Question About Gear Ratio
 

A quick question about gear ratio. I went on Mr. Sheldon Brown's site and looked at the gear inch for 48 X 18, and it's 70.1. This is what I'm currently running and I like it.

On a bike that I'll put together soon, I will have a chainring with 49 teeth. I want to stay as close to the 70.1 gear inch as I can, so I am thinking of using a 19T cog. So:

Current: 48 X 18 = 70.1

Considering: 49 X 19 = 67.8

Or maybe even go up a little: 48 X 18 = 71.5


The question: is there a tremendous difference between these two in how I will feel. My commute will be mostly flat with some light rolling hills. I'm pretty fit, but prefer not to show up to work always drenched in sweat, and I'm in no rush on the bike.

Thank you for your help!

There probably isn't that much of a difference in feel on the two. The 67.8 will be a little easier on your knees, a little more aerobic, and a little slower at the same pedaling cadence. The 71.5 will be a little harder on your knees, a little less aerobic, and a little faster at the same pedaling cadence.

If you are going to be using brakes to stop, I'd recommend the 71.5. If you are primarily going to be using the drivetrain to stop, I'd go with the 67.8.

please stop saying "hard on your knees". bigger gearing isn't "hard on your knees" it's hard on your muscles, which get accustomed.

please explain yourself.

I believe that there is an effect on the knees because the quadriceps pull on the quadriceps tendon, which pulls on the patella tendon. This increases retro-patella contact forces against the condyles of the femur while the knees are bent. So the results are more stress on the quadriceps tendon, patella tendon and the underside surface of the patella. But sp00kie is right in that the muscles adapt to this greater stressors, as do the tendons, given appropriate progression and time. Retro-patella contact forces, however, remains the same at relative cadences. In this case, frequency and duration will determine if the wear rate exceeds the repair rate.

After some thinking, I think I will keep the higher gear ratio of 53 X 17 for track use (less frequency and duration) and go with go with 49 X 19 for commuting and occasional trips (more frequency and duration).

Thank you both!

retro-patella...huh? Is this ssfg or medical skool? I want pics of femurs and condoyles so I can understand it.

Use your latin skill.
Retro = behind. Patella = kneecap.
You don't have to be a ****ing medical student if you paid attention in school.

And here's your ****ing pictures of femurs and condyles, you lazy ****.

http://images.google.com/imghp?hl=en&tab=wi

lol

I missed the Latin class, I was skidding with your sister

/Users/tim/Desktop/Condyles.png

Passe. You're behind on jokes.

And you don't know how to use the computer. Should have went to school instead practicing crappy one-liners, Timmy boy.

lol

good job!

Thanks beef, so I am an idiot. I'll work on it.