# Is 39x25 a low enough gear for climbs during a hilly century?



## lostPixels

Just got a new bike with a 59x39 crankset and 11-25 cassette. These together make it virtually impossible to maintain spinning cadence when ascending hills that have a 6%+ grade in the saddle. I'm worried because I have two centuries in the near-ish future that each have around 7000' of climbing. 

I've done one of these centuries on my old bike with 34x28 gearing, which was easy enough to keep me going upwards. Climbing out of saddle would be very difficult for more than a mile for me.

Is this simply a conditioning issue or am I crazy to attempt such climbs with a "racey" bike.


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## 4flattires

It's hard for others to dispense advice on something as personal as conditioning, however I think you answered your own question in the first paragraph.

Since you already own the bike you will be doing the century on, sounds like a great opportunity to head out on the route and put some ride time in and come up with the true answer to your question.


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## [email protected]

I agree, it's pretty much impossible for anyone to tell you what gears you'll need. However you've done the ride before, you know the climbs, the difference between 34x28 and 39x25 is HUGE.

I was in a similar situation recently doing the Shasta Super Century, 139 miles and 16,000 feet of climbing. I had a 53x39 and 11x26 on the bike but had ordered an 11x28 in case I decided I needed that 28... 99% of the time I don't need that 28 so i felt like it was a bit of a waste ordering the new cassette just for one ride. Morning of the ride I decided to use it, put it on and it saved my ride... i would have definitely struggled without it.

Do you still have your old bike? You could swap cassettes or rear wheels so you have that 28 on the back.


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## Chainstay

I would say that you need to be in quite good condition to handle those gears on those kinds of rides. If you are 15 lbs or more over your ideal weight you should look at a larger cassette, a compact crank or both.


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## lostPixels

You guys are right, it is a conditioning and weight question specific to me. 

That's a good idea to switch cassettes to the 11-28, do you think it'd make a radical difference? I love my new bike the idea of buying another Ultegra crankset that's a compact 50-34 is an expensive prospect. Unfortunately my bike didn't have the option when I bought it.

Sidenote: Climbing out of saddle is significantly easier with a carbon frame, I am definitely able to go further and faster than on my old bike. I am still worried about sustained 4-5 mile climbs but I'm extremely impressed by the power transfer on my foil.


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## [email protected]

The difference between 25 and 28 is definitely noticeable, especially as the climbs get steeper. It's gives you a low gear that's almost equivalent to swapping in a compact crankset with your current 11-25.

You can compare the numbers by looking at a gear calculator Bicycle Bike Gear Ratio Speed and Cadence Calculator


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## aramis

I'm 6 foot / 160 and I think I climb pretty well, have been doing fast group rides and all that lately and I use 34 with an 11-32. I'll do 100rpm up certain parts of a climb but usually stick around 80-90. I'll only stand to muscle up short steep stuff usually. I can maintain more power for longer at 90rpm than I can at 60 and that's probably true for most riders.

I think to judge gearing based on how in shape or "good" of a rider is silly. I think people slow themselves down using the wrong gearing, but it's just my opinion. Use the gearing that gets you through the ride the fastest imho, which for a regular rider on a climbing long ride is probably not a 39/25 (although I know really fast guys that can kill climbs with that gearing).


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## lostPixels

My old bike originally came with a 50-34 and 12-32. Being in 34-32 was great for long climbs but I almost feel like going to a 11-28 sped me up without much sacrifice. If I lived in a mountainous region I would definitely consider going back to the 12-32 cassette.


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## lostPixels

[email protected] said:


> The difference between 25 and 28 is definitely noticeable, especially as the climbs get steeper. It's gives you a low gear that's almost equivalent to swapping in a compact crankset with your current 11-25.
> 
> You can compare the numbers by looking at a gear calculator Bicycle Bike Gear Ratio Speed and Cadence Calculator


This is an awesome tool, thanks! Gonna have to switch cassettes now and see how much of a difference I feel in-person.


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## aramis

lostPixels said:


> My old bike originally came with a 50-34 and 12-32. Being in 34-32 was great for long climbs but I almost feel like going to a 11-28 sped me up without much sacrifice. If I lived in a mountainous region I would definitely consider going back to the 12-32 cassette.


