Taller Gearing to Offset BS Speedo? - Page 4 - Honda CBR250R Forum : Honda CBR 250 Forums
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post #31 of 47 Old 07-20-2015, 01:37 PM
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post #32 of 47 Old 07-20-2015, 09:55 PM
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post #33 of 47 Old 05-24-2018, 05:04 PM Thread Starter
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I finally got around to swapping the sprockets, so I wanted to revisit this and report the outcome.

I went with a 15t front and 37t rear, which puts it at around a 9.12% difference. The speedo reads at 101-102 kph when I'm actually going 100, which I'm liking as margin to prevent tickets. No longer running the numbers in my head frees up some mindspace, and I found that especially important last night when riding in an unfamiliar area in heavy traffic.

There is a definite reduction in acceleration, particularly in 2cd gear. The tradeoff is that 100 kph highways no longer make my hands numb, and 110 kph highways no longer feel like I'm sitting on a paint shaker. The increase in comfort over long distances is worth the loss of power IMO.

All in all, I'm happy with the change. I'm still out accelerating everything I care to, and since most of my riding is at 80+ kph reducing vibration makes my trips a lot more comfortable.

I keep a spreadsheet to track all my expenses, maintenance, etc, and I've modified it to account for the new sprockets so I know what the odo should read despite the sprocket change.

Every bike is a good bike. The question is whether or not it's the best bike for what you want to do.

The Little Sport Tourer That Could - 2011 CBR250R with touring windscreen, Saddlemen seat, tank cover, frame sliders, mirror extenders, taller gearing via sprockets to fix speedo and reduce vibration at highway speed.
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post #34 of 47 Old 05-24-2018, 06:37 PM
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CBR-250-R: The bikes that Honda sends to the USA tend to be right on with regard to the actual speed and mileage.

I think that this is the result of a class action lawsuit that Honda lost dealing with optimistic automotive speedometer and odometer numbers about a decade ago. Honda was sued because the cars had not really gone as far as the odometers claimed, thereby making the cars appear to be worth less when going for re-sale.

This is the only positive aspect of our litigious culture that I am aware of.

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post #35 of 47 Old 05-24-2018, 06:41 PM
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I finally got around to swapping the sprockets, so I wanted to revisit this and report the outcome.

I went with a 15t front and 37t rear, which puts it at around a 9.12% difference. The speedo reads at 101-102 kph when I'm actually going 100, which I'm liking as margin to prevent tickets. No longer running the numbers in my head frees up some mindspace, and I found that especially important last night when riding in an unfamiliar area in heavy traffic.

There is a definite reduction in acceleration, particularly in 2cd gear. The tradeoff is that 100 kph highways no longer make my hands numb, and 110 kph highways no longer feel like I'm sitting on a paint shaker. The increase in comfort over long distances is worth the loss of power IMO.

All in all, I'm happy with the change. I'm still out accelerating everything I care to, and since most of my riding is at 80+ kph reducing vibration makes my trips a lot more comfortable.

I keep a spreadsheet to track all my expenses, maintenance, etc, and I've modified it to account for the new sprockets so I know what the odo should read despite the sprocket change.
Good one, sounds like you got the result you were looking for.
I wish they wouldnt bring these small bikes out with too lower gearing and way way optimistic speedos.
I've not long bought a Ninja 400 and it's the same old process to go through again. Speedo is reading 6kph fast at 100kph.
So I changed the gearing (which needed done to stop it revving its head off in sixth gear) but it didnt change the speedo reading one bit. Turns out the speedo reads off the rear wheel ABS sensor, not the transmission like on the CBR.

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post #36 of 47 Old 05-25-2018, 06:06 PM Thread Starter
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Turns out the speedo reads off the rear wheel ABS sensor, not the transmission like on the CBR.
Which makes sense, really. It's tracking the wheel rotation rate anyway, so it may as well use that for the speedo as well. It's not like ABS is optional on that model, so there's no reason to not use the ABS sensor.

Every bike is a good bike. The question is whether or not it's the best bike for what you want to do.

