Gearing Question

[msl819]

I am not sure I even know how to accurately ask this question... but here goes. When climbing if I am in the 53/25 and climbing at say 14 mph, if i shift to 39/22 or 23, if seems like I can stay at 14 mph but with less effort. Is it better (more efficient) to climb with the chain rotating around a smaller circumference on the front or is this just imagined on my part?

[ultraman6970]

Depends on the climb and the rider... but the short answer is yes. (just to keep it simple)

If you want to figure it out better, start experimenting with different combinations, a lot of combos are and will feel similar to other ones. 53x25 is pretty light, should feel similar to 39x20 maybe.

[kramnnim]

So the question is if the drivetrain is more efficient when you use the small ring vs the large, and the gear ratio stays the same?

[ultraman6970]

Im under the impression the OP is just figuring out the differences and equivalences in gearing and how the feel.

[msl819]

I am now sure I know what I am asking. All I know is at times it feels easier to pedal in the say 39/21 at 14 mph than 53/25 at 14 mph. It is more spinning and less mashing but speed is the same. Is this matter of less friction on the drivetrain because I am not cross chained? Around here, like I would assume many places, there is a certain bravado in climbing a hill in the big ring. So I am try the small ring and ride the same pace but seemingly less effort.

[distanc3]

Do what's most comfortable to you. If you're a low cadence rider the big ring is pretty good especially if you're going 14mph on a 53T.

Some consideration would be how steep and how long the hill when comparing to your fitness.

[Louis]

Don't worry about the mechanical efficiency of the drivetrain - choose the gear that works best for your abilities.

However, if you do care about chain and gear efficiency, there are relatively small differences, where big-big is a bit more efficient than small-small, I believe at least in part due to the fact that the individual chain links don't have to pivot quite as much around the larger gears.

[kramnnim]

Yes, you should feel a difference between mashing vs spinning...up to you to figure out what is most efficient for you.

[k-mac]

Are you asking if spinning a higher cadence in the small ring vs a lower cadence in the big ring is better at a given speed, or are you asking if, given equivalent combined gear ratios (say 53/25 vs. 39/18) such that you'd be pedalling at the same cadence and speed, is one more efficient?

If the latter, there's a few things mechanically to consider:

1 - In the big/big combo, you have more physical inches of chain wrapped, so the rotational speed of any given link in the chain is higher, leading to more driveline friction.

2 - Also in big/big, you have the jockey spring of the rear derailleur under more tension as there is less chain slack to take up, due to the reason in 1 above. So that places more load on the chain.

3 - However, as already stated, there is more chain link loading on smaller diameter gears then on large, so that works to oppose 1 and 2.

Bottom line, I'm not sure there is an easy, definitive answer here.

[carpediemracing]

I am not sure I even know how to accurately ask this question... but here goes. When climbing if I am in the 53/25 and climbing at say 14 mph, if i shift to 39/22 or 23, if seems like I can stay at 14 mph but with less effort. Is it better (more efficient) to climb with the chain rotating around a smaller circumference on the front or is this just imagined on my part?

If you're going the same speed on the same hill (and wind and all that is the same) then technically you're putting down the same wattage. In other words regardless of your gear if you are going 14 mph up a given hill you're going to be using the same amount of power. The work done is the same.

Having said that there might be a difference in drivetrain efficiency. Doing the big-big is pretty high friction due to the significant lateral chain flex, especially if you set your chain length per Shimano's recommendation (shortest possible plus one pair of links). If you do the "longest possible without hanging in the small-small" you might have a bit less friction. That friction, even if it's just 5 watts of power, could make a difference if you're at your threshold.

I couldn't get my head wrapped around this idea until I tried different "tactics" to climb a 6-7 minute hill near my house. I used big gears, little gears, tried to set up for the second half of the hill by using the small-small when I started, etc. I realized that my power curve was basically the same, regardless of gear.

