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Speedo is off


Crash1647545504

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Yea, it's the sprockets. I knew it was going to change it, but I didn't think it was going to bug me. But now it makes me nervous to ride through places like Gahanna where the cops will turn around and follow me, just because I am on a sports bike, and I can't even tell if I am going the correct speed. Haha.
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anytime you change gearing the speedo will be off. Hell, they are off from the factory. Not only is it annoying, but you are racking up more miles on your bike.

 

I recommend a speedohealer. Its what I use and its nice. Also cool little features like top speed memory.

 

The best part about your post is that you actually said "speedo" then "healer" ha.

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Ben, I think your speedo should be reading high now, not low. So if it says you are doing 80, you might be doing more like 65. So if you go the indicated speed limit, you won't be speeding.

 

Run from the cops, pay attention to how fast you go, then, when they stop you ask them 'what was the fastest you clocked me - I'm trying to find out how much my speedometer error is' :D

 

[edit]: I assume you dropped teeth on the front or added some to the rear?

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Went from 15 to 14 up front, and 40 to 42 in the rear, with the OEM chain.

 

That is a approximate 12.5% change in gear ratio over the old ratio:

 

old ratio = 40/15 = 2.66

new ratio = 42/14 = 3

Percent difference = (2.66-3)/2.66 = 12.5%

 

To calculate actual speed, multiply your indicated speedoemeter by .875

To calculate how fast your speedometer needs to read to go an actual desired speed, multiply the desired speed by 1.125.

 

Examples:

1) You are doing 100 indicated on your speedo. Your actual speed is 100 * .875 = 87.5 mph = ~88 mph.

 

2) you want to actually go 45 mph. You speedo would need to read 45 * 1.125 = 50.6 = ~50 mph (rounding down for safety). Of course, bike speedometers read high, so you would still be going slower than you think, but nothing we can do about that.

 

If someone can verify my math, that would be a good idea. This is how I do it in my Cobra since I went from the stock 3.27s to the 4.30s but didn't have my speedometer changed.

 

One more thing to consider though - you odometer is racking up invisible miles because of the error - 1.125 more than actual. So, after 1000 actual miles, your odometer will show you have ridden 1125 miles.

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Since the stock speedo is off by about 5-10% from the get go, I wouldn't use the speedo to do the math. I would just go by a $99 GPS from Wal-mart and verify your inputs on the speedohealer/yellowbox and make adjustments accordingly.

 

The reason I say that is because even after you install the speedohealer/yellowbox, your speedo will NEVER be 100% accurate from 0mph all the way to TOPSPEED. Just about any speedo will read faster than you are actually going once over 80-100+ MPH depending on the bike and how you set the box.

 

For instance, I set the box and it's spot on at 70mph but at 160mph it's about 8-10% fast depending on the gearing. If I set it to be correct at 160mph it reads slow by about 8-10% at 70mph. Maybe I'm getting to technical with it but if you want it to read close or spot on at 70 and below, you can do that. Just don't think it's right when your speedo says 170+mph and your not really going that fast.

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