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Current-gen YZ250F gearing


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I need some advice on gearing for high-speed offroad on the current gen YZ250F.

I need gearing that's equivalent to about 14/48 on the 2006/7/8 YZ250Fs or 15/49 on the YZ250 2-strokes.

The stock gearing on the '14 seems a bit shorter than what I recall on the other bikes.

I have the following options to choose from: 14 or 13t counter shaft sprocket and 48 or 49 or 50 or 51t rear sprocket. I'm thinking 14/49 or 14/48 will be a good start. Any advice appreciated.

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I ran a 14 on th front for an enduro it was way too tall big mistake. In high speed stuff I think it would would pull it though. If its real desert stuff maybe even taller as you know it has plenty of power. 

https://www.youtube.com/watch?v=pbDJAsZf0Ck

In hindsight, there is about 4 miles of fast flat sand, but the rest of the course, needs shorter gearing. 14/49 it is. This bike's got legs to burn so I'll see how it fairs at the limiter.

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The stock gearing on the '14 seems a bit shorter than what I recall on the other bikes.

 

 

It's all in your head.  I pulled this together from a few sites.  With the exception of a 1 tooth difference on 4th gear, the '14 is actually geared taller with the 13/50 stock sprocket ratio.

 

2009 yz250f

Gear ratio 1 30/14 (2.143)

Gear ratio 2 28/16 (1.750)

Gear ratio 3 29/20 (1.450)

Gear ratio 4 27/22 (1.227)

Gear ratio 5 25/24 (1.042)

Primary Reduction: 3.353 (57/17)

Final Reduction: 3.923 (51/13)

 

2010 yz250f

Gear ratio-1st gear 30/14 2.143

Gear ratio-2nd gear 28/16 1.750

Gear ratio-3rd gear 26/18 1.444

Gear ratio-4th gear 22/18 1.222

Gear ratio-5th gear 25/24 1.042

Primary Reduction: 3.353 (57/17)

Final Reduction: 3.923 (51/13)

 

2014 yz250f

1st Gear: 2.143 (30/14)

2nd Gear: 1.750 (28/16)

3rd Gear: 1.444 (26/18)

4th Gear: 1.222 (22.18)

5th Gear: 1.042 (25/24)

Primary reduction ratio: 3.353 (57/17)

Final reduction ratio: 3.846 (50/13)

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It's all in your head.  I pulled this together from a few sites.  With the exception of a 1 tooth difference on 4th gear, the '14 is actually geared taller with the 13/50 stock sprocket ratio.

Awesome stuff, thank you. I'm stoked to know Yam R&D didn't shorten the trans to intensify the power. Really good offroad. I recall that when DR did a shootout of the 250fs back in 2010, the YZ250F had the highest top speed. The new bike has a 600 rpm higher rev ceiling and taller final reduction ratio, so it should almost certainly have a higher top speed (all other things being equal) than the 2009 and 2010 250fs. Not only that, but the greater hp and torque numbers should mean I can mod the final ratios (to close to 14/48) without a problem.

Do you have the stats on either the gear ratios for the 2006 or 7 or 8 250Fs?

My most recent bike was a 2006 YZ250 2t, and that bike has a final reduction ratio of 3.5 (w 49/14 sprockets). That's probably why I'm feeling that the 2014 YZ250f is short on top speed.

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I recall that in 2008 the YZ250F got a high comp piston and that brought more bottom to mid power.
Then, in 2009 I think Yam closed up the ratios in the middle part of the gearbox which further intensified the pwr. Then in 2010 they did some other mods which brought the power even more to the botttom-mid. Finally in 2012 they went to the bigger carb and new airboot and a few other things to bring back some of the pre-2008 engine character, but I beleive they retained the same close gear ratios as the 2010 and 2014 bike. This 2014 is my first YZ250F since 2008.

Edited by Swappa
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