Radical Gearing - Honda CBR250R Forum : Honda CBR 250 Forums
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post #1 of 6 Old 10-04-2018, 08:58 AM Thread Starter
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Radical Gearing

Building a naked rat bike. What is the most extreme gearing for power this CBR250R is capable of?
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post #2 of 6 Old 10-04-2018, 09:27 AM
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You can gear it "down" (increased RPMs at any speed - smaller front sprocket or larger rear) all you like, but cruising at speed gets hectic pretty quick.

That gives you more acceleration and better torque multiplication, but no gearing change will give you more "power".

Gearing "up" (higher/taller - drops RPMs) will do the opposite. It won't necessarily give you more top speed, and may even reduce it depending on a few factors.

I don't believe the CBR can pull redline (or rev limiter) in top gear anyway, so gearing "up" would only be beneficial to lower your hwy RPMs, but then again it may drop the revs into a lower spot with less power and cause you to downshift more often for hills or acceleration.
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post #3 of 6 Old 10-04-2018, 11:24 AM
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From a different perspective, my air-cooled 223 cc CRF230L had a 39-tooth rear sprocket, but climbed poorly. Going to a 48-tooth rear sprocket made climbing much better and only lowered the top speed from 72 to 55 mph. (it required a fairly steep downhill to get it to 72, as I don't tuck on a dirt bike)


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post #4 of 6 Old 10-04-2018, 12:02 PM Thread Starter
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I realize it does not add hp. I want as much accelerating energy as possible out of this bike. I know it is not a hayabusa. It’s only 250cc single.
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post #5 of 6 Old 10-04-2018, 12:53 PM
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Quote:
Originally Posted by samuelc View Post
I realize it does not add hp. I want as much accelerating energy as possible out of this bike. I know it is not a hayabusa. Itís only 250cc single.
Then gear it as low as you can and still obtain the top speed at redline in top gear that you want.

This site will tell you everything you need to know - https://www.gearingcommander.com/
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post #6 of 6 Old 11-01-2018, 04:42 PM
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Hello
I went down with a 13 front sproket (instead of OEM 14) and kept the same OEM 38 at the back.
Tork is much better and bike is much more interesting, especially in the city.
On the road, it revs a bit more at high speed but not an issue for me.
A cheap upgrade very simple to do by yourself!
Cheers!
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