which data he was drawing from to arrive at that.

I would think it would vary with the steepness of the descent and rider weight, though obviously even lightweight TDF riders prefer the aero tuck on a good many descents (i.e. where it's faster).


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## duriel (Oct 10, 2013)

Yesterday I hit 45.9mph, I was pedaling as I wanted to hit 45, but I was pretty maxed out. If I would not have pedaled, I would not have made it. My gears were 50/11.


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## Jay Strongbow (May 8, 2010)

SystemShock said:


> IIRC Kerry Irons used to say 35mph was the transition point beyond which you're better off deep aero-tucking, but I don't know which data he was drawing from to arrive at that.
> 
> *I would think it would vary with the steepness of the descent* and rider weight, though obviously even lightweight TDF riders prefer the aero tuck on a good many descents (i.e. where it's faster).


I can sprint 35 on the flats, so, yeah, either steepness matters or I'll never need to pedal again.


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## stevesbike (Jun 3, 2002)

that's pretty silly. For grades under 7% or so, pedaling will always beat someone in an aero tuck. Riders run out of gears far before the point where a larger gear wouldn't be useful. Most racers have experienced this when they need to pedal to get on someone's wheel descending. Track riders in relatively small gear (110 inch) often exceed 70 km/hr, so if you're not able to spin that gear, a larger gear would work. I used to ride a 54/39, which worked fine - the main issue would be chain wrap.



SystemShock said:


> IIRC Kerry Irons used to say 35mph was the transition point beyond which you're better off deep aero-tucking, but I don't know which data he was drawing from to arrive at that.
> 
> I would think it would vary with the steepness of the descent and rider weight, though obviously even lightweight TDF riders prefer the aero tuck on a good many descents (i.e. where it's faster).


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## T-20 (Aug 7, 2014)

SystemShock said:


> IIRC Kerry Irons used to say 35mph was the transition point beyond which you're better off deep aero-tucking,


It has to be in that ballpark. 50km/h is too slow for aero tuck and 60km/h you should be in the aero tuck already (if you want to be efficient down the hill)


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## SystemShock (Jun 14, 2008)

stevesbike said:


> That's pretty silly. For grades under 7% or so, pedaling will always beat someone in an aero tuck. Riders run out of gears far before the point where a larger gear wouldn't be useful. Most racers have experienced this when they need to pedal to get on someone's wheel descending. Track riders in relatively small gear (110 inch) often exceed 70 km/hr, so if you're not able to spin that gear, a larger gear would work. I used to ride a 54/39, which worked fine - the main issue would be chain wrap.


Grades under 7% aren't all that steep, and for shallower grades, no one's saying pedaling can't be beneficial. But for middling to steeper descents, on anything but a quite winding descent, aero tuck is faster. And btw, most riders can't spin like track riders, and even if they could, they wouldn't necessarily be efficient at those kind of cadences.

Watch the vid again... 62mph in an aero tuck, and those are lightweight pro racers. Wanna get there by pedaling instead? Okay... 62mph in a 54x11 is 162rpm. 

Perhaps a good trackie can do it, but as LeMond used to say 130rpm is about the max in the efficient range. If it's so awesome to pedal all the time on uber-fast descents, why then aren't the pros doing it? 

Now consider your typical recreational rider. Likely a heavier rider than the pros, and likely unable to spin @162rpm for more than a few seconds, much less efficiently. 

Seems fairly straightforward that a good aero tuck on any middling to steep, reasonably straight descent is going to beat the pants off any attempt to spin like a meth'd-out hummingbird for him. And not just for him, but as we've seen, pros like the aero tuck too.

In any case, right tool for the right job. Sometimes you wanna spin, but sometimes the tuck will indeed be quite a lot faster. Some ppl don't know how to tuck though.... they don't get low enough, and they don't narrow their profile well (knees are apart, arms are out too far, etc).


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## stevoo (Oct 26, 2011)

As far as the OP's question goes the answer is yes. Will the front shift in a manner which is acceptable? Every person is different. Some may say it will shift fine, some may not like it. 

As far as the actual gearing goes everyone is different. Gear the bike how you like. The best way is to try out different gearing and see how you like it. Many of us have different cog sets and chain rings so we can change gearing to suit differing needs and riding styles. 

I would encourage the OP to find the gearing that he likes and enjoy the ride.


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## metoou2 (Mar 18, 2009)

Shimano's specs for 'A' rated shifting are way too conservative. I have successfully used some 'whacked' combinations with no problems.