Finally, relating to gearing, if you load your muscles the perceived effort is higher. If you tried using a 53x11 and a 39x25 on a steep hill at a given speed you'll technically be putting down the same wattage/power/work but one gear combination will stress your muscles a lot more than the other.

If you want to be technical it's actually more efficient to use a straight chain-line 53x25 versus a straight chain line 39x22 (or whatever smaller cogs). More teeth make for rounder rings/cogs and have less friction. Smaller cogs, especially when you get to the 11-12-13 range, are significantly out of round. Consider a 1 tooth cog, or a 2 tooth cog. It's around the 14T that it gets pretty round. Back in the day Shimano actually dedicated one engineer to optimize a 12T cog, i.e. make it as round as possible. This is one of the reasons they tried that smaller pitch drivetrain, to keep tooth count high while reducing actual chainring/cog sizes.

[tiretrax]

I am now sure I know what I am asking. All I know is at times it feels easier to pedal in the say 39/21 at 14 mph than 53/25 at 14 mph. It is more spinning and less mashing but speed is the same. Is this matter of less friction on the drivetrain because I am not cross chained? Around here, like I would assume many places, there is a certain bravado in climbing a hill in the big ring. So I am try the small ring and ride the same pace but seemingly less effort.

I think you feel like there's less effort because the additional effort to turn the large chainring instead of the smaller one has been transferred to the rear of the bike (cassette, not chainrings under your feet). I believe it's similar to using a block and tackle instead of a single pulley to lift something.

Don't listen to braggarts about what chainring they ride in - climb what's fastest for you so you can beat them to the top. It's like climbing style - standing or sitting? Whichever is best for you to get there comfortably and faster.

[kramnnim]

Same hill, same speed, same wattage, yes...but X wattage at 40rpm might stress his muscles more than the same X wattage at 85rpm...

[marciero]

Doing the big-big is pretty high friction due to the significant lateral chain flex,

The latest I've read on this, either in Bicycle Quarterly or Jan Heine's blog, is that cross-chaining big-big did not create any measurable increase in friction in tests, in terms of increased power output. Not sure how the tests were performed, and though I think this could be true, I am not 100% convinced yet. You can certainly hear it though, and that can lead to the impression that pedaling is harder.


Mike

[Ti Designs]

If you're going the same speed on the same hill (and wind and all that is the same) then technically you're putting down the same wattage.

And this is why I put a piece of electrical tape over the wattage display when I coach riders...

[Mark McM]

And this is why I put a piece of electrical tape over the wattage display when I coach riders...

But wouldn't that be a good training aid when learning correct pedaling technique? To see that Wattage increased at the same effort level with better pedaling form?

[Ti Designs]

But wouldn't that be a good training aid when learning correct pedaling technique? To see that Wattage increased at the same effort level with better pedaling form?

Yeh, over the winter, on a trainer, tracking power, force vectors and heart rate.

[Ralph]

Of course it feels easier in a 39X22 or 39X23. That's a lower gear than a 53X25.

A 53X25 is a 57" gear. Almost equivalent in small ring is the 39X18.....58".

39X22 is 47", and 39/23 is 45".

So sure.....if you spinning at the most efficient RPM up a steep hill in a 39X22, it will fell better and easier than a 53X25. That's how gears work.

BTW....To figure gear inches.....divide the rear cog teeth into the front chainring teeth number, then multiply by 27, or some constant. I use 27". Do all your possible gear combinations this way to see where your gears are in relation to each other. I know all my gear inches automatically....that's how us old guys leared to ride years ago.

[p nut]

All personal preference, but I ride a singlespeed most of the time, so when I'm on my geared bike, I naturally feel more comfortable mashing a bigger gear.

And can't let a "mash vs spin" thread without quoting Eddy: When Eddy Merckx was asked, "Is it better to mash a big gear or spin a small gear?" He replied, "Its better to spin a big gear."

[Ralph]

I took the question to be why is it easier to pedal up a hill at 14 MPH in a 39X22 VS doing same in a 53X25. It's because the 39X22 is a lower gear.

