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Gear Ratio Question(14 posts)

Gear Ratio QuestionJBergland
Dec 4, 2002 11:20 AM
Given that you have the same amount of inches, what difference does it make to have a larger/smaller ring?? Higher top end?? Better jump?? Everything equal??

I run 45 X 17 and 42 X 16...Dave Hickey
Dec 4, 2002 11:25 AM
Gear inches are almost the same. I can't tell any difference.
Had a guy argue this point oncebigrider
Dec 4, 2002 1:03 PM
We were riding early spring rides and he said he would never use the big ring (53T) even if the gear combinations were the same ratio as using the 39T because of the difference in torque required to turn over the cranks. As a guy that should know the answer to that logic I scratched my head the rest of the ride and came up with this:

If your crank length stays the same and you have the same ratio then:

You will have to apply the same pressure to turn the wheels the same speed. I don't think there is a difference.
I run a 48/19 nmbigrider
Dec 4, 2002 1:04 PM
Less Chain Wear?timfire
Dec 4, 2002 1:18 PM
I don't have much experience in switching around your gearing, but I thought that with (physically) bigger gears you get less chain wear, since the chain doesn't have to make such a sharp turn.

Like I said I don't really have much experience in switching gears, but I don't see how the gearing would make a difference given that they end up with the same gear ratio.

--Tim Kleinert
Dec 4, 2002 2:12 PM
You would never tell the difference in a million years, if the ratio is the same. If we want to get really picky, then I suppose these are the differences:

more teeth on the front and rear = more chain bite/tooth engagement; less wear; longer chain/less wear per link; slightly more ring flex; less ground clearance; more weight; more efficient, as chain bends less sharply

The closer the ring and cog are in number of teeth, the smaller the change will be if you change one or the other. A one tooth change in the rear has about 2-3x the effect of 1 tooth on the ring.

For psychological effect, it might look cooler to have a giant ring, even if it means running a 20 tooth cog. It's harder to discern cog size differences.

I use 44x16. Works for me.
A friend of mine triedrwbadley
Dec 4, 2002 7:39 PM
running small chainring small rear cog, something like a 32-12 or some sort. This was on a road fixie, his comment was it kept pulling the rear hub forward in the dropouts. So he changed gearing to a 39 16 or similar, and said he hasn't had any trouble since.

I don't know if the gear inches changed much at all, but I'm wondering if the torque applied to the back hub was different. It seems like the small front ring combo would give you a little more leverage to the axle, but...hmmmm

re: Gear Ratio QuestionSteve_0
Dec 5, 2002 6:40 AM
Theoretically, smaller gears result in more friction. I agree with doug though, noones ever gonna feel the dif.
re: Gear Ratio Questionfixedgearhead
Dec 5, 2002 7:35 AM
There was a bike sold during the bike boom of the 1895-1900 that had a gigantic front chain ring and a large rear cog. It looked impressive. But when you did the calculations, it worked out to the same gear inches as a regular bike at the time. It was called the Raycycle Roadster a picture is viewable at:
that is a large chainwheel.

gotta getme a 1949 donaldduck special. nm.Steve_0
Dec 6, 2002 8:45 AM
gotta getme a 1949 donaldduck special. nm.fixedgearhead
Dec 6, 2002 9:06 AM
There is a guy in Mansfield Ohio at a local bikeshop that collects and restores bikes of that style and vintage. I seem to remember him having a picture of just such a bike in his collection. Truely wierd. I really like the horn that goes Quack-Quack instead of Honk Honk.

re: Gear Ratio QuestionLC
Dec 5, 2002 10:14 AM
A smaller ring/smaller cog weigh less, will have a shorter chain which weigh less, and the whole system has less rotating mass and better acceration. The extra friction from the the chain bending around a smaller cog is not really a factor unless you are looking at doing some really long distance. I still would not go below a 14 cog as will be easy to throw a chain and too much wear.
I'm planning on going muscles will be HUGE!!!ishmael
Dec 8, 2002 5:41 PM
I sold my old fixie and am getting a singlespeed with bigger gearing...I noticed I got really strong from the single gear, I dont think it was the fixed aspect which was a downer when I tried to ride with groups when downhills and turns came along..
sure will, if your joints survive it! nmDougSloan
Dec 9, 2002 2:56 PM