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## JCavilia (Sep 12, 2005)

stevoo said:


> As far as the OP's question goes the answer is yes. Will the front shift in a manner which is acceptable? Every person is different. Some may say it will shift fine, some may not like it.
> 
> As far as the actual gearing goes everyone is different. Gear the bike how you like. The best way is to try out different gearing and see how you like it. Many of us have different cog sets and chain rings so we can change gearing to suit differing needs and riding styles.
> 
> I would encourage the OP to find the gearing that he likes and enjoy the ride.


Yes, everyone is different. But my experience is that many relatively new riders haven't worked on spinning fast enough, and therefore think they need a higher top gear.

I like to descend fast. The highest gear on my road bike is 52x13, equivalent to 44x11. I never feel like I don't have enough gearing.

But everyone is different.


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## WheresWaldo (Nov 29, 2005)

I always love these short sighted observations. I need a bigger gear to bomb down the hills, Bullshit! like everyone with half a brain on here already said, learning to descend properly is more important that gearing on steep descents.

I have ridden down the eastern side of the Cascades at over 115 KPH (~72 mph), using a 53/12, Several times, years ago I bombed down the south hills into Eugene, OR in excess of 55 mph. Its not that hard with the right position on the bike. If you can turn a 55 on the flats then get one, but if you think it will make you faster for the one to two minutes that you are descending down a hill, I will show you someone who finishes at the back of every group ride.


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## myhui (Aug 11, 2012)

WheresWaldo said:


> I have ridden down the eastern side of the Cascades at over 115 KPH (~72 mph)


I thought my 32mph on urban roads with cars was brave.

You are in your own league at 72mph.


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## crit_boy (Aug 6, 2013)

myhui said:


> I thought my 32mph on urban roads with cars was brave.
> 
> You are in your own league at 72mph.


Agreed, I have always felt that my edge is 50 mph. Above that I am not comfortable. Never had the opportunity to bomb a real mountain. At this point in my life, 50 mph is about fast as my brain's risk meter will take.


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## SystemShock (Jun 14, 2008)

crit_boy said:


> Agreed, I have always felt that my edge is 50 mph. Above that I am not comfortable. Never had the opportunity to bomb a real mountain. At this point in my life, 50 mph is about fast as my brain's risk meter will take.


True, that is the x-factor... faster may not always be better, if faster is going to take you to speeds that scare the living s*** out of you. 

There is a mental/risk-assessment component.


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## robt57 (Jul 23, 2011)

WheresWaldo said:


> I always love these short sighted observations. I need a bigger gear to bomb down the hills, Bullshit! like everyone with half a brain on here already said, learning to descend properly is more important that gearing on steep descents.


Unless you have the need for the speed and the skill to get out of the saddle and sprint downhill from the drops to get that extra 5-8 MPH on past 50.... And stay low enough you are not giving most of it back... 

Yea, I agree and of course all this post is IMO.


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## WheresWaldo (Nov 29, 2005)

Believe me when I say this. I was a crazy rider. I do not do things like that anymore, always try to keep it around 40 mph on descents. I was always doing stupid stuff like this. We had a hillclimb that takes about 60 minutes if you are in great shape. I never climbed it that fast. But, and I believe this is still true, I held the record for descending that climb. Mind you it is all switchbacks and off camber corners. Total time for descent just over 13 minutes.

It was one of those checklist kind of things, wanted to break the double nickel. Check. Then it was just to see how fast I could actually go. Almost got in in trouble a few times, once when the light at the bottom of the hill changed to red, then another when a car pulled out in front of me. Nothing like a bike chattering around a corner to get your adrenaline pumping. I only managed 72 mph once, most of my other area rides would top out about 65 mph. I do recall the bike vibrating around 52-54 mph then smoothing out again just over 55 mph.

Still past about 45 mph it is all about the tuck, pedaling actually slows you down as you become a bigger profile into the wind. It is simply amazing how a 25 mm tire and wheel becomes infinitely more stable the faster you go.


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## myhui (Aug 11, 2012)

I once came within 2cm of hitting a SUV while rounding a corner at 10mph coming home, and I was the talk of the neighborhood for weeks.

I think my neighbors need to recalibrate their knowledge of what is possible on a bicycle.

You guys are awesome.

I want to try it.


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## TricrossRich (Mar 26, 2014)

I think Shimano recommends a tooth jump of no bigger than 16 teeth, so 55-39 would still fit within their guidelines.


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