Thanks, great stuff. I am going to copy into my other thread hoping okay since this is great stuff.

I am able with shorter cranks to get them spinning much faster than longer stuff.

Knee does not come up into my gut.

At the moment I am enjoying the lower cadence, like 75 to 80, which fits in real nice with 150's.

At this point, I will go with something short since so many have told me it cannot work, I want to try it and see what happens. :)

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Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

Boom Nutrition code 19F4Y3 $5 off 24 pack box | Bionic Runner | PowerCranks | Velotron | Spruzzamist

Lions don't lose sleep worrying about the sheep

I totally need this one explained to me.

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Amateur recreational hobbyist cyclist
https://www.strava.com/athletes/337152
https://vimeo.com/user11846099

He may have this backward. Looks like when cranks get shorter, the same gearing gets higher is what everyone is telling me.

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Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

Boom Nutrition code 19F4Y3 $5 off 24 pack box | Bionic Runner | PowerCranks | Velotron | Spruzzamist

Lions don't lose sleep worrying about the sheep

Dave we are saying the same thing. The gearing gets bigger with smaller cranks and I put it in terms of a 170 makes my compact 50 act like a 52.

Here is Sheldon Brown's site with a calculator to explain: http://sheldonbrown.com/gear-calc.html

Smaller cranks make for gear gains. I put it in terms of approximate teeth added to the front chain ring.

So if you are going way small on your cranks, you probably don't want a 53 on the front. Maybe a 50/34 compact would get you right back to what you are using today.

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Indoor Triathlete - I thought I was right, until I realized I was wrong.

See answer below to Dave and go to Sheldon Brown's web page with calculator. Sheldon is a wealth of information and funny.

When making the change from 175s to 170s, I came across it. Not a huge difference but it could impact one's choice of chain rings or cassette because crank length effects gear "gain/loss". To keep things the same a person might want a compact set up rather than a 52 or 53 when going with a shorter crank or maybe a bigger cassette ratio for going up hills, etc.

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Indoor Triathlete - I thought I was right, until I realized I was wrong.

Yep

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Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

Boom Nutrition code 19F4Y3 $5 off 24 pack box | Bionic Runner | PowerCranks | Velotron | Spruzzamist

Lions don't lose sleep worrying about the sheep

Okay, what am I doing wrong. If I put in my gearing, and just change the crank length, his output has the same gear inches for both. So, what should I be looking at?

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Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

Boom Nutrition code 19F4Y3 $5 off 24 pack box | Bionic Runner | PowerCranks | Velotron | Spruzzamist

Lions don't lose sleep worrying about the sheep

Wrong output unit choice. Crank length is irrelevant in "gear inch" calculation. Use the pull down menu in the "Gear Units" section and select "gain ratio"

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"They're made of latex, not nitroglycerin"

A shorter crank increases your equivalent gear size, a long crank reduces your equivalent gear size.

Power = Torque x RPM
Power = Force x crank length x RPM

Assume for a second that you keep Power the same and RPM the same

If you reduce crank length, then the only way for Power to stay the same is for Force to go up given your crank length went down.

So by reducing crank length, and keeping the pedal force the same and keeping RPM the same, your power would drop. That's basically what happens when you reduce your gear size at a fixed RPM and crank length. At that fixed crank length you can't go in a lower gear and same RPM and keep power fixed, you need to be in the gear you were in.

So if you keep the same gear ratios and reduce crank length, then force has to go up to keep the same power for a given RPM, or if you keep force the same then RPM can do down if you stay at the same crank length and reduce RPM. In other words, when you go to a smaller crank length, its basically the same as pushing a harder gear if you did not change crank length and reduced RPM

I probably went around in circles as I typed the first half last nite and the second half this morning without coffee, but hopefully the salient points came through.

Smaller crank length is higher effective gearing with everything being the same compared to long cranks which in effect are lower gearing. This is why H20fun used to climb better on long cranks sitting up....he just had the equivalent to lower gearing. The key to this last statement was "sitting up". It's why he had so many issues riding aero.