The Little Sport Tourer That Could - 2011 CBR250R with touring windscreen, Saddlemen seat, tank cover, frame sliders, mirror extenders, taller gearing via sprockets to fix speedo and reduce vibration at highway speed.
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post #37 of 47 Old 05-25-2018, 09:06 PM
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Which makes sense, really. It's tracking the wheel rotation rate anyway, so it may as well use that for the speedo as well. It's not like ABS is optional on that model, so there's no reason to not use the ABS sensor.
Surprisingly there is still a non-ABS option available in North America but it still has the same rear wheel sensor (for speedo only) which gets a few of the owners puzzled! Free ABS??
Down here in NZ we are into our second year now of compulsory ABS on all bikes sold in the country.
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post #38 of 47 Old 05-29-2018, 11:17 AM
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Quote:
Originally Posted by tegs View Post
I finally got around to swapping the sprockets, so I wanted to revisit this and report the outcome.

I went with a 15t front and 37t rear, which puts it at around a 9.12% difference. The speedo reads at 101-102 kph when I'm actually going 100, which I'm liking as margin to prevent tickets. No longer running the numbers in my head frees up some mindspace, and I found that especially important last night when riding in an unfamiliar area in heavy traffic.

There is a definite reduction in acceleration, particularly in 2cd gear. The tradeoff is that 100 kph highways no longer make my hands numb, and 110 kph highways no longer feel like I'm sitting on a paint shaker. The increase in comfort over long distances is worth the loss of power IMO.

All in all, I'm happy with the change. I'm still out accelerating everything I care to, and since most of my riding is at 80+ kph reducing vibration makes my trips a lot more comfortable.

I keep a spreadsheet to track all my expenses, maintenance, etc, and I've modified it to account for the new sprockets so I know what the odo should read despite the sprocket change.
I'm looking at doing the same as I do a ton of long highway riding to work. Can you, if possible tell me the revs you are getting at 120km/h that is my highway speed limit in South Africa.

Also anyway you can let me know the specifications of both sprockets due to idiots who work here.

Your help is appreciated.

Safe riding.

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post #39 of 47 Old 05-29-2018, 12:37 PM
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In most instances, adding 1T to the countershaft sprocket will drop your revs in top gear by close to 500, but there are gearing calculators out there if you want a more specific answer.

Because the cost is low for a countershaft sprocket, it's not a big investment to give it a shot. I geared my SV up by adding 1T to the countershaft, it dropped the revs by about 500, and it smoother out the high speed cruise quite a bit. That was over 10 years ago. I didn't see a big MPG gain - maybe 1 or 2.

The trade-off is less torque multiplication (acceleration potential) in each gear, but each gear does stretch a little farther (less shifting).

Depending on your size, engine power available at cruise, terrain, and conditions, it can be an improvement - or not.

For me, it made no change to the odometer, as it drives off of the front wheel. I did change to a 70-series front tire from the stock 60-series, which helped correct a crazy optimistic (high) speedo. Still off by a couple, but not bad. Just use a GPS (I use SpeedView app on a phone) to check your speed and make a metal note of the difference.
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post #40 of 47 Old 05-30-2018, 12:25 AM Thread Starter
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Originally Posted by Mufasa View Post
I'm looking at doing the same as I do a ton of long highway riding to work. Can you, if possible tell me the revs you are getting at 120km/h that is my highway speed limit in South Africa.

Also anyway you can let me know the specifications of both sprockets due to idiots who work here.
With 15T/37T, 120 is at about 7200 RPM. As always, your mileage may vary.

One thing I have noticed is that the loss of power JKV mentioned leads to the bike really not wanting to accelerate in 6th gear, and it's struggling with headwinds and inclines. I'm choosing to view that as an opportunity to become a better rider by learning how to use the power band more effectively, but it might be a problem for you at higher speeds. In my area, people go up to 10 kph over the limit before being ticketed, and if that's also true of SA than the bike will really struggle at 130 kph in sixth. It defeats the purpose if you end up having to run in fifth to maintain the speed you want.

https://www.gearingcommander.com/ is a fantastic resource, but don't trust the default values. Another thread here says 74 inches or 1879.6 mm circumference is the correct tire circumference to get the speed at RPM range where it should be.
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Every bike is a good bike. The question is whether or not it's the best bike for what you want to do.

The Little Sport Tourer That Could - 2011 CBR250R with touring windscreen, Saddlemen seat, tank cover, frame sliders, mirror extenders, taller gearing via sprockets to fix speedo and reduce vibration at highway speed.
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