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Newbee question on gearing(7 posts)

Newbee question on gearingchskin
May 22, 2003 12:12 PM
Hi

How does 42*23 or 39*23 apply to gearing? What are the numbers all about?

Thanks
Craig
re: Newbee question on gearingClydeTri
May 22, 2003 12:17 PM
the number of teeth in a chainring...42 and 23 .....you will also see similiar numbers for the rear cogset, such as 11-22, showing the smallest and largest number of teeth...
re: Newbee question on gearingDave Hickey
May 22, 2003 12:28 PM
The 42 x 23 are the number of teeth on the front and rear gears respectively. Gear inches is the distance your bike will travel for 1 complete revolution of the crank.

Assuming you're using 700c wheels, Using a 42x23 gearing, your bike will travel 49.3 inches for every revolution of the crank. 39 x 23, will result in 45.8 inches.
Well this is completely wrongKerry
May 22, 2003 5:31 PM
I'm sure you just mis-spoke Dave, but gear inches is the "equivalent diameter of the wheel" not the distance traveled per revolution of the cranks. Gear inches = front/rear times wheel diameter. To get the distance traveled per crank revolution (called development), you would multiply gear inches by Pi (3.14).
Kerry, you are correct.. my bad nmDave Hickey
May 22, 2003 5:57 PM
Here's a site for youcoonass
May 22, 2003 1:34 PM
http://www.panix.com/~jbarrm/cycal/cycal.30f.html
Enter your values and see the differences.
good God guys, spare the newbie the gear inch stuffBergMann
May 23, 2003 6:38 AM
If you live near anywhere with any hills at all, get the 39*23. In general, the smaller 39 ring will give you a wider gearing range. I like to pair it with a 53 front (vs. the traditional 52 tooth big ring) to spread the range a little more.
Spin up the hill, hammer back down!

Gear inches are a one way to quantify exactly what sort of gearing a given chainring/cog combination will produce vis-a-vis another.
I for one don't even bother with the extra math: I just calculate gear ratios (divide chainring by cog size e.g. both a 52/26 and a 48/24 combo give you a gear ratio of 2:1) to get a grasp on how new cog or ring sizes will compare with what I am riding now.