Gear chart using Gain Ratios For our purposes simply put in chain ring sizes of 52 and 50.


For 700 X 25 / 25-622 tire with 175 mm cranks With 11-12-13-14-15-17-19-21-23-25-28 11-speed Cassette

For 700 X 25 / 25-622 tire with 170 mm cranks With 11-12-13-14-15-17-19-21-23-25-28 11-speed Cassette


Once you notice about a .3 change in gain ration, it's fun to play around with it to match up crank, chain rings and cassette(s) to get the gearing you want.

It might be hard for those manly men on 52 or 53 chain rings to admit that your 170 crank with a compact 50 /34 or 36 is much closer to their gain ratios than they might think.

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Indoor Triathlete - I thought I was right, until I realized I was wrong.

Yep

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Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

Boom Nutrition code 19F4Y3 $5 off 24 pack box | Bionic Runner | PowerCranks | Velotron | Spruzzamist

Lions don't lose sleep worrying about the sheep

That is correct to a certain extent but not totally. If your cranks are too long causing a dead spots in you pedal action and with shorter cranks you engage more degrees of the rotation pedal force may stay the same but efficiency and power goes up. The same as when you sit up on a hill power tends to go up for a same pedal force because gravity is causing your pedal efficiency to improve not letting you coast the deed spots. The more aero you get the less efficient your pedalling becomes closing off the hip angle and more reason to go to shorter cranks.

So, just out of sheer curiosity, and not that i really care, but why in past 100 yrs or so that "gear inches" has been used to determine how hard a gear is to turn, why has no one ever ever felt the need to worry about crank length??? I mean, gear inches worked for Lance, Lemond, Merckx, and a whole host of other cycling greats that i can't recall, and/or spell, off the top of my head. AFAIK, the traditional wisdom has always been that taller riders gen more power with longer cranks and shorter riders with shorter cranks. So why, after all these 100 or more years, does this Sheldon guy think he can just come in and up-end tradition??? If it was good enough for Merckx, then by the Gospel it's good enough for me.

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"Anyone can be who they want to be IF they have the HUNGER and the DRIVE."

Because it's a quick and easy comparison that's why. The folks who talk most about gear inches are track riders where they have only one gear and, until recently, 165mm cranks were pretty much standard across all riders, negating the impact of crank length and the need to think of 'gain' altogether.

Ok. But assume also that you mount a 50 instead of a 52 when reducing crank length. Then you go slower because the RPM stayed the same. This is not possible, because how can you go slower when keeping Power the same? The only way to keep Power (and thus speed of the bike) constant when reducing crank length while reducing chain wheel teeth number is thus to increase RPM. But that's probably what you mean anyway?

Ummm, excuse me??? I've heard gear inches discussed in bike shops for 30 yrs.

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"Anyone can be who they want to be IF they have the HUNGER and the DRIVE."

Sheldon was one of the greatest mechanics in North America at his time. Read his thoughts on chain cleaning - classic humor.

Merckx was the greatest cyclist (and I read the first to use 11 teeth on his cassette).

Lemond would have been unbelievable if he hadn't been shot. Lance...

Cycling like anything has traditions that persist. When I was racing if it wasn't in the CONI blue manual, you didn't do it.

However if I had known enough to put 170 cranks on my bike to match my shorter comprades, I would have been way better off with more clearance cornering and matching their accelerations.

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Indoor Triathlete - I thought I was right, until I realized I was wrong.

As have I, but I think you will find more folks at the track rather than the road referring to gear inches when discussing gearing. How often do you hear a roadie say "I made it over that hill on a 76 inch gear" versus "I made it over in the big ring" or "I sprinted in the 13".

Right on on the "i made it up that hill in the big ring". My main use of gear inches is simply to compare the various combos of front and rear teeth as to their ease/difficulty to push, and i only do those calculations when changing out either the front or rear tooth numbers. I've ridden 175s for around 20-25 yrs but i guess i can see how if i were to go down to 165s, i'd need to look at the "gain ratios".

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"Anyone can be who they want to be IF they have the HUNGER and the DRIVE."

