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Gear calculator and chain length

2K views 8 replies 5 participants last post by  JCavilia 
#1 ·
I am a little confused. When I do a calculation at Sheldon's site I get gear inches, what does that number mean? Is 70 the magic number, is that what most people ride? I live in an area that's mostly rolling hills, to save my knees what would be a good number for me? 70s? Mid 60s?

-Links
 
#2 ·
Your title is a bit confusing. Chain length has nothing to do with gear inches.
As far as gearing, 65 to 70 gear inches is a good starting point. Are you doing a conversion or building from scratch?
 
#3 ·
You're right my title wasn't the best, I'm glad you responded though. This is a conversion and it's going to be awesome. Right now I have a 42T front ring with a 17T freewheel/16T fixed flip flop hub. It sounds like it's going to be perfect, right in the 65-70 range. Thanks.
 
#4 ·
the biggest problem with making a fixed easy enough to climb effortlessly is the descent on the other side....

I run 48/18 on one and 50/19 on another.......rolling hills here too
 
#5 ·
Now, if I know I'm going to be dealing with long descents I'll grab my single speed over the fixed gear, especially if I'm going to be riding with others with gears.
 
#6 ·
That's why I am glad it's a flip flop hub. I've ridden this bike before early one morning and loved the fixed ride. On the other hand, being able to coast will be nice every now and then. Touch, it looks like your in the high 60s range when it comes to gear inches. With my set up I think I'm in the mid to low 60s, so I think it'll work for now.
 
#7 ·
70.something on both according to Sheldon's calculator......frankly I have flip flop but have not used the ss since I got my track cogs.....coasting means flipping the wheel.....if I want to coast I just ride with gears
 
#8 ·
I have two single speeds. The commuter has 60 gear inches. This is the bike that goes traffic light to traffic light. I don't need a taller gear here. With this gear, I get up to speed early then slow down for the next light or traffic. It is good for going up the hills (not that there are many hills where I am, downtown area).

My second bike is set at 70 gear inches. A little bit faster, but takes me longer to get up to speed.This is the bike if I take the long ride into work where I don't stop and go so much.

But like everything 70 inches is just a starting point. It depends on your terrain, your strength and your preferences.
 
#9 ·
Gear Inches

To answer one of your original questions, it's a historical curiosity, dating from the days of direct-drive high wheelers. If you have a 70-inch gear, it's the equivalent of a direct-drive wheel 70 inches in diameter (of course only an extremely long-legged person could ride such a wheel). To put it another way, with a 70-inch gear, each pedal revolution will move you pi times 70 inches, or about 220 inches, or 18 ft., 4 inches. You don't need a fancy online calculator to determine it. It's simple math: chainring teeth divided by cog teeth, times wheel diameter in inches. A typical 700C wheel with 23mm tire has a diameter of about 26.3 inches.
 
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