Tuesday, August 4, 2009
can't bike cuz ya hate the hills
We have our fair share of hills here in Chester County. Climbing these hills can be made easier with better gearing. Now you say, "what the heck are you talking about, Libby?"
Right now on my bike I have a compact crank. That refers to the two chain rings up front, one is a size 50, that means it has 50 little knobbies sticking out. yeah yeah, that is not the right terminology but ya know what i mean.
My smaller ring has 34, so the size of my crank is 50/34. A normal crank is 52/39.
Now you are still saying, "what the heck are you talking about libby?"
Well the sizes of your front chain rings and the sizes of the cogs in your cassette determines what your gears can and cannot do on hills and on flat land.
The cassette in back can vary. I am on an old bike so I only have 7 cogs, most of you have 10 cogs. The smallest having 10-11 little knobbies sticking out and the biggest having anywhere from 26-29 or maybe even more.
Now when i was trying to learn all this stuff, I had to have my brother in law and my son helping me naviagate the math. My son said his 3rd grade students know more math than me, well that is a given. But nonetheless, even my thick brain finally figured out the gearing
So if you take your largest cog in back, say it is 29 and your small front chain is 34. Divide 34 by 29 and multiply by 27, this works out to 31.6. This means each time your crank goes around once you cover 31 inches, hence you are spinning your wheels but this is a good gear for hills.
and for the flat land gears, take your largest ring up front, 50 (for me) and divide by your smallest cog in back - 12 (for me) and mlutiply by 27, you get approx 112 inches, again the distance covered with each revolution of your crank. By the way, the crank is the part where your pedals are, the arms holding your pedals.
God only knows I hope i have this right but i think i do. So to the point of my post. Yeah, i know, you feel asleep 3 paragraphs ago.
Look at your bike and see what the smallest ring up front size is and then look at the biggest in back. Remember, the smaller your formula answer, the easier it is for you to climb hills. 31 inches is an easy climbing gear, if your gear combos is higher than this which mine is, then climbing hills is gonna be harder than it needs to be.
I am getting a new bike this winter and I can pick my gearing plan in advance and I am deciding between a 3 front chain ring or a compact.
But with this formula--- front chainring divided by back cog times 27, I can compare the gears with a degree of knowledge.
A typical triple might be 50-39-30 and with a little math, I can now easily compare a triple or a compact or a normal crank and decide what I need.
Holy flying bike wheels Batman, I think i got it!!
p.s. this took me a full 2 days to finally comprehend this stuff but it was very worthwhile and very helpful