50/34 vs 52/36 for climbing

Discuss light weight issues concerning road bikes & parts.
Boshk
Posts: 410
Joined: Wed Jul 19, 2017 2:59 am

by Boshk

Playing with this calculator to see what the difference is between a 34 and 36 chainring for climbing.

I basically entered the following data:
Chainring: 34 vs 36
Cadence: 60, 70, 80, 90
Cassette cog: 28, 29, 30, 32, 34 (basically campy, DA and ultegra cassettes)

It gives speed for each combo, is there anyway to work out power required to sustain those speeds?

Example: On my current compact 50/34, 11/32, cadence at 60rpm, I'll be theoretically going 5.01mph (8.06kph) on the 32 cog.
Jumping onto a 52/36, same 32 cog, speed would be 5.34mph (8.59kph) .........how much more power is required?
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Last edited by Boshk on Mon Sep 02, 2019 2:18 am, edited 1 time in total.

furiousferret
Posts: 19
Joined: Sun Aug 11, 2019 6:11 am

by furiousferret

I run a 52/34 which is perfect for climbing. It isn't as crisp shifting but its functional.

I don't care what people say about average cadences, I just know when I'm descending and I need to close a gap quickly, a 52 is going to get me there faster than a 50.

by Weenie


talltales
Posts: 80
Joined: Mon Mar 11, 2019 10:43 pm

by talltales

Play around with this:

http://bikecalculator.com/

RocketRacing
Posts: 886
Joined: Thu May 10, 2018 2:43 am

by RocketRacing

TLDR version: chose your chainring gears based on being 2-3 cogs down from your biggest and smallest cogs on the casette

I have run similar calculations between my current light climbing bike with 34/50 and 11-32, and my new tri bike that will have sram axs 35/48 and 12 speed 10-28. For climbing, it should be fine, but there will be no relaxed climbing. However, if I want any pace in my climbs, a 34/32 is just overkill. I am usually down a couple cogs to 25 or max 28 in the steep stuff, so a 34/32 is only really useful in recovery imho.

I don't know the power calculations. power to sustain givel speeds really depends more on your bike position, not gearing. A better way to do it would be to use you FTP, and calculate from there. I look at it this way: I can only put out so much power. But more gears allows me to keep maximum forces down, and allow me to instead create power through cadence (lower force, but higher frequency). So power may be the same, but I am puttign less strain on my knees (my weakest link). For climbing, I like gearign that allows me to hit my FTP power at 90rpm. So as I have gotten stronger, I need less gearing.

So my tri bike will have all the gearing I need to climb, but to avoid grinding up hills at 70rpm, I will need to be on it. There will be no recovery on grades above 10 degrees.

Now, the complexity is in chainlines. THe best performance will come when you match your ideal gearing with the straightest possible chainline between the front and rear cogs. so for a 2x, your biggest cog in the back is one of the more inefficient. So me being down a couple of cogs from the big cog in the back is synergistic for climbing efficiency. This is why compact casettes are fastest for most riders (Pros are mutants).

Where the Sram AXS system becomes theoretically inefficient in on the top end of things. a 10 cog will be very inefficient. ONe because less cogs is less mechanically efficient, and also because the chainline is not ideal. Now, for a mortal like me, I will not be in my 48/10 cog at 90rpm that often (54km/hr) unless a downhill or sprint is part of the equation. A more efficient gear and chainline will come in the form of the 12/13/14 cogs in the back. And those cover 39-45km/hrs... which is a pretty solid speed for sustained efforts on the flats.

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pdlpsher1
Posts: 2424
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

At that low of a speed the forces you must overcome should be fairly linear to the speed. So a rough calculation says it’s 6-7%.


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Boshk
Posts: 410
Joined: Wed Jul 19, 2017 2:59 am

by Boshk

RocketRacing wrote:
Mon Sep 02, 2019 3:23 am
TLDR version: chose your chainring gears based on being 2-3 cogs down from your biggest and smallest cogs on the casette

I have run similar calculations between my current light climbing bike with 34/50 and 11-32, and my new tri bike that will have sram axs 35/48 and 12 speed 10-28. For climbing, it should be fine, but there will be no relaxed climbing. However, if I want any pace in my climbs, a 34/32 is just overkill. I am usually down a couple cogs to 25 or max 28 in the steep stuff, so a 34/32 is only really useful in recovery imho.

I don't know the power calculations. power to sustain givel speeds really depends more on your bike position, not gearing. A better way to do it would be to use you FTP, and calculate from there. I look at it this way: I can only put out so much power. But more gears allows me to keep maximum forces down, and allow me to instead create power through cadence (lower force, but higher frequency). So power may be the same, but I am puttign less strain on my knees (my weakest link). For climbing, I like gearign that allows me to hit my FTP power at 90rpm. So as I have gotten stronger, I need less gearing.

So my tri bike will have all the gearing I need to climb, but to avoid grinding up hills at 70rpm, I will need to be on it. There will be no recovery on grades above 10 degrees.