Today while riding on the 170s, I noticed that they were lighter than my 175s. ;)

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Indoor Triathlete - I thought I was right, until I realized I was wrong.

I know you were joking, but this is exactly the kind of bro-science that people start quoting like it's gospel at some point. We have 167.5 to 175 cranks in our house. Shimano does not trim the ends of their short cranks (at least not in the lower end groupsets) so the crank weight is the same whether you get "shorter" or "longer" drillings in your cranks.

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Less is more.

Sheldon's gain ratios are really helpful but they miss one important concept.
Imagine you go to the leg press machine in a gym. First you set the machine so that you must go through a full range of motion with lots of hip and knee flexion. Maybe at that setting you can leg press 400 lbs. Now, you set the machine so that you barely bend your knee and hip at all. Now how much can you leg press? Quite a bit more right? That's because your leg is stronger when its more extended. This is what some refer to as "biomechanical gear ratio" the ratio of change in position of the end of the limb segment to the change in muscle length.
How does this apply to cycling?
Lets say your baseline seat ht with 170mm cranks is 74cm from the top of the saddle to the center of the bottom bracket. This means that the pedal spindle in its most extended position is around 91cm from the top of the saddle.
When the pedal is at 3 oclock, it will be about the same distance away from the top of the saddle as the bottom bracket, 74cm. So your leg is extended to 74cm. By the way, the height to the bb would also be the average length of your leg extension throughout the pedal cycle. Sure there will be small differences related to geometry and pedal stack height but lets just go with this for simplicity.
Now, lets change to 150mm cranks. Standard procedure would generally be to raise your saddle by 2cm so that the maximum extension is the same; 91cm. So now the height is 76cm to the bottom bracket and your leg is extended to 76cm at 3 oclock.
Just like in the leg press example, you are stronger at 76cm than at 74cm. Not much, but a little bit.
Because of this you don't actually give up as much torque as you would expect based on the decrease in crank length / lever arm. That is, you might expect to give up about 12%. But, because of the increase in leg extension and strength, you only see about half of that loss of torque. Th effect I'm describing comes for our 2001 crank length paper in EuroJAP with values for optimal pedaling rate and pedal speed.
So, the simple message is that you don't need to adjust your gearing as much as you would expect based on simple lever arm ratios or the gain ratios in Sheldon's chart. Instead only adjust them by about half as much from your baseline crank length and gearing. In the example of going from 170 to 150mm cranks, you need only change gearing by about 6%. This is also why you almost certainly won't self select the same pedal speed when changing cranks. You’ll probably self select a lower pedal speed with shorter cranks. Tom Korff has data on this but left academia and we’ll probably never see that paper.
I'll stop now and I hope I didn't give you a headache.
Happy New Year,
Jim

Dang. Say it ain't so. They had an opportunity to drop weight and didn't?

Did you measure them in grams to be certain or are you messing with STers? Given the laws of physics how can they possibly not be lighter? Next thing you will be saying is that a size 52 frame weighs the same as 60 because the manufacturer doesn't trim the 52.

Dang. Will you measure them on a digital scale and post the pics? Thank you in advance.

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Indoor Triathlete - I thought I was right, until I realized I was wrong.

Don't quite have a headache. Appreciate your thoroughness. You make good points.

To simplify: It makes a difference yet not as much a difference as one would think when taking the leg as a lever too. Yet it makes a difference.

What I find rather interesting with shorter cranks, is that the difference seems to be more important as we age and our leg "levers" or hip flexors are not as flexible or strong. Triathletes may also be sensitive to this due to the demands of the run after the bike.

There are other small advantages like pedaling through curves and corners like the riders on their 52 frames with their 170s.

Somebody seems to have dashed my hopes that they are lighter. Hopefully they will provide digital scale backup.

Are smaller cranks more aero? The cranks and legs are traveling in smaller circles and that might make them more aero. Maybe?

Thank you for the content of your answer as it brings new info.

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Indoor Triathlete - I thought I was right, until I realized I was wrong.