Longer gearing available? - Honda CBR250R Forum : Honda CBR 250 Forums
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post #1 of 381 Old 06-19-2011, 09:13 AM Thread Starter
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Longer gearing available?

Since my CBR250R will be my commuter and hypermiler (the Ninja250 will be the "fast bike/ fuel hog") I am going to play with longer gearing. Has anyone seen any larger front sprokets available yet? I may eventually go up as much as 17% total with changes to the front and the rear sprokets making it into a 5th gear/ top speed bike with overdrive to put 70mph highway cruising right at the first torque peak of 6000 rpm in 6th.
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post #2 of 381 Old 06-19-2011, 09:51 AM
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interesting.
suscribed.
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post #3 of 381 Old 06-19-2011, 10:46 AM
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Garage
On bikes I have had it was no problem fitting different sprockets. The same sprockets fit a range of bikes, though probably not all. My guess is a dealer, or an engineer will have something that fits, or that can be made to fit. Just ask around.

Here is a website that will help you choose suitable gearing; the CBR250R is on it already:

Gearing Commander: Motorcycle Speed, RPM, Chain & Sprockets Calculator

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post #4 of 381 Old 06-19-2011, 02:20 PM
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Quote:
Originally Posted by sendler View Post
Since my CBR250R will be my commuter and hypermiler (the Ninja250 will be the "fast bike/ fuel hog") I am going to play with longer gearing. Has anyone seen any larger front sprokets available yet? I may eventually go up as much as 17% total with changes to the front and the rear sprokets making it into a 5th gear/ top speed bike with overdrive to put 70mph highway cruising right at the first torque peak of 6000 rpm in 6th.
We will look forward to hearing your results with spocket size experimentation...
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post #5 of 381 Old 06-19-2011, 05:30 PM Thread Starter
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16/ 38

If the stock gearing is indeed 14/ 38 there is not much smaller to go in the back. It will all have to be done on the front. I hope there is room to go up 2 teeth in front. I have read of one person using a 17 on his CBR125 which originally comes with a 15. A 16, which is up 2, would be perfect my CBR250R. I played with the Gearing Commander calculator. By comparing my actual values with the charts, my rear tire is running slightly smaller than spec at 77.00 inches circumference according to my verified speedo error which is 1% slow, and, my indicated speed/ rpm which is 66 mph/ 7000 rpm in 6th. Going up 2 teeth in front will give me 68.5 mph at 6020 rpm in 6th and 93.2 mph top speed at 9500 rpm in 5th. 6th will probably also top out near 94 although I have seen youtube videos of people reaching 160Kmh/ 99.4 mph.
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post #6 of 381 Old 06-20-2011, 12:18 PM
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When I give it wot in 5th, (up hill, passing, against the wind,) it doesn't do any good to shift into 6th because the bike slows down then. I guess you could get some extra speed on the flats. I don't think it would pull very good at >68.5 mph at 6020 rpm in 6th.
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post #7 of 381 Old 06-20-2011, 12:56 PM Thread Starter
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Roll on gone

Quote:
Originally Posted by qlred View Post
When I give it wot in 5th, (up hill, passing, against the wind,) it doesn't do any good to shift into 6th because the bike slows down then. I guess you could get some extra speed on the flats. I don't think it would pull very good at >68.5 mph at 6020 rpm in 6th.
.
Roll on in 6th will be gone with the longer gears but I want to try it to see if it will at least maintain 70 mph on the flats. I am an amature bicycle racer so am very comfortable with both awareness and fitness while riding in a tuck. This must make a big difference because I was in and out of the fast lane at 68-73 all the way to work (30 mile highway run) and find that me and my CBR250R can roll on in 6th at 65 to squirt through blind spots no problem. I might have to drop down 2 after the gearing change. If I don't like the 16T I can always just change it back and only be out $30.
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post #8 of 381 Old 06-21-2011, 09:17 AM
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Honestly, it's already geared to be at the best fuel economy it can be at 60-70mph. Changing the gears up will probably only make it slower. I personally would rather go the other way with it and go down 2 teeth.

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post #9 of 381 Old 06-21-2011, 10:01 AM Thread Starter
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Originally Posted by somebody5788 View Post
Honestly, it's already geared to be at the best fuel economy it can be at 60-70mph. Changing the gears up will probably only make it slower. I personally would rather go the other way with it and go down 2 teeth.
We shall see about the fuel economy. Definitely needs at least 1 tooth for efficient cruising at 70 mph. 67 mph is 7000 rpm which is higher than needed. With a slip on, nearly flat torque is available even lower than stock, down below 5800. First is low enough for launches as it is. If you were to drop 2 more teeth you would have to shift so soon, you wouldn't even get your foot on the peg before the engine is wound out.
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post #10 of 381 Old 06-22-2011, 01:15 PM
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Quote:
Originally Posted by sendler View Post
We shall see about the fuel economy. Definitely needs at least 1 tooth for efficient cruising at 70 mph. 67 mph is 7000 rpm which is higher than needed. With a slip on, nearly flat torque is available even lower than stock, down below 5800. First is low enough for launches as it is. If you were to drop 2 more teeth you would have to shift so soon, you wouldn't even get your foot on the peg before the engine is wound out.
I can't put both feet on the ground so that foot is usually already on the peg lol

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