Thread: Drz250 Thread
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Old 01-21-2013, 09:35 AM   #1640
mountainduro
hardened rider
 
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Joined: Dec 2011
Location: Honduras Central America
Oddometer: 56
I found this useful information at TT:


According to the official parts fiche, the
DR-Z250 has a 13 tooth front sprocket. It
has always had that front sprocket.
To figure out how changes in tooth count
will affect the bike, take the ratio of the
front tooth count over the rear tooth
count. Thus, stock is
13/49 = 0.2653
If you change to a 51 tooth rear, the new
ratio is
13/51 = 0.2549
The percentage change in mechanical
advantage is
(0.2653 - 0.2549) / 0.2653 x 100 = 3.9%
If, instead, you change the front from a
13 to a 12, the new ratio would be
12/49 = 0.2449
The percentage change in mechanical
advantage is
(0.2653 - 0.2449) / 0.2653 x 100 = 7.7%
Because there are fewer teeth in the
front, the change of one tooth is a bigger
percentage change. However, 12 teeth is
a fairly small sprocket and requires the
chain to bend more quickly. That is why,
when I upgraded my DR-Z250, I added 2
teeth in the back, rather than dropping
one in the front. I also changed the
chain, but the stock chain should be able
to fit with a 2 tooth increase in the rear.
Going to a 53 in the rear will get you a
7.5% mechanical advantage. However,
the stock chain may no longer fit. Is
7.5% enough to loft your front wheel? I
don't know, but it is a step in the right
direction.


And...

Front Rear Rpm Kph Mph
14 41 4500 100 62
14 41 4950 110 68
14 41 7800 173 108
14 43 4700 100 62
14 43 5200 110 68
14 43 7800 165 103
15 46 4700 100 62
15 46 5200 110 69
15 46 7800 166 103
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