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Best Sprokets


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Does anyone have any advise on the optimum sproket and counter sproket sizes for a '74 TY250. I am wanting to make second more usable and mabey even see what third feels like. I was really wanting to change out the counter sproket because it's obviously cheaper. Is it true that dropping one tooth on the counter sproket is like adding 4-5 on the rear sproket?

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I think it's a simple percentage.

A one-tooth change on a 10-tooth sprocket is 10%, and a one-tooth change on a 50-tooth sprocket is 2%.

Changing the countershaft sprocket also usually allows you to use the same chain.

Add a few teeth to the rear sprocket and you're in for a new chain.

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Terry, hi!

It's very hard to say what's best for somebody else, it depends so much on personal riding style and preference, and riding conditions. Some people will go so far as to change gearing for muddy conditions from what they use when it's dry, for example.

Dropping one tooth on the countershaft will make a very noticeable difference and, like you said, is a lot cheaper. It does sound like you could use lower gearing , so it's worth a try.

I like Charlie's idea of thinking of the change as a percentage, I think it might give you more of an idea what the difference will be like before you try it.

If you want to find the exact ratio of counter shaft sprocket to rear sprocket, you divide the number of teeth on the rear sprocket by the number of teeth on the countershaft sprocket. For example, if there are 12 teeth on the counter and 48 on the back then you have exactly 4 teeth on the back for every 1 on the counter (48 divided by 12 = 4).

Well, that's a lot of words to basically just say that you'll have to try it and see if you like it, but maybe there's something useful in there for you. Good luck!


Edited by brucej
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I had a yellow 250. I think the stock gearing was 15t front, seemed ridiculous. The back, being dished, was about unobtainable. (I think bob ginder had a kit with spacer to convert to flat rear sprockets.)

anyway I ended up with 11 or 12 front I think. I bought a 10T but remember that it was too small for the chain to clear the transm shaft or swing arm or something.

I digress, here's why I wrote: Get the transmission ratios from the manual, then divide the two ratio numbers of two gears, say first and second. That gives you the % spread between those gears.

I am picking numbers to use in this example (have no idea), say 15.00:1 in one gear, and 12.50:1 reduction in the next gear. Dividing these two is 15.00/12.50 = 1.20. This means they are 20% apart from each other.

Now, decide which gear you like. First is way too low, second is too fast, but I think second is closer to what I want. Therefore I want about 15% faster than low gear. Now you have some idea of the goal.

Just do the math from there.

If the original is 11/53, that is 4.818 reduction

12/53 would be 4.417 reduction, slightly faster.

Comparing the two is 4.817/4.417 = 1.09 or 9% increase in speed.

13/53 would be 4.078 reduction. 4.818/4.078 = 18% increase.

For decreasing speed, the math works the same. You are just looking at how much does it change compared to what I have now.

Maybe thats close enough. I would buy a couple front sprockets and try them. After that, if you want to change back ones you will likely only have to buy one, and it should be close.



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  • 1 month later...

I use 10T front and 40T rear. I am used to the ratio and its perfect for me.

Just got my new spockets and chain last week from Sandifords, VERY impressed with them. Its a Talon front (as normal on my bike) and a SuperSprox rear, which is very nice, and looks very strong.

Also with TrialPro Iris chain...all for about

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