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Yz250f sprocket advice

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I ride orv trails so a lot of them are very fast and somewhat straight. My 2013 yz250f tops out at around 50-55mph. It's geared 13/48 right now (stock). If I went to 14 in the front how much top speed would it add and how much would it make the engine bog down (if at all because right now it won't bog in anything even crawling in sand in 5th) and how much acceleration would I lose? Thanks!

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If you aren't noticing the fact that the bike lacks throttle response by clicking the thing into 5th in deep sand at slow speeds, you will not notice the difference in bottom end if you go up to a 14 tooth front sprocket. It will not make a huge difference to your top speed, but would be enough for you to notice it. Whether that satisfies what you want, that is another question. You can always drop sprocket sizes on the rear to help further, and once you do, go hunt down some salt flats !!

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If you aren't noticing the fact that the bike lacks throttle response by clicking the thing into 5th in deep sand at slow speeds, you will not notice the difference in bottom end if you go up to a 14 tooth front sprocket. It will not make a huge difference to your top speed, but would be enough for you to notice it. Whether that satisfies what you want, that is another question. You can always drop sprocket sizes on the rear to help further, and once you do, go hunt down some salt flats !!

What's the lowest I should go? The only reason I'm kinda hesitant on going lower is next year I will start to ride track but only about 20% of the time I ride.

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What's the lowest I should go? The only reason I'm kinda hesitant on going lower is next year I will start to ride track but only about 20% of the time I ride.

 

I would recommend starting with the 14 tooth front, see if you like the change, and that will still suit all but the tightest MX tracks. Might just have to sit on the limiter in top gear a bit more !!

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If you want to have exact numbers on your final drive ratio,

simply divide the number of teeth on the rear sprocket by the number on the front.

 

The higher the numerical ratio you have, the slower top speed but 'gruntier' the bike gets, but in this case

the lower numericaly you get equals more top speed, lower revs but also less grunt (will require more downshifting/clutch work)

 

48/13 = 3.69:1

47/13 = 3.61:1

46/13 = 3.54:1

45/13 = 3.46:1

 

48/14 = 3.42:1

 

Going to a 14T front sprocket with a 48T rear as Shredjim mentioned is about equivalent to a 3 tooth smaller rear sprocket which is a pretty drastic change.

If your trails have any low speed gnarly sections where low rpm grunt is required or some hillclimbs, you'll really notice the difference there.

 

Since it's rather a small investment go ahead and experiment with a 14T front sprocket, easy to switch over if ever you change riding areas or go to an MX track.

As well there are probably no changes required in the chain's length between both front sprocket sizes.

 

By thumbing thru a few parts catalog I have here it doesn't seem like many sprockets manufacturers offer sizes smaller than 48T as an option for your bike,

pretty much the same for most dirt bikes actually as wanting to go to a larger size is a more common occurence.

Edited by mlatour

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By thumbing thru a few parts catalog I have here it doesn't seem like many sprockets manufacturers offer sizes smaller than 48T as an option for your bike,

Rubbish !! JT sprockets make everything from 36 through to 53. The late model Yamaha YZ rear sprocket is the same as an early Honda sprocket that fit a whole bunch of small capacity road bikes, XR's etc etc.

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Didn't say no one made any, simply mentionned that smaller sprockets aren't listed for that exact application by many manufacturers.

Anyhow, a 3 tooth change should be plenty as a start for the OP to see a positive difference if more top speed is required.

Edited by mlatour

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