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Gearing changes and their effects

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I have a gearing question that I'm hoping some of you guys can clear up for me. With both chain wheels (or sprockets) able to be changed it makes for a multitude of gearing combinations. I understand that a smaller engine sprocket or larger rear sprocket lower the gear ratio (numerically larger) and a larger engine sprocket or smaller rear sprocket do the opposite. What I'm curious about are the differences resulting from the same gear ratios produced by different sprocket combinations. For example, 14/42, 15/45 and 16/48 all produce the same 3:1 gear ratio. When riding, how are they different? I'd think the smaller gears are give a more torquey feel and larger gears would be more doggy. Am I on the right track hear?

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If the ratio stays the same, 3:1 in this case, the speed per rpm will not change. 3:1 is 3:1 no matter what the combination of teeth is to get there.

To raise the rpm for a given speed you need to raise (or is it lower, I get confused) the ratio numerically. That is when you drop from 15/45 (3:1) to say 14/45 (3.214:1) the engine will run faster at any given speed.

Here is a link to a spread sheet made by crf250guy that is pretty handy. You can plug in different ratios and see what it does to the overall speed and rpm for each gear.

https://thumpertalk.com/forum/showthread.php?t=562230&highlight=spreadsheet

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What I'm curious about are the differences resulting from the same gear ratios produced by different sprocket combinations. For example, 14/42, 15/45 and 16/48 all produce the same 3:1 gear ratio. When riding, how are they different?

They are exactly the same. NO DIFFERENCE.

The gear ratio is the only factor.

You WERE NOT on track. Now you are.👍

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They are exactly the same. NO DIFFERENCE.

The gear ratio is the only factor.

You WERE NOT on track. Now you are.👍

I don't think you're correct, although I could be the one that's wrong. :worthy:

In theory, larger sprockets are harder to turn, even if the overall gear ratio is the same. Imagine a 100 tooth engine sprocket and a 300 tooth rear sprocket. The 3:1 ratio is maintained, but I don't think you'd get the same response as you would with a 15/45 setup.

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The only difference in your various gearing scenarios (where the resulting ratio is the same) is the demands placed on the chain and the risk of fitment/ground clearance with the sprockets.

Running a large rear and a large front provides you with more tooth contact and tends to spread out the loads better. Higher friction due to more contact area but less pressure per tooth. Running small front and read you have less teeth and greater loads. Less friction but increased pressure per tooth.

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lower ratio's are like a 3.9 or so and a higher ratio is like a 3.1 for examples

3.9 more low speed power

3.1 would produce higher speeds, and less rpm's, at the same highway speeds

using like 55 mph for examples

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another point to think about is that smaller sprockets weigh less, and that's rotating mass, so its easier for the engine to spin them.

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I tend to go for as large as practical front sprocket and smaller rear sprocket for any given cog reduction ratio. I might be joking myself, but I might get more life out of the chain this way.

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In theory, larger sprockets are harder to turn, even if the overall gear ratio is the same.

More mass requires more force to spin up larger cogs, and the greater inertia will be more resistant to acceleration. But the difference is insignificant on a 13/14/15T scale.

As others pointed out, CS wear is worthy of greater consideration as larger cogs spread the work over a larger area.

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