WR-250R Lower Gearing

With a 12-tooth front sprocket, has anyone discovered how large of a rear sprocket will fit yet still achieve proper chain slack? :)

Edit:
Looking to keep the stock chain. :)

YZEtc wrote:

With a 12-tooth front sprocket, has anyone discovered how large of a rear sprocket will fit yet still achieve proper chain slack? :)

errrrrr...what? Your rear axle is adjustable for chain slack.

Changing the front does not require changing the rear. Or visa-versa.

Not sure what you're asking.

I changed my front down to 12t. Rear is stock. Chain slack was adjusted with rear wheel axle position adjusters.

I think what he is asking is how big a rear sprocket can you install with a 12 up front and still use the stock chain.

Yes, I'm sorry for leaving that part out.
I'm talking about using a larger rear sprocket with a 12-tooth and the stock chain. :)

i think i remember someone squeezing in a 45 rear with a 12c/s....but man thats gonna be a tight fit even if it does go.

Yeah a 45 will fit but you won't have much for adjustment. I'm running the stock 43 and there's plenty of room.

Alrighty, then.
I'm gettin' me a 45-tooth.
I'll report back about how it went. :)

i bet your gonna love that gear ratio. let us know how you feel about it when you try it out.
i'm trying to just live with the 12/43 combo until i can afford a whole new drive(chain and sprockets).
i keep re-thinking what i want/need....i keep going lower on the gearing everytime i think about it. i'm leaning on a 13/49 or maybe even a 50t.

45-tooth rear sprocket installed.
I have a 12-tooth front sprocket on there, too, and I was able to achieve proper chain slack without trouble.
I'll report back with my thoughts on the 12/45 ratio after I take it for my next off-road jaunt, which will probably be Saturday after work.

Keep in mind that if you buy a rear sprocket that is listed for 1999-2009 Yamaha YZ models like this one is, you should also buy new sprocket mounting bolts with countersunk heads that are designed to match the countersunk mounting holes.
The stock WR-250R sprocket and bolt heads are not countersunk. :)

that's how mine looked when i bought it(purchased new)...it wasn't adjusted...the axle was just slid all the way forward.

i'll be looking for your report on how it does for ya.
i'm pretty sure though on the outcome.

Be interesting to see what your top speed is.

SheWolf wrote:

Be interesting to see what your top speed is.

How about "theoretical"?

Assuming for the sake of argument, 10,000 rpm is max power RPM, you get something like this:



12/45... 82.7 mph.

13/46... 87.7 mph.

13/43... 93.8 mph.

Jager that's cool stuff, I like how you faded the Yamaha logo in there
Now i want 13/45 thank's to you

I've got a 13 tooth front and 49 tooth rear. Everything still works just fine. Very short 1st gear but 2nd gear rocks. Still have problems pulling the front wheel off the ground in 3rd. Any suggestions?

Paulie, what length chain are you using with the 49T rear sprocket and did the rear chain guide require adjustment?

I am currently using 12/45 gearing on trail rides & will try 13/50 next because I got a cheap 50T.

Wheelies are not my forte, I need the help of a steep hill to get the front end up