As part of the on going 'On A Fixie...' Series, this time I'm going to attempt to tackle the mysterious system of thoughts dealing with gear inches.
Gear inches if you were unaware is defined by Sheldon Brown as...
'One of the three comprehensive systems for numbering the gear values for bicycle gears. It is the equivalent diameter of the drive wheel on a high-wheel bicycle. When chain-drive "safety" bikes came in, the same system was used, multiplying the drive wheel diameter by the sprocket ratio. It is very easy to calculate: the diameter of the drive wheel, times the size of the front sprocket divided by the size of the rear sprocket. This gives a convenient two- or three-digit number. The lowest gear on most mountain bikes is around 22-26 inches. The highest gear on road racing bikes is usually around 108-110 inches. Unfortunately, the handwriting is on the wall for all inch-based measurement systems.'
Clear as mud? That's what I thought. If you want to be more confused go here. In normal person terms, gear inches is simply how far the wheel rolls on one full rotation of the pedal.
Now, there is a lot of questioning and playing around with what is the proper gearing on a fixie. Most people simply think about the front chain ring and the rear cog and talk in terms of that. Take my fixie, Red, she has got a 46x17 respectively. Which if you put in to a gear calculator comes out to 71.4 inches [note: if you are using this gear calculator be sure to switch the 'gear units' from 'gear ratios' to 'gear inches']. Which is the closest I can get to 70 gear inches without changing the front chain ring [which is typically the more expensive of the two options].
You might be wondering, ok Adam, you've made your point about being aware of what you're running but really haven't made any real point on why 70 is the magic number... and to be perfectly honest, I have to give credit where it is due. Geoff basically insisted on this as the magic number. Why? BECAUSE IT WON'T KILL YOU! It is what I'd consider to be the perfect gearing right out of the box for climbing and giving you a solid top end speed. I started out with a set up that put me around 59 gear inches and once I got up to stop speed I would literally be hopping in the saddle becuase I was spinning so fast. Sure climbing was super easy but what is really necessary is a solid balance of both.
With the 70 gear inches, it won't kill you on the hills and won't slow you down on the flats. As one begins to ride more, ones legs become stronger going to a tougher gearing could be some thing to consider, or an easier one if you're looking to be the ultra cool hypster skidder... but really, it gives you the most control.
NOTE TO ALL OF YOU WHO WANT TO GET YOUR HANDS ON THE 'MANIFESTO' T's: They are very close to being done and then I'll be taking orders for them. I'll have some with me when I'm back in Iowa at the first of January and would love to get them your way then. Michiganders and everyone else. I'm hoping that the No Drive Website will be transformed shortly to be able to handle orders, or we can always line up a time to meet up.