Now, the complexity is in chainlines. THe best performance will come when you match your ideal gearing with the straightest possible chainline between the front and rear cogs. so for a 2x, your biggest cog in the back is one of the more inefficient. So me being down a couple of cogs from the big cog in the back is synergistic for climbing efficiency. This is why compact casettes are fastest for most riders (Pros are mutants).
I actually try and do that most times, to stay in the middle range of the cogs to keep chainline as straight as possible, shifting FD more than usual.

For the actual cassettes themselves....11-29, 11-32, 11-34.....I try to keep the last cog as an 'emergency' saver

I know roughly what my FTP is (over a year ago) but was curious if I would 'blow up' if I went 52/36 with 11-32 for a long long climb.

RocketRacing
Posts: 886
Joined: Thu May 10, 2018 2:43 am

by RocketRacing

I say, try it. Worst case scenario, get compact rings if you find you are suffering, or always in the largest gog in the casette.

gorkypl
Posts: 67
Joined: Fri Sep 21, 2018 9:31 am
Location: Poland

by gorkypl

pdlpsher1 wrote:
Mon Sep 02, 2019 5:23 am
At that low of a speed the forces you must overcome should be fairly linear to the speed. So a rough calculation says it’s 6-7%.
This exactly.

And I have to say I like 36 more than 34, it is more useful when things become less than steepest. So for me it's 36 front, and rear depends on your W/kg. I am quite average (I estimate myself around 4W/kg, though never really measured it) and on typical rides up to 200-250km 2-3k up I never found the need to use anything lower than 36x29. Said that, when doing ultra endurances with lots of climbing (sth around 600km/10k up) I was praising gearing as low as 36x36.

StevenH72
Posts: 37
Joined: Sun Jun 11, 2017 3:17 pm

by StevenH72

Crumbs, if 4W/KG over 200km is average I'm a long way off.... (mentally ramps up training plan)

I've an FTP of ~3.3W/KG (260W @ 77-78kg) and currentl use a 50/34 - 11/30 set-up.

I don't race so have no need to really push descents and will hit 60-65kph before I feel like I am spinning out.... quicker than that and I don't feel the need to continue pedalling / pushing.

On recent trips to Mallorca and the Alps (Bourg d'Oisan) I was thankful to have a 34-30 option available. At an 8-9% gradient I was in this gearing to maintain my ideal cadence (around 80-85rpm).

A 52/36 option might have worked in Mallorca where most climbs are 20-30 minutes in duration and fairly steady gradients, but I never felt wanting with 50/34. But in the Alps with 1-2hour climbs, I'm not climbing anywhere near my FTP and 50/34 was perfect for me. I'd have been grinding my cadence with 52/36

gorkypl
Posts: 67
Joined: Fri Sep 21, 2018 9:31 am
Location: Poland

by gorkypl

Nah, I absolutely do not attempt to ride with full FTP over 200km!

But indeed, length of ascents is an important consideration. Still the difference between 36x30 and 34x30 is not that huge, and I'd take 36x32 over 34x30 most of the times :)

topt
Posts: 8
Joined: Fri Jul 19, 2019 5:13 pm
Location: Slovenija

by topt

just for info; pogacar was riding 36-32 in Vuelta stage 9

tarmackev
Posts: 492
Joined: Sat Jan 15, 2011 9:59 pm

by tarmackev

furiousferret wrote:
Mon Sep 02, 2019 1:51 am
I run a 52/34 which is perfect for climbing. It isn't as crisp shifting but its functional.

I don't care what people say about average cadences, I just know when I'm descending and I need to close a gap quickly, a 52 is going to get me there faster than a 50.
This works for me also.

rides4beer
Posts: 185
Joined: Wed Nov 28, 2018 5:27 am
Location: SC

by rides4beer

My road bike is 52/36 (11/28 out back) and my gravel bike is 48/32 (11-34). Love the gravel bike gearing for climbing on the road, but wouldn't mind a hair more topend. So on the new road bike build I'm going with 50/34 (11-34), should get me through any of the climbs around here, even if I'm tired.

Interesting note, I did have a guy comment on my "cheater" gears recently...as I was passing him on one of our local tough climbs. If you feel better about yourself while working harder and going slower, then more power to you. lol

Boshk
Posts: 410
Joined: Wed Jul 19, 2017 2:59 am

by Boshk

Thanks!
Think I'll stick with 50/34 and have option of 11-32/11-34 in the back.

alcatraz
Posts: 2212
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Once you have a power meter you can see what kind of power you need to maintain for the climbs you wanna ride on.

I live in a coastal city with some climbs where I need to maintain 300w on a 34front and 36rear gear. Some say it looks like a granny gear but when you need it and don't have it, it's a different story. Better granny gear than grinding gear.

Anyway, I'd say if you are at your ftp wattage for the toughest climbs in your area you have a good climbing gear.

by Weenie


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