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Old 05-17-2008, 09:02 PM   #1 (permalink)
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Post dirt bike gearing

I'm wanting to make my son's rm85L slower off the line, actually decrease low end power. I think the best way to do this is to change the sprockets out but I don't know if I need to decrease or increase them in tooth count. Any one know?

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Old 05-18-2008, 08:53 AM   #2 (permalink)
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front smaller/ back bigger = lower gearing. Front bigger/back smaller = more top end. Remember a one tooth jump makes a huge difference. Hope that helps
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Old 05-18-2008, 11:21 AM   #3 (permalink)
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Gearing wont really reduce the power much. It only changes how the power is spread. It will still haul ass when it gets going.

Two good ways to reduce power is to run two base gaskets, which lowers compression, or a flywheel weight, which slows the revs. You could also run a combination of both if you feel the need.
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Old 05-19-2008, 07:25 PM   #4 (permalink)
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Are you trying to slow it down for his skill level or get some more grunt off the bottom?
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Old 05-20-2008, 08:26 AM   #5 (permalink)
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X2 .... what are you tring to gain from this??

as for sprockets .... think of how mountain bike gears works, same thing with a motorcycle.


sounds like a heavy flywheel would be best......

Is this your sons first bike?
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Old 05-21-2008, 07:14 PM   #6 (permalink)
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I'm trying to slow it down for his skill level but then be able to return it to current condition as he gains experence.

Thanks for all the info.
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Old 05-22-2008, 07:37 AM   #7 (permalink)
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I dropped my front sprocket from 15T to 14T and love it...so lower gearing is better for controle...
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Old 05-25-2008, 08:48 AM   #8 (permalink)
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could you use a throttle governer?
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Old 05-25-2008, 12:37 PM   #9 (permalink)
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Or an exhaust governer.
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Old 05-25-2008, 02:52 PM   #10 (permalink)
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If you want to take away bottom end, jump up a tooth on the front sprocket. That will make the gearing taller, like going to 3.90 gears in your truck from 4.10's or whatever. A flywheel weight might help him out a lot though, they'll make the bike easier to get rolling from a start and smooth out the hit a little when it gets on the pipe. My dad and I put one in a CR250 for a guy, it really helped him out in the trail because he was all over the place once he got into the power. Front sprockets are cheap, if he hates it after you put it on, they are easy to change out and you didn't lose that much on the deal.

I did it on my first bike, to make it easier to control taking off on a hill or whatever, I was running out of time in 1st gear before I could get ready to shift again. I kept it on because I liked the extra speed on sections where fire roads connected trails. I geared my current bike lower than stock (dropped one tooth off the front) for more low speed control (I ride a ton more technical trails than I used to), and this one has a 6 speed that still lets it go all of the 65+ mph I care to do on knobbies.
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Old 05-25-2008, 05:24 PM   #11 (permalink)
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i beleive it takes 3 teeth on a rear sprocket to equal 1 tooth on a front sprocket....learned that from some sand drag guys that have gearing fine tuned
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Old 05-26-2008, 06:55 PM   #12 (permalink)
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should I drop 1 tooth or 2 on the front sprocket? The stoch gear is 14 teeth. Does it affect chain length at all?
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Old 05-27-2008, 08:07 PM   #13 (permalink)
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should I drop 1 tooth or 2 on the front sprocket? The stoch gear is 14 teeth. Does it affect chain length at all?
You want to add teeth to the front to take bottom end out of it, dropping teeth will make the bike quicker. Just do one, that is a notieable difference. One tooth shouldn't require anything more than a chain adjsutment. BrianGriff is correct, one tooth on the front is equal to 3-4 on the rear.

More teeth in front = taller gearing
Less teeth in front = lower gearing
More teeth in the rear = lower gearing
Less teeth in the rear = taller gearing.
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Old 05-28-2008, 02:31 PM   #14 (permalink)
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Quote:
Originally Posted by Turner-2000TJ View Post
should I drop 1 tooth or 2 on the front sprocket? The stoch gear is 14 teeth. Does it affect chain length at all?
2 teeth on the front is huge. stick with one. and your chain will be fine you should be within adjustment range.
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