Sprockets

[sorny]

Ok, me and my dad were having a discussion about how to get some more low end power out of my YZ 250. I let him ride it (he's prob owned about 6-8 bikes in his day, mostly dirt bikes) and he kept complaining about how its geared so high he rarely got out of 1st gear or 2nd gear riding around in the field. I agreed, but since it was my first bike I didn't know if that was normal or not. He recommended changing at least one sproket, but it had been so long since he's even been on a bike he's forgotten whether I should go bigger or smaller.

I'll mostly be doing trail riding and the only reason I got a YZ to do that is because it was $1200 and I couldn't pass it up. It has TONS of power and I've never been in 4th or 5th gear since I've had it so I think it could stand to be geared a little lower. Do I go bigger or smaller in the rear? What about the front? Does it matter as much as the rear (meaning, should I do one at a time or do both). I guess I should probably just add or subtract a tooth at a time instead of going like 3 teeth either way.

When I bought it the guy said he put a new sprocket on the rear and I *thought* he said he was giving it more low end power, but if he did I'd hate to see what this thing was like stock. Almost seems like it could do 100mph in 5th gear ;)

 

[RM_guy]

A larger rear sprocket will gear it down and reduce the overall top speed (which is what you seem to want). I don't know what the stock gearing is for that bike but you should check. The previous owner may have gone to a smaller rear sprocket by mistake.

You can get the same effect by changing the front sprocket too. A 1 tooth smaller front sprocket equals approx. 3 additional teeth on the rear. One tooth on the rear can make a big difference so I'd advise only changing it. A smaller front sprocket can be bad because you are reducing the number of teeth that engage on the chain

 

[sorny]

Cool, thanks for explaining that. That makes me think of another question though... My chain adjuster is about 1/2 way now... Do you think by changing the rear 1 or 2 teeth if I'll need a new chain or will the adjuster be ok for just 1-2?

 

[darringer]

More than likely going up 2 teeth in the rear you will have enough room for adjustment. 2 teeth may not seem like much, but it will be a noticeable difference for the better.

 

[sorny]

Cool, thanks guys. I'll try doing the rear sprocket like 2 teeth at first see how it goes.

 

[darringer]

A friend of mine has a 99yz250, and if I remember correctly he was running 14/50 gearing, which I think is stock for that year. You may want to check and see how far off you are.

 

[sorny]

Good idea. See if the guy accidentally went and made it even higher geared instead. I was thinking a smaller rear sprocket would make it geared lower before my dad (and you guys) told me different, so I dunno. I'll check that when I get home.

 

[Caper007]

two find the gear ratio of your sprockets divide the number of teeth on your rear by the number of teeth on your front.
example 51/13= 3.92
54/13=4.15 and so on
the higher the number you get the more bottom end you get and the less top speed

 

[Rcannon]

If possible try to experiment with the front first. It is much cheaper. I bought a whole selection of sprokets for my yz 250 and ended up with one larger in the rear and a closet full of larger rears. Are you interested in a Renthal 51 tooth for your bike ?? I have it. Used once. My bike came stock with a 13/49. I ended up at 13/50.

Anything more than that made me feel like I was shifting all the time. The bike had plenty of power to pull any gearing. The larger rears just made the power spread feel smaller.

One tooth in the rear allowed me to follow my nephew around on his xr 50, yet have enough top end for anything.

 

[sorny]

The bike really has a lot of power across the board so it's not like i don't have pulling power down low, its just that it could be a little lower.