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Old 05-08-2013, 06:24 AM   #4681
Auto-X Fil
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Quote:
Originally Posted by Ed@Ford View Post
Auto-X Fil:

Nice buncha math. If you're a car guy or a drag racer, it's worth it to add to those charts the "equivalent" car axle ratio...like 15/45 = 3.00 (45/15=3)
I have all that and way more in my spreadsheet. I even have hp and tq curves and iteratively solved for the best shift points in each gear to maximize acceleration.

FYI, this engine dies so hard up top, and the gearing is so tight, that this bike makes a perfect example of something that should be shifted well below redline.

The best shift points for the stock gearing are:

2 - 9850
3 - 9400
4 - 8950
5 - 8900
6 - 8850

The real take-away for those with a tach is that there's no reason to spend any time above 9k rpm.
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Old 05-08-2013, 06:35 AM   #4682
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Originally Posted by Auto-X Fil View Post
I have all that and way more in my spreadsheet. I even have hp and tq curves and iteratively solved for the best shift points in each gear to maximize acceleration.

The real take-away for those with a tach is that there's no reason to spend any time above 9k rpm.
Fil: My seat of the pants kinda told me short shifting is what this engine likes...and even 9K is frikkin' buzzy enough....thanks
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Old 05-08-2013, 06:48 AM   #4683
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@Auto-X Fil

Good post thanks for the info.

I am currently running 13/42 and I am able to use my stock chain, I think it could stand to have another tooth or two in the back, but I am completely satisfied with the low end that I am getting at the moment, at least for the type of riding that I do.

I haven't heard much talk on a 15T front, does it fit OK?

Sent from my rooted XT912 running AOKP Aviator
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Old 05-08-2013, 07:20 AM   #4684
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Quote:
Originally Posted by MBRedline View Post
@Auto-X Fil

Good post thanks for the info.

I am currently running 13/42 and I am able to use my stock chain, I think it could stand to have another tooth or two in the back, but I am completely satisfied with the low end that I am getting at the moment, at least for the type of riding that I do.

I haven't heard much talk on a 15T front, does it fit OK?

Sent from my rooted XT912 running AOKP Aviator
I'm running 13/40, and that seems to be fine for what I do. Ramz did a 43 rear, but said it was difficult to fit. Remembering someone who did a bigger sprocket in the back but had to put the chain guide on upside down. That was quite some time ago. http://www.rickramsey.net/CRF250Lmods.htm#gearing
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SAPB screwed with this post 05-08-2013 at 07:31 AM
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Old 05-08-2013, 07:22 AM   #4685
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Tire mileage

I know there is a lot of factors involved in tire mileage but has anyone got 4000 miles out of the rear? I'm trying to decide if I should change my rear tire before taking off on a 2000 mile trip or just wear out the one that's on it that's approaching 2000 miles already. I'll probably ending up changing it for peace of mind but would still like to know. Thanks
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Old 05-08-2013, 07:27 AM   #4686
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I know there is a lot of factors involved in tire mileage but has anyone got 4000 miles out of the rear? I'm trying to decide if I should change my rear tire before taking off on a 2000 mile trip or just wear out the one that's on it that's approaching 2000 miles already. I'll probably ending up changing it for peace of mind but would still like to know. Thanks
My mileage just clicked over 2,100, and there's more miles left on it, and I hate to take off a good tire. Any place on the way for your trip where you could get a tire while during the trip? If not, probably just swap it now. Someone else can chime if they got 4K kind of miles on an original.
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Old 05-08-2013, 07:35 AM   #4687
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Quote:
Originally Posted by SAPB View Post
I'm running 13/40, and that seems to be fine for what I do. Ramz did a 43 rear, but said it was difficult to fit. Remembering someone who did a bigger sprocket in the back but had to put the chain guide on upside down. That was quite some time ago. http://www.rickramsey.net/CRF250Lmods.htm#gearing
I didn't have to do any fab work or remove the chain guard to get a 13/42 on but it was tight. I would say 14/42 or 13/43 would require guard to be removed or at least fabricated a bit.