I think part of it is people use it as a bail out when not needed. So putting in a harder gear will force you to work harder to keep up cadence. It will make you slower if you go into the 32 when you're just tired. I do better if I don't pay attention to what gear I'm in on a climb, but if I notice power dipping I downshift, if my cadence is falling I go to an easier gear but keep power fairly constant (on long climbs).

39/25 is used by pros, but I'm guessing the OP makes half or less of the power that a pro is using with that gearing.


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## Eyorerox

If you and the bike weigh 80Kg then with a 39X25 at a cadence of 80 you would need to produce 235W for a 6% slope and at 90Kg 262W


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## Undecided

aramis said:


> I think to judge gearing based on how in shape or "good" of a rider is silly. I think people slow themselves down using the wrong gearing, but it's just my opinion. Use the gearing that gets you through the ride the fastest imho, which for a regular rider on a climbing long ride is probably not a 39/25 (although I know really fast guys that can kill climbs with that gearing).


Do you see any tension between your first sentence and the parenthetical comment in your last sentence?

I took the OP's "low enough" to mean "to not limit my performance," which is largely a fitness and terrain question.


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## Matador-IV

Get a 28t or 32t.


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## lostPixels

Based on the comments in this thread I will be switching my Mavic Cosmic Elites, which are a 1900g aero wheelset with 11-25 cassette to my climbing wheels, which are closer to 1450g and have a 11-28 cassette.


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## lostPixels

Update:

I went up riding with Mavic Cosmic Elites and a 11-28 cassette this Saturday. The route changed and it became 111 miles and 9,000 feet of climbing with a mix of cat 2-4 climbs. 

Anything below 7% I could pedal up with decent cadence, but I had to go out of the saddle to get up the sometimes 12% grade hills. This definitely took a toll on my energy levels, as I ended up bonking extremely hard around mile 85. I kept on riding though and finished it up.


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## mmlee

Congrats on completing the ride. The extra 26 miles after bonking is quite the accomplishment in itself as well. 

I did a 109K ride Sat with 6,200ft of hills and I'm so glad that I had a 34/29 to get me through some of the hills toward the end of the ride. It's always better to be safe then sorry....or in this case walking or taking a detour. It's also nice to finish with some extra water and food. My toughest ride involved running out of food and water with no money......almost called the wife to pick me up but my pride wouldn't allow it and I just sucked it up and nearly killed myself finishing. 

I have a 37 mile ride with 8,000 ft of hills coming up this weekend that will push me to my limit and I'm hoping that my 34/29 will be enough to get my 52yr old legs up to the summit.

Congrats again.


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## Social Climber

lostPixels said:


> Update:
> 
> I went up riding with Mavic Cosmic Elites and a 11-28 cassette this Saturday. The route changed and it became 111 miles and 9,000 feet of climbing with a mix of cat 2-4 climbs.
> 
> Anything below 7% I could pedal up with decent cadence, but I had to go out of the saddle to get up the sometimes 12% grade hills. This definitely took a toll on my energy levels, as I ended up bonking extremely hard around mile 85. I kept on riding though and finished it up.


Congrats on finishing! So do you think switching to a 30 or 32 would have made a big difference? I currently have a 34/11-28 and was thinking of swapping out the cassette for a 12-30. My LBS guy talked me out of it when I brought it up a couple of weeks ago but I am still thinking it would be nice to have a lower gear for some of the climbs in my area, particularly as I get older.


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## Floppybike

It depends on your level of fitness. The bigger gear, the more wear on your legs. If you want to ensure your legs aren't cooked, I would go with a 27


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## mpre53

Social Climber said:


> Congrats on finishing! So do you think switching to a 30 or 32 would have made a big difference? I currently have a 34/11-28 and was thinking of swapping out the cassette for a 12-30. My LBS guy talked me out of it when I brought it up a couple of weeks ago but I am still thinking it would be nice to have a lower gear for some of the climbs in my area, particularly as I get older.


If you have the tools to switch a cassette out yourself, you could probably find a Tiagra 12-30 for somewhere around $35-$40. Not a huge investment for experimentation. Personally, if I had hills that made me use a 34/28, I'd want the 11 for the flip side. The 12-30 gives you a 27 between the 24 and 30, so you have that.


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## CleavesF

If I do THOUSANDS of feet of climbing... I bust out the bike with the triple and 27 in the back.


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