Sprockets

[atcoracing2123]

I have a 2004 honda crf250r andI wanted to know what my manual is talking about when it says you can change the final drive ratio by using optional sized rear sprockets. I also would like to know about what it means when you can use more teeth or less teeth. How do you change all of this anyway?

 

[TimberPig]

When you add teeth to the rear sprocket, the rear wheel turns fewer times relative to the front sprocket, when compared to stock gearing. The effect is the rear wheel turns slower, but there is greater torque multiplication, making for lower top speed, but greater throttle response and snappier power as the torque multiplication makes it respond quicker. Fewer teeth on the rear will give less torque multiplications, and a higher top speed.

The front sprocket responds in the opposite manner, with fewer teeth giving greater torque multiplication and less speed, and more teeth giving less torque multiplication and greater speed.

You need to identify if there is an issue with the stock gearing for your riding. It may be just fine as is. Many riders find adding a tooth or two on the rear only, makes the bike easier to ride, and more suited to their riding style and conditions, as stock gearing is a compromise intended for the "average" rider, who may be a complete beginner or a top pro, so they have to target the gearing somewhere in the middle of these extremes.

 

[dezryder]

Timberpig nailed it. I'll add that changing the countershaft sprocket is far and away easier and mucho less expensive to swap. A general rule of thumb: One tooth on the front is about equal to 3-4 teeth on the rear.

 

[atcoracing2123]

Thanks a lot but how do you add or remove the teeth. Also where is it located on the bike?

 

[Jaybird]

You have to buy sprockets with the amount of teeth on them that will obtain the desired ratio of revolutions of the front sprocket to the revolutions of the rear.

A good all around ratio for woods riding and supercross would be 4:1 which means that the front sprocket will turn 4 complete turns to make the rear complete one full turn.

The 04 CRF250R comes with a 13 tooth front sprocket and a 51 tooth rear. If you divide the front sprocket tooth number into the rear sprocket tooth number it will give you the ratio you have on the bike now. 51 divided by 13 = 3.92:1 ratio

If you wanted a lower ratio for slower torquy riding in the woods, you could increase the amount of teeth on the rear (by buying another sprocket). Or you could purchase a front sprocket with less teeth, like a 12.

 

[rmc_olderthandirt]

Like Jaybird said, you don't add or subtract teeth to your sprocket, you buy a new one and bolt it on. Rear sprocket is generally easy, front sprocket can be a bitch.

Note that the front has very few teeth so adding/removing one would make a HUGH difference, probably not what you want to do. The rear sprocket has a lot of teeth so the changes are easier to manage.

Here, look at this as an example:
http://www.gmo1.com/product_p/renthal 154-st.htm

Enter the model of bike and the number of teeth you want and order it up!

Changing the sprocket will require removal of the rear wheel, but after that it should be pretty easy.

 

[robwbright]

. . . front sprocket can be a bitch.

Really? I can change my front in 5 minutes or less - loosen rear wheel, slide forward a bit, remove circlip, remove sprocket, reverse steps . . . The rear requires removal of 6 bolts which are hard to get a box end wrench on and it takes a lot longer.

What's the difference on the bikes that are hard to change the front on?

 

[Jaybird]

Rob,
Some bikes CS sprocket is fastened with a nut. This nut can be a pain to get loose if you do not have an impact wrench handy.

 

[dezryder]

Really? I can change my front in 5 minutes or less - loosen rear wheel, slide forward a bit, remove circlip, remove sprocket, reverse steps . . . The rear requires removal of 6 bolts which are hard to get a box end wrench on and it takes a lot longer.

Rear sprocket also requires rear wheel R&R. I can probably change my counter shaft sprocket 3 times (including a test ride)in the same amount of time as one rear sprocket change.