Sent from my rooted XT912 running AOKP Aviator
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Old 05-08-2013, 07:51 AM   #4688
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Originally Posted by MBRedline View Post
I haven't heard much talk on a 15T front, does it fit OK?
Here's one random guy who says he did:

http://www.thumpertalk.com/topic/997...#entry10500135

And some detail on where to get them - search for CBR250R sprockets:

http://www.thumpertalk.com/topic/995...ront-sprocket/

Really, the only reason to go 15t on this bike is if you're getting a big rear, like the 45t or 48t, and want to be able to swap from street to off-road gearing. I think this is why we haven't heard too much about it, although for certain people, it makes sense.

I commute on my bike, and am leaving it 14/40. My buddy does mostly off-road, and is going 13/48. Having the 15t around means that if we want to road trip it, he can have his bike ready to go in less than 10 minutes.

Quote:
Originally Posted by SAPB View Post
I'm running 13/40, and that seems to be fine for what I do. Ramz did a 43 rear, but said it was difficult to fit. Remembering someone who did a bigger sprocket in the back but had to put the chain guide on upside down. That was quite some time ago. http://www.rickramsey.net/CRF250Lmods.htm#gearing
13/42 drops right in. 13/43 requires flipping the chain guard front-to-back, in order to provide enough clearance. Either will work with the stock chain length.
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Old 05-08-2013, 09:17 AM   #4689
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13x42, 13% reduction from stock: (13x43 is 16%)

13/40 must be minus 7.9%, that's what I had to plug into the speedo DRD.
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Old 05-08-2013, 09:28 AM   #4690
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Originally Posted by SAPB View Post
13x42, 13% reduction from stock: (13x43 is 16%)

13/40 must be minus 7.9%, that's what I had to plug into the speedo DRD.
Using the sprocket formula on 12OclockLabs site I came up with -11.6% for 13/42 but I think it is still reading a couple mph high at 55mph, I plan to re-adjust soon. 13% sounds like that would be about right. I have heard that the speedo is not dead accurate from the factory so that could be part of the problem.

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Old 05-08-2013, 09:32 AM   #4691
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Originally Posted by MBRedline View Post
Using the sprocket formula on 12OclockLabs site I came up with -11.6% for 13/42 but I think it is still reading a couple mph high at 55mph, I plan to re-adjust soon. 13% sounds like that would be about right. I have heard that the speedo is not dead accurate from the factory so that could be part of the problem.

Sent from my rooted XT912 running AOKP Aviator
Didn't ride with the Garmin with the 14t. The speedo reacts quicker, the Garmin lags (electronically apparently), kinda like looking down at your feet as you walk with a digital camera. But maintaining a steady speed, it's smack on now.
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Old 05-08-2013, 09:44 AM   #4692
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If it stops raining by the time I get off work I may input 13 and go test it out, if I remember right at 60mph 1% would be like 0.6mph difference so that should put me in there pretty close if I'm around 1-1.5mph off at 60mph.

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Old 05-08-2013, 10:01 AM   #4693
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CRF250L Tach

Auto-X Fil: So....got a tach on your CRF? Same as RamZ or something different?

Thanks
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Old 05-08-2013, 10:26 AM   #4694
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Originally Posted by Ed@Ford View Post
Auto-X Fil: So....got a tach on your CRF? Same as RamZ or something different?

Thanks
No, I do not. I evaluated the rev band by speed and gear, and then looked at my speadsheet to see what revs that was. There's some small error in this, as the stock speedo seems to read a touch high for me (1-2%), but it's close enough for establishing those rough bands of operation to help me select gears.

Auto-X Fil screwed with this post 05-08-2013 at 10:33 AM
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Old 05-08-2013, 10:32 AM   #4695
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Originally Posted by SAPB View Post
13x42, 13% reduction from stock: (13x43 is 16%)

13/40 must be minus 7.9%, that's what I had to plug into the speedo DRD.
13/40 should be 7.7%, so your bike must have been pretty close given your tire wear and pressure. Just wearing the tread down or lowering the pressure can change the reading by several %, so it's not worth trying to nail it any closer than 1-2%.
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