17T and Speedo - Wrist Twisters
 
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post #1 of 10 Old 09-25-2007, 01:06 PM Thread Starter
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17T and Speedo

Early in my ownership of my '04 919, I put a 17T countersprocket on (mostly for the increased gas mileage). One of the benefits is that it goes a long ways to eliminate the stupid speedo offset. Recently I entered my subdivision and noticed the local gendarme had dropped one of those radar trailers on my route. You know, the ones that post the speed limit and give you an instant read of your speed. I drove by it about ten times over the next few days noticing my speedo reading and the trailers readout. between 10 and 30 mph it was right on.

Is this relationship linear so I can extrapolate that the error has disappeared all the way up the scale?

Has anyone else observed the healing effect of the 17T sprocket?

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post #2 of 10 Old 09-25-2007, 01:15 PM
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A GPS device would give you your speed as well.

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post #3 of 10 Old 09-25-2007, 01:17 PM
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Yes, the 17t fixes the speedo. For proof, see www.919.org. Go to the mods page, and click on 17t sprocket. On the first page is a tab for an excel spreadsheet that will show you speeds in relation to sprocket selection.

Also, I had the 17t, and I checked speed with a GPS. Almost dead on, within 1mph either way throughout the curve.

-Joe
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post #4 of 10 Old 09-25-2007, 01:53 PM
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While I have not had the opportuntiy to check the accuracy of my speedo, my previous Honda, an '88 NT650 Hawk, had an error of 15% on the speed, but the odometer was accurate to less than .2% (!) This was checked while traveling through Oregon and keeping track of my trip meter reading which was reset at the border. At mile marker 200, my trip read 200.3 and some. Has anybody checked their odometer instead of the speedo?

If it has already been done, it is safe to assume it is possible to do it.
On the other hand, if it has not been done never assume it is impossible to do it.
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post #5 of 10 Old 09-25-2007, 02:06 PM
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Going down the road I have checked between mile markers and every time my tach has shown just less than 10% over what the distance on the mile markers is.

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post #6 of 10 Old 09-25-2007, 07:55 PM Thread Starter
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Yup, I'm aware of the info on 919.org. Just wondered if anyone put the theoretical to the test. Mostly I'm looking for confirmation that my speedometer is close to actual.

Guess I'll check my odo now.

Thanks,

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post #7 of 10 Old 09-26-2007, 03:19 AM
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I can't answer your question specificaly but I can say that with a GPS on my bike that the speedo is always about 5mph low no matter what my speed is. So if the error is linear I would think that the fix would have to be linear also. There is nothing about that 17t sprocket that can be nonlinear.

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post #8 of 10 Old 09-26-2007, 06:20 AM
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The few times I've checked my speedo with a gps I've noticed that under 30-35 mph it's pretty close. 35-80 it's about 5 mph off, 80-100mph it's 7-8 mph off, and an indicated 140 was about 131 actual.

In a few roughly 100 mile tests the odometer was within a few tenths of the actual miles

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post #9 of 10 Old 10-29-2007, 03:57 PM
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a speedo inaccuracy should be proportional, so I totally agree with what CPG74 indicates.

My speedo is like WAAAAY off. I haven't counted the rear teeth yet, but the front seems to be a 15. I have an extra 15 in the box, which was supposed to be the "stock" front sprocket, but I'm the 3rd owner, so who knows...

anyone want to trade a 17 for one of my 15's?

2003 Honda 919
2003 Yamaha WR450f
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post #10 of 10 Old 10-29-2007, 04:03 PM
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Quote:
Originally Posted by async View Post
A GPS device would give you your speed as well.

LOL. Right. So I'm supposed to go get a GPS just to tell my speed. I think not.

(I'm not an instigator. I swear )

2 > 4
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