I'm not saying that's the most efficient way to go 14 MPH for a stronger more experienced rider.

[Mark McM]

Of course it feels easier in a 39X22 or 39X23. That's a lower gear than a 53X25.

A 53X25 is a 57" gear. Almost equivalent in small ring is the 39X18.....58".

39X22 is 47", and 39/23 is 45".

So sure.....if you spinning at the most efficient RPM up a steep hill in a 39X22, it will fell better and easier than a 53X25. That's how gears work.

BTW....To figure gear inches.....divide the rear cog teeth into the front chainring teeth number, then multiply by 27, or some constant. I use 27". Do all your possible gear combinations this way to see where your gears are in relation to each other. I know all my gear inches automatically....that's how us old guys leared to ride years ago.

That's not really what the OP was asking. He was going up the hill in larger and smaller gear at the same speed. The actual power was the same, yet he felt the total effort level (pedal force and cadence) was less in the lower gear.

Gear ratio and effort level don't directly correspond for a constant power output. For example, if you were drafting another rider, so that you couldn't choose your speed, which gearing and cadence would be easier - a 53/17 at 90 rpm, or a 39/25 at 180 rpm? Even though a 39/25 is only half the ratio of a 53/17, going the same speed is not easier if the requisite cadence is too high.

[Ralph]

That's not really what the OP was asking. He was going up the hill in larger and smaller gear at the same speed. The actual power was the same, yet he felt the total effort level (pedal force and cadence) was less in the lower gear.

Gear ratio and effort level don't directly correspond for a constant power output. For example, if you were drafting another rider, so that you couldn't choose your speed, which gearing and cadence would be easier - a 53/17 at 90 rpm, or a 39/25 at 180 rpm? Even though a 39/25 is only half the ratio of a 53/17, going the same speed is not easier if the requisite cadence is too high.

We know that, but does poster? I believe he is just feeling the effects of a lower gear.

[Bostic]

I have a bike with a triple 52/39/30 and 11-28 Sram 10 speed cassette.

I've used the Sheldon Gear Inch Calculator a lot over the years. 39x25 is 41 gear inches. The 25 on a Sram 10 speed cassette is the second largest cog. 30x19 is 41.5 gear inches and the chain is on the fourth largest cog.

For me, 30x19 is 'easier' to spin than 39x25 even though it should be a fraction harder. For chain angle comparison the bike has 40.6cm chain stays.

[notsew]

I've used the Sheldon Gear Inch Calculator a lot over the years. 39x25 is 41 gear inches. The 25 on a Sram 10 speed cassette is the second largest cog. 30x19 is 41.5 gear inches and the chain is on the fourth largest cog.


gear-calculator.com (http://www.gear-calculator.com) is a bit prettier. It's fun to play with.

[msl819]

Of course it feels easier in a 39X22 or 39X23. That's a lower gear than a 53X25.

A 53X25 is a 57" gear. Almost equivalent in small ring is the 39X18.....58".

39X22 is 47", and 39/23 is 45".

So sure.....if you spinning at the most efficient RPM up a steep hill in a 39X22, it will fell better and easier than a 53X25. That's how gears work.

BTW....To figure gear inches.....divide the rear cog teeth into the front chainring teeth number, then multiply by 27, or some constant. I use 27". Do all your possible gear combinations this way to see where your gears are in relation to each other. I know all my gear inches automatically....that's how us old guys leared to ride years ago.

I think this is what I was looking for. The numbers used in the original post are just guesses. So if I understand this right if the gear inch is the same, whether I am in the big or small front ring, there is no difference. Is that right? Or is it more complicate than this?

[Ralph]

That's pretty much it. You could discuss if extreme chainline makes a difference, or if chain has same efficiency over a very small cog VS a larger one, but basically you got it.
Once you get more experience, and maybe stronger, like some say above, a lower gear doesn't always feel better when climbing. Also....climbing well is something to learn. It's not all about gears.