Bicycle Gears, Gear Inches, Etc...

The Crank Forward Electra that is going on the Cherokee Forrest
logging trail has gear inches 16.8-52. That is with a single 22 tooth
chain ring and 11-34 gears. It has 26" wheels.

 

That's it. That is bear country and I will carry a 45 and a 9mm with over
80 rounds total. Yes, I have a carry permit that is recognized by TN and NC.
Wouldn't carry a gun, but a ranger is too cumbersome.

 

Hi,

I am partial to Sheldon Brown's gear calculator since it includes the effect of crank length if you choose what he calls "gear ratios". This way you can see that a longer crank say a 175mm gives a lower gear ratio for a given set of gears than a 152mm. Or in layman's terms it is easier to push a given gear with a longer crank. Of course this excludes any leg range of motion problems that a rider might have due to longer cranks.

Also check out the analytical cycling site
http://www.analyticcycling.com/GearSelectionTouring_Page.html
for choosing gears for a long climb. If you define a set of gears in their calculators and vary the crank length you can see that effective force required on the pedals goes up for shorter cranks.

I was aware of the crank length vs gearing issues before I tried shorter cranks. I dropped to 152mm's vs the 175mm's I had had on my 'bent. To make a long story short I can't fight the physics as they were effecting my knees !! Despite high pedaling cadence (> 90 rpm), the short cranks cause too much pressure on them and I went back to the 175mms about a month ago. Since then my speed has increased, I feel better climbing and I can still maintain a 90+ rpm cadence.

I realize this might be some what blasphemous to say in a 'bent forum but that is the way it is, I don't like short cranks....

 

Many in our group find they like shorter cranks versus the standard road bicycle cranks. I use 170 cranks and they work fine for me. But I also have a mountain bike chain ring!

 

* A.D.

Wow, nice information. Was looking for it, glad I found this thread.

PS. I'm unable to quote your post (and then submit it), coz it contain links and images, and I'm not allowed to post links and images.

 

And you will notice we don't get much spam and you won't get junk mail because you belong to our site. AD is very rigorous about keeping us clean and friendly.

Thanks again AD!!!!!!

 

Try this one out

http://home.earthlink.net/~mike.she...=75&hRMP=110&G=show&S=no&TITLE=Rans Mini&HL=1

 

I'm a little confused, no make that a lot confused

Hi all,

I'm a little confused, no make that a lot confused. The computer in the above link provided by Osco uses crank arm lengths in it calculations.

I don't understand what the crank arm length has to do with the calculations of gear ratios, gear inches, speed, etc.

Here is my thoughts on the topic:

No matter how long the crank arms are, the bottom axle rotates just one revolution per revolution of the cranks. Yes longer cranks travel in a larger circle (circumference = diameter times Pi), 170 mm cranks have a 1068 mm circumference where 165 mm crank will have a 1037 mm circumference. While there is a 31 mm difference in the circumference of the crank arms the circumference of the Bottom Bracket axle has not changed. At a crank RPM of 85 the 170 cranks, 165 cranks, the bottom bracket, and the chain rings all turn at the same speed. 85 RPM.

It is the ratios between the chain rings and the cogs on the cluster along with the wheel size that determines how far the bike will move for each revolution of the crank.

Since one turn of the crank be it 170 or 160 or any length still results in only one turn of the chain rings, the crank arm length does not have a direct influence on distance traveled per revolution.

The RPM of the cranks along with the distance the bike moves per revolution of the cranks determines the speed of the bike.

I've looked a Sheldon Browns web page on the topic and he does not explain his theory as to how the crank arm length creates a ratio with the wheel size or how it has an influence on the gear ratio etc.

Dividing the radius of the bikes wheels by the length of the crank arms on a bike is like saying, that dividing the radius of the tires on my motor vehicles by the radius of the flywheels of the respective engines, and since my trucks engine has a bigger flywheel then my cars engine and with all other things being equal including the same wheel/tire size, the truck will travel farther and faster then the car at a given engine speed.

Again that is not True, the rotation of the flywheel, no matter what the diameter or radius, is still just one revolution per revolution of the crankshaft. It is the transmission and the differential (chain rings and cluster) along with the wheel size that determines distance traveled per revolution be it a bicycle, trike or automobile. Again the RPM of the engine (cranks) along with the distance traveled per engine revolution sets the speed of the vehicle.

Longer crank arms should be easier to turn then shorter ones because with longer crank arms you gain a mechanical advantage, thus reducing the effort to pedal.

If I'm total off base on this and if someone can explain it in PLAIN English so I and the others that are confused can understand it, please do.

Regards,

Gary